Apparatus and method

Abstract

An apparatus comprising: an energy cell configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein; and a controller configured to obtain an indication of at least one operational parameter of the energy cell, and wherein the controller is configured to: determine, based on at least one obtained indication of a first operational parameter, if the energy cell is in either of: (i) a normal mode of operation, or (ii) a start up mode of operation; in the event that it is determined that the energy cell is in the start up mode, control operation of the energy cell and / or the liquid supplied to the energy cell to increase the generation of bubbles of plasma in the energy cell; and in the event that it is determined that the energy cell is in the normal mode, control operation of the energy cell so that a second operational parameter remains within a selected range.

Description

[0001] Apparatus and Method

[0002] Technical Field

[0003] The present disclosure relates to the field of energy cells. In particular, the present disclosure relates to the field of energy cells in which plasma is generated for indirect and direct heating of a fluid.

[0004] Background

[0005] GB 2604853 discloses a heating system including a cell which applies electrical energy to liquid in that cell to generate bubbles of plasma therein. In turn, this causes energy to be released into the cell, both into the fluid contained within the cell and also into a housing of the cell. The result of this energy release is to generate a heated fluid within the cell. The heated fluid can then be output from the cell and used by a work extraction system to extract useable work from this heated fluid. This arrangement disclosed in GB 2604853 provides for a highly efficient generation of heated fluid.

[0006] Summary

[0007] Aspects of the disclosure are set out in the independent claims and optional features are set out in the dependent claims. Aspects of the disclosure may be provided in conjunction with each other, and features of one aspect may be applied to other aspects.

[0008] Embodiments of the present disclosure may provide systems and methods for controlling operation of an energy cell. For example, embodiments may relate to systems and methods for controlling operation of an energy cell of the type disclosed in GB 2604853. In the present disclosure, control of energy cells is such that they operate in a more efficient and / or reliable manner. This may include controlling operation of an energy cell to maintain a tradeoff between maximising output from the cell and also minimising the likelihood of breakdown occurring within the cell. For example, in the present disclosure, cells may be controlled according to a ‘normal’ mode of operation. In the normal mode of operation, the cell may be regulated to avoid operating above a level at which breakdown and subsequent arcing may be likely to occur and / or to avoid operating below a level at which cell operation significantly decreases in efficiency. Embodiments may relate to control of the cell in a ‘start up’ mode in which the cell is regulated during an initial period of operation so that the cell may suitably enter into the normal mode of operation once start up operation of the cell has been completed. Embodiments may relate to control of the cell in a ‘cooldown’ mode in which the cell is no longer used to generate heated fluid. Controlling the cell in the cooldown mode may comprise controlling the cell in a ‘dormant’ mode in which the cell is monitored and / or regulated so that it is ready for a quick restart back into its normal mode of operation.

[0009] In an aspect, there is provided an apparatus comprising: an energy cell configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein; and a controller configured to obtain an indication of at least one operational parameter of the energy cell, and wherein the controller is configured to: determine, based on at least one obtained indication of a first operational parameter, if the energy cell is in either of: (i) a normal mode of operation, or (ii) a start up mode of operation; in the event that it is determined that the energy cell is in the start up mode, control operation of the energy cell and / or the liquid supplied to the energy cell to increase the generation of bubbles of plasma in the energy cell; and in the event that it is determined that the energy cell is in the normal mode, control operation of the energy cell so that a second operational parameter remains within a selected range.

[0010] The selected range may be below an upper threshold value associated with breakdown occurring in the cell. Breakdown may comprise electrical arcing occurring in the cell (e.g. between an electrode to which electrical energy is applied and an electrically grounded component of the cell, such as another electrode of the cell). The selected range may be above a lower threshold value associated with sub optimal efficiency for cell operation. For example, the selected range may be associated with efficient operation of the cell which will not lead to complete breakdown (e.g. arcing) occurring within the cell.

[0011] The first operational parameter may comprise at least one of a temperature and / or a pressure. The second operational parameter may comprise at least one of a current and / or a voltage. The controller may be configured to monitor both a current flow and a voltage applied to an electrode of the energy cell. The controller may be configured to control the voltage applied to the electrode based on the current flow. The controller may be configured to reduce the applied voltage in the event that the current exceeds a threshold current value. The controller may be configured to control application of voltage to the electrode according to a selected applied power level. The controller may be configured to increase the power applied to the electrodes while the current remains below a threshold current. For example, the controller may be configured to inhibit operation of the cell causing the current to exceed a threshold value. When operating in the normal mode of operation, the cell may be configured to apply a certain power to the cell, wherein the power is selected based on a level of demand for the cell. The power may be applied in the form of electrical energy (e.g. a voltage) being applied to an electrode of the cell. The cell may be configured to apply that same voltage, while the demand for the cell remains the same, as long as the current remains below the threshold value.

[0012] The controller may be configured to obtain at least one indication of a third operational parameter. The controller may be configured to determine an indication of a process quality for operation of the cell based on the third operational parameter. The third operational parameter may comprise at least one of an intensity and / or wavelength of light emissions in the cell. The process quality may provide an indication of an efficiency of cell operation. For example, the process quality may provide an indication of the number and / or range of different energy level transitions (and associated photon transmissions) occurring within the cell. The controller may be configured to control operation of the energy cell based on the determined indication of process quality. The controller may be configured to increase the power applied to the electrode of the energy cell in the event that the process quality is below a lower threshold. The controller may be configured to continue increasing the power applied to the electrode of the energy cell while the process quality remains below the lower threshold and a current flow remains below a current threshold. For example, the controller may be configured to control operation of the cell to increase the process quality (e.g. the efficiency), as long as the second operational parameter (e.g. a current) remains within the selected range. The controller may be configured to control operation to keep the process quality within a selected quality range as long as the second operational parameter remains within the selected range.

[0013] Controlling operation of the energy cell and / or the liquid supplied to the energy cell may comprise varying a separation distance between electrodes of the energy cell. Varying the separation distance between electrodes may comprise decreasing the separation distance for the start up mode of operation. Varying the separation distance between electrodes in the normal mode of operation may comprise increasing separation to increase output from the cell (e.g. in the event that plasma generation in the cell is above a threshold level), and / or decreasing the separation distance in the event that plasma generation is below a threshold level. The electrodes may be movable relative to one another to vary a separation distance between minimum and maximum separation values. The controller may be configured to select a separation distance in this range of values. For example, the range of values may be up to 10 cm, such as up to 5 cm, such as up to 2 cm, such as approximately 1 cm. For example, a minimum electrode separation may be at least 5 cm, such as at least 6 cm, such as at least 7 cm, such as at least 8 cm. For example, the electrodes may be separated by a minimum of 5 cm and a maximum of 10 cm, e.g. a minimum of 6 cm and / or a maximum of 9 cm. For example, the electrodes may be movable between a minimum separation distance of 8 cm and a maximum separation distance of 9 cm.

[0014] Controlling operation of the energy cell and / or the liquid supplied to the energy cell may comprise selectively providing bubbles in the liquid supplied to the energy cell. For example, the apparatus may be configured to provide bubbles in the liquid supplied to the cell. The bubbles may comprise any oxygen bearing gas, such as CO2or NO2etc (i.e. the bubbles may be of any gas which contains oxygen). The gas may be soluble in liquid, e.g. the gas may be soluble in the liquid to be supplied to the cell. Selectively providing bubbles in the liquid supplied to the energy cell may comprise providing bubbles in the liquid for the start up mode of operation. Selectively providing bubbles in the liquid supplied to the energy cell may comprise increasing an amount of bubbles in the liquid provided to the cell to increase output from the cell and / or decreasing an amount of bubbles in the liquid provided to the cell to decrease output from the cell. The apparatus may be configured to continually provide bubbles in the liquid supplied to the cell. For example, the apparatus may comprise means for providing gaseous (oxygen bearing) bubbles within the liquid supplied to the apparatus. The means may be operated such that liquid supplied to the cell has at least a threshold amount of bubbles therein.

[0015] Providing bubbles in the liquid supplied to the cell may comprise blowing a gas into the liquid. The gas may be blown into the liquid upstream of the energy cell, e.g. in a reservoir coupled to the cell and / or between the reservoir and the cell, and / or it may comprise blowing bubbles into the cell itself. Providing bubbles may comprise actively adding gaseous bubbles to an existing liquid and / or it may comprise using a liquid with additional bubbles already included. For example, the apparatus may be configured to aerate existing liquid, e.g. in a reservoir. Additionally, or alternatively, the apparatus may be operable to selectively apply different liquids to the cell. For example, the apparatus may utilise a first liquid and a second liquid, wherein the first liquid is more gassified, e.g. contains more bubbles, as compared to the second liquid. The controller may be configured to selectively use an increased amount of the first (gassier) liquid when an increased amount of bubbles is to be used.

[0016] The controller may be configured to switch operation of the energy cell into a cooldown mode (e.g. in which the generation of bubbles of plasma in the energy cell is reduced and / or inhibited, and / or in which no heated fluid is to be output from the cell). The cooldown mode may comprise at least one of: (i) a dormant mode of operation, and (ii) a shutdown mode of operation. The controller may be configured to receive a signal and / or have stored data indicative of a time at which future usage of the cell to generate heated fluid is expected. In other words, the controller may be configured to determine (e.g. predict) a time period over which there is no demand for heated fluid from the cell (e.g. an estimated time period for inactivity of the energy cell). For example, the cell may be configured to control operation of the cell according to a selected timing schedule, e.g. which stipulates times at which heated fluid is to be output and times at which it is not. The controller may be configured to switch operation of the energy cell into the cooldown mode in the event that there is no demand for heated fluid output from the cell. The controller may be configured to determine whether to switch the energy cell into the dormant mode or the shutdown mode based on an indication of the next time at which the energy cell is to be used to generate heated fluid. For example, the controller may be configured to utilise the dormant mode in the event that there will be (and / or there is likely to be) a demand for cell restarting within a threshold time period (e.g. and otherwise to use the shutdown mode).

[0017] Switching operation of the energy cell into the cooldown mode may comprise switching operation of the cell into a dormant mode in the event that the cell is to be disactivated and then subsequently restarted within a threshold time period. In the dormant mode, the controller may be configured to obtain an indication of at least one operational parameter of the cell and to control operation of the cell so that said operational parameter remains within a threshold range. The threshold range may be selected so that an amount of time and / or energy required to restart the cell into operating in its normal mode of operation is below a threshold level. Switching operation of the energy cell into the cooldown mode may comprise switching operation of the cell into a shutdown mode in the event that the cell is to be disactivated and then not subsequently restarted within the threshold time period.

[0018] The obtained indication of a first operational parameter may be an indication of a variation in an electrical signal applied to an electrode of the cell, e.g. a variation in at least one property / parameter of the applied electrical signal. The variation in the electrical signal may be based on (e.g. it may comprise) a variation in at least one of a voltage, a current and / or a resistance associated with that signal. For example, the apparatus may be configured to: (i) apply an electrical signal to the electrode (for application of electrical energy to the liquid in the cell), and (ii) monitor one or more values of that applied electrical signal. The apparatus may be configured to apply the electrical signal according to a selected input power level and / or with maximum values for permitted voltage and / or current. The apparatus may be configured to apply a voltage signal to the electrode and to monitor one or more properties (e.g. current, voltage or resistance) of the resulting signal (e.g. of that signal as it is applied to the electrode). The first operational parameter may comprise an indication of values of the electrical signal applied to the electrode and / or an indication of a variation in said values. The controller may be configured to determine that the energy cell is in the start up mode in the event that the variation in the electrical signal is below a threshold level. The controller may determine an indication of variation in the electrical based on differences in magnitude between the different obtained values. For example, the controller may determine that there is a greater variation in the electrical signal where the difference between maximum and minimum recorded values is greater. The applied electrical signal may be an applied voltage. The controller may be configured to determine that the energy cell is in the start up mode in the event that the variation in the applied signal (e.g. voltage, current or resistance) is below a threshold level. The indication of the variation may be based on a mean and / or a range of obtained values for the applied electrical signal. For example, the indication of variation may be based on a ratio of the range to the mean (for the obtained values for the electrical signal).

[0019] The second operational parameter may comprise an indication of the variation in the electrical signal applied to the electrode. The controller may be configured to control operation in the normal mode to retain the variation in the electrical signal above a threshold level. The controller may store an indication of two threshold values for variation in the applied electrical signal. A first, lower, value may be associated with plasma generation initiating, and a second, higher, value may be associated with satisfactory plasma generation. The controller may be configured to control operation of the cell to be in the start up mode until the first value has been reached for the variation in the electrical signal. The controller may be configured to control operation of the cell to continue increasing the variation in the signal until the second threshold has been reached. The controller may be configured to control operation in the normal mode to inhibit the variation in the electrical signal dropping below the second value.

[0020] In an aspect, there is provided an apparatus comprising: an energy cell configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein; and a controller configured to control the cell to operate in: (i) a normal mode of operation, and (ii) a dormant mode of operation, wherein: in the normal mode of operation, the controller is configured to receive an indication of a first operational parameter of the energy cell and to control operation so that the first operational parameter remains within a first selected range associated with normal operation of the energy cell; and in the dormant mode of operation, the controller is configured to receive an indication of a second operational parameter of the energy cell and to control operation so that the second operational parameter remains within a second selected range associated with dormant operation of the energy cell.

[0021] The controller may be configured to switch operation of the cell from the normal mode into the dormant mode in the event that the cell is to be disactivated and then subsequently restarted within a threshold time period. The controller may be configured to switch operation of the cell from the normal mode into a shutdown mode in the event that the cell is to be disactivated and then not subsequently restarted within the threshold time period. For example, the controller may be configured to control the cell to operate in three modes: (i) normal, (ii) dormant, and (iii) shutdown. The controller may also be configured to control the cell to operate in a start up mode. The controller may be configured to use the start up mode after the shutdown mode has been used. The controller may be configured to restart the cell into the normal mode of operation from the dormant mode quicker than from the shutdown mode. The second threshold range may be selected so that an amount of time and / or energy required to restart the cell into operating in its normal mode of operation is below a threshold level.

[0022] The first selected range may be below an upper threshold value associated with breakdown occurring in the cell. The first selected range may be above a lower threshold value associated with sub optimal efficiency for cell operation. The second selected range may be below the lower threshold value associated with sub optimal efficiency for cell operation. The second selected range may be below a threshold level above which plasma generation occurs within the cell. The second selected range may be above a threshold level associated with applying no energy to the cell. The second selected range may be selected to be within a threshold amount from the level above which plasma generation occurs in the cell, e.g. so that the cell remains within a threshold time period from being restarted into operating in its normal mode of operation (e.g. where that threshold time period is less than the time period associated with restarting the cell into its normal mode of operation from the shutdown mode of operation).

[0023] The second operational parameter may comprise at least one of a temperature and / or a pressure. The first operational parameter may comprise at least one of a current and / or a voltage. The controller may be configured to monitor both a current flow and a voltage applied to an electrode of the energy cell. The controller may be configured to control the voltage applied to the electrode based on the current flow. The controller may be configured to reduce the applied voltage in the event that the current exceeds a threshold current value. The controller may be configured to control application of voltage to the electrode according to a selected applied power level. The controller may be configured to increase the power applied to the electrodes while the current remains below a threshold current. The controller may be configured to obtain at least one indication of a third operational parameter. The controller may be configured to determine an indication of a process quality for operation of the cell based on the third operational parameter. The third operational parameter may comprise at least one of an intensity and / or wavelength of light emissions in the cell. The controller may be configured to control operation of the energy cell based on the determined indication of process quality. The controller may be configured to increase the power applied to the electrode of the energy cell in the event that the process quality is below a lower threshold. The controller may be configured to continue increasing the power applied to the electrode of the energy cell while the process quality remains below the lower threshold and a current flow remains below a current threshold.

[0024] Controlling operation of the energy cell and / or the liquid supplied to the energy cell may comprise varying a separation distance between electrodes of the energy cell. Varying the separation distance between electrodes may comprise decreasing the separation distance for the start up mode of operation. Varying the separation distance between electrodes in the normal mode of operation may comprise increasing separation to increase output from the cell (e.g. in the event that plasma generation in the cell is above a threshold level), and / or decreasing the separation distance in the event that plasma generation is below a threshold level. Controlling operation of the energy cell and / or the liquid supplied to the energy cell may comprise selectively providing bubbles in the liquid supplied to the energy cell. Selectively providing bubbles in the liquid supplied to the energy cell may comprise providing bubbles in the liquid for the start up mode of operation. For example, the apparatus may be configured to provide bubbles in the liquid supplied to the cell. The bubbles may comprise any oxygen bearing gas, such as CO2or NO2etc. Selectively providing bubbles in the liquid supplied to the energy cell may comprise providing bubbles in the liquid for the start up mode of operation. Selectively providing bubbles in the liquid supplied to the energy cell may comprise increasing an amount of bubbles in the liquid provided to the cell to increase output from the cell and / or decreasing an amount of bubbles in the liquid provided to the cell to decrease output from the cell. The apparatus may be configured to continually provide bubbles in the liquid supplied to the cell. For example, the apparatus may comprise means for providing gaseous (oxygen bearing) bubbles within the liquid supplied to the apparatus. The means may be operated such that liquid supplied to the cell has at least a threshold amount of bubbles therein.

[0025] The obtained indication of a first operational parameter may be an indication of a variation in an electrical signal applied to an electrode of the cell. For example, the apparatus may be configured to: (i) apply an electrical signal to the electrode (for application of electrical energy to the liquid in the cell), and (ii) monitor one or more values of that applied electrical signal. The first operational parameter may comprise an indication of values of the electrical signal applied to the electrode and / or an indication of a variation in said values. In the normal mode, the controller may be configured to control operation of the energy cell to retain the variation in the electrical signal above a threshold level (e.g. associated with satisfactory plasma generation within the energy cell).

[0026] In an aspect, there is provided an apparatus comprising: an energy cell comprising a plurality of electrodes and configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein; and a controller configured to obtain an indication of at least one operational parameter of the energy cell, and wherein the controller is configured to control a separation distance between two electrodes in the energy based on the obtained indication.

[0027] The controller may be configured to decrease the electrode separation to increase cell output and / or to increase the electrode separation to decrease cell output. The controller may be configured to obtain an indication of a process quality for operation of the energy cell. The controller may be configured to control the electrode separation based on the obtained indication of process quality. The controller may be configured to control the electrode separation so that the obtained indication of process quality is above a quality threshold. The controller may be configured to increase the electrode separation distance in the event that plasma generating activity within the cell is above a threshold level (e.g. in the event that there is demand for more heated fluid output from the cell). The controller may be configured to decrease the electrode separation distance in the event that plasma generating activity within the cell is below a threshold level.

[0028] The electrodes may be movable relative to one another to vary a separation distance between minimum and maximum separation values. The controller may be configured to select a separation distance in this range of values. For example, the range of values may be up to 10 cm, such as up to 5 cm, such as up to 2 cm, such as approximately 1 cm. For example, a minimum electrode separation may be at least 5 cm, such as at least 6 cm, such as at least 7 cm, such as at least 8 cm. For example, the electrodes may be separated by a minimum of 5 cm and a maximum of 10 cm, e.g. a minimum of 6 cm and / or a maximum of 9 cm. For example, the electrodes may be movable between a minimum separation distance of 8 cm and a maximum separation distance of 9 cm. The controller may be configured to control the cell to operate in a normal mode of operation and a second mode of operation. The second mode of operation may comprise a start up mode or a dormant mode. The controller may be configured to control electrode separation so that, when the cell is operating in the start up mode, the electrode separation is lower than when operating in the normal mode of operation. In the normal mode of operation, the controller may be configured to control electrode separation so that said operational parameter remains within a first selected range. The first selected range may be below an upper threshold value associated with breakdown occurring in the cell. The first selected range may be above a lower threshold value associated with sub optimal efficiency for cell operation. In the dormant mode, the controller may be configured to control the electrode separation so that said operational parameter remains within a second selected range. The second selected range may be below a threshold level above which plasma generation occurs within the cell.

[0029] Wherein the second selected range may be above a threshold level associated with applying no energy to the cell. Wherein the second selected range may be selected to be within a threshold amount from the level above which plasma generation occurs in the cell, e.g. so that the cell remains within a threshold time period from being restarted into operating in its normal mode of operation (e.g. where that threshold time period is less than the time period associated with restarting the cell into its normal mode of operation from the shutdown mode of operation).

[0030] The controller may be configured to monitor both a current flow and a voltage applied to an electrode of the energy cell. The controller may be configured to control the voltage applied to the electrode based on the current flow. The controller may be configured to reduce the applied voltage in the event that the current exceeds a threshold current value. The controller may be configured to control application of voltage to the electrode according to a selected applied power level. The controller may be configured to increase the power applied to the electrodes while the current remains below a threshold current. The controller may be configured to obtain at least one indication of a third operational parameter. The controller may be configured to determine an indication of a process quality for operation of the cell based on the third operational parameter. The third operational parameter may comprise at least one of an intensity and / or wavelength of light emissions in the cell. The controller may be configured to control operation of the energy cell based on the determined indication of process quality. The controller may be configured to increase the power applied to the electrode of the energy cell in the event that the process quality is below a lower threshold. The controller may be configured to continue increasing the power applied to the electrode of the energy cell while the process quality remains below the lower threshold and a current flow remains below a current threshold.

[0031] Controlling operation of the energy cell and / or the liquid supplied to the energy cell may comprise selectively providing bubbles in the liquid supplied to the energy cell. Selectively providing bubbles in the liquid supplied to the energy cell may comprise providing bubbles in the liquid for the start up mode of operation. Selectively providing bubbles in the liquid supplied to the energy cell may comprise increasing an amount of bubbles in the liquid provided to the cell to increase output from the cell and / or decreasing an amount of bubbles in the liquid provided to the cell to decrease output from the cell. For example, the apparatus may be configured to provide bubbles in the liquid supplied to the cell. The bubbles may comprise any oxygen bearing gas, such as CO2or NO2etc. Selectively providing bubbles in the liquid supplied to the energy cell may comprise providing bubbles in the liquid for the start up mode of operation. Selectively providing bubbles in the liquid supplied to the energy cell may comprise increasing an amount of bubbles in the liquid provided to the cell to increase output from the cell and / or decreasing an amount of bubbles in the liquid provided to the cell to decrease output from the cell. The apparatus may be configured to continually provide bubbles in the liquid supplied to the cell. For example, the apparatus may comprise means for providing gaseous (oxygen bearing) bubbles within the liquid supplied to the apparatus. The means may be operated such that liquid supplied to the cell has at least a threshold amount of bubbles therein.

[0032] The obtained indication may be an indication of a variation in an electrical signal applied to an electrode of the cell. For example, the apparatus may be configured to: (i) apply an electrical signal to the electrode (for application of electrical energy to the liquid in the cell), and (ii) monitor one or more values of that applied electrical signal. The obtained indication of at least one operational parameter may comprise an indication of values of the electrical signal applied to the electrode and / or an indication of a variation in said values. The controller may be configured to decrease the separation distance in the event that the variation is below a first threshold amount, e.g. which is associated with insufficient plasma generation (to facilitate an increase in plasma generation). The controller may be configured to increase the separation distance in the event that the variation is above a second threshold amount, e.g. which is associated with satisfactory plasma generation (to increase output from the cell).

[0033] In an aspect, there is provided an apparatus comprising: an energy cell configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein; a controller configured to obtain an indication of at least one operational parameter of the energy cell, and wherein the controller is configured to control an amount of bubbles provided in the liquid supplied to the energy cell based on the obtained indication.

[0034] The controller may be configured to increase the amount of bubbles provided to increase cell output and / or to decrease the amount of bubbles provided to decrease cell output. The controller may be configured to provide bubbles in the liquid supplied to the energy cell in the event that the energy cell is operating in a start up mode of operation. The controller may be configured to reduce, e.g. inhibit, the provision of bubbles in the liquid supplied to the energy cell in the event that the cell is operating in a normal mode of operation (e.g. reducing the provision of bubbles as compared to when operating in the start up mode). For example, wherein a smaller volume of bubbles is provided in the liquid supplied to the cell when operating in the normal mode as compared to the start up mode. The bubbles may comprise any oxygen bearing gas, such as CO2or NO2etc. Selectively providing bubbles in the liquid supplied to the energy cell may comprise providing bubbles in the liquid for the start up mode of operation. Selectively providing bubbles in the liquid supplied to the energy cell may comprise increasing an amount of bubbles in the liquid provided to the cell to increase output from the cell and / or decreasing an amount of bubbles in the liquid provided to the cell to decrease output from the cell. The apparatus may be configured to continually provide bubbles in the liquid supplied to the cell. For example, the apparatus may comprise means for providing gaseous (oxygen bearing) bubbles within the liquid supplied to the apparatus. The means may be operated such that liquid supplied to the cell has at least a threshold amount of bubbles therein.

[0035] The apparatus may comprise a liquid supply system configured to supply the liquid to the energy cell. The controller may be configured to control operation of the liquid supply system to control the supply of liquid and the supply of bubbles within that liquid to the energy cell. The liquid supply system may comprise a bubble generating machine, such as a carbonator, configured to generate bubbles within the liquid to be supplied to the energy cell. The controller may be configured to receive an indication of at least one operational parameter of the energy cell. The controller may be configured to provide bubbles in the liquid supplied to the cell in the event that the at least one operational parameter does not satisfy a threshold criterion. The operational parameter may comprise at least one of a temperature and / or a pressure. The controller may be configured to control operation of the apparatus to supply liquid containing bubbles to the energy cell in the event that the energy cell is operating in a start up mode. The controller may be configured to limit, e.g. inhibit, the supply of liquid into the cell after the liquid containing bubbles has been provided to the cell while the cell is operating in a start up mode.

[0036] The controller may be configured to obtain at least one indication of an operational parameter of the energy cell, such as a temperature and / or a pressure, and to determine based on said indication when the cell has transitioned from a start up mode to a normal mode of operation. The controller may be configured to increase the flow rate for the supply of liquid to the energy cell once the cell operation has transitioned into the normal mode of operation. The controller may be configured to reduce, e.g. inhibit, the provision of bubbles in the liquid supplied to the cell when the cell is operating in its normal mode.

[0037] Providing bubbles in the liquid supplied to the cell may comprise blowing a gas into the liquid. The gas may be blown into the liquid upstream of the energy cell, e.g. in a reservoir coupled to the cell and / or between the reservoir and the cell, and / or it may comprise blowing bubbles into the cell itself. Providing bubbles may comprise actively adding gaseous bubbles to an existing liquid and / or it may comprise using a liquid with additional bubbles already included. For example, the apparatus may be configured to aerate existing liquid, e.g. in a reservoir. Additionally, or alternatively, the apparatus may be operable to selectively apply different liquids to the cell. For example, the apparatus may utilise a first liquid and a second liquid, wherein the first liquid is more gassified, e.g. contains more bubbles, as compared to the second liquid. The controller may be configured to selectively use an increased amount of the first (gassier) liquid when an increased amount of bubbles is to be used.

[0038] The obtained indication may be an indication of a variation in an electrical signal applied to an electrode of the cell. For example, the apparatus may be configured to: (i) apply an electrical signal to the electrode (for application of electrical energy to the liquid in the cell), and (ii) monitor one or more values of that applied electrical signal. The obtained indication of at least one operational parameter may comprise an indication of values of the electrical signal applied to the electrode and / or an indication of a variation in said values. The controller may be configured to provide bubbles (e.g. to maintain the provision of bubbles or to increase the amount of bubbles provided) in the liquid supplied in the event that the variation is below a first threshold amount, e.g. which is associated with insufficient plasma generation (to facilitate an increase in plasma generation). The controller may be configured to reduce or inhibit the provision of bubbles in the event that the variation is above a second threshold amount, e.g. which is associated with satisfactory plasma generation (to reduce demand upon the provision of bubbles within the liquid). In an aspect, there is provided an apparatus comprising: an energy cell configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein; and a controller configured to obtain an indication of at least one of an intensity and / or a wavelength of light emissions in the energy cell, and wherein the controller is configured to control operation of the energy cell based on said obtained indication.

[0039] The controller may be configured to control operation of the cell to increase output in the event that the intensity is below a lower threshold value and / or that the number of different wavelengths is below a lower threshold number. The controller may be configured to control operation of the cell to decrease output in the event that the intensity is above an upper threshold value and / or that the number of different wavelengths is above an upper threshold number. The controller may be configured to control operation of the cell to increase the number of different wavelengths of light, e.g. to provide whiter light. The controller may be configured to control operation of the cell to remain within a selected whiteness range. For example, the upper threshold value for the selected whiteness range may be below a value at which cell breakdown occurs and / or wherein the lower threshold value for the selected whiteness range is above a value at which cell operation efficiency drops below a selected level. The controller may be configured to determine based on the obtained indication whether the energy cell is operating in a start up mode of operation or a normal mode of operation. The controller may be configured to control operation of the cell to maintain the intensity and / or wavelength(s) of emitted light within a selected range. The selected range may be below an upper threshold value associated with breakdown occurring in the cell. The selected range may be above a lower threshold value associated with sub optimal efficiency for cell operation.

[0040] The controller may be configured to determine an indication of a process quality for operation of the cell based on the obtained indication. The controller may be configured to control operation of the energy cell based on the determined indication of process quality. The controller may be configured to increase the power applied to one or more electrodes of the energy cell in the event that the process quality is below a lower threshold. The controller may be configured to continue increasing the power applied to the electrode of the energy cell while the process quality remains below the lower threshold. The controller may be configured to continue increasing the power applied to the electrode while a current flow remains below a threshold value.

[0041] Controlling operation of the energy cell and / or the liquid supplied to the energy cell may comprise varying a separation distance between electrodes of the energy cell. Varying the separation distance between electrodes may comprise decreasing the separation distance for the start up mode of operation. Varying the separation distance between electrodes in the normal mode of operation may comprise increasing separation to increase output from the cell (e.g. in the event that plasma generation in the cell is above a threshold level), and / or decreasing the separation distance in the event that plasma generation is below a threshold level. Controlling operation of the energy cell and / or the liquid supplied to the energy cell may comprise selectively providing bubbles in the liquid supplied to the energy cell. Selectively providing bubbles in the liquid supplied to the energy cell may comprise providing bubbles in the liquid for the start up mode of operation. Selectively providing bubbles in the liquid supplied to the energy cell may comprise increasing an amount of bubbles in the liquid provided to the cell to increase output from the cell and / or decreasing an amount of bubbles in the liquid provided to the cell to decrease output from the cell. For example, the apparatus may be configured to provide bubbles in the liquid supplied to the cell. The bubbles may comprise any oxygen bearing gas, such as CO2or NO2etc. Selectively providing bubbles in the liquid supplied to the energy cell may comprise providing bubbles in the liquid for the start up mode of operation. Selectively providing bubbles in the liquid supplied to the energy cell may comprise increasing an amount of bubbles in the liquid provided to the cell to increase output from the cell and / or decreasing an amount of bubbles in the liquid provided to the cell to decrease output from the cell. The apparatus may be configured to continually provide bubbles in the liquid supplied to the cell. For example, the apparatus may comprise means for providing gaseous (oxygen bearing) bubbles within the liquid supplied to the apparatus. The means may be operated such that liquid supplied to the cell has at least a threshold amount of bubbles therein.

[0042] In an aspect, there is provided an apparatus comprising: an energy cell comprising a plurality of electrodes and configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein; and a controller configured to: control application of a voltage to an electrode of the energy cell and to monitor a resulting current flow; increase the voltage applied to the electrode while the resulting current remains below a threshold value; and in the event that the current excess the threshold value, decreasing the voltage applied to the electrode.

[0043] The threshold current value may be below a current value associated with breakdown occurring in the cell. The controller may be configured to control the cell to operate in: (i) a start up mode of operation, and (ii) a normal mode of operation. In the normal mode of operation, the controller may be configured to control application of the voltage to the electrode to maintain the resulting current above a lower threshold value. The lower threshold value may be associated with sub optimal efficiency for cell operation. The controller may be configured to control the application of voltage to the electrode according to a selected applied power level. The controller may be configured to increase the power applied to the electrodes while the current remains below a threshold current.

[0044] The controller may be configured to obtain at least one indication of an operational parameter. The controller may be configured to determine an indication of a process quality for operation of the cell based on the third operational parameter. The operational parameter may comprise at least one of an intensity and / or wavelength of light emissions in the cell. The controller may be configured to control operation of the energy cell based on the determined indication of process quality. The controller may be configured to increase the power applied to the electrode of the energy cell in the event that the process quality is below a lower threshold. The controller may be configured to continue increasing the power applied to the electrode of the energy cell while the process quality remains below the lower threshold and a current flow remains below a current threshold.

[0045] Controlling operation of the energy cell and / or the liquid supplied to the energy cell may comprise varying a separation distance between electrodes of the energy cell. Varying the separation distance between electrodes may comprise decreasing the separation distance for the start up mode of operation. Varying the separation distance between electrodes in the normal mode of operation may comprise increasing separation to increase output from the cell (e.g. in the event that plasma generation in the cell is above a threshold level), and / or decreasing the separation distance in the event that plasma generation is below a threshold level. Controlling operation of the energy cell and / or the liquid supplied to the energy cell may comprise selectively providing bubbles in the liquid supplied to the energy cell. For example, the apparatus may be configured to provide bubbles in the liquid supplied to the cell. The bubbles may comprise any oxygen bearing gas, such as CO2or NO2etc. Selectively providing bubbles in the liquid supplied to the energy cell may comprise providing bubbles in the liquid for the start up mode of operation. Selectively providing bubbles in the liquid supplied to the energy cell may comprise increasing an amount of bubbles in the liquid provided to the cell to increase output from the cell and / or decreasing an amount of bubbles in the liquid provided to the cell to decrease output from the cell. The apparatus may be configured to continually provide bubbles in the liquid supplied to the cell. For example, the apparatus may comprise means for providing gaseous (oxygen bearing) bubbles within the liquid supplied to the apparatus. The means may be operated such that liquid supplied to the cell has at least a threshold amount of bubbles therein. The controller may be configured to obtain an indication of a variation in an electrical signal applied to an electrode of the cell. For example, the apparatus may be configured to: (i) apply an electrical signal to the electrode, e.g. in the form of a voltage signal, (for application of electrical energy to the liquid in the cell), and (ii) monitor one or more values of that applied electrical signal, e.g. values of the applied voltage. The controller may be configured to determine an indication of the amount of plasma being generated based on the variation in the applied electrical signal (e.g. based on variation in the voltage applied to the electrode and / or the resulting current). The controller may be configured to increase the voltage applied in the event that the variation in electrical signal is below a threshold level.

[0046] In an aspect, there is provided an apparatus comprising: an energy cell comprising an electrode configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein; and a controller configured to monitor an electrical signal applied to the electrode and to determine an indication of an amount of plasma generation occurring within the energy cell based on a variation in the applied electrical signal.

[0047] The applied electrical signal may be an applied voltage. Monitoring the electrical signal applied to the electrode may comprise monitoring at least one of a voltage, a current and a resistance associated with the applied signal. For example, the electrical signal is applied to the electrode, and the apparatus may be configured to obtain an indication of at least one of: (i) a current value resulting from that applied signal, (ii) a value of the applied voltage, and / or (iii) a resistance to that applied signal. The controller may be configured to determine the indication of plasma generation occurring based on a variation in any of said obtained indications, e.g. based on variation in current, voltage and / or resistance. Determining the indication of the amount of plasma generation may be based on a range between lower and higher values for the electrical signal, e.g. voltage values. Determining the indication may be based on a ratio of the range between lower and higher values relative to an average value for the applied electrical signal. For example, the controller may be configured to determine that at least some bubbles of plasma are being generated in the cell in the event that the applied electrical signal (e.g. voltage) varies by more than a threshold amount, e.g. as compared to a mean value for that applied electrical signal (e.g. a mean voltage). The controller may be configured to determine that an increased generation of plasma bubbles is occurring as the variation increases above the threshold amount. The controller may be configured to determine that satisfactory plasma generation is occurring in the event that the variation in signal exceeds a second, higher, threshold amount. The controller may be configured to control operation of the cell to increase the plasma generation until the variation in signal exceeds the second threshold value (e.g. as part of a start up mode of operation). The controller may be configured to then control operation of the cell to inhibit the variation in signal dropping below the second threshold value (e.g. when operating in a normal mode of operation).

[0048] The apparatus may be configured to control operation of the energy cell based on the determined indication of the amount of plasma generation occurring within the cell, e.g. based on the variation in electrical signal. The apparatus may be configured to increase the electrical energy applied to the electrode in the event that the variation in the applied electrical signal is below a threshold value. The apparatus may be configured to determine that plasma generation is occurring in the event that the variation in the applied electrical signal is at or above the threshold value. The apparatus may be configured to increase the electrical energy applied until the variation in the applied electrical signal is at or above a second, greater, threshold value. The apparatus may be configured to apply the electrical signal to the electrode according to a selected power level. The apparatus may be configured to vary the applied voltage in dependence on the resulting current associated with that applied voltage, thereby to apply electrical energy according to the selected power level. The controller may be configured to determine the indication of an amount of plasma generation occurring within the energy cell based on a variation in the current and / or voltage of the applied signal.

[0049] Aspects of the present disclosure may comprise a system comprising: any of the apparatuses disclosed herein; a liquid supply system coupled to the energy cell and configured to supply a liquid to be heated to the energy cell; and a work extraction system coupled to the energy cell and configured to extract useable work from heated fluid output from the energy cell.

[0050] Aspects of the present disclosure comprise any of the methods disclosed herein for controlling operation of an energy cell. Aspects of the present disclosure also comprise computer program products for controlling operation of an energy cell to perform any of said methods disclosed herein.

[0051] Figures

[0052] Some examples of the present disclosure will now be described, by way of example only, with reference to the figures, in which: Fig. 1 is a schematic diagram illustrating an energy cell.

[0053] Fig. 2a is a graph illustrating possible operational characteristics of an energy cell over time. Fig. 2b is a graph illustrating possible operational characteristics of an energy cell over time. Fig. 3a is a flowchart illustrating an example method for operating an energy cell.

[0054] Fig. 3b is a table showing different indications for observable parameters of an energy cell. Fig. 4a is a flowchart illustrating an example method for operating an energy cell.

[0055] Fig. 4b is a table showing different indications for observable parameters of an energy cell.

[0056] In the drawings like reference numerals are used to indicate like elements.

[0057] Specific Description

[0058] The present disclosure relates to controlling operation of an energy cell. Electrical energy is applied to a fluid in the energy cell to generate bubbles of plasma therein. In turn, this causes a release of energy into surrounding fluid and the cell housing which results in the fluid being heated up. In turn, this heated fluid provides a higher quality of fluid from which work can be extracted, as the pressure and temperature will be higher (due to the fixed volume of the cell). For example, the heated fluid may be in the form of a hot and highly pressurised gas. The heated fluid is then output from the cell and useable work may be extracted from this heated fluid. The cell may be operated to maintain sufficient generation of plasma bubbles to provide efficient heating of the fluid, while also being operated to inhibit breakdown occurring in the cell where a low resistance current path forms between an electrode and an electrical earthing point, i.e. when electrical arcs occur without providing the same heating effect associated with the plasma generation. Operation of the cell may also be controlled during a start up period to prepare the cell for subsequently operating in the normal mode of operation in which cell output is maintained at a suitably high level while also avoiding the likelihood of breakdown occurring.

[0059] An example of an energy cell will now be described with reference to Fig. 1 .

[0060] Fig. 1 shows a schematic diagram of an energy cell 100. The cell 100 includes a fluid inlet 101 and a fluid outlet 103. The cell 100 has a housing 150. The housing 150 defines an internal portion 156 of the cell 100. The cell 100 also includes a plurality of electrodes. As shown, this includes a first electrode 110, a second electrode 120 and a third electrode 130. The cell 100 may also include a resistive element 140. Although not shown, the cell 100 may be connected to a supply system. The supply system may supply liquid to the cell 100 through the inlet 101. The liquid supplied may also contain some gas therein, e.g. gas bubbles. Likewise, although not shown, the cell 100 may be connected to a work extraction system. The work extraction system may extract useable work from heated fluid from the outlet 103.

[0061] The housing 150 of the cell 100 encapsulates the internal portion 156. The fluid inlet 101 provides a flow path for fluid into the internal portion 156 of the cell 100. The fluid outlet 103 provides a flow path for fluid out from the internal portion 156 of the cell 100. Fluid may flow along any suitable path between the fluid inlet 101 and the fluid outlet 103. For example, it may flow along a very indirect (e.g. tortuous) path. The internal portion 156 of the cell 100 may otherwise be sealed by the housing 150.

[0062] The first electrode 110 is at least partially disposed within the internal portion 156 of the cell 100. The second electrode 120 may also be disposed at least partially within the internal portion 156 of the cell 100. The first and second electrode 120 are arranged concentrically. The first electrode 110 extends within a central region of the internal portion 156 of the cell 100. The second electrode 120 is arranged radially outward from the first electrode 110. The second electrode 120 may be cylindrical, as may the first electrode 110. The first and second electrode 120 are arranged co-axially in the example shown in Fig. 1. The second electrode 120 is located adjacent to an internal surface of the housing 150 (however in some examples, the second electrode 120 may be integrated with the housing 150, e.g. to form a part thereof, and / or a portion of the housing 150 may provide the second electrode 120, e.g. if said portion of the housing is electrically conductive).

[0063] A first end of the first electrode 110 is located outside the internal portion 156 of the housing 150. A second end of the first electrode 110, distal to the first end, is located within the internal portion 156 of the housing 150. The second electrode 120 may extend along some, or all, of the length of the internal portion 156 of the housing 150. At least one end of the second electrode 120 may extend out of the internal portion 156 of the cell 100. Although not shown in Fig. 1 the first and / or second electrode 120 may each be coupled to a power supply. For example, each electrode may have one end which extends outside the internal portion 156 (e.g. into the housing 150), and this end may be coupled to the power supply. In some examples, the housing 150 may provide a ground, and the first electrode 110 may be connected to a positive terminal of the power supply. In Fig. 1 , the second electrode 120 is shown as being a separate component to the housing 150, but this need not be the case, as the second electrode 120 may be provided by the housing 150 (e.g. the housing 150 may be made of an electrically conductive material which may function to provide the second electrode 120).

[0064] The third electrode 130 is also provided in the internal portion 156 of the cell 100. A first end of the third electrode 130 may be located outside the internal portion 156, and the third electrode 130 may extend form the first end to a second end located within the internal portion 156. The second end of the third electrode 130 may be located proximal to the second end of the first electrode 110 within the internal portion 156. The first and third electrodes 110, 130 may be parallel (e.g. they may be co-axial). The second and third electrodes 120, 130 may be parallel (e.g. coaxial). The first electrode 110 may extend from outside a first end of the housing 150 into the internal portion 156 towards an opposite end of the housing 150. The third electrode 130 may extend from outside the opposite end of the housing 150 into the internal portion 156 towards the first end. The first and third electrodes 110, 130 may extend into the internal portion 156 so that there is no spatial overlap between these electrodes 110, 130 (e.g. their respective second ends do not to uch / o verlap). The second electrode 120 may extend along the length of the internal portion 156 from at or outside the first end to at or outside the opposite end. The distance between the second end of the first electrode 110 and the second end of the third electrode 130 may be less than the smallest distance between the first electrode 110 and the second electrode 120. The third electrode 130 may be located away from an expected current path between the first and second electrode 120.

[0065] A resistive element 140 may also be included in the internal portion 156. The resistive element 140 may also be cylindrical. The resistive element 140 may be arranged to increase the electrical resistance of the conductive path between the first electrode 110 (anode) and the second electrode 120 (cathode). The resistive element 140 may be provided by a single (e.g. contiguous) piece of material or it may be provided by multiple pieces of material. For example, different portions of the resistive element 140 could be provided by different components, wherein each potion may contribute to providing an electrical resistance for the resistive element 140 as a whole. Different portions of the resistive element could be electrically connected and provided by different materials / components. For example, the resistive element 140 could include circuitry, such as a sensor (e.g. a photovoltaic sensor). The different portions of the resistive element 140 need not be physically and / or electrically connected. The resistive element 140 may increase the electrical resistance between the first and second electrodes 110, 120. The resistive element 140 may extend around a majority (e.g. all) of the internal portion 156 (e.g. along a length and width of the internal portion to impede the majority of possible conductive paths from anode to cathode). The resistive element 140 may be located between the first / third and second electrodes 110, 120. For example, the resistive element 140 may be located radially outward from the first / third electrodes 110, 130, but not as far radially outward than the second electrode 120. The resistive element 140 may extend along some or all of the length of the internal portion 156.

[0066] The housing 150 may be cylindrical. That is, a cross-sectional shape (i.e. when viewed in plan) of the housing 150 may be circular. Alternatively, the housing 150 may be polygon shaped. The housing 150 may be provided by a shape which is tessellatable (i.e. which is capable of being tessellated with other copies of that same shape). For example, multiple cells 100 may be provided together, e.g. to increase output as compared to that provided by a single cell 100. In which case, the cells 100 may be stacked together. The cells 100 may be designed to facilitate more space efficient stacking. For example, the cells 100 may be arranged so that, when stacked together, they tessellate with each other (or at least substantially tessellate to provide more space efficient stacking). As will be appreciated, any suitable tessellatable shape may be used for this purpose. For example, the shape may be any suitable polygon, such as a hexagon or an octagon. The shape may be imparted by an outer surface of the housing 150, e.g. with everything thereinside being circular (including the inner surface of the housing 150), or the shape may be impaired by the inner surface of the housing 150.

[0067] The fluid inlet 101 is arranged at an opposite end of the housing 150 to the fluid outlet 103. The first and second electrode 120 extend along an axis extending from the fluid inlet 101 to the fluid outlet 103 (e.g. a longitudinal axis of the cell 100). The fluid outlet 103 may be arranged higher (e.g. above, such as directly above or above and laterally offset from) the fluid inlet 101. The housing 150 is configured to encapsulate the internal portion 156. The housing 150 is arranged to define the internal portion 156 to provide a region in which liquid may be heated. An internal surface of the housing 150 (e.g. which faces / defines the internal portion 156) may be configured to generate heat in response to incident photons (for example, the housing 150 may be conductive). The internal surface may comprise the region of the housing 150 which lies adjacent to the internal portion 156. This may comprise part of the housing 150 and / or it may comprise an additional component, such as a layer / film provided there to absorb incident photons, and in response to generate heat. For example, the internal surface may be configured to absorb electromagnetic energy, such as in the form of visible light. The internal surface is configured to heat up as it receives incident photons. The internal surface is configured to provide heating of fluid within the internal portion 156, e.g. as it heats up from incident photons. The housing 150 may be made of a metal, such as steel, or other materials may be used, such as a ceramic. For example, a glass with e.g. boron or lead may be used. The housing 150 may be formed of multiple different materials. The different materials may be selected based on their photon absorption characteristics. For example, materials may be selected which absorb photons in different wavelength range(s) for which photons are expected within the internal portion 156, e.g. for visible, infrared, ultraviolet. The housing 150 may comprise a plurality of layers, e.g. with an outer housing layer, and an inner layer, such as a sleeve, inside the outer layer. The different layers may be made of different materials. The housing 150 is configured to retain fluid in the internal portion 156 under pressure.

[0068] The fluid inlet 101 , the internal portion 156, and the fluid outlet 103 are arranged to define a flow path for fluid to flow through the internal portion 156 of the housing 150. The internal portion 156 is arranged to receive liquid to be heated through the fluid inlet 101. The cell 100 is arranged to heat this liquid in the internal portion 156 to provide a heated fluid. The fluid outlet 103 is arranged to provide a flow path for this heated fluid away from the internal portion 156.

[0069] The first and second electrodes 110, 120 are configured to provide a current flow path through the internal portion 156 of the cell 100. One of the electrodes 110, 120 may provide an anode, and the other may provide a cathode. For instance, the first electrode 110 may provide the anode for bringing current into the internal portion 156 of the cell 100. The second electrode 120 may then provide the cathode for carrying current away from the internal portion 156 of the cell 100. The first and second electrode 120 are spaced apart from each other. The first electrode 110 is arranged to receive a voltage so that a potential difference exists between the first and second electrodes 110, 120. The first and second electrodes 110, 120 are arranged capacitively. The presence of fluid in the internal portion 156 may provide a conductive path between the first and second electrode 120. The fluid will provide electrical resistance between the two electrodes 110, 120. The first and second electrode 120 with fluid in the cell 100 may effectively provide a circuit having a capacitance and a resistance. The first and second electrodes 110, 120 are configured to provide a voltage stress to fluid and / or plasma within the internal portion 156.

[0070] The third electrode 130 may be active or passive. When active, a voltage is applied to the third electrode 130. When passive, the third electrode 130 may be conductive for receiving current within the internal portion 156, but without receiving power from the power supply 30. The third electrode 130 may be configured to provide a balancing electrode (e.g. it may be arranged to balance electric field / current generated within the internal portion 156). The third electrode 130 may comprise a tip of electrically conductive material (i.e. which is arranged within the internal volume 156 of the cell 1). The tip need not be electrically connected to a component outside of the cell 100. For example, where the third electrode 130 is passive, the provision of an electrical conductor within the housing 100 may provide passive balancing. For example, such a tip could be capable of charging and discharging by itself.

[0071] For example, the first electrode 110 may be active, the second electrode 120 may be passive and third electrode 130 could be active or passive. A distal tip of the first electrode 110 (i.e. the exposed tip within the cell would be electrically connected to a voltage source (e.g. external to the cell 100). The second electrode 120 may be electrically grounded (e.g. so that current may flow from the second electrode 120 to ground). The third electrode 130, when passive, may provide an exposed portion of electrically conductive material within the internal volume 156 of the cell 100. That passive exposed portion of electrically conductive material may be arranged to be charged and / or discharged within the cell (e.g. due to internal electrical conditions of the cell). The third electrode 130, when active, may be connected to a voltage source. An exposed portion of the third electrode 130 within the cell 100 may then be connected to the voltage source.

[0072] The resistive element 140 may be arranged on a current flow path between the first electrode 110 and the second electrode 120, e.g. so that current would need to flow through the resistive element 140 to get from the first electrode 110 to the second electrode 120. The resistive element 140 may extend along one or both of the ends of the internal portion 156 (e.g. to reduce the likelihood of a conductive path from anode to cathode not via the resistive element 140 being possible). The resistive element 140 may be configured to be of relatively high resistance (e.g. as compared to the resistance of the electrodes and / or fluid within the internal portion 156). The resistive element 140 may be of sufficient resistance to effectively provide an electrical insulator (between the anode and cathode).

[0073] In operation, a liquid is supplied through the fluid inlet 101 and into the internal portion 156 of the cell 100. In this example, the liquid will be water, but other liquids may be used. For example, the liquid may be any aqueous solution, such as tap water, sea water, ionised water etc. The liquid may be any non-Newtonian liquid. The liquid may be a non-electrically insulating liquid. The liquid may be at least partially electrically resistive (but not fully resistive). The cell 100 will fill up with water. Any gas previously in the cell 100 may be forced out through the fluid outlet 103 of the cell 100. The cell 100 may then be substantially filled with water. A voltage is applied to the first electrode 110 (anode). This will cause some current flow into the water. Due to the electrical resistance of water, this current flow and resistance will cause some heating of the water (e.g. I2R heating). This process of resistive heating continues as a voltage is applied to the first electrode 110. As the temperature of the water within the internal portion 156 rises, microbubbles of gas will start to form within the water in the internal portion 156. These may be steam bubbles forming or bubbles of gas being released which were trapped in the water supplied to the internal portion 156 of the cell 100. As will be appreciated, a number of different gases may be present in the liquid, such as dissolved gases. For example, CO2, or air may be present, as may other gases. As a result, some pockets of gas will develop within the liquid in the internal portion 156 of the cell 100. With continued application of the voltage to the first electrode 110, bubbles of plasma will be generated within the internal portion 156 of the housing 150. These bubbles will release energy into the surrounding fluid and the internal surface of the housing 150. In turn this provides heating of the fluid within the internal portion 156.

[0074] By applying the voltage to the first electrode 110, this may charge up the capacitor provided by the first and second electrode 120. As the fluid within the internal portion 156 heats up, its permittivity may change, and this may change a capacitance of the cell 100 (e.g. between the first and second electrodes 110, 120). For example, when water is used, its permittivity will decrease as it heats up (and then also when it becomes steam). In particular, where microbubbles of gas (e.g. steam) begin to form within the liquid in the internal portion 156, these will provide localised regions of lower permittivity. This process may effectively provide a permittivity collapse in localised regions. For example, where water is used, this difference in permittivity between bubbles forming in the water and the surrounding water may be a factor of approximately 40 (e.g. the capacitance per unit volume in those bubbles may be 1 / 40th of that of the surrounding water). During this process, the volumetric energy density for fluid and / or plasma within the internal portion 156 will remain constant. Due to the permittivity collapse within the bubbles of gas, capacitance will decrease in this region. As the volumetric energy density remains constant and the capacitance decreases, the voltage per meter will rise accordingly (e.g. to conserve energy as per E=1 / 2 CV2). For examples where water is used, the voltage per meter will rise by a factor of approximately ^40.

[0075] With electrical energy still being applied to the first electrode 110, these microbubbles of gas (at lower density than surrounding liquid) will try to rapidly expand into their surroundings. However, the surrounding liquid will resist this expansion, e.g. due to the non-Newtonian nature of the liquid in these conditions. This will cause the microbubbles to rapidly increase in temperature and pressure. In turn, their capacitance will further decrease (e.g. causing an increased dV / dr), thereby giving rise to further increased voltage stress across the bubble. With sufficient voltage stress across the bubble, ionization may occur leading to the formation of plasma within the bubble. Thus, one or more plasma bubbles may form in the liquid in the internal portion 156. The plasma may be at an even lower density than the gas, and so with a voltage still applied to the first electrode 110, the plasma bubble will further try to rapidly expand. In particular, this process of plasma bubble generation will occur rapidly, and so each bubble of plasma will drive for rapid expansion. In turn, this will bring about nonNewtonian fluid responses in the liquid in the internal portion 156 of the cell 100. For instance, where water is used, the water does not immediately yield before the pressure wave brought about by the bubble of plasma trying to expand. The bubble of plasma is therefore held in a relatively fixed volume (e.g. it may only expand relatively slowly). While the volume of the plasma remains relatively constant, the temperature and pressure within this bubble rise rapidly in response to the voltage stress brought about by the voltage applied to the first electrode 110.

[0076] As mentioned above, the breakdown of gas may occur such that a low impedance bridge forms (e.g. the gas resistivity drops), but not as far as a full breakdown in which electrical arcing occurs. In addition to this, thermionic emission may occur within the cell 100. Electron spraying may occur with electrons moving between different electrodes of the cell. In particular, electrons may pass from the first electrode 110 to the second electrode 120 and / or from the first electrode 110 to the third electrode 130. In turn, this may also cause electrons to pass from the third electrode 130 to the second electrode 120. In other words, the third electrode 130 may act to draw in electrons (i.e. from the first electrode 110) before then sending them out (i.e. to the second electrode 120). This may act to stretch out the plasma generating region, which in turn may increase the stability thereof. The electrons may accelerate through the gas bubbles which have formed.

[0077] The electrodes may be designed to provide a preferential flow for the electron movement. For example, the material of each electrode (and in particular its valence) may be selected to impart this preferential flow of electrons. For example, tungsten may be used for the first electrode as it has a high valence. The electrodes may be arranged to provide a preferential flow from the first electrode 110 to the third electrode 130 (as compared to a flow from the first electrode 110 to the second electrode 120). This may act to stretch out the plasma generating region, which in turn may provide greater stability and / or a greater amount of work output.

[0078] Energy may be absorbed by atoms (and molecules) within the bubble. The energy levels (e.g. states) of these particles may therefore rise. Within the plasma, atoms may have their electrons move to higher electron energy levels, and / or spin states for these particles may change. For example, Hydrogen atom spin states may change from their lower energy parastate to their higher energy ortho-state. Molecules may also move to higher rotational and / or vibrational energy levels, and / or further splitting up of these molecules may occur. As a result, the atoms within each bubble will be at disproportionately high energy levels (e.g. as compared to conventional fluids / the fluid within the internal portion 156). Photon emission from the plasma may occur to accommodate for the high energy within the plasma. Electrons may move to lower energy electron states, and / or changes to lower energy vibrational / rotational / spin states may occur for atoms / molecules. It is this returning to lower energy configurations which gives rise to the emission of photons (e.g. to accommodate for the drop in energy levels as per the Bohr model). This emission of photons may occur on a relatively large scale. Where water is used, a large proportion of this photon emission may occur in the visible light spectrum.

[0079] The photons emitted from each plasma bubble will then be absorbed by either fluid in the internal portion 156 or the housing 150 of the cell 100. In response to receiving such incident photons, the fluid and / or housing 150 will heat up as it absorbs said photons. The inner surface of the housing 150 in particular may absorb a large number of these photons and thus increase in temperature. As the inner surface of the housing 150 heats up, it will in turn provide conductive heating of the fluid within the internal portion 156. This may give rise to convection currents occurring and thus increased turbulence for fluid within the internal portion 156 of the cell 100. As a result of this process, the fluid within the internal portion 156 will heat up. The majority of the liquid provided to the internal portion 156 of the cell 100 may then evaporate to provide a gas (e.g. steam). It is to be appreciated in the context of the present disclosure that some of the fluid which exits the cell 100 may have somewhat unconventional, or at least lower energy configurations, as compared to the liquid that was provided to the cell 100. This is as a consequence of the plasma generation and subsequent energy release which occurred within the cell 100.

[0080] In this sense, the cell 100 may operate as a heat pump. That is, the cell 100 is receiving a liquid, such as water (e.g. cold water) and turning this into steam. Although not shown, the cell 100 may also include one or more filters. The filters may be for filtering solid contaminants, such as Manganese, Iron compounds or other material deposits which may accumulate within the cell 100. For example, this may comprise a gravity filter or another suitable type of filter arranged to prevent excess build up of such material deposits within the cell. This heated fluid then passes through the fluid outlet 103. Typically, the heated fluid is in the form of steam, which is generated within the internal portion 156, and which rises up and out through the fluid outlet 103. This heated fluid output from the cell 100 may then used in a work extraction system to extract useable work from that heated fluid.

[0081] In embodiments of the present disclosure, operation of the cell 100 may be monitored and controlled to yield more optimal operating conditions and to reduce the risk of a breakdown in operating conditions occurring.

[0082] Several different modes of operation will be described below in which the cell 100 is monitored and controlled.

[0083] A first mode is a ‘start up’ mode for when the cell is initially started (i.e. first turned on). For this, the cell 100 is monitored and controlled to ensure a quick and efficient progression from its initial operating conditions (i.e. when cold and with little or no plasma generation occurring) to conditions when the cell 100 is running more optimally.

[0084] A second mode is a ‘normal’ mode of operation for when the cell 100 is up and running (i.e. once the start up has completed). During the normal mode, the cell 100 is monitored and controlled to ensure it operates efficiently, without the operating conditions dropping into a sub-optimal zone (at which efficiency is reduced) and without the operating conditions getting to close to cell breakdown occurring.

[0085] A third mode is a ‘cooldown’ mode of operation for when the cell 100 is to be disactivated (i.e. switched off). In the cooldown mode, the cell 100 is controlled based on when the cell 100 is next to be used. If the cell 100 may be used again shortly, a ‘dormant’ mode of control is employed in which operating conditions of the cell 100 are maintained at a level which permits quick and efficient restarting of the cell 100 (i.e. so that the cell may quickly return to its normal mode of operation). If the cell 100 may not be used again shortly, a ‘shutdown’ mode of control is employed in which the cell 100 is permitted to return to a lower energy state (e.g. from which a full start up operation may be needed to return the cell 100 to operating in its normal mode of operation).

[0086] Example control mechanisms and feedback loops for this modes of operation will be described in more detail below, and with reference to Figs. 3 and 4, but first, reference will be made to Figs. 2a and 2b to illustrate these different operational modes of the cell 100, how different operational parameters may affect the output from the cell 100, and how the cell 100 may be controlled in these modes.

[0087] Figs. 2a and 2b show graphs illustrating different example timelines for operation of the cell 100.

[0088] Fig. 2a shows operation of the cell 100 when in start up and normal modes.

[0089] The cell 100 may be operated in one of two modes: a ‘start up’ mode, and a ‘normal’ mode. As described above, high efficiency heating of fluid in the cell 100 may arise due to bubbles of plasma being generated in the fluid within the cell 100 (and energy subsequently being released therefrom). Before this occurs, heating of fluid in the cell 100 will be due to (lower efficiency) resistive heating of the fluid. As will be appreciated, generation of plasma bubbles may not occur immediately, and so there may be a time delay between initiating operation of the energy cell 100 and plasma bubbles being generated for heating. This initial period in which cell conditions are insufficient to sustain plasma bubble generation and heating is referred to as a ‘start up’ period (i.e. the period during which operation of the cell 100 starts up, and before the intended operation of the cell 100 may commence). After completion of the start-up period, the cell 100 may be in a normal mode of operation where plasma bubbles are being generated and heat released therefrom. This normal mode provides much greater efficiency for the conversion of input power to output heating.

[0090] These two modes are shown in Fig. 2a. As can be seen, to begin with the cell 100 is in a start up mode. After a certain amount of time has passed (shown by the dashed vertical line), the cell 100 transitions into a normal mode of operation. The lowest horizontal dashed line in Fig. 2a shows a transition threshold for output from the cell 100. Above this threshold, the cell 100 may be considered to be in its normal mode of operation. Below this threshold, the cell 100 may be unable to sustain the generation of plasma bubbles and heat release therefrom.

[0091] The output shown in Fig. 2a may be any suitable measure of cell operation, e.g. which indicates how well the cell 100 is functioning to generate heated fluid. For example, the output may relate to a thermal output from the cell 100, such as an amount of heat being generated or a volume of heated fluid (e.g. steam being output from the cell 100). In examples where the heated fluid output from the cell 100 is used by a work extraction system to extract useable work therefrom, the output may provide an indication of an amount of useable work which could be extracted from cell output (e.g. a potential energy). In this sense, the output shown in Fig. 2a may represent an efficiency factor for the energy cell 100 (e.g. an amount of useable energy which could be extracted from the cell 100 for a given input power being provided to the cell 100).

[0092] At the start, the cell 100 is in a start up mode. The output from the cell 100 in the start up mode is very low. To begin with, the power applied to the cell 100 (e.g. from the voltage being applied to the first electrode 110) will be generating heat almost entirely due to resistive heating of the liquid in the cell 100. That is, initially, no bubbles of plasma may be forming and releasing heat. During this period, conversion of input power (e.g. voltage being applied to the electrode) into useful output (e.g. heated fluid) will be lower than during normal operation. As power is continually applied to the cell 100, the output will begin to increase. The power applied may also be increased, e.g. by increasing the voltage being applied to the electrode. In turn, the liquid in the cell 100 may heat up (and heat up more rapidly), such that air bubbles may begin to form, and then resulting bubbles of plasma and heat release may occur. This start up process occurs until a point 201 is reached. At point 201 , the output from the cell 100 is at the start up transition level, which may indicate that the start up process has finished, and normal cell operation is now underway.

[0093] The start up transition may represent a threshold level above which bubbles of plasma are being generated and heat is being released therefrom within the cell 100. As will be appreciated, above this threshold, at least some of the input power being provided to the cell 100 may cause plasma generation and heat release therefrom. Some of the input power may also be providing resistive heating. Due to the energy transitions involved within the plasma bubbles and the resulting energy releases therefrom, the cell efficiency will increase with more plasma activity occurring in it. This additional output (e.g. efficiency gains) will continue to increase with increased plasma activity up to a point above which breakdown occurs. Cell breakdown may comprise arcing of current. That is, an electrical arc may occur between the electrodes within the energy cell 100. Such arcing may drastically reduce the efficiency of the cell 100 to generate heated fluid output, as well as potentially causing damage to the cell 100 itself.

[0094] Once in the normal of operation, the cell 100 may be monitored and controlled to operate between a value associated with sub-optimal efficiency (e.g. in which operating conditions revert back to those associated with start up) and a value associated with cell breakdown occurring (e.g. above which arcing may occur). To illustrate this, four horizontal dashed lines are shown in Fig. 2a. The lowest line is that mentioned above associated with the transition between start up and normal modes of operation. The highest line is a line above which breakdown (e.g. arcing) will start to occur. When operating in the normal mode, the cell 100 may be controlled to exist between these two lines.

[0095] For this, a lower threshold and an upper threshold are defined. These are shown as the second and third horizontal lines in Fig. 2a. The lower threshold is at an output greater than the start up transition. The lower threshold may still be at a relatively low level of output, but it is at least a selected amount higher than the start up transition level. The upper threshold is at an output lower than the breakdown transition. The upper threshold may still be at a relatively high level of output, but it is at least a selected amount lower than the breakdown transition level. The upper and lower threshold are at values selected such that, upon crossing that threshold, there is still time for the cell operation to be modified so as to avoid crossing the relevant transition associated with each threshold level. In other words, the upper threshold may be selected so that, in response to crossing the upper threshold, operation of the cell 100 may be modified to avoid subsequently crossing the breakdown transition. Likewise, the lower threshold may be selected so that, in response to crossing the lower threshold, operation of the cell 100 may be modified to avoid subsequently crossing the start up transition.

[0096] The normal mode of operation may encompass a range of different output values. This includes relatively low cell output values (which are above the start up transition) and also relatively high cell output values (which are below the breakdown transition). Operation of the cell 100 may be controlled at least in part based on an obtained indication of demand for the cell 100. For example, where demand is higher, the cell 100 may operate in a higher output mode, and where demand is lower, the cell 100 may operate in a lower output mode. In whichever mode of operation, the cell 100 may still be monitored and controlled to avoid passing either transition. For this, the cell 100 may be controlled so that, in response to passing one of the thresholds, operation of the cell 100 will be switched to avoid further progressing towards the relevant transition.

[0097] To illustrate these different feedback loops, two separate trajectories are shown in Fig. 2a. Firstly, the cell output may be increased upon having passed the start up transition and into its normal mode of operation. This may increase up to point 202 shown in Fig. 2a. At point 202, the cell operation is in the normal mode, and not particularly close to either threshold. Cell operation may continue in this zone for an extended period of time. The particular output value may be varied depending on demand for the cell 100.

[0098] A first, lower, example trajectory is shown in Fig. 2a. This starts at point 202, and gradually cell output decreases. For example, this lower trajectory may be associated with a scenario where the demand for heated fluid output from the cell 100 is relatively low (and so the cell is not run at, or close to, maximum output conditions). When operating at a lower level of output, the operating conditions within the cell 100 may become less efficient. For example, there may be fewer plasma transitions occurring. In turn, this may mean that less heating of the fluid in the cell 100 is provided. If this decline in output continues, the cell operation will continue to drop until the cell output crosses the lower threshold value (shown as point 203 in Fig. 2a). At this point (point 203), the risk of suboptimal output from the cell 100 is much more significant. At such levels, the efficiency of the cell (e.g. the amount of heated fluid output per each unit of energy input to the cell may be much lower). With each further drop in output, the cell 100 may be more likely to revert to a start up style operation in which plasma activity is minimal or non-existent in the cell 100 (and thus in which cell operation is at substantially lower efficiency). In response to crossing this threshold, the cell operation is modified to increase output. Examples of this are described later, but this may include e.g. increasing the voltage applied to the electrode. The cell output is increased such that the output increases back above the lower threshold before approaching too close to the start up transition. For example, the cell 100 may immediately change operation when crossing the threshold level.

[0099] The cell output is then increased back up to a level more comfortably within the normal mode of operation. For example, the cell output may be returned to a value at or close to the point 202. Again, this value may be changed over time depending on cell demand. In other words, the cell operation may be regulated to avoid the cell output dropping too low and thus running a substantially elevated risk of suboptimal output occurring.

[0100] A second, higher, example trajectory is shown in Fig. 2a. This starts at point 202, and gradually cell output increases. For example, in this scenario, there may be a demand for a greater amount of heated fluid output from the cell 100 (and / or a drive to achieve a higher level of cell efficiency). When operating at these higher levels, the operating conditions within the cell 100 may become more efficient, but they may also become closer to conditions associated with breakdown. For example, there may be more plasma transitions occurring, but also a greater risk of arcing. This may mean that heating of the fluid in the cell 100 is increased, but with it there may also be a corresponding increase in the likelihood of cell breakdown occurring. As this increase continues, the cell operation will eventually cross the upper threshold value (shown as point 204 in Fig. 2a). At this point (point 204), the risk of breakdown is much more significant. With each further increase in output, the cell 100 would be more likely to undergo a breakdown. In response to crossing this threshold, the cell operation is modified to decrease output. Again, examples of this are described later, but this may include e.g. decreasing the voltage applied to the electrode. The cell output is decreased such that the output decreases back below the upper threshold before approaching too close to the breakdown transition. For example, the cell 100 may immediately change operation when crossing the threshold level.

[0101] The cell output then returns back down to a level more comfortably within the normal mode of operation. For example, the cell output may be returned back towards to a value at or close to the point 202. Again, this value may be changed over time depending on cell demand. In other words, the cell operation may be regulated to avoid the cell output running too high and thus running a substantially elevated risk of suboptimal output occurring.

[0102] In other words, operation of the cell 100 may be controlled first in a start up mode. In the start up mode, the cell performance is monitored to detect once the cell 100 has progressed from its start up mode and into its normal mode of operation. Once in the normal mode, the cell operation is controlled to remain within the bounds of normal operation. Cell output may be increased or decreased depending on demand levels for the cell 100, but either way the cell output is monitored to keep this output within a selected range of operation (e.g. which is both safe and efficient). For example, this may comprise preventing the output from ever getting too high or too low when in the normal mode.

[0103] Fig. 2b shows operation of the cell 100 when in normal and cooldown modes.

[0104] In Fig. 2b, operation starts in the normal mode (e.g. as shown in Fig. 2a). In Fig. 2a, the timeline starts at point 211 , where the cell 100 is operated as per the normal mode of operation described above in relation to Fig. 2a. This continues until a point 212, at which it is determined that the cell 100 is no longer to operate in its normal mode of operation.

[0105] At this point 212, it is determined that the cell 100 will be operated in a cooldown mode. That is, there is no longer any demand for the cell 100 to generate and output a heated fluid for extracting work therefrom. Instead, operation of the cell 100 is to be cooled down. At point 212, operation of the cell 100 begins to switch towards its cooldown mode of operation. For example, at point 212, a signal may have been received indicating that a cooldown mode of operation is wanted (e.g. a user may select that no further heated fluid output is wanted). As another example, operation of the cell 100 may occur according to a selected timing schedule, and point 212 may represent a selected time at which no further heated fluid output is wanted. For example, the cell 100 may be used as part of a building heating system. The heating system may include one or more components (e.g. a thermostat) for controlling a desired amount of heating. This may include enabling a user to select that more heating is wanted / not wanted, that heating should maintain the building temperature at a certain level, or that there are periods of time when heating / no heating is wanted. As will be appreciated, the cell 100 output may be used to provide this heating, and so operation of the cell may be controlled accordingly.

[0106] In any case, at step 212 it is determined that the cell 100 should be switched into operating in a cooldown mode. It may also be determined for how long the cell 100 is to be operated in the cooldown mode. For example, a signal indicating that a cooldown mode is to be initiated may be received. This signal may also indicate the next time that the cell 100 is to be operated in its normal mode (e.g. or an estimate of a predicted next time of normal mode operation). One of two cooldown modes of operation will be selected based on the determined length of time until the cell 100 is to be operated in its normal mode of operation. The first of these is the dormant mode of operation, which is for when the cell 100 is to be restarted again within a threshold time period. The second of these is the shutdown mode, which is for when the cell 100 is not to be used again with the threshold time period. Both will be described in more detail below.

[0107] From step 212, the inputs provided to the cell are reduced. For example, less electrical energy may be applied to the electrode(s) of the cell. The cell output then begins to decrease. The cell output will therefore pass below the lower threshold mentioned above in relation to Fig. 2a, as well as passing below the start up transition level (i.e. the level above which plasma generation and heated fluid output occurs). This is shown at point 213 in Fig. 2b. The decline in output is shown as continuing in Fig. 2b until point 214.

[0108] From point 214, two different trajectories are shown.

[0109] The first trajectory (the lower of the two) shows the output continuing to decline towards the lowest level. This is the shutdown mode of operation. For instance, if it is determined that no cell 100 operation is likely to be wanted within the threshold time period, then this shutdown mode is employed. Here, the cell 100 is allowed to revert to its initial conditions. As such, no electrical energy may be applied to the electrode(s) of the cell. Similarly, no heating etc. of the fluid may be provided. The cell 100 may return to a lowest energy state, as shown at point 215a in Fig. 2a. This point may effectively be at the same (or a similar) level as that shown at the start in Fig. 2a. In effect, the cell 100 is no longer controlled in any way, it is just left to be maintained at this level. A point 215b is shown in Fig. 2b to show that any future use of the cell 100 once it has been operated in shutdown mode may entail restarting the cell 100, e.g. as per the start up mode shown in Fig. 2a. In other words, once the cell has been operated in shutdown mode, to reinitiate normal mode operation of the cell 100, the cell operation must start again with the start up mode (i.e. it must return to scratch to get the cell 100 operating in its normal mode). The shutdown mode may be used when it is determined (e.g. predicted) that the cell 100 is not to be used for an extended period of time.

[0110] The second trajectory (the higher of the two) shows the output being maintained in a dormancy range of operation. This is the dormant mode of operation. For the shutdown mode of operation, the cell conditions may no longer be monitored and / or regulated (or at least relatively low, e.g. minimal, amounts of this may be employed). Conversely, for the dormant mode of operation, the cell conditions may still be monitored and regulated. For example, the dormant mode of operation may be a more active mode than the shutdown mode, as the cell 100 may still be monitored and its operating conditions regulated when operating in the dormant mode.

[0111] For the dormant mode, it is determined that the cell 100 may be restarted into the normal mode of operation shortly. For this reason, the cell 100 may be maintained at conditions which keep it near to the start up transition. In other words, the cell 100 may be monitored and regulated so that, once it is determined that the normal mode of operation for the cell 100 should commence, it will not take much time and / or energy to return the cell 100 to its normal mode of operation. The cell 100 may be controlled to remain within the dormancy range during this time period. The dormancy range may be slightly below the start up transition level, e.g. so that when operating in the dormancy range, significant cell operation (e.g. the generation of plasma and heated fluid output from the cell 100) will not occur. The dormancy range may be above the minimum energy conditions for the cell 100 (e.g. so that a full start up mode of operation is not required to restore the cell 100 to its normal mode). In the dormant mode, the application of electrical energy to the electrode(s) of the cell 100, and / or any heating or pressurising of liquid in the cell 100 (or to be supplied to the cell 100) may be controlled to maintain the cell 100 in a more energised state, e.g. one which is close to the start up transition, but just below it. For example, in the dormant mode, pressure and / or temperature of liquid to be heated may be monitored and regulated, e.g. kept within a selected dormancy range. Although not shown in Fig. 2b, when it is next determined that the normal mode of operation is wanted, it may not take long for the cell 100 to reach this mode of operation. For instance, increasing the energy applied to the electrodes may cause normal mode conditions to occur in a short time period.

[0112] Examples of how the current state of the cell 100 may be determined (e.g. which mode it is in and / or whether it is close to a transition / threshold level) and how the cell 100 may be controlled based on its current state (e.g. to increase / decrease output accordingly) will now be described with reference to Figs. 3 and 4.

[0113] Fig. 3a shows a flowchart for operation of the cell 100 during start up and Fig. 3b shows a table containing different observable parameters which may be monitored during this period. Fig. 4a shows a flowchart for operation of the cell 100 during a normal mode and Fig. 4b shows a table containing different observable parameters which may be monitored during this period. Before describing these Figs, in more detail, reference will first be made again to Fig. 1 to describe properties which may be controlled, as well as operational parameters which may be monitored.

[0114] For the cell 100 of Fig. 1 , at least one of the electrodes may be movable. That is, the cell 100 may be configured to enable relative movement between the electrodes. In particular, the cell 100 may be configured to provide a variable electrode separation distance between the electrodes. The separation distance may be varied between a minimum separation distance (which still does not cause contact between the electrodes) and a maximum separation distance (in which the movable electrode(s) still remains within the energy cell 100). At least one of the first electrode 110 and the third electrode 130 may be movable. The first and / or third electrode 130 may be movable to vary a separation distance between the two electrodes. The electrode(s) may be movable to vary a separation distance between the second end of the first electrode 110 (the end inside the cell 100) and the second end of the third electrode 130 (the end inside the cell 100). The electrode(s) may be movable between a minimum distance of separation between the two second ends and a maximum distance of separation. The minimum distance may still have no contact between the two ends. The electrode(s) may move along their longitudinal axis (e.g. so that the first and third electrodes remain coaxial).

[0115] For this, the third electrode 130 may be movable. The cell 100 may be configured to control movement of the third electrode 130. For example, the cell 100 may comprise a mover (e.g. a mechanical actuator) configured to move the third electrode 130 in either: a distal direction (towards the first electrode 110) or a proximal direction (away from the first electrode 110). The cell 100 may be configured to control this movement based on a received indication of at least one operational parameter of the cell 100. In other words, the cell 100 may be configured to vary a separation distance between the first electrode 110 and the third electrode 130. The third electrode 130 may be active or passive, and the first electrode 110 may be active. The second electrode 120 may be grounded. In the event that breakdown were to happen, the arcing may occur from the first electrode 110 to the second electrode 120. The location of the first and third electrodes 110, 130 may limit the volume in which plasma generation occurs. For example, the separation distance of those electrodes 110, 130 may define a longitudinal extent of a plasma generating zone within the cell 100.

[0116] Increasing the separation distance between the electrodes of the cell 100 may reduce the likelihood of breakdown occurring (e.g. because this may act to stretch out the plasma generating volume within the cell). When this separation distance is lower, there may be greater electrical stress within that volume, which may increase the likelihood of breakdown occurring once the cell 100 is in its normal mode of operation. Similarly, the reduced separation distance may increase the speed with which plasma generation begins to occur, i.e. when starting from the start up mode. However, as the separation distance increases, the likelihood of breakdown occurring will decrease (up to a point).

[0117] In other words, the cell 100 may be operated to increase the electrode separation in order to reduce the likelihood of breakdown occurring. Likewise, the cell 100 may be operated to decrease the electrode separation in order to facilitate a quicker and / or more efficient transition of the cell 100 from its start up mode into its normal mode.

[0118] Once the cell 100 is operating in its normal mode of operation, i.e. with plasma generation occurring within the cell, increasing the separation distance may facilitate greater output from the cell 100. This may depend upon the current operating conditions of the cell 100. With sufficient electrical energy being applied to the cell 100, increasing the electrode separation distance may increase the plasma generating volume within the cell, and in turn increase the amount of heated fluid being generated by the cell 100. For a given amount of electrical energy being applied, decreasing the electrode separation may increase the stress within the cell, which in turn could make breakdown more likely to occur. Therefore, when operating in the normal mode of operation, control of the electrode separation distance may be different to that in the start up mode. For example, the normal mode control may involve increasing the separation distance to increase power output (and vice-versa), and the start up control may involve decreasing the separation distance to facilitate the transition towards the normal mode of operation (and vice-versa). The electrode separation distance may be controlled according to a feedback loop in which, in response to determining the electrode separation distance should be changed, the electrode separation distance is changed accordingly (e.g. to increase and / or decrease separation on demand).

[0119] Although not shown in Fig. 1 , the cell 100 may comprise a variable source of electrical energy. For example, this may be a variable voltage source. The source is coupled to at least one of the electrodes of the cell 100. For example, the source may be coupled at least to the first electrode 110 (it may also be coupled to the third electrode 130). The source is configured to vary an amount of electrical energy applied to the electrode(s). For example, the source may be configured to vary a voltage applied, e.g. to the first electrode 110. The source may also be configured to vary a voltage applied to the third electrode 130.

[0120] Increasing the amount of electrical energy applied (e.g. increasing the voltage at the first electrode 110) may increase the output from the cell 100, but may also increase the likelihood of breakdown occurring. In other words, the cell 100 may be operated to: increase the electrical energy (e.g. voltage) applied in order to increase the output from the cell 100, and / or decrease the electrical energy (e.g. voltage) applied in order to reduce the likelihood of breakdown occurring. The applied electrical energy may be controlled according to a feedback loop in which the amount of energy applied is varied depending on measurements obtained indication an operational state of the cell 100. The cell 100 may be configured to increase the voltage applied to the first electrode 110 to facilitate the cell 100 transitioning from start up mode to normal mode, and / or to increase power output when operating in the normal mode. In the normal mode, the cell 100 may be configured to decrease the voltage applied to the first electrode 110 to inhibit breakdown occurring within the cell 100. The cell 100 may also be configured to increase the voltage applied to the third electrode 110 (or start applying a voltage to the third electrode 130) to facilitate the cell 100 transitioning from start up mode to normal mode, and / or to increase power output when operating in the normal mode.

[0121] The cell 100 may be configured to control the amount of electrical energy applied based on input power. For example, the control may be input power limited, e.g. so that the amount of electrical energy being applied to the cell 100 is limited based on a selected input power. As will be appreciated, the input power is linked to both voltage and current (e.g. as per P=IV). By regulating the amount of energy applied to the electrodes of the cell 100 according to the input power, the voltage applied to the cell 100 will be controlled based on the resulting current it provides. For example, by regulating on input power, as the current increases, the voltage applied will decrease (and vice-versa). The cell 100 may be operated to vary the input power (e.g. it may be increased over time / in response to greater demand). The cell 100 may be configured to increase this input power as long as the resulting current remains below a threshold current. For example, in order to drive higher cell output, the input power may be increased (e.g. iteratively and / or continuously), as long as the current does not exceed a threshold value.

[0122] Although not shown in Fig. 1 , the cell 100 may be coupled to a supply system which is configured to provide the fluid to be heated to the cell 100 (e.g. to the internal portion 156 of the cell 100). The supply system may couple one or more reservoirs to the fluid inlet 101 of the cell 100. For example, the liquid to be supplied may comprise partly or wholly a fluid which exhibits non-Newtonian behaviour in the environment of the cell 100. The liquid may be water or an aqueous solution.

[0123] The supply of fluid to the cell 100 may be controlled in a number of different ways. Firstly, a temperature (and / or pressure) of the fluid may be controlled. Secondly, bubbles may be selectively provided in the fluid. Thirdly, a volumetric flow rate may be controlled.

[0124] For the first example, the apparatus may be configured to control the temperature of the fluid supplied to the cell 100. For example, the apparatus may include a heater. The heater may be configured to selectively heat the fluid supplied to the cell 100. The apparatus may be configured to operate the heater to pre-heat fluid provided to the cell 100 under certain circumstances (e.g. in response to determining, based on an obtained indication of cell operation, that fluid should be pre-heated). An amount of heating provided may be controlled on demand.

[0125] For the second example, the apparatus may be configured to selectively provide bubbles in fluid provided to the cell 100. This may comprise us of a bubble making element which may deliver gas into liquid to be supplied to the cell 100. For example, a carbonator (or other suitable element) may be used to deliver bubbles of gas into the liquid. The fluid provided to the cell 100 may comprise a liquid with gas bubbles therein. Additionally, or alternatively, the supply system may have a liquid reservoir and a liquid with bubbles reservoir, and fluid may be chosen from either reservoir. The apparatus may be configured to provide bubbles in the fluid provided to the cell 100 under certain circumstances (e.g. in response to determining, based on an obtained indication of cell operation, that fluid should contain bubbles). For example, a bubble maker may be selectively actuated depending on whether or not bubbles are wanted in the fluid (e.g. so that when ‘on’, the bubble maker is actuated to provide bubbles in fluid delivered to the cell 100, but when ‘off’, the bubble maker is not providing bubbles). An amount of bubbles provided may be controlled on demand.

[0126] For the third example, a volumetric flow rate of the fluid provided to the cell 100 may be controlled. For example, the supply system may comprise a pump which may be operated to control the rate of fluid provided to the cell 100. The volumetric flow rate of fluid may be increased or decreased, e.g. the pump may operate at a higher or lower output. The operational state of the pump may be controlled to vary the volumetric flow rate (e.g. to increase / decrease flow rate depending on demand).

[0127] Increasing the temperature of and / or the amount of bubbles in the fluid provided to the cell 100 may speed up the start up process. For example, this may reduce the time taken between fluid being delivered to the cell 100 and plasma energy release processes initiating. These two options may be of particular utility during start up mode, as they may help to reduce the time taken to transition into the normal mode of operation. Decreasing the flow rate may help to increase cell output in the short term. For example, more of the fluid already in the cell 100 may be undergoing plasma energy release, and so by retaining this fluid there for longer, greater energy release (and also greater risk of breakdown) may occur. During start up, having no flow rate may be advantageous (once the cell 100 has been filled with fluid). For example, the pump may be inactive during start up (once the cell 100 has been filled with fluid). During start up, the fluid which is delivered to the cell 100 (before flow rate dropping, e.g. back to zero) may be pre-heated and / or contain bubbles. This arrangement may advantageously reduce start up times. During normal operation pre-heating / bubbles may not be used at all (but it could be, if wanted). During normal mode of operation, i.e. once plasma generation is occurring within the cell 100, increasing the flow rate may be used to increase the total output from the cell (i.e. to increase the amount of heated fluid being output by the cell 100).

[0128] The apparatus may comprise a controller coupled to the components described above to control operation thereof. For example, the controller may be configured to selectively vary the electrode separation distance, to control the application of electrical energy to the electrode(s) of the cell 100 and / or to control operation of the supply system (e.g. pre-heater, bubble maker and / or pump). The controller may be configured to control operation of said components based on one or more received indications of an operational parameter of the cell 100. For this, the cell 100 may comprise one or more sensors. The controller may also monitor elapsed time. The controller may take into account existing operating conditions of the energy cell 100 and / or supply system. For example, the controller may store an indication of the electrode separation distance, an amount of electrical energy being applied (e.g. voltage and / or current), and / or a flow rate of liquid being provided to the cell. The controller may control operation based on these existing operating conditions as well as based on data indicative of one or more other operational parameters.

[0129] The sensor(s) may be configured to sense one or more of: (i) pressure and / or temperature, (ii) light intensity and / or wavelength, and / or (iii) current and / or voltage.

[0130] The pressure and / or temperature being sensed may be the pressure / temperature within the cell 100 (e.g. in the internal portion 156 of the cell 100). This may be the pressure / temperature of the fluid in there. As will be appreciated, the internal volume of the cell 100 may be fixed and so pressure and temperature may provide the same information (e.g. as per the ideal gas laws). As such, only one of pressure and temperature may be sensed (and temperature is generally preferable, as temperature sensing is typically cheaper and / or more reliable than pressure sensing). Increased pressure / temperature may indicate that the output of the cell 100 is higher. For example, as more heat is released from plasma energy transitions (and more steam generated within the cell 100), the pressure and temperature therein will also be higher.

[0131] The light intensity and / or wavelength being sensed may be detecting emissions which are occurring within the cell 100 due to the energy level transitions. For example, an optical sensor could be used to detect intensity and / or wavelength of such light. This sensor may be located inside the cell 100 or outside the cell 100 adjacent to an at least partially optically transparent portion of cell housing 150.

[0132] The overall intensity may provide an indication of the total number of emissions / energy transitions occurring (e.g. as more transitions occur, and thus more photons are emitted, the greater the intensity of received light will be, as more photons will be incident on the detector).

[0133] The wavelength(s) of emitted light may provide an indication of the particular transitions occurring, and thus of the different elevated energy levels within the cell 100. A more diverse range of wavelengths may indicate greater process quality / efficiency. For example, this may indicate that a larger number of elevated energy levels are being occupied, which may suggest that the conditions within the cell 100 are improved for efficient energy release / heating. As will be appreciated, the greater the range of wavelengths occurring, the closer the light will appear to white light. For example, initial transitions may tend to be yellow / green in colour, but as additional transitions happen, the visible light will tend more towards a whiteish colour. The sensor may be configured to detect an indication of the total number of different wavelengths being received and / or an indication of what those wavelengths are.

[0134] The voltage and current being sensed may be a voltage / current associated with the application of electrical energy to the electrode(s) of the cell 100. For example, a voltage may be applied to the first electrode 110, and the sensed voltage may be that at the first electrode 110. The current being sensed may be any suitable current indicative of the resulting current flow due to that applied voltage. For example, the current could be measured at the first electrode 110, the second electrode 120 and / or the third electrode 130. The combination of current and voltage may provide an indication of the input power being applied to the cell 100. Increased current and / or sudden changes in current / voltage may suggest conditions are closer to breakdown. A low current may suggest further away from breakdown. The controller may store an indication of a threshold voltage above which plasma generation is expected to occur. A voltage above this value may suggest plasma activity is (or will shortly commence) occurring in the cell 100.

[0135] Elapsed time may also provide an indication of development through the process. For example, the controller may store an indication of an expected elapsed time beyond which plasma activity would be expected to occur. For example, this may comprise a plurality of different timing profiles depending on the input power which has been applied to the cell 100. The controller may infer that plasma activity is likely to occur if a selected voltage has been applied for a certain amount of time to the cell 100.

[0136] The controller may be configured to control operation based on any and / or all of the above- mentioned parameters. Each parameter may have its own associated advantages and / or may provide particular utility under certain circumstances. The different parameters could be used to detect different cell conditions themselves, but there may be particular utility in sensing multiple different parameters, and using different sensed parameter for determining different cell operation conditions.

[0137] Pressure and / or temperature may be relatively slow-moving parameters. That is, the time window over which these measurements are particularly useful is longer than for other parameters. Pressure and / or temperature may provide a reliable indication as to whether the cell 100 is in start up mode or normal mode. Current and voltage monitoring may provide real time feedback about proximity to breakdown occurring. That is, elevated current or sudden jumps (e.g. down) in voltage may suggest breakdown is close, whereas a lower current may suggest breakdown is far away. The time window over which these measurements are useful may therefore be relatively quick-moving. In other words, they may provide a greater proxy to immediate cell conditions. Light intensity and / or wavelength may provide an indication as to the quality of process occurring within the cell 100. That is, as intensity and / or wavelength diversity increase, this may indicate that cell operation is functioning efficiently (as lots of plasma generation is occurring). Intensity and / or wavelength diversity may provide a good indication of immediate quality when operating in the normal mode (e.g. when emissions are occurring much more frequently).

[0138] As one example of how parameters may be combined, the controller may be configured to utilise an indication of pressure and / or temperature to determine whether the cell 100 is in start up mode or normal mode. Depending on that determination, the cell 100 may be controlled accordingly (e.g. as will be described with reference to Figs. 3 and 4). In either or both of the start up and normal modes of operation, the controller may be configured to utilise an indication of voltage and / or current to control the application of electrical energy based on these measurements. For example, this may comprise avoiding applying too great a voltage in the event that the sensed voltage / current indicates breakdown may be close. The controller may be configured to utilise an indication of light intensity and / or wavelength to determine an indication of cell operation quality. This may comprise determining how efficiently the cell 100 is operating based on this obtained information about light emissions within the cell 100. The controller may control operation of the cell 100 to try to improve the cell operation quality (e.g. to increase efficiency).

[0139] Some examples of control will now be described with reference to Figs. 3 and 4.

[0140] Fig. 3a shows a method of controlling operation during start up, and Fig. 3b shows what parameters may be observed and what those parameters may indicate.

[0141] At step 310, an indication of at least one operating parameter is obtained. This may comprise receiving sensor data from one or more sensors of the apparatus. Two or more parameters may be monitored concurrently. An indication of any of the parameters disclosed herein (or shown in Fig. 3b) may be received at step 310. Step 310 may also comprise obtaining an indication of one or more current operating conditions of the cell 100, such as: (i) electrode separation distance, (ii) current / voltage being applied, (iii) flow rate. At step 320, it is determined whether or not the cell 100 is in start up mode. For example, the method of Fig. 3a may be repeated until it has been determined that the normal mode operation may be commenced. If it is determined at step 320 that the cell 100 is no longer in start up mode, the method moves to step 325, where control is switched to normal mode monitoring.

[0142] At step 320, determining whether the cell 100 is in start up mode may comprise determining, based on the one or more parameters received at step 310, whether said parameter(s) are at a value associated with normal mode operation, or not. For example, this may comprise determining whether the received parameter exceeds a threshold value. If it does, it may be determined that the cell 100 is no longer in start up mode, but if it does not, it may be determined that the cell 100 is in start up mode. For example, the parameter may be a pressure / temperature and step 320 may comprise determining whether that pressure / temperature exceeds a threshold value associated with normal mode operation (e.g. above which the cell 100 is likely to be in a normal mode of operation). Additionally, or alternatively, the parameter could be one or more of voltage, current, light intensity, number of light wavelengths, and / or time, and in the event that said parameter exceeds a threshold value, then it is determined that the cell 100 is in a normal mode of operation. Examples of what the parameter could be, and how that parameter suggests whether the cell 100 is in start up mode or not, are shown in the Table of Fig. 4b.

[0143] For example, if an obtained indication of pressure and / or temperature exceeds a selected threshold value, it may be determined that the cell 100 has completed its start up mode. If the light intensity within the cell 100 and / or a spectrum of wavelengths being emitted in the cell 100 exceeds a threshold value, it may be determined that the cell 100 has completed its start up mode. If a voltage and / or current is above a threshold value and / or changes in the voltage and / or current exceed a threshold amount, it may be determined that the cell 100 has completed its start up mode. If a selected length of time has passed since starting operation of the cell 100 (e.g. a selected period of time has passed while voltage has been applied to the electrode(s) of the cell 100), it may be determined that the cell 100 has completed its start up mode.

[0144] If it is determined that the cell 100 remains in start up mode, the method proceeds to step 330 (and step 340).

[0145] At step 330, it is determined whether or not more input to the cell 100 is needed, and if more input is needed, then the method proceeds to step 340 where operation of the cell 100 is controlled to increase cell activity (e.g. to facilitate leaving start up mode). If no further input is needed, then the method returns to step 310 and the start up monitoring process continues until normal mode of operation has commenced.

[0146] Where more input is needed at step 340, a number of different examples for controlling operation are shown. These different examples may be linked to the determination at step 330, and so the different examples for these two steps will be described together.

[0147] As described above, increasing an amount of electrical energy applied to the cell 100 may facilitate transition from start up mode to normal mode. In particular, the voltage applied to the cell 100 (e.g. to the first electrode 110) may be increased at least until normal mode operation commences. The determination at step 330 may comprise checking that there is no reason not to further increase the voltage. For example, the received parameter may comprise an indication of current and / or voltage. If the current is above a threshold (e.g. associated with breakdown), then no more voltage will be applied, but if not, then the voltage may be increased. For example, if the voltage is below a threshold associated with plasma activity, then voltage may be increased. If not, then voltage may only be increased if current is below the threshold current value. In other words, the start up operation may comprise repeatedly increasing the voltage until either start up mode has ended (and normal mode has commenced) or the resulting current is above a threshold value. Steps 330 and 340 may comprise determining whether or not to increase the voltage, and if the decision is to increase voltage, then doing so. The amount by which the voltage is increased may be selected based on the indicated parameter (e.g. the voltage may be increased by a greater amount if it is determined that breakdown and / or normal mode operation is further away).

[0148] As described above, decreasing the electrode separation may facilitate the transition from start up mode to normal mode. As with increasing the voltage, decreasing the electrode separation may also increase the likelihood of breakdown occurring. At step 330, determining whether more input is needed may comprise determining whether a decrease in electrode separation is likely to lead to breakdown (e.g. is current above threshold etc.). In the event that it is determined that more input is needed, then the electrode separation may be decreased, e.g. by moving the third electrode 130 towards the first electrode 110. The amount by which the electrode separation is decreased may be selected based on the indicated parameter (e.g. with a greater decrease when further from breakdown / normal mode).

[0149] The method shown in Fig. 3a may occur before the cell 100 is filled with fluid to be heated. For example, it may be determined, e.g. based on time, that the process is just starting. At this point, the cell 100 may be filled with a fluid to be heated, as provided by the supply system. That same fluid may remain within the cell 100 for the entirety of the start up process (e.g. once the cell 100 is filled, it may no longer be refilled until start up has completed). In which case, operation of the supply system to condition the fluid supplied to the cell 100 for start up may occur at the start of the process. For instance, the supply system may pre-heat the fluid supplied to the cell 100 for the start up process. Likewise, the supply system may provide bubbles within the fluid supplied to the cell 100 for the start up process. For example, the supply system may be configured to provide bubbles in (the majority of or all) fluid provided to the cell 100 to be used during start up. In examples where additional fluid may be provided to the cell 100 during start up, steps 330 and 340 may comprise determining whether the new fluid to be provided should be pre-heated and / or have bubbles in it, and then acting accordingly.

[0150] Fig. 4a shows a method of controlling operation during a normal mode, and Fig. 4b shows what parameters may be observed and what those parameters may indicate.

[0151] At step 410, an indication of at least one operating parameter is obtained. This may comprise receiving sensor data from one or more sensors of the apparatus. Two or more parameters may be monitored concurrently. An indication of any of the parameters disclosed herein (or shown in Fig. 4b) may be received at step 410. Step 410 may also comprise obtaining an indication of one or more current operating conditions of the cell 100, such as: (i) electrode separation distance, (ii) current / voltage being applied, (iii) flow rate. Selecting how to adjust the control of the cell 100 may be based also on the current operating conditions of the cell 100.

[0152] Steps 420 and 440 relate to controlling operation of the cell 100 so that the output is in a selected zone for maintaining suitable operation of the cell 100 (i.e. efficient operation which is not too close to breakdown). Step 430 relates to determining if operation of the cell 100 is consistent with a demand for output from the cell 100. Step 430 may be optional and not included in some methods. The steps may be repeated over time. For example, the method may comprise repeatedly monitoring one or more parameter(s) and controlling operation of the engine accordingly. An input stream of operating parameter data may be monitored until an item of data indicates that a parameter is at a level which may warrant a change in the operation of the cell 100. While the cell 100 is running (and in its normal mode), the method may comprise monitoring (e.g. continually) the parameter(s) and regulating operation such that the parameter(s) remain within a selected zone, and / or to ensure that the output being provided from the energy cell 100 is consistent with the demand for output from the cell 100.

[0153] At step 420, it is determined whether the cell 100 is too close to breakdown occurring. This may comprise determining whether the obtained operating parameter satisfies a threshold criterion. This may be a threshold criterion associated with an elevated risk of breakdown occurring. For example, the threshold criterion may be selected such that it suggests that operating conditions are moving closer to breakdown occurring. The criterion may also be sufficiently far from breakdown that the cell operation can be modified to avoid breakdown occurring. For example, the threshold criterion may comprise a threshold value for the operating parameter. In the event that the operating parameter exceeds the threshold value (e.g. is greater than), then it may be determined that the cell 100 is operating too close to breakdown. Examples of what the parameter could be, and how that parameter suggests proximity to breakdown are shown in the Table of Fig. 4b.

[0154] For example, if an obtained indication of current exceeds a selected threshold value and / or a change in current (amount of change and / or rate of change) exceeds a threshold value, it may be determined that the cell 100 is too close to breakdown. If an obtained indication of change in voltage (amount and / or rate) exceeds a threshold value, and / or if the voltage is above a threshold voltage, it may be determined that the cell 100 is too close to breakdown. If the light intensity within the cell 100 and / or a spectrum of wavelengths being emitted in the cell 100 exceeds a threshold value, it may be determined that the cell 100 is too close to breakdown. If a pressure and / or temperature within the cell 100 exceeds a threshold value, it may be determined that the cell 100 is too close to breakdown.

[0155] For each example, the obtained parameter provides an indication of relative risk for operation of the cell 100. In other words, based on the obtained parameter(s), it may be inferred how likely it is that continued operation of the cell 100 will lead to breakdown (e.g. arcing) occurring within the cell 100.

[0156] If it is determined at step 420 that the cell 100 is too close to breakdown, the method proceeds to step 425. If the risk of breakdown is too high, e.g. if there is a realistic chance of breakdown occurring, then operation may be controlled to reduce that risk. Controlling operation to reduce the risk of breakdown may comprise altering the conditions within the cell 100 to reduce the ability of current to arc between the electrodes of the cell 100 (e.g. from the first electrode 110 to another electrically conductive region of the cell 100, such as the second electrode 120). Controlling operation to reduce the risk of breakdown may comprise adjusting operation so that at least one of: an electrical resistance of any intervening medium for that conductive path is higher, and / or a voltage difference across that conductive path is lower. Controlling operation to reduce the risk of breakdown may comprise controlling operation to provide arc suppression.

[0157] At step 425, operation is controlled to reduce the likelihood of breakdown. Several different examples for this operation are shown. This may comprise controlling operation of one or more parameters of the cell 100 and / or of the supply system. As one example, the amount of electrical energy applied to the cell 100 may be decreased. For instance, the voltage applied to the first electrode 110 may be reduced (or even stopped, e.g. temporarily). This may reduce the voltage difference between two points across which an arc may otherwise form. As another example, a separation distance between electrodes of the cell 100 (e.g. the first electrode 110 and the third electrode 130) may be increased. For instance, the third electrode 130 may be moved further away from the first electrode 110. This may increase a plasma generating volume within the cell, which in turn may decrease localised electrical stress in any one area of the cell 100 (which may thus reduce the likelihood of arcing occurring). As another example, fluid within the cell 100 may be at least partially replaced by new fluid, e.g. a volumetric flow rate of fluid supplied to the cell 100 may be increased. For example, a temporary increase in flow rate may be provided to replace some of the plasma containing fluid within the cell with a cooler, less plasmatic liquid. This may lead to a higher electrical resistance intervening medium between two points across which an arc may otherwise form (e.g. because the ‘newer’ fluid may contain fewer plasma bubbles).

[0158] If at step 420 it is determined that the cell 100 is not too close to breakdown, the method moves to step 430. Step 430 is an optional step, and if not included, the method would otherwise proceed to step 440.

[0159] At step 430, it is determined if there is a demand for increased output. This may comprise receiving a signal containing an indication of demand for output from the cell 100. The signal may indicate additional demand for heated fluid output from the cell 100. In which case, it may be determined that there is demand for increasing the cell output. For example, the cell 100 may be controlled according to a selected timing schedule stipulating when, and / or how much, heated fluid is wanted from the cell 100.

[0160] Additionally, or alternatively, determining if there is a demand for increased output may be based on an obtained indication of a performance and / or quality of cell operation. For example, a received indication of an operating parameter (as at step 410) may provide an indication of efficiency and / or quality level for cell operation. In the event that this is below a threshold level, it may be determined that there is a demand for increased output. As an example, an efficiency / quality for cell operation may be determined based on an amount and / or a type of light emissions occurring within the cell 100. It may be determined that cell efficiency / quality is higher if there is a greater number of such emissions (i.e. a greater intensity of light) and / or a greater variety of different wavelengths forming such emissions. Frequency (frequencies) of current flow may be used in a similar manner to light to detect efficient operation.

[0161] In other words, at step 430, it may be determined whether the cell operation satisfies a threshold quality criterion. This may comprise determining, based on obtained light data (e.g. intensity and / or wavelength data), whether cell operation efficiency is above a threshold level. If not, then it may be determined that there is a demand for increased output (e.g. based on the efficiency being too low), but if it is, then it may be determined that there is no demand for increased output (e.g. as the efficiency level is already satisfactory).

[0162] If it is determined that there is demand for increased output, the method proceeds to step 435 and if not, the method proceeds to step 440.

[0163] At step 440, it is determined whether the cell operation is too low. As will be appreciated, there may be some overlap between steps 430 and 440 (e.g. they could be provided by a single method step). Step 440 may comprise determining whether the obtained operating parameter satisfies a threshold criterion. This may be a threshold criterion associated with an elevated risk of sub optimal cell operation. For example, the threshold criterion may be selected such that it suggests that operating conditions are moving closer towards a region at which plasma generation may stop occurring (or at least be significantly reduced). The criterion may also be sufficiently far from this that the cell operation can be modified to avoid such sub optimal performance occurring. For example, the threshold criterion may comprise a threshold value for the operating parameter. In the event that the operating parameter drops beneath the threshold value (e.g. is less than), then it may be determined that the cell 100 is operating too close to a risk of sub optimal performance. Examples of what the parameter could be, and how that parameter suggests suboptimal performance are shown in the Table of Fig. 4b.

[0164] For example, if an obtained indication of current is below a selected threshold value and / or a change in current (amount of change and / or rate of change) is below a threshold value, it may be determined that the cell 100 is too close to suboptimal operation. If an obtained indication of change in voltage (amount and / or rate) is below a threshold value, and / or if the voltage is below a threshold voltage, it may be determined that the cell 100 is too close to suboptimal operation. If the light intensity within the cell 100 and / or a spectrum of wavelengths being emitted in the cell 100 is below a threshold value, it may be determined that the cell 100 is too close to suboptimal operation. If a pressure and / or temperature within the cell 100 exceeds a threshold value, it may be determined that the cell 100 is too close to suboptimal operation.

[0165] For each example, the obtained parameter provides an indication of a likelihood of the cell 100 reverting back towards non-plasma generating operation. As will be appreciated in the context of the present disclosure, the generation of plasma bubbles within the cell 100 enables greater efficiency for converting input power (e.g. the electrical energy applied to the electrode(s) of the cell 100) into heated fluid. With increased plasma generation and energy release therefrom, this efficiency will increase. However, when the cell conditions drop below a lower threshold level and bubbles of plasma are no longer generated, the resulting energy release from the bubbles of plasma will cease and the efficiency will be reduced (the cell 100 will then effectively act just as a resistive heater). In other words, step 440 may comprise determining whether the operation is above a lower threshold level associated with no (or insufficient) plasma generation.

[0166] If at step 440 it is determined that the cell operation is above the threshold minimum, the method repeats itself by returning to step 410 where operating parameter(s) are received and monitored (e.g. to ensure cell operation remains within a selected range). If at step 440 it is determined that the cell operation is not above the minimum threshold and / or if at step 430 it is determined that there is demand for increased output from the cell 100, the method proceeds to step 435.

[0167] At step 435, operation is controlled to increase cell output. In Fig. 4a, this is shown as only one step which applies to both: (i) a Yes from step 430, and (ii) a No from step 440. However, it will be appreciated that this step 435 may differ depending on which the previous step was. In particular, where the parameter was not above a threshold minimum at step 440, the control at step 435 may be to ensure operating conditions of the cell 100 are sufficiently efficient and that the cell does not revert back towards a start up mode. Where there was a demand for increased output at step 430, the control at 435 may be to increase output from the cell. This may comprise altering conditions to increase efficiency or increasing the overall output from the cell 100. In other words, after a no at step 440, there need not necessarily be any demand for additional output from the cell 100, but the cell 100 may be controlled so that it is operating at a high enough efficiency level, whereas after a yes at step 430, there may be a demand for increased output.

[0168] In other words, operation of the cell 100 and / or supply system may be controlled to make the conditions within the cell 100 more conducive to plasma bubble generation (and energy release therefrom). For example, the electrical energy being applied to the cell 100 (e.g. the voltage applied to the first electrode 110) may be increased. This may be the case whichever way the method approaches step 435.

[0169] Where there is demand for more output at step 435, it may be assumed that cell operating conditions are already sufficiently efficient (e.g. there is plasma bubble generation and heat release occurring). In which case, controlling operation to increase output may comprise generating greater quantities of heated fluid being output from the cell 100. For this, a greater flow rate may be used, and / or an increased separation distance for electrodes may be used. This may enable output of a greater amount of heated fluid from the cell 100 (e.g. due to the increased volume of plasma generation within the cell, and / or the greater throughput of fluid to be heated). When increasing the separation and / or flow rate the amount of electrical energy being applied to the electrodes may also be increased correspondingly. For example, the voltage may be increased as well, e.g. to compensate for the greater separation / flow rate.

[0170] Where the parameter is not above the minimum threshold at step 440, it may be assumed that the cell operating conditions are approaching (or at) a level which is not sufficiently efficient (in contrast to that mentioned in the above paragraph). Increasing output in this manner may comprise restoring the operating conditions of the cell 100 to a more efficient level. In turn, this may lead to generating a greater amount of heated fluid, but the primary driver is to increase efficiency in this scenario. For this scenario, the electrode separation may be decreased and / or a flow rate may be reduced. The purpose being to return the cell 100 towards conditions which provide sufficient plasma generation (and thus cell efficiency). Decreasing the electrode separation may provide a higher level of electrical stress in the resulting plasma generating volume, and / or decreasing the flow rate may ensure that the fluid within the cell has a higher proportion of bubbles of plasma. Both actions may restore the cell operation to a scenario in which plasma generation is higher (and thus the cell 100 is operating more efficiently).

[0171] As will be appreciated, the methods shown in Figs. 3 and 4 may form one longer method for controlling operation. That is, the method may start with the start up mode of operation before then transitioning into the normal mode of operation (once it is determined that the time is right to do so). For example, once it is determined that start up mode is completed (at step 320), the subsequent step (step 325) may lead to step 410 (where parameters are monitored for controlling normal mode operation).

[0172] One example ‘combined’ method with specific examples for the operational parameters being monitored and the corresponding controlled operations will now be described with reference to both Figs. 3a and 4a.

[0173] The start up mode operation may comprise monitoring an indication of pressure and / or temperature for determining whether the cell 100 remains in its start up mode. The normal mode operation may comprise monitoring light intensity and / or wavelengths for determining a quality and / or efficiency for the process occurring within the cell 100. In both modes, an indication of voltage and current is monitored, and the electrical energy applied to the cell 100 is input power regulated.

[0174] The method starts with the start up mode shown in Fig. 3a. An indication of pressure and / or temperature is received at step 310, as is an indication of voltage and current. It is determined based on the pressure / temperature whether the start up mode has finished - if above a threshold value (at step 320), the method proceeds to step 325 / 410. While the pressure / temperature is not above the threshold associated with start up mode being complete, the start up mode comprises monitoring and regulating voltage applied to the first electrode 110. As long as the resulting current remains below a threshold value, the applied voltage will be increased (e.g. incrementally). At each instant in time, the voltage being applied to the first electrode 110 may be input power controlled, so that the power applied to the cell 100 is at a selected value. As such, the voltage applied will be regulated based on the resulting current (e.g. as per P=IV) so that the power being applied is that of the selected value. During this period, there may be no flow through the cell 100 - i.e. it may be the same fluid which remains in the cell 100 for the entire process. As long as the cell 100 remains in start up mode, and the current does not exceed a threshold value (or a change in current / voltage does not exceed a threshold value), the method comprises repeatedly increasing the power being applied to the cell 100, i.e. increasing the voltage applied to the first electrode 110.

[0175] After a certain period of time, the resulting conditions in the cell 100 will be such that plasma generation and energy release is occurring within the cell 100 (and so the cell 100 may no longer be in a start up mode). This is detected based on an obtained indication of pressure and / or temperature. For example, once the temperature / pressure exceeds a threshold value, it is determined that the start up mode is complete (at step 320) and the method continues with the process shown in Fig. 4a.

[0176] At step 410, the method comprises receiving an indication of light generation (e.g. intensity and / or wavelength information), as well as an indication of voltage and current. As with during start up, the electrical energy applied to the cell 100 may be power limited according to a selected input power. A voltage will be applied to the first electrode 110 according to this input power, and the resulting current is monitored. The determination at step 420 of whether the cell 100 is too close to breakdown is based on the current and / or voltage measurements. If the current exceeds a threshold value and / or any change in current / voltage values exceeds a threshold, it is determined that the cell 100 is too close to breakdown. In which case, the voltage applied to the cell 100 will be reduced. The voltage may then be input power-limited but to a lower input power value. A corresponding determination is made at step 440, at which point it is determined whether the voltage / current is too low. If it is below a lower threshold value, then it may be determined that the cell 100 is approaching sub optimal operation. In which case, the selected input power may be increased, and the voltage applied to the first electrode 110 may be input-power limited according to a higher input power (i.e. a greater voltage).

[0177] If, there is a demand for increased output, e.g. at step 430, the flow rate may be increased. While the flow rate is increased, the amount of electrical energy applied to the cell 100 is also increased. For this, a current may be monitored and / or regulated. Current and / or voltage may be increased with the increased flow to ensure satisfactory efficiency levels are maintained. For example, an indication of light intensity and / or wavelength(s) may also be monitored, e.g. to ensure the resulting light emissions are sufficiently multispectral (i.e. closer to white light). The voltage may be increased until the light is sufficiently multispectral. For example, if the current / voltage is too low, the light emissions may be more monochromatic (and yellow in colour).

[0178] When decreasing output, the flow may be reduced. At the same time, the electrical energy being applied may be decreased. While decreasing, voltage may be monitored and controlled (e.g. to ensure it is above a threshold value). While increasing, current may be monitored and controlled (e.g. to ensure it does not get above a threshold value). For a given flow rate, there may be an optimal electrode separation distance. The electrode separation may be controlled along with the flow rate, e.g. if the flow rate changes then so too will the electrode separation. In other words, during the normal mode, current and voltage values are monitored, and the operation is controlled so that these values remain within a selected range. This operation may comprise monitoring current and voltage, and controlling the applied input power, to maintain the resulting current / voltage within a selected range (i.e. above a lower threshold and below an upper threshold). As such, this input power regulation may cause the cell 100 to operate above a lower threshold (below which suboptimal cell operation may occur) and below an upper threshold (above which cell breakdown may occur).

[0179] During this normal mode operation, light emissions within the cell 100 are also monitored. This comprises monitoring at least one of light intensity and / or light wavelengths. The properties of the light emissions are monitored, and a quality of operation occurring within the cell 100 is determined based on these properties. For this, if it is determined that the quality of cell operation is too low (i.e. if the intensity and / or range of wavelengths being emitted is too low), then the cell 100 is controlled to increase this quality. To increase the quality, the input power being applied to the cell 100 may be increased. The voltage / current monitoring will take precedent, and so if the voltage / current monitoring determines that the input power needs to be reduced (i.e. to avoid breakdown), then the voltage will be reduced (even if the quality indicator suggests that the voltage should be increased). Assuming the input power is not above an upper threshold (indicative of breakdown), then the input power will be increased if the quality indicator is below a threshold value. If the quality indicator remains above the threshold value (e.g. there is intense, white light in the cell 100), then the operating conditions may be maintained. As such, while the cell 100 remains operating within its selected operating bounds (i.e. to avoid breakdown or non-plasma generation), the process may be regulated to ensure the quality of the process is occurring satisfactorily.

[0180] When operating in the dormant mode described above, the monitoring and regulating may be similar to that mentioned above for the start up mode. That is, a pressure / temperature may be monitored, and based on this, a current status for the cell may be determined. In particular, the operational parameter (e.g. temperature / pressure) may be monitored and regulated so that it remains within a selected range, rather than so that it is increased to lead to the normal mode of operation (as in the start up mode). In other words, the cell may be monitored and regulated so that a pressure and / or temperature remain within a selected range. In that range, plasma generation will be low (e.g. minimal), but the cell 100 would not require much additional energy to reach plasma generating conditions).

[0181] In examples described herein, the cell 100 (a controller thereof) is configured to determine an indication of an operating condition for the cell 100. For this, one or more operational parameters are obtained, e.g. from sensors of the cell 100. A mode of operation for the cell 100 is then determined based on the obtained operational parameter(s). For example, it may be determined whether the cell 100 is in a start up mode of operation, a normal mode of operation or a cooldown mode of operation. As described herein, one of the key indicators for determining the mode of operation for the cell 100 relates to whether plasma is being generated within the cell 100 and / or how much plasma is generated. An example will now be described for how the cell 100 may determine an indication of plasma generation occurring.

[0182] Cells of the present disclosure may be configured to determine an indication of plasma generation based on variability in the applied electrical signals to the cell 100. In particular, as already mentioned, the cell 100 is configured to apply an electrical signal to the first electrode 110 for generating bubbles of plasma therein. The signal applied may be in the form of a voltage signal. For example, the cell 100 may be configured to apply a selected voltage to the first electrode 110. This selected voltage may be controlled to be a fixed voltage value or a selected voltage profile. As one example, the cell 100 may be configured to apply the voltage according to a selected input power value. In which case, for a given selected power value, the applied voltage will vary in dependence upon the resulting current (e.g. as per P=IV, thereby to remain at the selected power value). Additionally, or alternatively, the cell 100 may be configured to apply the electrical energy with maximum limits for voltage and / or current. For example, in the event voltage or current reaches or exceeds its maximum value, the amount of electrical energy applied may be reduced or stopped.

[0183] The cell 100 is configured to apply the electrical signal to the electrode 110 (e.g. to apply a selected voltage to the first electrode 110) and to monitor one or more resulting properties associated with that applied electrical signal. As already mentioned, the applied electrical signal may be in the form of an applied voltage signal. The one or more resulting properties associated with the applied electrical signal may comprise an indication of an applied voltage, a resulting current and / or a corresponding resistance. That is, the property may comprise an indication of at least one of a current, a voltage and / or a resistance for the applied signal. For example, a measured value (or magnitude) associated with the electrical signal being applied to the electrode 110 may be used to determine the presence of plasma within the cell. For instance, where the property being measured is the applied voltage, indication of how much (if any) plasma is being generated within the cell 100 may be determined based on the variations in this resulting applied voltage signal. Likewise, an indication of resulting current and / or resistance could be used when determining how much, if any, plasma is being generated within the cell 100. In particular, the present inventors have identified that, where there is a greater variability in the applied signal, it may be determined that there is more plasma generation occurring. At above a first threshold amount of variability, it may be determined that plasma generation has started. At above a second threshold amount of variability, it may be determined that satisfactory plasma generation is occurring.

[0184] As one example, the cell 100 may be configured to apply an electrical signal in the form of a voltage signal to the first electrode 110. The cell 100 may also be configured to monitor one or more properties of this applied electrical signal. In this example, the cell 100 may be configured to monitor a magnitude of the voltage applied to the first electrode 110.

[0185] In this example, the applied voltage may be limited according to a selected input power level. As such, the product of the applied power and resulting current (i.e. P=IV) will be at a selected, and constant, level. The applied voltage may be measured repeatedly. As such, a plurality of voltage measurements may be obtained. Based on these plurality of voltage measurements, an indication of a variation in the voltage may be determined. As will be appreciated in the context of the present disclosure, this may be performed in a number of different manners, e.g. using different statistical approaches. For example, a variance or standard deviation from a mean may be utilised, as may be a measure of range of voltage measurements. In this example, a mean voltage value is determined, as is a range from lowest to highest voltage value. The determination of plasma is performed based on a ratio of the range to the mean. For example, it may be determined that a plasma is present in the event that the range is above a selected proportion of the mean value.

[0186] A rolling window of voltage values may be used, e.g. so that each determination of plasma is based on the most recent subset of values (e.g. as compared to using all of the obtained voltage values). Two threshold values may be defined. A first threshold is a lower threshold associated with there being some plasma generation, but below a satisfactory level. A second, higher, threshold is associated with sufficient plasma generation occurring. For example, in the event that the proportion of the voltage range to the voltage mean is above the first threshold level, it may be determined that plasma generation has commenced in the cell 100. In the event that the proportion of the voltage range to the voltage mean is above the second threshold level, it may be determined that satisfactory plasma generation is occurring.

[0187] Without wishing to be bound by theory, the electrical conditions experienced by the electrode within the cell 100 may vary depending on the state of the material in close proximity to it. For example, initially, there may be a high degree of uniformity in the water between the electrodes within the cell 100. In which case, the capacitance therebetween may remain relatively constant. As the bubbles of plasma begin to fall however this impacts the capacitance, which in turn will affect the electrical conditions felt by the electrode. This is further apparent as the bubbles of plasma will typically form on or close to the electrode tip within the cell. As a result, the current may increase due to this plasma bubble formation, and / or the resistance may further decrease as ionisation of gas occurs in the cell 100. Where the applied electrical energy is limited according to a maximum permitted value for current (and / or voltage), this may also influence the applied electrical signal. These factors may contribute to increased volatility in the resulting electrical signal, and so monitoring variation in this signal may provide an indication of increased plasma generation occurring.

[0188] As will be appreciated, the above description is of one approach for quantifying variation in the applied signal (based on a ratio between range and mean), but the measurement of variation could take other forms. Any suitable metric could be used which provides an indication of the amount of variability in the applied electrical signal. Such a metric may take into account properties such as an average (e.g. mean, median, mode) value and / or a measure of the width of the distribution of different values (e.g. range, FWHM, average deviation etc.).

[0189] Likewise, while in this example the obtained measurement is a measurement of the applied voltage, the same approach could be used for a measurement of another property of that electrical signal, such as a resulting current from the signal applied to the first electrode 110 and / or a resistance to that applied signal. In which case, the above description of determining the indication of variation in the applied electrical signal would refer to values indicative of current and / or resistance (rather than voltage). It will of course be appreciated that any suitable metric representative of the resulting electrical signal could be used which would reflect this variation. Similarly, the applied voltage signal need not be power limited, e.g. it could be a fixed or constant voltage, or it could follow a selected voltage profile.

[0190] In the examples described above, one cell 100 is used. However, multiple cells may be used in conjunction with each other. For example, the apparatus may comprise a plurality of cells. The cells may be shaped so that they can be stacked together, e.g. side by side. For example, they may tesselate. This may provide more space efficient storage of cells, as compared to e.g. circular cells. The collective plurality of cells may be controlled according to the methods disclosed herein. In particular, each cell may be monitored and controlled to provide sufficiently efficient operation.

[0191] The plurality of cells may be controlled together. For this, each cell may either be ‘on’ or ‘off’, with the on cells contributing to the output of heated fluid. The number of on cells may be selected based on a demand level for heated fluid. All but one of the on cells may be operated at or close to optimal operating conditions for outputting heated fluid. The final on cell may be operated at a level so that the amount of heated fluid output from that cell, plus the amount of heated fluid being output from the other on cells corresponds to the amount demanded. That way, the majority of the operating cells may be operated at very high efficiency levels, while the total demand is met by the combination of cells. This may increase efficiency as compared to running a single cell at much higher output levels. For any off cells, these may be monitored according to the cooldown mode disclosed herein. For example, some or all of the off cells may be maintained in a dormant mode of operation (e.g. if they are likely to be used again within the threshold time period). That way, the apparatus may be able to quickly respond to increased demand for heated fluid output.

[0192] It will be appreciated in the context of the present disclosure that the above described control method is just one example, and that different parameters may be monitored and / or different variables may be controlled accordingly. The methods may comprise monitoring at least two different observable parameters. One of the parameters selected may provide a slower moving variable, such as pressure or temperature. The slower moving parameter may fluctuate over a much larger time scale, e.g. the time it takes for a significant difference to be observed in that parameter may be substantially longer than that associated with a quicker moving variable. One of the parameters selected may provide a quicker moving (i.e. more responsive) variable, such as light information (intensity / wavelength) and / or current / voltage. The determination of whether the cell 100 is in start up mode or not may be made based on the slower moving variable. The feedback loop(s) for maintaining normal mode operation may be based on the quicker moving variable. A feedback loop associated with cell operation quality may also be based on a quicker moving variable.

[0193] Examples described above have generally related to the energy cell 100 shown in Fig. 1. However, it will be appreciated that the cell 100 of Fig. 1 should not be considered limiting. For example, the third electrode 130 need not be included, and / or the resistive element need not be included. For example, any suitable energy cell (such as the cells disclosed in GB 2604853 could be used. It will also be appreciated that the ordering of the methods disclosed herein need not be considered limiting, the different steps could be performed in a different order. In particular, each decision step may form part of (or the entirety of) a feedback loop for controlling cell operation. These feedback loops may occur simultaneously with each other, and / or they may operate independently of each other. For example, received indication(s) may be continually analysed to determine if any control mechanism needs to be activated for regulating operation.

[0194] It will also be appreciated that any of the different parameters and control operations for the cell could be used together in combination. Controlling based on an indication of any parameter may comprise controlling based on the value of that parameter. For example, the indication may be of a certain parameter being at a certain value, and the control may be based on that value. This processing and control could be digital or analogue. For current, voltage, light intensity, pressure and / or temperature, the observable parameter may be an absolute value (e.g. the value for that parameter). The parameter could also be a frequency of such parameters (e.g. for current etc.). Where the parameter relates to wavelength(s) of light, the parameter could be an indication of a value for one or more detected wavelengths, it could be a count number of different wavelengths detected, and / or it could be visual data indicative of the colours of visible light being emitted. As the process initially starts, the light emitted may be yellow / green in colour, but as it operates more efficiently, the colour may converge on a broader spectrum (i.e. towards white light). The indication of wavelength may comprise an indication of the number of wavelengths (i.e. where a greater number indicates broader spectrum), an indication of different values being received (i.e. where greater diversity would be apparent), and / or an indication of the resulting colour (i.e. which would be whiter when a broader spectrum is present and yellow / greener when not).

[0195] It will be appreciated from the discussion above that the examples shown in the figures are merely exemplary, and include features which may be generalised, removed or replaced as described herein and as set out in the claims. With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. In addition, the processing functionality may also be provided by devices which are supported by an electronic device. It will be appreciated however that the functionality need not be divided in this way, and should not be taken to imply any particular structure of hardware other than that described and claimed below. The function of one or more of the elements shown in the drawings may be further subdivided, and / or distributed throughout apparatus of the disclosure. In some examples the function of one or more elements shown in the drawings may be integrated into a single functional unit.

[0196] As will be appreciated by the skilled reader in the context of the present disclosure, each of the examples described herein may be implemented in a variety of different ways. Any feature of any aspects of the disclosure may be combined with any of the other aspects of the disclosure. For example, method aspects may be combined with apparatus aspects, and features described with reference to the operation of particular elements of apparatus may be provided in methods which do not use those particular types of apparatus. In addition, each of the features of each of the examples is intended to be separable from the features which it is described in combination with, unless it is expressly stated that some other feature is essential to its operation. Each of these separable features may of course be combined with any of the other features of the examples in which it is described, or with any of the other features or combination of features of any of the other examples described herein. Furthermore, equivalents and modifications not described above may also be employed without departing from the invention.

[0197] Certain features of the methods described herein may be implemented in hardware, and one or more functions of the apparatus may be implemented in method steps. It will also be appreciated in the context of the present disclosure that the methods described herein need not be performed in the order in which they are described, nor necessarily in the order in which they are depicted in the drawings. Accordingly, aspects of the disclosure which are described with reference to products or apparatus are also intended to be implemented as methods and vice versa. The methods described herein may be implemented in computer programs, or in hardware or in any combination thereof. Computer programs include software, middleware, firmware, and any combination thereof. Such programs may be provided as signals or network messages and may be recorded on computer readable media such as tangible computer readable media which may store the computer programs in non-transitory form. Hardware includes computers, handheld devices, programmable processors, general purpose processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and arrays of logic gates.

[0198] Other examples and variations of the disclosure will be apparent to the skilled addressee in the context of the present disclosure.

Claims

Claims1 . An apparatus comprising: an energy cell configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein; and a controller configured to obtain an indication of at least one operational parameter of the energy cell, and wherein the controller is configured to: determine, based on at least one obtained indication of a first operational parameter, if the energy cell is in either of: (i) a normal mode of operation, or (ii) a start up mode of operation; in the event that it is determined that the energy cell is in the start up mode, control operation of the energy cell and / or the liquid supplied to the energy cell to increase the generation of bubbles of plasma in the energy cell; and in the event that it is determined that the energy cell is in the normal mode, control operation of the energy cell so that a second operational parameter remains within a selected range.

2. The apparatus of claim 1 , wherein the selected range is below an upper threshold value associated with breakdown occurring in the cell.

3. The apparatus of claim 1 or 2, wherein the selected range is above a lower threshold value associated with sub optimal efficiency for cell operation.

4. The apparatus of any preceding claim, wherein the first operational parameter comprises at least one of a temperature and / or a pressure.

5. The apparatus of any preceding claim, wherein the second operational parameter comprises at least one of a current and / or a voltage.

6. The apparatus of claim 5, wherein the controller is configured to monitor both a current flow and a voltage applied to an electrode of the energy cell; and wherein the controller is configured to control the voltage applied to the electrode based on the current flow.

7. The apparatus of claim 6, wherein the controller is configured to reduce the applied voltage in the event that the current exceeds a threshold current value.

8. The apparatus of claim 6 or 7, wherein the controller is configured to control application of voltage to the electrode according to a selected applied power level.

9. The apparatus of claim 8, wherein the controller is configured to increase the power applied to the electrodes while the current remains below a threshold current.

10. The apparatus of any preceding claim, wherein the controller is configured to obtain at least one indication of a third operational parameter; and wherein the controller is configured to determine an indication of a process quality for operation of the cell based on the third operational parameter.

11. The apparatus of claim 10, wherein the third operational parameter comprises at least one of an intensity and / or wavelength of light emissions in the cell.

12. The apparatus of claim 10 or 11 , wherein the controller is configured to control operation of the energy cell based on the determined indication of process quality.

13. The apparatus of any of claims 10 to 12, wherein the controller is configured to increase the power applied to the electrode of the energy cell in the event that the process quality is below a lower threshold.

14. The apparatus of claim 13, wherein the controller is configured to continue increasing the power applied to the electrode of the energy while the process quality remains below the lower threshold and a current flow remains below a current threshold.

15. The apparatus of any preceding claim, wherein controlling operation of the energy cell and / or the liquid supplied to the energy cell comprises at least one: varying a separation distance between electrodes of the energy cell; and selectively providing bubbles in the liquid supplied to the energy cell.

16. The apparatus of any preceding claim, wherein at least one of: varying the separation distance between electrodes comprises decreasing the separation distance for the start up mode of operation; varying the separation distance between electrodes in the normal mode of operation comprises increasing separation to increase output from the cell and / or decreasing the separation distance in the event that plasma generation is below a threshold level; and selectively providing bubbles in the liquid supplied to the energy cell comprisesproviding bubbles in the liquid for the start up mode of operation; and selectively providing bubbles in the liquid supplied to the energy cell comprises increasing an amount of bubbles in the liquid provided to the cell to increase output from the cell and / or decreasing an amount of bubbles in the liquid provided to the cell to decrease output from the cell.

17. The apparatus of any preceding claim, wherein the controller is configured to switch operation of the energy cell into a cooldown mode.

18. The apparatus of claim 17, wherein switching operation of the energy cell into the cooldown mode comprises switching operation of the cell into a dormant mode in the event that the cell is to be subsequently restarted within a threshold time period.

19. The apparatus of claim 18, wherein, in the dormant mode, the controller is configured to obtain an indication of at least one operational parameter of the cell and to control operation of the cell so that said operational parameter remains within a threshold range.

20. The apparatus of claim 19, wherein the threshold range is selected so that an amount of time and / or energy required to restart the cell into operating in its normal mode of operation is below a threshold level.

21. The apparatus of any of claims 18 to 20, wherein switching operation of the energy cell into the cooldown mode comprises switching operation of the cell into a shutdown mode in the event that the cell is not to be subsequently restarted within the threshold time period.

22. The apparatus of any preceding claim, wherein the obtained indication of a first operational parameter is an indication of a variation in an electrical signal applied to an electrode of the cell.

23. The apparatus of claim 22, wherein the controller is configured to determine that the energy cell is in the start up mode in the event that the variation in the electrical signal is below a threshold level.

24. The apparatus of claim 22 or 23, wherein the applied electrical signal is an applied voltage, and wherein the controller is configured to determine that the energy cell is in the start up mode in the event that the variation in one or more properties of the applied signal is below a threshold level, optionally wherein said one or more properties comprises a voltage,a current and / or a resistance of the applied signal.

25. The apparatus of any of claims 22 to 24, wherein the indication of the variation is based on a mean and / or a range of obtained values for the applied electrical signal.

26. The apparatus of any of claims 22 to 25, wherein the second operational parameter comprises an indication of the variation in the electrical signal applied to the electrode.

27. The apparatus of claim 26, wherein the controller is configured to control operation in the normal mode to retain the variation in the electrical signal above a threshold level.

28. An apparatus comprising: an energy cell configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein; and a controller configured to control the cell to operate in: (i) a normal mode of operation, and (ii) a dormant mode of operation, wherein: in the normal mode of operation, the controller is configured to receive an indication of a first operational parameter of the energy cell and to control operation so that the first operational parameter remains within a first selected range associated with normal operation of the energy cell; and in the dormant mode of operation, the controller is configured to receive an indication of a second operational parameter of the energy cell and to control operation so that the second operational parameter remains within a second selected range associated with dormant operation of the energy cell.

29. The apparatus of claim 28, wherein the controller is configured to switch operation of the cell from the normal mode into the dormant mode in the event that the cell is to be disactivated and then subsequently restarted within a threshold time period, optionally wherein the controller is configured to switch operation of the cell from the normal mode into a shutdown mode in the event that the cell is to be disactivated and then not subsequently restarted within the threshold time period.

30. The apparatus of claim 28 or 29, wherein the second threshold range is selected so that an amount of time and / or energy required to restart the cell into operating in its normal mode of operation is below a threshold level.31 . An apparatus comprising:an energy cell comprising an electrode configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein; and a controller configured to monitor an electrical signal applied to the electrode and to determine an indication of an amount of plasma generation occurring within the energy cell based on a variation in the applied electrical signal.

32. The apparatus of claim 31 , wherein the applied electrical signal is an applied voltage signal.

33. The apparatus of claim 31 or 32, wherein monitoring an electrical signal applied to the electrode comprises monitoring at least one of a voltage, a current and a resistance associated with the applied signal.

34. The apparatus of any of claims 31 to 33, wherein determining the indication of the amount of plasma generation is based on a range between lower and higher values for the applied electrical signal.

35. The apparatus of claim 34, wherein determining the indication is based on a ratio of the range between lower and higher values relative to an average value for the applied electrical signal.

36. The apparatus of any of claims 31 to 35, wherein the apparatus is configured to control operation of the energy cell based on the determined indication of the amount of plasma generation occurring within the cell.

37. The apparatus of claim 36, wherein the apparatus is configured to increase the electrical energy applied to the electrode in the event that the variation in the applied electrical signal is below a threshold value.

38. The apparatus of claim 37, wherein the apparatus is configured to determine that plasma generation is occurring in the event that the variation in the applied electrical signal is at or above the threshold value.

39. The apparatus of claim 37 or 38, wherein the apparatus is configured to increase the electrical energy applied until the variation in the applied electrical signal is at or above a second, greater, threshold value.

40. The apparatus of any of claims 31 to 39, wherein the apparatus is configured to apply the electrical signal to the electrode according to a selected power level.

41. The apparatus of claim 40, wherein the apparatus is configured to vary the applied voltage in dependence on the resulting current associated with that applied voltage, thereby to apply electrical energy according to the selected power level.

42. The apparatus of claim 40 or 41 , wherein the controller is configured to determine the indication of an amount of plasma generation occurring within the energy cell based on a variation in the current and / or voltage of the applied signal.

43. A system comprising: the apparatus of any preceding claim; a liquid supply system coupled to the energy cell and configured to supply a liquid to be heated to the energy cell; and a work extraction system coupled to the energy cell and configured to extract useable work from heated fluid output from the energy cell.

44. A method of operating an energy cell, wherein the energy cell is configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein, the method comprising: determining, based on an obtained indication of a first operational parameter of the energy cell, if the energy cell is in either of: (i) a normal mode of operation, or (ii) a start up mode of operation; controlling operation of the energy cell and / or the liquid supplied to the energy cell to increase the generation of bubbles of plasma in the energy cell when the energy cell is in the start up mode; and controlling operation of the energy cell so that a second operational parameter remains within a selected range when the energy cell is in the normal mode.

45. A method of operating an energy cell, wherein the energy cell is configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein, the method comprising: controlling the cell to operate in: (i) a normal mode of operation, and (ii) a dormant mode of operation, wherein: in the normal mode of operation, an indication of a first operational parameterof the energy cell is received, and operation of the cell is controlled so that the first operational parameter remains within a first selected range associated with normal operation of the energy cell; and in the dormant mode of operation, an indication of a second operational parameter of the energy cell is received, and operation is controlled so that the second operational parameter remains within a second selected range associated with dormant operation of the energy cell.

46. A method of operating an energy cell, wherein the energy cell comprises an electrode configured to apply electrical energy to liquid in the energy cell to heat the liquid by generating one or more bubbles of plasma therein, the method comprising: monitoring an electrical signal applied to the electrode; and determining an indication of an amount of plasma generation occurring within the energy cell based on a variation in the applied electrical signal.

47. A computer program product comprising computer program instructions configured to program a controller to control operation of an energy cell to perform the method of any of claims 44 to 46.

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