Apparatus and method

Abstract

An apparatus comprising: a plasma generating vessel comprising an electrode; a fluid supply system configured to supply fluid to the plasma generating vessel; an electrical supply system coupled to the electrode to apply electrical energy to liquid in the plasma generating vessel to generate one or more bubbles of plasma therein; a thermal energy store configured to store thermal energy from the heated fluid output from the plasma generating vessel; a work extraction system coupled to the thermal energy store; and a controller configured to control the flow of thermal energy between: (i) the plasma generating vessel, (ii) the thermal energy store, and (iii) the work extraction system, based on an indication of a demanded amount of thermal energy by the work extraction system.

Description

[0001] Apparatus and Method

[0002] Technical Field

[0003] The present disclosure relates to the field of plasma generating vessels. In particular, the present disclosure relates to the field of apparatuses and methods for controlling operation of one or more plasma generating vessels.

[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] In an aspect, there is provided an apparatus comprising: a plasma generating vessel comprising an electrode; a fluid supply system configured to supply fluid to the plasma generating vessel; an electrical supply system coupled to the electrode to apply electrical energy to liquid in the plasma generating vessel to generate one or more bubbles of plasma therein; a thermal energy store configured to store thermal energy from the heated fluid output from the plasma generating vessel; a work extraction system coupled to the thermal energy store; and a controller configured to control the flow of thermal energy between: (i) the plasma generating vessel, (ii) the thermal energy store, and (iii) the work extraction system, based on an indication of a demanded amount of thermal energy by the work extraction system.

[0009] Embodiments may enable more efficient operation of the apparatus. That is, the apparatus may enable operation of the vessel to be controlled so as to cause vessel operation to be at higher efficiencies. For example, by enabling the storage of thermal energy, the vessel may be operated at higher efficiencies (and greater outputs) while enabling that thermal energy to be used in due course. Likewise, by enabling the storage of thermal energy, the vessel may be controlled not to operate when demand is low, with stored energy being used instead, so as to enable the vessel to only be operated when at high enough efficiency levels.

[0010] Controlling said flow of thermal energy may comprise, in the event that the demanded amount of thermal energy is below a lower threshold amount: (i) controlling operation of the vessel to output heated fluid and providing at least some of the thermal energy from said heated fluid to the thermal energy store, or (ii) providing thermal energy from the thermal energy store to the work extraction system. Step (ii) may further comprise stopping or reducing the application of electrical energy to the electrode, and / or stopping or reducing the supply of fluid to the vessel. Controlling said flow of thermal energy may comprise: in the event that the demanded amount of thermal energy is above a threshold amount, controlling operation of the vessel to output heated fluid and providing at least some of the thermal energy from said heated fluid to the work extraction system. The controller may be configured to: (i) determine an amount of thermal energy to be output from the vessel based on the indication of the demanded amount of thermal energy by the work extraction system, and (ii) control operation of the apparatus to output the determined amount of heated fluid. Determining the amount of thermal energy to be output from the vessel may comprise: in the event that the demanded amount of thermal energy is at a first value below an upper threshold amount but above a lower threshold amount, determining the amount of thermal energy to be output from the vessel to be at or above the upper threshold amount. The apparatus may be configured to store some or all of the thermal energy from said heated fluid output from the vessel in excess of the first value in the thermal energy store. Determining the amount of thermal energy to be output from the vessel may comprise: in the event that the demanded amount of thermal energy is at a second value below the lower threshold amount, determining the amount of thermal energy to be output from the vessel to be that associated with dormant or inactive operation of the vessel. The apparatus may be configured to provide thermal energy from the thermal energy store to the work extraction system to meet the second value. Determining the amount of thermal energy to be output from the vessel may comprise: in the event that the demanded amount of thermal energy is at a third value above the upper threshold amount, determining the amount of thermal energy to be output from the vessel to be at or above the third value. The apparatus may be configured to store some or all of the excess thermal energy from the heated fluid output from the vessel in the thermal energy store in the event that the amount of thermal energy output from the vessel is above the third value. The controller may be configured to control the vessel to operate at or above a threshold coefficient of performance, and in the event that the demanded amount of thermal energy would result in vessel operation being under the threshold coefficient of performance, to either: (i) control the vessel to be in a dormant or inactive mode, or (ii) control the vessel to operate at or above the threshold coefficient of performance and to store some of the thermal energy from said heated fluid in the thermal energy store. The controller may be configured to control an input power to be supplied to the electrode by the electrical supply system, and wherein the controller is configured to select an amount of thermal energy to be output from the vessel so that the input power is above a threshold value. In the event that the demanded amount of thermal energy corresponds to an input power value below the threshold value, the controller may be configured to control operation of the apparatus to either: (i) increase the input power applied to a value at or above the threshold value and store excess thermal energy from said heated fluid in the thermal energy store, or (ii) stop or reduce the input power applied and provide the majority or all of the demanded thermal energy from the thermal energy store. The controller may be configured to control a flow rate of fluid to be delivered to the vessel by the fluid supply system. The controller may be configured to select: (i) the flow rate of fluid based on the input power, and / or (ii) the input power based on the flow rate of fluid.

[0011] In an aspect, there is provided an apparatus comprising: a plurality of plasma generating vessels, each comprising an electrode; one or more fluid supply systems configured to supply fluid to the plasma generating vessels; one or more electrical supply systems coupled to the electrodes to apply electrical energy to liquid in the plasma generating vessels to generate one or more bubbles of plasma therein; a work extraction system coupled to the plasma generating vessels; and a controller configured to select which and / or how many of the plurality of plasma generating vessels are to be active for generating plasma based on an indication of a demanded amount of thermal energy by the work extraction system.

[0012] Embodiments may enable more efficient operation of the apparatus. That is, the apparatus may enable operation of the vessel to be controlled so as to cause vessel operation to be at higher efficiencies. For example, by being able to selectively use a different number of plasma generating vessels, each individual vessel may be operated at higher efficiencies (or not at all), e.g. so as to control efficiency to always be at an elevated level for each vessel being operated in an active mode.

[0013] The controller may be configured to select which and / or how many of the plurality of plasma generating vessels are active so that each individual active vessel is operating at or above a threshold efficiency level. The controller may be configured to control an additional plasma generating vessel to be active in the event that the demanded amount of thermal energy is great enough for each of the existing active vessels and the additional vessel to operate at or above the threshold efficiency level. Selecting which and / or how many of the plurality of plasma generating vessels to be active may comprise: in the event that the demanded amount of thermal energy is below a first threshold amount, controlling at least one of the plasma generating vessels to be in a dormant or inactive mode. Selecting which and / or how many of the plurality of plasma generating vessels to operate may comprise: in the event that the demanded amount of thermal energy is above the first threshold amount, but below a second, higher, threshold amount, controlling the same number of plasma generating vessels to be active but operating one or more of the already active plasma generating vessels to output a greater amount of thermal energy. Selecting which and / or how many of the plurality of plasma generating vessels to operate may comprise: in the event that the demanded amount of thermal energy is above the second threshold amount, controlling at least one additional vessel to be active to generate plasma and output heated fluid. The controller may be configured to: (i) determine an amount of thermal energy to be output from each individual vessel based on the indication of the demanded amount of thermal energy by the work extraction system, and (ii) control operation of the apparatus to output the determined amount of thermal energy. Determining the amount of thermal energy to be output from each individual vessel may comprise: in the event that the demanded amount of thermal energy is at a first value below an upper threshold amount but above a lower threshold amount, determining that some but not all of the plasma generating vessels should be active. In the event that the demanded amount of thermal energy increases from the first value, the controller may be configured to operate an additional vessel to be active in the event that the demanded amount of thermal energy is at a value which facilitates any existing active vessels, as well as the additional vessel, to be operating at above a threshold efficiency level. In the event that the demanded amount of thermal energy decreases from the first value, the controller may be configured to disactivate at least one of the existing active vessels in the event that the demanded amount of thermal energy is at a value which inhibits each of the existing active vessels to be operating at above a threshold efficiency level. Determining the amount of thermal energy to be output from each individual vessel may comprise: in the event that the demanded amount of thermal energy is at a third value above the upper threshold amount, determining that all of the plasma generating vessels should be active. The controller may be configured to control an input power to be supplied to the electrode by the electrical supply system and to control a flow rate of fluid to be delivered to the vessel by the fluid supply system. The controller may be configured to select the input power and flow rate for each active vessel based on the amount of thermal energy to be provided for that vessel. In response to detecting a fault with one of the active vessels, the controller may be configured to increase the input power and / or flow rate to other active vessels. The apparatus may further comprise a thermal energy store configured to store thermal energy from heated fluid output from the plasma generating vessels. The controller may be configured to control the flow of thermal energy between: (i) the plasma generating vessels, (ii) the thermal energy store, and (iii) the work extraction system, based on an indication of a demanded amount of thermal energy by the work extraction system.

[0014] In an aspect, there is provided a method comprising: supplying fluid to a plasma generating vessel, wherein the plasma generating vessel comprises an electrode operable to apply electrical energy to liquid in the vessel to generate one or more bubbles of plasma therein; and controlling the flow of thermal energy between: (i) the plasma generating vessel, (ii) a thermal energy store configured to store thermal energy from heated fluid output from the plasma generating vessel, and (iii) a work extraction system, based on an indication of a demanded amount of thermal energy by the work extraction system.

[0015] In an aspect, there is provided a method comprising: supplying fluid to one or more of a plurality of plasma generating vessels, wherein each of the plasma generating vessels comprises an electrode operable to apply electrical energy to liquid in that plasma generating vessel to generate one or more bubbles of plasma therein; and selecting which and / or how many of the plurality of plasma generating vessels are to be active for generating plasma based on an indication of a demanded amount of thermal energy by a work extraction system coupled to the plasma generating vessels.

[0016] In an aspect, there is provided an apparatus comprising: a plasma generating vessel comprising an electrode; a fluid supply system configured to supply fluid to the plasma generating vessel; and an electrical supply system coupled to the electrode to apply electrical energy to liquid in the plasma generating vessel to generate one or more bubbles of plasma therein, wherein the electrical supply system comprises a voltage boost apparatus comprising: an input power connection; an output power connection coupled to the electrode; a transformer, wherein the input power connection is coupled to the output power connection via the transformer; and a switching arrangement configured to switch electrical connections between the input power connection and the transformer between: (i) a positive voltage mode, and (ii) a negative voltage mode.

[0017] Embodiments may enable the provision of smaller and lighter electrical power supply for the vessel. In turn, this may enable the overall apparatus to be provided a smaller and / or more compact package, e.g. making it more suitable for use in smaller places. Also, the apparatus may be designed to better withstand rapid increases in current (e.g. due to electrical arcing occurring), e.g. due to the inductance of the transformer, thereby making the apparatus safer, as the likelihood and extend of electrical arcing occurring is lower.

[0018] The input power connection may comprise a positive terminal and a negative terminal. The switching arrangement may be configured to switch the electrical connections between each terminal and the transformer to switch between the positive and negative voltage modes. The switching arrangement may be configured to: connect: (i) the positive terminal to a first end of the transformer, and (ii) the negative terminal to a second end of the transformer, to operate in the positive voltage mode; and connect: (iii) the positive terminal to the second end of the transformer, and (iv) the negative terminal to the first end of the transformer, to operate in the negative voltage mode. The apparatus may further comprise: a first switch between the positive terminal and the first end of the transformer; a second switch between the negative terminal and the first end of the transformer; a third switch between the positive terminal and the second end of the transformer; and a fourth switch between the negative terminal and the second end of the transformer. The apparatus may be configured to control either: (i) the first and fourth switches to be electrically conductive together, or (ii) the second and third switches to be electrically conductive together. The apparatus may be configured to control: the first and fourth switches to be electrically conductive and the second and third switches to be electrically non-conductive in the positive voltage mode; and the second and third switches to be electrically conductive and the first and fourth switches to be electrically non-conductive in the negative voltage mode. The input power connection may comprise an AC input connection and a rectifier coupled to the AC input connection. The positive and negative terminals may be terminals of the rectifier. The apparatus may comprise a plurality of voltage boost apparatuses coupled to the electrode. The apparatus may comprise a controller configured to control the switching arrangement to switch between the positive and negative voltage modes. The controller may be configured to control switching of the switching arrangement based on a frequency of an AC electrical input supplied to the input power connection. The controller may be configured to control the switching arrangement to operate in a positive voltage mode during a positive portion of the input AC waveform and to operate in a negative mode during a negative portion of the input AC waveform.

[0019] In an aspect, there is provided a method comprising: supplying fluid to a plasma generating vessel, wherein the plasma generating vessel comprises an electrode operable to apply electrical energy to liquid in the vessel to generate one or more bubbles of plasma therein; and wherein controlling the application of electrical energy to the electrode comprises: connecting, via a transformer, an input power connection to an output power connection coupled to the electrode with electrical connections between the input power connection and the transformer in a positive voltage mode; and connecting, via the transformer, the input power connection to the output power connection coupled to the electrode with electrical connections between the input power connection and the transformer in a negative voltage mode.

[0020] Figures

[0021] Some examples of the present disclosure will now be described, by way of example only, with reference to the figures, in which:

[0022] Fig. 1 is a schematic diagram of an apparatus comprising a plasma generating vessel.

[0023] Fig. 2 is a graph illustrating example operating parameters for a plasma generating vessel. Fig. 3 is a schematic diagram of an apparatus comprising a plasma generating vessel.

[0024] Fig. 4 is a schematic diagram of an apparatus comprising a plurality of plasma generating vessels.

[0025] Figs. 5a to 5c are schematic diagrams of an example electrical supply system for a plasma generating vessel.

[0026] In the drawings like reference numerals are used to indicate like elements.

[0027] Specific Description

[0028] Embodiments of the present disclosure relate to methods and apparatuses for controlling operation of one or more plasma generating vessels. The present inventors have identified that there is a non-linear relationship between the input power applied to an electrode of such a plasma generating vessel and the thermal energy which can be obtained from that vessel. In particular, at lower input powers, a coefficient of performance (‘COP’) for the vessel may be relatively low, whereas at higher input powers, that COP will be much higher. Embodiments of the present disclosure relate to methods and apparatuses for exploiting this relationship by controlling vessel(s) to operate in a higher efficiency region or not at all.

[0029] In embodiments, a thermal energy store is used for storing excess thermal energy brought about due to operating the vessel at a higher input power (and thus higher COP) than would be needed to match the demand for output from the vessel. Similarly, this thermal energy store may also be used as a source of heated fluid at times when the demand is sufficiently low that the vessel would be operating at too low a COP to satisfy that demand. Such arrangements may enable the vessels to be always operating at above a threshold COP.

[0030] In embodiments, multiple vessels may be controlled together, where the number of vessels operating at any one time may be chosen so that each of the active vessels is operating at above a threshold COP. The number of active vessels and how those active vessels are operated may be controlled dynamically to satisfy the demand, while ensuring that vessels are only used if they can be used at above the threshold COP.

[0031] An example apparatus with a plasma generating vessel will first be described with reference to Fig. 1. After this, different operating parameters for that vessel will be described with reference to Fig. 2. Finally, different apparatuses which utilise these operating parameters shown in Fig. 2 will be described with reference to Figs. 3 and 4.

[0032] Plasma generating vessel

[0033] Fig. 1 shows a schematic diagram of an apparatus 100. The apparatus 100 includes an energy vessel 1, as well as an electrical supply system 60, a fluid supply system 70 and a work extraction system 80.

[0034] The vessel 1 includes a fluid inlet 54 and a fluid outlet 58. The vessel 1 has a housing 50. The housing 50 defines an internal volume 56 of the vessel 1. The vessel 1 also includes a plurality of electrodes. As shown, this includes a first electrode 10, a second electrode 20 and a third electrode 30. The vessel 1 may also include a resistive element 40. A mount 32 for the third electrode 30 is shown in Fig. 1. The vessel 1 may also include an earth connector 22. The earth connector 22 is coupled to the second electrode 20 and an electrical earth 24.

[0035] The electrical supply system 60 is coupled to the first electrode 10. The fluid supply system 70 is coupled to the fluid inlet 54 of the vessel 1. The work extraction system 80 is coupled to the fluid outlet 58 of the vessel 1.

[0036] The electrical supply system 60 is configured to supply electrical energy to the first electrode 10. The fluid supply system 70 is configured to supply fluid to the internal volume 56 of the vessel 1. The work extraction system 80 is configured to extract useable work from heated fluid received from the fluid outlet 58 of the vessel 1.

[0037] The housing 50 of the vessel 1 encapsulates the internal volume 56. The fluid inlet 54 provides a flow path for fluid into the internal volume 56 of the vessel 1. The fluid outlet 58 provides a flow path for fluid out from the internal volume 56 of the vessel 1. Fluid may flow along any suitable path between the fluid inlet 54 and the fluid outlet 58. For example, it may flow along a very indirect (e.g. tortuous) path. The internal volume 56 of the vessel 1 may otherwise be sealed by the housing 50.

[0038] The first electrode 10 is at least partially disposed within the internal volume 56 of the vessel 1. The second electrode 20 may also be disposed at least partially within the internal volume 56 of the vessel 1. The first and second electrode 20 are arranged concentrically. The first electrode 10 extends within a central region of the internal volume 56 of the vessel 1. The second electrode 20 is arranged radially outward from the first electrode 10. The second electrode 20 may be cylindrical, as may the first electrode 10. The first and second electrode 20 are arranged co-axially in the example shown in Fig. 1. The second electrode 20 is located adjacent to an internal surface of the housing 50 (however in some examples, the second electrode 20 may be integrated with the housing 50, e.g. to form a part thereof, and / or a portion of the housing 50 may provide the second electrode 20, e.g. if said portion of the housing 50 is electrically conductive).

[0039] A first end of the first electrode 10 is located outside the internal volume 56 of the housing 50. A second end of the first electrode 10, distal to the first end, is located within the internal volume 56 of the housing 50. The second electrode 20 may extend along some, or all, of the length of the internal volume 56 of the housing 50. At least one end of the second electrode 20 may extend out of the internal volume 56 of the vessel 1. Although not shown in Fig. 1 the first and / or second electrode 20 may each be coupled to a power supply. For example, each electrode may have one end which extends outside the internal volume 56 (e.g. into the housing 50), and this end may be coupled to the power supply. In some examples, the housing 50 may provide a ground (e.g. via the earth connector 22 to the electrical ground), and the first electrode 10 may be connected to a positive terminal of the power supply. In Fig. 1 , the second electrode 20 is shown as being a separate component to the housing 50, but this need not be the case, as the second electrode 20 may be provided by the housing 50 (e.g. the housing 50 may be made of an electrically conductive material which may function to provide the second electrode 20).

[0040] The third electrode 30 is also provided in the internal volume 56 of the vessel 1. As shown in Fig. 1 , the third electrode 30 may be located entirely within the internal volume 56. For example, a mount 32 is shown for attaching the third electrode 30 to the housing 50. The third electrode 30 may extend from a first end (e.g. where it is held by the mount 32) to a second end located proximal to the second end of the first electrode 10 within the internal volume 56. The first and third electrodes 10, 30 may be parallel (e.g. they may be co-axial). The second and third electrodes 20, 30 may be parallel (e.g. coaxial). The first electrode 10 may extend from outside a first end of the housing 50 into the internal volume 56 towards an opposite end of the housing 50. The third electrode 30 may extend towards the first electrode 10 within the housing 50. The first and third electrodes 10, 30 may extend into the internal volume 56 so that there is no spatial overlap between these electrodes 10, 30 (e.g. their respective second ends do not touch / overlap). The second electrode 20 may extend along the length of the internal volume 56 from at or outside the first end to at or outside the opposite end. The distance between the second end of the first electrode 10 and the second end of the third electrode 30 may be less than the smallest distance between the first electrode 10 and the second electrode 20. The third electrode 30 may be located away from an expected current path between the first and second electrode 20. The third electrode 30 may be arranged to electrically float within the internal volume 56. While the third electrode 30 and first electrode 10 are shown as being coaxial, parallel and central within the vessel 1, this need not be the case. One or both electrodes 10, 30 may be laterally offset from the centre of the vessel. For example, the third electrode 30 may be laterally offset from the first electrode, e.g. the third electrode 30 may not be central (e.g. but the first electrode 10 may still be central). Additionally, or alternatively, the first electrode 10 may not be central.

[0041] A resistive element 40 may also be included in the internal volume 56. The resistive element 40 may be cylindrical. The resistive element 40 may be arranged to increase the electrical resistance of the conductive path between the first electrode 10 (anode) and the second electrode 20 (cathode). The resistive element 40 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 40 could be provided by different components, wherein each potion may contribute to providing an electrical resistance for the resistive element 40 as a whole. Different portions of the resistive element 40 could be electrically connected and provided by different materials / components. For example, the resistive element 40 could include circuitry, such as a sensor (e.g. a photovoltaic sensor). The different portions of the resistive element 40 need not be physically and / or electrically connected. The resistive element 40 may increase the electrical resistance between the first and second electrodes 10, 20. The resistive element 40 may extend around a majority of the internal volume 56 (e.g. along a length and width of the internal volume 56 to impede the majority of possible conductive paths from anode to cathode). The resistive element 40 may be located between the first / third and second electrodes 10, 20. For example, the resistive element 40 may be located radially outward from the first / third electrodes 10, 30, but not as far radially outward than the second electrode 20. The resistive element 40 may extend along some or all of the length of the internal volume 56.

[0042] The housing 50 may be cylindrical. That is, a cross-sectional shape (i.e. when viewed in plan) of the housing 50 may be circular. Alternatively, the housing 50 may be polygon shaped. The housing 50 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 vessels 1 may be provided together, e.g. to increase output as compared to that provided by a single vessel. In which case, the vessels 1 may be stacked together. The vessels 1 may be designed to facilitate more space efficient stacking. For example, the vessels 1 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 50, e.g. with everything thereinside being circular (including the inner surface of the housing 50), or the shape may be impaired by the inner surface of the housing 50.

[0043] The fluid inlet 54 is arranged at an opposite end of the housing 50 to the fluid outlet 58. The first and second electrode 20 extend along an axis extending from the fluid inlet 54 to the fluid outlet 58 (e.g. a longitudinal axis of the vessel 1). The fluid outlet 58 may be arranged higher than (e.g. above, such as directly above or above and laterally offset from) the fluid inlet 54. For example, the fluid outlet 58 may extend vertically out of the internal volume 56 of the vessel or it may extend with a lateral component, such as diagonally or horizontally from an upper portion of the vessel 1. The housing 50 is configured to encapsulate the internal volume 56. The housing 50 is arranged to define the internal volume 56 to provide a region in which liquid may be heated. An internal surface of the housing 50 (e.g. which faces / defines the internal volume 56) may be configured to generate heat in response to incident photons (for example, the housing 50 may be conductive). The internal surface may comprise the region of the housing 50 which lies adjacent to the internal volume 56. This may comprise part of the housing 50 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 volume 56, e.g. as it heats up from incident photons.

[0044] The housing 50 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, or Quartz may be used. The housing 50 may be formed of multiple different materials. The different materials may be selected based on their photon absorption and / or transmissive characteristics (e.g. based on application needs). For example, materials may be selected which absorb photons in different wavelength range(s) for which photons are expected within the internal portion 56, e.g. for visible, infrared, ultraviolet. The housing 50 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 50 is configured to retain fluid in the internal volume 56 under pressure.

[0045] The fluid inlet 54, the internal volume 56, and the fluid outlet 58 are arranged to define a flow path for fluid to flow through the internal volume 56 of the housing 50 (e.g. from the fluid supply system 70 through the vessel 1 and to the work extraction system 80). The internal volume 56 is arranged to receive liquid to be heated through the fluid inlet 54. The vessel 1 is arranged to heat this liquid in the internal volume 56 to provide a heated fluid. The fluid outlet 58 is arranged to provide a flow path for this heated fluid away from the internal volume 56.

[0046] The first and second electrodes 10, 20 are configured to provide a current flow path through the internal volume 56 of the vessel 1. One of the electrodes 10, 20 may provide an anode, and the other may provide a cathode. For instance, the first electrode 10 may provide the anode for bringing current into the internal volume 56 of the vessel 1 (e.g. from the electrical supply system 60). The second electrode 20 may then provide the cathode for carrying current away from the internal volume 56 of the vessel 1. The first and second electrode 20 are spaced apart from each other. The first electrode 10 is arranged to receive a voltage so that a potential difference exists between the first and second electrodes 10, 20. The first and second electrodes 10, 20 are arranged capacitively. The fluid may provide an electrical resistance between the two electrodes 10, 20 (e.g. so that they are arranged capacitively across this fluid). As will be appreciated, the fluid may not have an infinite resistance, and so some electrical conduction may occur through the fluid from the first electrode 10 to the second electrode 20. In this sense, the electrodes 10, 20 and the fluid in the vessel 1 may act as a leaky capacitor. For instance, the first and second electrodes 10, 20 with fluid in the vessel 1 may effectively provide a circuit having a capacitance and a resistance. This resistance provided by this fluid may be sufficiently large that only a relatively small current will flow across the fluid, even in response to high voltages being applied. The first and second electrodes 10, 20 are configured to provide a voltage stress to fluid and / or plasma within the internal volume 56.

[0047] The third electrode 30 may be active or passive. When active, a voltage is applied to the third electrode 30. When passive, the third electrode 30 may be conductive for receiving current within the internal volume 56, but without receiving power from the power supply 30. The third electrode 30 is shown passive in Fig. 1. The third electrode 30 may be configured to provide a balancing electrode (e.g. it may be arranged to balance electric field / current generated within the internal volume 56). The third electrode 30 may comprise a tip of electrically conductive material (i.e. which is arranged within the internal volume 56 of the vessel 1). The tip need not be electrically connected to a component outside of the vessel 1. For example, where the third electrode 30 is passive, the provision of an electrical conductor within the housing 50 may provide passive balancing. For example, such a tip could be capable of charging and discharging by itself.

[0048] For example, the first electrode 10 may be active, the second electrode 20 may be passive and third electrode 30 could be active or passive. A distal tip of the first electrode 10 (i.e. the exposed tip within the vessel 1 would be electrically connected to a voltage source (e.g. external to the vessel 1). The second electrode 20 may be electrically grounded (e.g. so that current may flow from the second electrode 20 to ground). The third electrode 30, when passive, may provide an exposed portion of electrically conductive material within the internal volume 56 of the vessel 1. That passive exposed portion of electrically conductive material may be arranged to be charged and / or discharged within the vessel 1 (e.g. due to internal electrical conditions of the vessel 1). The third electrode 30, when active, may be connected to a voltage source. An exposed portion of the third electrode 30 within the vessel 1 may then be connected to the voltage source.

[0049] The resistive element 40 may be arranged on a current flow path between the first electrode 10 and the second electrode 20, e.g. so that current would need to flow through the resistive element 40 to get from the first electrode 10 to the second electrode 20. The resistive element 40 may extend along one or both of the ends of the internal volume 56 (e.g. to reduce the likelihood of a conductive path from anode to cathode not via the resistive element 40 being possible). The resistive element 40 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 volume 56). In other words, the resistive element 40 may increase the electrical resistance for current flow from one electrode to the other (e.g. across the fluid).

[0050] In operation, a fluid is supplied from the fluid supply system 70 through the fluid inlet 54 and into the internal volume 56 of the vessel 1. In this example, the fluid will be water, but other liquids may be used. For example, the fluid may be any aqueous solution, such as tap water, sea water, ionised water etc. The fluid may comprise one or more minerals therein, e.g. in either solution or suspension within the liquid. The minerals(s) may comprise one or more transition metals. The fluid 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 vessel 1 will fill up with fluid (e.g. water). Any gas previously in the vessel 1 may be forced out through the fluid outlet 58 of the vessel 1. The vessel 1 may then be substantially filled with water. It will be appreciated that the fluid supplied to the vessel 1, while predominantly liquid (e.g. water) may contain trapped gasses and / or solid substances (e.g. which are otherwise trapped within the fluid.

[0051] A voltage is applied to the first electrode 10 (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 10. As the temperature of the water within the internal volume 56 rises, microbubbles of gas will start to form within the water in the internal volume 56. These may be steam bubbles forming or bubbles of air being released which were trapped in the water supplied to the internal volume 56 of the vessel 1. As a result, some pockets of gas will develop within the liquid in the internal volume 56 of the vessel 1. With continued application of the voltage to the first electrode 10, bubbles of plasma will be generated within the internal volume 56 of the housing 50. These bubbles will release energy into the surrounding fluid and the internal surface of the housing 50. In turn this provides heating of the fluid within the internal volume 56.

[0052] By applying the voltage to the first electrode 10, this may charge up the capacitor provided by the first and second electrode 20. As the fluid within the internal volume 56 heats up, its permittivity may change, and this may change a capacitance of the vessel 1 (e.g. between the first and second electrodes 10, 20). 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 volume 56, 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 volume 56 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.

[0053] With electrical energy still being applied to the first electrode 10, 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 further increasing the 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 volume 56. The plasma may be at an even lower density than the gas, and so with a voltage still applied to the first electrode 10, 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 non-Newtonian fluid responses in the liquid in the internal volume 56 of the vessel 1. 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 10.

[0054] 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 vessel 1. Electron spraying may occur with electrons moving between different electrodes of the vessel 1. In particular, electrons may pass from the first electrode 10 to the second electrode 20 and / or from the first electrode 10 to the third electrode 30. In turn, this may also cause electrons to pass from the third electrode 30 to the second electrode 20. In other words, the third electrode 30 may act to draw in electrons (i.e. from the first electrode 10) before then sending them out (i.e. to the second electrode 20). 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.

[0055] 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 and high melting point. The electrodes may be arranged to provide a preferential flow from the first electrode 10 to the third electrode 30 (as compared to a flow from the first electrode 10 to the second electrode 20). 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. 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 para-state 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 volume 56). 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.

[0056] The photons emitted from each plasma bubble will then be absorbed by either fluid in the internal volume 56 or the housing 50 of the vessel 1. In response to receiving such incident photons, the fluid and / or housing 50 will heat up as it absorbs said photons. The inner surface of the housing 50 in particular may absorb a large number of these photons and thus increase in temperature. As the inner surface of the housing 50 heats up, it will in turn provide conductive heating of the fluid within the internal volume 56. This may give rise to convection currents occurring and thus increased turbulence for fluid within the internal volume 56 of the vessel 1. As a result of this process, the fluid within the internal volume 56 will heat up. The majority of the liquid provided to the internal volume 56 of the vessel 1 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 vessel 1 may have somewhat unconventional, or at least lower energy configurations, as compared to the liquid that was provided to the vessel 1. This is as a consequence of the plasma generation and subsequent energy release which occurred within the vessel 1.

[0057] In this sense, the vessel 1 may operate as a heat pump. That is, the vessel 1 is receiving a liquid, such as water (e.g. cold water) and turning this into steam. Although not shown, the vessel 1 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 vessel 1. 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 vessel 1. This heated fluid then passes through the fluid outlet 58. Typically, the heated fluid is in the form of steam, which is generated within the internal volume 56, and which rises up and out through the fluid outlet 58. This heated fluid output from the vessel 1 may then used in the work extraction system 80 to extract useable work from that heated fluid.

[0058] Operating parameters of the vessel 1 will now be described with reference to Fig. 2. of the vessel

[0059] Fig. 2 shows a graph illustrating how the present inventors have identified certain operational parameters of the vessel 1 of Fig. 1 to influence the performance characteristics for operation of that vessel 1.

[0060] Fig. 2 shows three different curves. The first curve is for the amount of power applied to the first electrode 10 in the form of applied electrical energy ‘kWe^’ (e.g. kilowatts of electricity in). The second curve is for the coefficient of performance ‘COP’ for operation of the vessel 1. The COP is a measure which links the input power to the output thermal energy, e.g. a measure of efficiency for operation of the vessel 1. For example, COP may be formulated as the amount of thermal energy output from the vessel 1 divided by the amount of electrical energy applied to the electrode. The third curve is for the amount of thermal energy output from the vessel 1 ‘kWthout (e.g. kilowatts of thermal energy out). The thermal energy output is in the form of thermal energy associated with the heated fluid (e.g. steam) being output from the vessel 1.

[0061] The left-hand vertical axis is for both COP and kWein, the right hand vertical axis is for kWth0Ut, and the horizontal axis is for flow rate. The scales for the two vertical axes may not be the same (e.g. the values on the right-hand axes may be larger). The flow rate increases from left to right along the horizontal axis, and the values on the vertical axes increase from bottom to top.

[0062] The COP curve increases approximately linearly with flow rate. That is, at higher flow rates, the COP will be higher. Similarly, the kWth0Ut curve increases approximately linearly with flow. Again, that is that at higher flow rates, kWth0Ut will be higher. As a result, in order to increase COP and / or kWth0Ut, higher flow rates should be employed. For this, the fluid supply system 70 may be operated to increase the flow rate of fluid supplied to the vessel 1.

[0063] In addition to increasing the flow rate to increase COP and / or kWth0Ut, kWein should also be increased. For this, the electrical supply system 60 may be operated to increase the amount of electrical energy applied to the first electrode 10. The kWe^ curve shown in Fig. 2 illustrates what value of input power should be used for any given flow rate of fluid to be provided to the vessel 1. As shown, the kWe^ curve follows an approximately logarithmic trajectory. That is, at low flow rates (on the left-hand side), the gradient of the curve is relatively steep, whereas at high flow rates (on the right-hand side), the gradient is much shallower. This gradient continues to decrease with increased flow rate.

[0064] Three zones for the kWein curve are shown in Fig. 2: zone 1 , zone 2, and zone 3. The zones are separated by dashed vertical lines.

[0065] Zone 1 contains the lowest flow rates. In zone 1 , the curve is relatively steep in gradient. Even though the curve is continually decreasing in gradient, the absolute gradient value at the higher flow rate end of zone 1 remains relatively high. Within zone 1 , both COP and kWth0Ut are low. That is, the amount of input power applied to the first electrode 10 will be relatively high compared to the amount of thermal energy output by the vessel 1.

[0066] Zone 2 contains the middle flow rates. In zone 2, the curve is getting shallower in gradient, and is shallower than in zone 1. The curve is still continually decreasing in gradient, with the absolute gradient value at the higher flow rate end of zone 2 becoming relatively low. Within zone 2, both COP and kWth0Ut are at middling values. That is, the amount of input power applied to the first electrode 10 will be moderate compared to the amount of thermal energy output by the vessel 1.

[0067] Zone 3 contains the highest flow rates. In zone 3, the curve is relatively shallow in gradient. The curve continues to decrease in gradient through zone 3, but the rate of change of gradient is much less, especially towards the higher flow rate values within zone 3. Within zone 3, both COP and kWth0Ut are high. That is, the amount of thermal energy output by the vessel 1 will be relatively high compared to the input power applied to the first electrode 10.

[0068] In other words, at higher input powers and higher flow rates, the vessel 1 may operate more efficiently. This efficiency may get higher at greater input powers and flow rates.

[0069] To demonstrate the difference, a pair of points is shown for each of the three zones. Each point is shown by a black dot, and there are dashed lines to intersect the relevant axes for these points. In each pair, the two points are separated by the same increment in flow rate. Due to the linear relationship between flow rate and thermal energy output shown in Fig. 2, the two points within each pair are also separated by the same increment in thermal energy output. However, as can be seen with the intersection points on the left-hand vertical axis, the differences in input power vary between the different zones. For zone 1 , the required increase in input power to match the increment in flow rate / output thermal energy is relatively large. For zone 2, this increase in input power to increment the output thermal energy is smaller, and for zone 3 it is very small.

[0070] In other words, it can be seen that the present inventors have identified that significant increases in COP (i.e. efficiency) can be achieved by choosing to operate the vessel 1 at higher input powers and higher flow rates.

[0071] Reference will now be made to Figs. 3 and then 4 to described example apparatuses 100 in which this identification may be utilised.

[0072] Inclusion of a thermal energy store within the apparatus

[0073] Fig. 3 shows an apparatus 100 similar to that shown in Fig. 1. As with the apparatus 100 of Fig. 1, the apparatus 100 of Fig. 3 includes a plasma generating vessel 1 , as well as an electrical supply system 60, a fluid supply system 70 and a work extraction system 80. For simplicity, many of the features from the apparatus 100 shown in Fig. 1 are not reproduced in Fig. 3.

[0074] The apparatus 100 of Fig. 3 further includes a thermal energy store 90 and a fluid flow control system 95. Three flow paths are also shown in Fig. 3: first flow path 91, second flow path 92, third flow path 93.

[0075] The vessel 1 , the electrical supply system 60 and the fluid supply system 70 are configured to operate in the manner described above in relation to Fig. 1. That is, the electrical supply system 60 is configured to supply electrical energy to the first electrode 10 of the vessel 1, and the fluid supply system 70 is configured to supply fluid to the vessel 1. Although not shown, the apparatus 100 may include a controller. The controller is configured to control operation of the electrical supply system 60 (e.g. to control the amount of input electrical power applied) and to control operation of the fluid supply system 70 (e.g. to control the amount of fluid supplied to the vessel 1). The first electrode 10 of the vessel 1 is configured to apply the electrical energy to the liquid within the vessel 1 to generate one or more bubbles of plasma therein. The vessel 1 is configured to output heated fluid (typically gaseous, such as steam, although it could be in the form of a heated fluid, or some combination thereof).

[0076] In other words, the apparatus 100 is configured to output heated fluid from the vessel 1 (through the heated fluid outlet 58). As will be appreciated, this heated fluid output from the vessel 1 will have an associated thermal energy. For heated fluid output in greater quantities (e.g. higher pressure / flow rate) and / or at higher temperatures, the amount of thermal energy will be higher. As will now be described in more detail, the apparatus 100 of Fig. 3 is configured to control the flow and / or storage of this thermal energy. In particular, this thermal energy may be used by the work extraction system 80 (for extracting work therefrom) or stored in the thermal energy store 90 (for subsequent by the work extraction system 80).

[0077] The thermal energy store 90 is coupled to the vessel 1 (e.g. to the heated fluid outlet 58). The work extraction system 80 is coupled to the thermal energy store 90. The work extraction system 80 may also be coupled to the heated fluid outlet 58 of the vessel 1. As shown in Fig. 3, the first flow path 91 couples the vessel 1 to the thermal energy store 90, and the second flow path 92 couples the thermal energy store 90 to the work extraction system 80. The optional third path may couple the vessel 1 to the work extraction system 80.

[0078] A fluid flow control system 95 is shown in Fig. 3 to control the flow of thermal energy between the vessel 1, the thermal energy store 90 and the work extraction system 80. For example, the fluid flow control system 95 may comprise one or more valves selectively operable to control the flow of fluid. The fluid flow control system 95 may be coupled to each of the first path, the second path and the third path, e.g. with valves in those paths to control flow. The fluid flow control system 95 may comprise one or pumps to control the direction of fluid flow. The fluid flow control system 95 may selectively couple the vessel 1 to the thermal energy store 90 (e.g. using the first flow path 91). The fluid flow control system 95 may selectively couple the thermal energy store 90 to the work extraction system 80 (e.g. using the second flow path 92). The fluid flow control system 95 may selectively couple the vessel 1 to the work extraction system 80 (e.g. using the third flow path 93).

[0079] The thermal energy store 90 may comprise means for storing thermal energy. This may be in the form of a thermal reservoir, such as a fluid tank. For example, the thermal energy store 90 may comprise a liquid tank, e.g. a hot water tank. For example, the thermal energy store 90 may comprise a plurality of different volumes for storage of thermal energy, e.g. which may be the same or different to each other (e.g. for storage at different temperatures, pressures or with different materials to store thermal energy).

[0080] The thermal energy store 90 is coupled to the fluid outlet 58 of the vessel 1 to permit transfer of thermal energy into the thermal energy store 90 from heated fluid output from the vessel 1. For example, for this, heated fluid may flow along the first flow path 91 towards the thermal energy store 90. This heated fluid may be delivered into the thermal energy store 90, e.g. for storage, or it may be provided in a heat exchange relationship with material within the thermal energy store 90, e.g. to use the heated fluid to heat and / or pressurise material therein. For example, the fluid flow control system 95 may be configured to selectively permit such flow of heated fluid along the first flow path 91 to permit this transfer of thermal energy from the heated fluid output from the vessel 1 to the thermal energy store 90. The work extraction system 80 is coupled to the thermal energy store 90 to permit transfer of thermal energy from the thermal energy store 90 to the work extraction system 80. For example, for this, heated fluid may flow along the second flow path 92 from the thermal energy store 90 towards the work extraction system 80. This heated fluid may be a fluid received from the thermal energy store 90, e.g. where it was stored, or it may be a separate fluid which has been in a heat exchange relationship with material within the thermal energy store 90, e.g. so that said fluid has been heated and / or pressurised by material stored in the thermal energy store 90. For example, the fluid flow control system 95 may be configured to selectively permit such flow of heated fluid along the second flow path 92 to permit this transfer of thermal energy from the thermal energy store 90 to the work extraction system 80.

[0081] The work extraction system 80 may also be coupled to the vessel 1 to permit transfer of thermal energy from the heated fluid output from the vessel 1 to the work extraction system 80. For example, for this, heated fluid may flow along the third flow path 93 from the vessel 1 towards the work extraction system 80. This heated fluid may be the fluid which has been output from the vessel 1, or it may be a separate fluid which has been in a heat exchange relationship with the fluid output from the vessel 1 , e.g. so that said fluid has been heated and / or pressurised by the fluid output from the vessel 1. For example, the fluid flow control system 95 may be configured to selectively permit such flow of heated fluid along the third flow path 93 to permit this transfer of thermal energy from the heated fluid output from the vessel 1 to the work extraction system 80.

[0082] The thermal energy store 90 is configured to store thermal energy. In particular, for the heated fluid output from the vessel 1, the thermal energy store 90 may be configured to store some or all of the thermal energy from this heated fluid. The thermal energy store 90 is configured to store thermal energy which may subsequently be used by the work extraction system 80.

[0083] The work extraction system 80 is configured to extract useable work. The work extraction system 80 is configured to extract useable work from a fluid which has been heated and / or pressurised. For example, said fluid which has been heated / pressurised may be the fluid which has been output from the vessel 1 and / or it may be heated / pressurised fluid from the thermal energy store 90 (e.g. which was stored in the thermal energy store 90 and / or heated / pressurised by fluid stored therein).

[0084] In particular, the work extraction system 80 may be configured to utilise a heated fluid received from the thermal energy store 90, e.g. for extraction of work therefrom. The work extraction system 80 may also be configured to utilise heated fluid received from the vessel 1. The fluid flow control system 95 may be configured to control the flow of thermal energy (e.g. heated fluid) between the vessel 1, the thermal energy store 90 and the work extraction system 80. For example, the fluid flow control system 95 may be coupled to the controller, and the controller may be configured to control operation of the fluid flow control system 95 (e.g. the opening / closing of valves) to control this flow of thermal energy.

[0085] In particular, the fluid flow control system 95 is configured to selectively permit the flow of heated fluid from the vessel 1 towards the thermal energy store 90 (for storage of thermal energy from that heated fluid in the thermal energy store 90). Likewise, the fluid flow control system 95 is configured to selectively permit the flow of heated fluid from the thermal energy store 90 towards the work extraction system 80 (for extraction of work therefrom). The fluid flow control system 95 may optionally be configured to selectively permit the flow of heated fluid from the vessel 1 towards the work extraction system 80 (for extraction of work therefrom).

[0086] As will now be described in more detail, the apparatus 100 is configured to control this flow of thermal energy (e.g. the flow of heated fluids) between: (i) the vessel 1 , (ii) the thermal energy store 90, and (iii) the work extraction system 80. In particular, the apparatus 100 is configured to permit excess thermal energy generated from the vessel 1 to be stored in the thermal energy store 90 (e.g. when it is determined that the vessel 1 should over-produce thermal energy to achieve a high enough efficiency level). Likewise, the apparatus 100 is configured to permit thermal energy to be transferred from the thermal energy store 90 to the work extraction system 80 (e.g. when it is determined that the vessel 1 should not be operated, as to do so would result in too low an efficiency level, but some thermal energy is demanded from the vessel 1).

[0087] Controlling the flow of thermal energy and the operation of the plasma generating vessel

[0088] As described above, the apparatus 100 of Fig. 3 is configured to store thermal energy, e.g. a heated liguid, in the thermal energy store 90. This stored thermal energy may be provided as an input to the work extraction system 80 for extraction of work therefrom. Likewise, thermal energy in the heated fluid output from the vessel 1 may be provided as an input to the work extraction system 80 for extraction of work therefrom. The controller of the apparatus 100 is configured to control the flow of thermal energy through the apparatus 100, as well as the operation of the vessel 1 to provide satisfactory efficiency levels for operation of the vessel 1.

[0089] As shown in Fig. 2, by operating at higher levels of input power (applied to the first electrode 10) and higher associated flow rates, the COP for operation of the vessel 1 may be much higher. Conseguently, a threshold level may be defined for operation of the vessel 1, wherein the vessel 1 is only to be operated at or above that threshold level. This may be a threshold value for COP, input power and / or output thermal energy (as they are all effectively linked, as shown in Fig. 2). The particular value for this threshold level may be selected depending on the particular use case or implementation for the apparatus 100, and a precise number for this should not be considered limiting.

[0090] The controller may be configured to control operation of the vessel 1 to be operating at or above threshold level when active. For this, the controller is configured to control the flow rate of fluid supplied to the vessel 1 (by the fluid supply system 70) to be at or above a threshold flow rate. The controller is also configured to control the amount of input power to be applied to the first electrode 10 to be at or above a threshold power level. A value for the input power may be selected based on a chosen value for the flow rate, or vice-versa. As a result, when operating the vessel 1, the COP for the vessel 1 (and also the amount of thermal energy output by the vessel 1) will be at or above a respective threshold level.

[0091] With the vessel 1 active, heated fluid will be output from the vessel 1. In the event that the amount of thermal energy being output from the vessel 1 (e.g. the amount and / or temperature of fluid) is greater than the amount desired by the work extraction system 80, at least some of this excess output thermal energy will be stored in the thermal energy store 90. For example, some heated fluid may flow along the third path from the vessel 1 towards the work extraction system 80, and some heated fluid may flow along the first path from the vessel 1 towards the thermal energy store 90. The controller may be configured to control operation of the fluid flow control system 95 to implement this flow of thermal energy (heated fluid).

[0092] If more thermal energy were wanted by the work extraction system 80 than that being output by the vessel 1 , additional thermal energy may be supplied from the thermal energy store 90 to the work extraction system 80. For example, some heated fluid may flow along the third path from the vessel 1 towards the work extraction system 80, and some heated fluid may flow along the second path from the thermal energy store 90 towards the work extraction system 80. The controller may be configured to control operation of the fluid flow control system 95 to implement this flow of thermal energy (heated fluid). Similarly, thermal energy may be solely supplied to the work extraction system 80 from the thermal energy store 90 (e.g. with the vessel 1 not active). In which case, heated fluid may flow along the second path from the thermal energy store 90 to the work extraction system 80.

[0093] The apparatus 100 may therefore be designed to ensure that satisfactory thermal energy may be provided to the work extraction system 80 while still enabling the vessel 1 to be operated at or above a minimum threshold efficiency level. The apparatus 100 may be configured to provide further control for operation of the different components to facilitate higher operating efficiencies.

[0094] As mentioned above, the vessel 1 may be operated so that, when active, efficiency is at or above the threshold level. The controller may be configured to control whether or not the vessel 1 itself is active. For this, the vessel 1 may be controlled to be in an active state (for outputting thermal energy), or inactive or dormant states (in which no, or little, thermal energy is output).

[0095] For an active vessel 1, the fluid supply system 70 is operated to supply fluid to the vessel 1 (e.g. at a selected flow rate), and the electrical supply system 60 is operated to supply power to the first electrode 10 (e.g. at a selected input power).

[0096] For an inactive vessel 1, the fluid supply is stopped (or at least significantly reduced). Likewise, the input power supply is also stopped (or at least significantly reduced). As such, plasma generation will cease to occur, and the vessel 1 will output little or no thermal energy. For an inactive vessel 1 , the controller may permit a complete cooldown of the vessel 1. In which case, no or little energy is applied to that vessel 1 while inactive, and it may take longer for the vessel 1 to return to an active state once input power and supplied fluid are restarted.

[0097] For a dormant vessel 1, the fluid supply may be stopped (or at least significantly reduced), but the input power may be kept at above a minimum level. For example, the input power may be applied to retain a temperature and / or pressure within the vessel 1 at above a threshold level. The controller may select a dormant state of operation in the event that the vessel 1 is to be restarted within a threshold time period (e.g. relatively soon). In which case, it may be preferable to retain the vessel 1 in the dormant mode to facilitate a quicker restart, once desired.

[0098] The controller may be configured to select whether to turn an active vessel 1 into an inactive or dormant state in the event that the thermal energy for the work extraction system 80 may be provided by that stored in the thermal energy store 90. For example, where little thermal energy is needed, the controller may turn off (e.g. to inactive / dormant) the vessel 1, rather than to use it at below the threshold efficiency level. Instead, thermal energy may then be supplied to the work extraction system 80 from the thermal energy store 90.

[0099] The work extraction system 80 may be coupled to the controller of the apparatus 100 to indicate to the controller a demanded amount of thermal energy. The indication of a demand for thermal energy may indicate an amount of thermal energy wanted instantaneously, and / or a profile for future thermal energy demand for the work extraction system 80. As will be appreciated in the context of the present disclosure, apparatuses 100 disclosed herein may find beneficial utility with a number of different work extraction systems. For example, one such work extraction system 80 could be a heating system, e.g. central heating. Other examples include electricity generators, e.g. using a steam cycle. Numerous other uses may be employed for high temperature and / or high pressure fluid, as output from the vessel 1.

[0100] As will be appreciated, such work extraction systems 80 may be configured to output an indication of demand for how much thermal energy they need. This may be in the form of a quantity of demanded pressurised / heated fluid. For example, in the case of a heating system, the demand may represent a quantity, e.g. volume, of heated liquid to be provided to the work extraction system 80. Similarly, such work extraction systems 80 may be configured to output an indication of future demand for thermal energy / heated fluid. Again, in the example of a heating system, this may represent times of day at which central heating is programmed to turn on and / or an indication of how much heat is needed to meet that future demand.

[0101] The controller of the present apparatus 100 may be configured to obtain an indication of a demanded amount of thermal energy from the work extraction system 80. The controller is configured to control operation of the apparatus 100 based on this demanded amount. That is, the controller may be configured to obtain an indication of the amount of thermal energy that is to be delivered to the work extraction system 80 and / or a quantity of heated / pressurised fluid that is to be delivered.

[0102] Based on this obtained indication, the controller is configured to determine how to operate the apparatus 100. Specifically, the controller may be configured to determine how to source the thermal energy for the work extraction. As will be described in more detail below, for this, the controller may determine that: (i) all of the demanded thermal energy is to be provided from the thermal energy store 90, (ii) all of the demanded thermal energy store 90 is to be provided from the vessel 1, or (iii) the demanded thermal energy is to be provided from a combination of the thermal energy store 90 and the vessel 1 together. In turn, the controller may also be configured to determine: (i) whether or not the vessel 1 is to be active (or if it is to be in an inactive or dormant mode), and (ii) if the vessel 1 to be active, how to operate that vessel 1 (e.g. to determine input power and flow rate values for operating the vessel 1).

[0103] When determining how to source the thermal energy for the work extraction system 80, the controller may be configured to compare the demanded amount of thermal energy against one or more different threshold values. Firstly, at low demands, the controller may determine that the demanded amount of thermal energy is insufficiently high to warrant operating the vessel 1 in an active mode. For this, the controller may compare the demanded amount of thermal energy against a low threshold value. If the demanded amount of thermal energy is below this low threshold value, the controller may determine that the vessel 1 should be inactive. In which case, any thermal energy to be supplied to the work extraction system 80 may be sourced using that stored in the thermal energy store 90. If the demanded amount of thermal energy is above this low threshold value, the controller may determine that the vessel 1 should be active.

[0104] Secondly, at middling demand, the controller may determine that the demanded amount of thermal energy is sufficiently high to warrant operating the vessel 1 in an active mode. At middling demand, the controller may determine that, while the demanded amount of thermal energy warrants operating the vessel 1 in an active mode, by operating the vessel 1 at or above its threshold minimum efficiency level, there will be excess thermal energy generated by the vessel 1 (as compared to that demanded by the work extraction system 80). For example, the controller may compare the demanded amount of thermal energy against a middle threshold value. If the demanded amount of thermal energy is below the middle threshold value (and above the lower threshold value), the controller may determine that the vessel 1 should be active. In which case, the controller may determine that the vessel 1 should be operated at or above its minimum threshold efficiency level (e.g. with the input power and flow rate being above their respective threshold levels).

[0105] The controller may control operation of the apparatus 100 when at middling demand to deliver at least some of the excess thermal energy generated by the vessel 1 into the thermal energy store 90. For example, some or all of the demanded thermal energy for the work extraction system 80 may be sourced by the heated fluid output from the vessel 1. In which case, the remaining thermal energy / heated fluid output from the vessel 1 may be delivered to the thermal energy store 90. When at middling demand, the controller may ensure that the vessel 1 efficiency does not drop below the threshold value. The controller may operate the vessel 1 at the threshold efficiency, or it may operate the vessel 1 at values above the threshold efficiency. In either case, any excess thermal energy generated by the vessel 1 may be stored in the thermal energy store 90.

[0106] Thirdly, at high demand, the controller may determine that the demanded amount of thermal energy is sufficiently high that the vessel 1 needs to be operated in an active mode. At high demand, the controller may determine that the demanded amount of thermal energy requires the vessel 1 to operate at above its threshold minimum efficiency. For example, the controller may compare the demanded amount of thermal energy against a high threshold value. If above the high threshold, it may be determined that the vessel 1 needs to be active. The controller may be configured to determine the level at which the vessel 1 needs to be operated to satisfy the demanded amount of thermal energy, e.g. how far above the minimum threshold operating conditions the vessel 1 needs to be operated. For this, the controller may be configured to determine the input power and flow rate to be applied to the vessel 1 in order to give rise to an output thermal energy at or above the demanded amount of thermal energy.

[0107] The controller may control operation of the apparatus 100 when at high demand to deliver all of the thermal energy generated by the vessel 1 to the work extraction system 80. For example, the operating conditions for the vessel 1 may be selected so that the output thermal energy from the vessel 1 meets the demanded amount of thermal energy, e.g. the vessel 1 may be operating to satisfy the demanded amount of thermal energy by the work extraction system 80 without use of the thermal energy store 90.

[0108] Additionally or alternatively, at high demand, the controller may control operation of the apparatus 100 to use the thermal energy store 90. This may comprise operating the vessel 1 to generate extra thermal energy than the demanded amount, and the excess thermal energy may be stored in the thermal energy store 90. Alternatively, this may comprise operating the vessel 1 to generate less thermal energy than the demanded amount and supplementing this with thermal energy stored in the thermal energy store 90 (e.g. thereby to satisfy the demanded amount of thermal energy by the work extraction system 80). For example, at very high demand, the controller may determine that the vessel 1 will not be able to satisfy the demanded amount of thermal energy, and thermal energy from the thermal energy store 90 may be used to supplement this demand. For example, at high (but not very high) demand, the controller may determine that excess thermal energy is to be generated and stored, e.g. if the thermal energy store 90 is running low or if future demand is set to be higher. For example, at high (but not very high) demand, the controller may determine that the vessel 1 output should be that to meet the demand, e.g. if the thermal energy store 90 is full or close to full.

[0109] The controller may be configured to take one or more other factors into account when determining how to operate the vessel 1. Such factors may include one or more of: (i) the amount of thermal energy stored in the thermal energy store 90, (ii) a storage capacity of the thermal energy store 90, (iii) an indication of future demand for thermal energy by the work extraction system 80, (iv) an indication of preferred operating conditions for the vessel 1, and / or (v) an indication of intended future use for the vessel 1.

[0110] For example, the controller may determine how to operate the vessel 1 based on an indication of the current state of the thermal energy store 90. Such an indication may be of a temperature or pressure for material stored in the thermal energy store 90, e.g. which is indicative of the amount of thermal energy stored therein. For example, where the thermal energy store 90 is a tank, e.g. a hot water tank, this may comprise an indication of the temperature of fluid therein and / or a fullness of the tank (e.g. a level sensing for the liquid therein).

[0111] The controller may determine whether or not to operate the vessel 1 in an active mode, and if so, how much thermal energy to obtain from the vessel 1 , based on the thermal energy stored in the thermal energy store 90. For example, where the thermal energy store 90 is low (e.g. below a threshold) on stored energy, the controller may control the vessel 1 to operate at a sufficiently high level to generate excess thermal energy for delivering to the thermal energy store 90. Where the thermal energy store 90 is high (e.g. above a threshold) on stored energy, the controller may control the vessel 1 to operate at a level to avoid excess (or much excess) thermal energy being generated which is to be stored in the thermal energy store 90, and / or the controller may control operation of the apparatus 100 so that heated fluid will be delivered from the thermal energy store 90 to the work extraction system 80 (with the vessel 1 active or not). For example, for this determination, the controller may be configured to compare the current stored amount of thermal energy within the thermal energy store 90 against a capacity for that thermal energy store 90.

[0112] The controller may determine how to operate the vessel 1 based on an indication of future demand for heated fluid for the work extraction system 80. Such an indication may be in the form of a time profile for what thermal energy is demanded, and when that is demanded. The controller may determine whether or not to operate the vessel 1 in an active mode, and if so, how much of the resulting thermal energy is to be stored based on future demand. For example, if future demand is high enough to require supplementation from the thermal energy store 90 or if future demand is low enough to not warrant operation of the vessel 1 in an active mode (e.g. because doing so would be sufficiently below the minimum threshold efficiency), the controller may control (instantaneous) operation of the vessel 1 to ensure the requisite amount of thermal energy is stored (e.g. to top up to a required amount). For example, this may comprise operating the vessel 1 so as to generate excess thermal energy to be stored. Similarly, if the controller identifies that the vessel 1 itself is unlikely to be active for a while (e.g. due to a drop in demand), it may determine that excess thermal energy should be generated until a satisfactory amount of thermal energy is stored in the thermal energy store 90.

[0113] The controller may determine how to operate the vessel 1 based on preferred working conditions for the vessel 1. For example, there may be an upper limit to the amount of thermal energy which can be output by the vessel 1 and / or a limit above which it is not preferable to operate the vessel 1 (e.g. due to increased likelihood of failure or increased wear of components). Additionally, or alternatively, the vessel 1 may have an associated preferential range in which to operate (e.g. which straddles increased efficiency and longevity for vessel 1 operation). The controller may control operation of the vessel 1 to operate within the preferred region (e.g. where possible). This may comprise deciding on whether to generate and store excess thermal energy or to generate insufficient thermal energy and to use stored thermal energy (or to generate exactly the required amount of energy and not use the thermal energy store 90) based on selecting operating conditions to be within the preferred region (and then letting this decision dictate whether to store or not store).

[0114] As described above, embodiments may control operation of the apparatus 100 to maintain an efficiency for operation of the vessel 1 at or above a minimum threshold level. In turn, this may result in more efficient generation and use of thermal energy. Another example for how to implement similar teaching will now be described with reference to Fig. 4, and the control of multiple vessels.

[0115] Inclusion of multiple plasma generating vessels

[0116] Fig. 4 shows an apparatus 100 similar to that of Figs. 1 and 3. The apparatus 100 of Fig. 4 includes an electrical supply system 60, a fluid supply system 70, and a work extraction system 80. Additionally, the apparatus 100 comprises a plurality of plasma generating vessels 1. In Fig. 4, three vessels 1 are shown: a first vessel 1a, a second vessel 1b, and a third vessel 1c.

[0117] Each vessel 1 is arranged in the same manner as described above, and so for the sake of brevity, this will not be repeated. Of note, a fluid supply system 70 is configured to supply fluid to each vessel 1 for plasma generation thereof and an electrical supply system 60 is configured to apply electrical energy to the first electrode 10 of each vessel 1. One of each system is shown in Fig. 4, but it will be appreciated that the apparatus 100 may include a plurality of electrical supply systems 60 and / or fluid supply systems 70. For example, each vessel 1 may have a respective electrical supply system 60 and / or fluid supply system 70. Irrespective of the number of different systems, the controller is configured to control the supply of fluid (e.g. the flow rate) to each vessel 1 , and the input power supply (e.g. the amount of electrical energy applied to the first electrode 10).

[0118] Each vessel 1 is configured to output heated fluid (through its outlet 58). The work extraction system 80 is coupled to each of the vessels 1. That is, the work extraction system 80 is configured to receive heated fluid output from each of the plurality of vessels 1 , e.g. it may be coupled to the outlet 58 of each vessel 1.

[0119] As will be described below, operation of the collective of vessels 1 is controlled so that each individual vessel 1 will operate at an efficiency level greater than a minimum threshold for that vessel 1. The individual vessels 1 may be the same as each other, or they may be different. For example, one of the vessels 1 may be bigger and / or capable of outputting more thermal energy. The different vessels 1 may have different thermal energy output capabilities and / or they may have different minimum efficiency levels. For example, the thermal energy output at the minimum efficiency level may be different for the different vessels 1 , e.g. one of the vessels may be operable to output thermal energy at its minimum efficiency where the thermal energy being output by that vessel 1 is less than the amount of thermal energy another vessel 1 would output when operating at its minimum efficiency (e.g. so that lower energy outputs may be permissible).

[0120] Operation of the apparatus 100 will now be described for providing a high efficiency of output from the plurality of vessels, as well as from each individual vessel 1.

[0121] Controlling operation of the plasma generating vessels individually and collectively

[0122] No thermal energy store 90 is shown in the apparatus 100 of Fig. 4, but it will be appreciated that one or more such stores could be incorporated and utilised, e.g. as described above.

[0123] The controller is configured to control operation of the apparatus 100 (i.e. the plurality of vessels together, and each individual vessel 1) based on similar efficiency constraints to those described above in relation to Fig. 3. In particular, the controller is configured to control operation to inhibit any individual vessel 1 operating at below its minimum threshold efficiency. For this, the controller is configured to obtain an indication of the demanded amount of thermal energy to be provided to the work extraction system 80. The controller may utilise stored data indicating the operational characteristics for each of the plurality of vessels. This may include the thermal energy associated with minimum accepted efficiency for each vessel 1. For example, the controller may store data for the different possible operating conditions and associated parameters for each vessel 1 (e.g. of the type shown in Fig. 2).

[0124] The controller may select which vessel(s) are to be active, and / or how to operate those active vessels based on the demanded amount of thermal energy. If the demanded thermal energy is below an upper threshold, the controller may determine that not all of the vessels are to be active. For example, the upper threshold may be indicative of the minimum amount of total energy output by all vessels operating at their minimum efficiency level. For demanded thermal energy at values below the upper threshold, the number of vessels to be active and / or which vessels those are, may be selected to provide efficiency levels at or above the minimum threshold for each individual active vessel 1. If the demanded thermal energy is below a lower threshold, the controller may determine that only one of the vessels is to be active. For example, this may be the vessel 1 associated with the lowest thermal energy output at its minimum efficiency level (if the vessels are different).

[0125] At values above the lower thresholds, the controller may determine the number of vessels to be active based on the demanded amount. For increasing values for the demanded amount, the controller may determine that an additional vessel should be active if the demanded amount exceeds an additional threshold value. That additional threshold value may a number greater than the sum of the thermal energy outputs for all of the vessels operating together at minimum efficiency. In other words, the controller may only use an nthactive vessel if the demanded amount is greater than the sum of thermal outputs at minimum efficiency for the n vessels by more than a threshold amount. That is, to satisfy a demand which is above the minimum thermal energy but not by a significant amount, the controller may instead just operate the already active vessel(s) to operate at higher thermal energy outputs (e.g. in preference to operating the already active vessel(s) and the additional vessel at lower thermal outputs, and thus lower individual efficiencies).

[0126] If it is determined that an additional vessel is to be active, the controller may be configured to adjust the operating parameters for one or more of the already active vessel(s). For example, one or more of the already active vessel(s) may be operated to then provide a reduced output (e.g. where the combined output is then greater due to the additional active vessel). Additionally, or alternatively, the controller may be configured to prioritise operating some or all of the active vessels in a preferred range of operation for said vessel(s). That is, each individual vessel 1 may have a preferred range of operation, e.g. with efficiency in a selected range and potential risk / damage at below a threshold level. The controller may control operation of the plurality of vessels so that one of the vessels may operate at a variable level. Any remaining vessel(s) may be operated in their preferred range of operation. For example, with n active vessels, n-1 of the vessels may be operated in their preferred range. The nthvessel may then be operated at a variable level. The variable level may be selected to satisfy the demanded amount (e.g. while remaining at or above the threshold efficiency for that vessel). For example, the controller may determine that an n+1thvessel is to be rendered active if the demanded amount exceeds the amount resulting from n of the vessels operating in their preferred range, and the n+1thvessel operating at (or above) its minimum efficiency level.

[0127] If the demanded amount of thermal energy drops, the controller may reduce the number of active vessels. For this, the remaining active vessel(s) may be operated at an elevated output level to compensate for the drop in number of active vessels. For example, when dropping from n+1 to n active vessels, some or all of the remaining n active vessels may then operate at an elevated level (e.g. above their preferred range of operation or at a higher level within this preferred range).

[0128] In other words, the controller is configured to select which of the vessel(s) to operate, and how to operate said vessel(s), to satisfy the demanded amount of thermal energy while ensuring each active vessel is operating at or above its threshold efficiency. This provision of dynamic control as to the operation of vessels may enable individual vessel’s operation to be adjusted to compensate for the number of active vessels and the demanded amount. Advantageously, this may enable each individual vessel to be operating at elevated efficiency levels irrespective of how much thermal energy is demanded.

[0129] The controller may also control operation of the plurality of vessels and / or individual vessels within the plurality based on detecting of faults with one or more of the vessels. For this, if the controller detects a fault with one of the vessels, the controller may stop operation of that vessel (e.g. stop or reduce the application of input power and / or fluid). To compensate for this drop in number of vessels, the controller may operate the remaining vessel(s) at elevated output to compensate for the dropped vessel. For example, the controller may operate the remaining vessel(s) in this manner until another vessel can be active (e.g. it may take time to start that vessel up), or if there are no more possible vessels, the vessels may continue to operate in this manner.

[0130] Electrical

[0131] An example electrical supply system 60 will now be described with reference to Figs. 5a to 5c.

[0132] As described above, the electrical supply system 60 is configured to supply electrical energy to the vessel 1 (via electrode 10). This connection to the vessel 1 is shown in Fig. 5a.

[0133] The electrical supply system 60 includes a transformer 67. The transformer 67 has an input portion 67a and an output portion 67b. A switching arrangement is included. In Fig. 5a, this is shown as being formed of: a first switch 61, a second switch 62, a third switch 63 and a fourth switch 64. The electrical supply system 60 may also include an AC input connection 65 and a rectifier 66.

[0134] The electrical supply system 60 provides a voltage boost apparatus. In particular, the system 60 is formed of an input side (on the left-hand side of Fig. 5a) and an output side (on the right-hand side of Fig. 5a). The input side is for the components connected to the input portion 67a of the transformer 67, and the output side is for the components connected to the output portion 67b of the transformer 67 (i.e. the side connected to the vessel 1 itself). The AC input connection 65 is connected to the rectifier 66. The rectifier 66 may comprise a diode bridge / bridge rectifier. The rectifier 66 may include two output terminals: (i) a positive terminal (shown on the right side of the rectifier 66 in Fig. 5a), and (ii) a negative terminal (shown on the left side of the rectifier 66 in Fig. 5a).

[0135] For simplicity, from hereon in, reference will be to “first” and “second” ends of the transformer 67. In Fig. 5a, the first end of the input portion 67a of the transformer 67 is the top side, and the second end is the bottom side of the output portion 67b of the transformer 67. As will be appreciated in the context of the present disclosure, the transformer 67 may be arranged to scale the input voltage to be applied to the vessel 1. For example, the transformer 67 may be arranged to boost the input voltage (i.e. so that the voltage on the output side to be provided to the vessel 1 is greater than the corresponding voltage on the input side of the transformer 67).

[0136] The positive terminal of the rectifier 66 is selectively connectable to the first end of the transformer 67 (the input portion 67a) and the second end of the transformer 67 (the input portion 67a). The negative terminal of the rectifier 66 is selectively connectable to the first end of the transformer 67 (the input portion 67a) and the second end of the transformer 67 (the input portion 67a). The switching arrangement is included to provide these selective connections to the input portion 67a of the transformer 67.

[0137] The positive terminal of the rectifier 66 is connected to the first end of the transformer 67 (the input portion 67a) via the first switch 61. The positive terminal of the rectifier 66 is connected to the second end of the transformer 67 (the input portion 67a) via the third switch 63. The negative terminal of the rectifier 66 is connected to the first end of the transformer 67 (the input portion 67a) via the second switch 62. The negative terminal of the rectifier 66 is connected to the second end of the transformer 67 (the input portion 67a) via the fourth switch 64.

[0138] In other words, each terminal of the rectifier 66 is connected to two conductive paths: one which leads to one end of the transformer 67, and one which leads to the other end of the transformer 67. Likewise, each end of the transformer 67 is connected to two conductive paths: one which leads to / comes from one terminal of the rectifier 66, and another which leads to / comes from the other terminal of the rectifier 66.

[0139] On the output side of the system 60, the transformer 67 (the output portion 67b thereof) is connected to the vessel 1 (e.g. to the electrode). Although not shown in Fig. 5a, the system 60 may include a plurality of such voltage boosting apparatuses. Each such apparatus may provide a connection from an input power source (e.g. an AC input connection) to an output side via a transformer 67. The output side may be common to all such apparatuses. For example, the output side (the right-hand side in Fig. 5a) may comprise a plurality of transformers, each for connection to a separate input. Each of these transformers may be coupled to the vessel 1. For example, the transformers may be arranged so that their voltages sum (e.g. in series). Such an arrangement may then be used to increase the overall voltage provided to the vessel 1, as compared to using a single transformer arrangement to one source. In which case, the righthand portion of the circuit in Fig. 5a (the output side) may include a plurality of transformers, with the output from all of those transformers connected to the vessel 1.

[0140] Each of the switches is operable in either an electrically conductive state or an electrically non- conductive state. Although not shown in Fig. 5a, the apparatus may comprise a controller configured to selectively control operation of each switch. For example, each switch may be provided by one or more transistors, and the controller may be configured to selectively apply an electrical signal (e.g. a voltage pulse) to the transistor to control whether or not it is electrically conductive. When electrically conductive, each switch will provide a conduction path between a terminal of the rectifier 66 and an end of the transformer 67 (the input portion 67a). The system 60 may be configured to selectively control the operation of the switches so that there is one conduction path from one terminal of the rectifier 66 to one end of the transformer 67 (the input portion 67a) and one conduction path from the other terminal of the rectifier 66 to the other end of the transformer 67 (the input portion 67a).

[0141] The system 60 may be configured to control only one of the first and second switches 61, 62 to be electrically conductive (e.g. at the same time). Likewise, the system 60 may be configured to control only one of the third and fourth switches 63, 64 to be electrically conductive (e.g. at the same time). That way, each end of the transformer 67 may only be connected to one electrically conductive switch. Similarly, the system 60 may be configured to control only one of the first and third switches 61, 63 to be electrically conductive (e.g. at the same time). Likewise, the system 60 may be configured to control only one of the second and fourth switches 62, 64 to be electrically conductive (e.g. at the same time). That way, each terminal of the rectifier 66 may only be connected to one electrically conductive switch.

[0142] In other words, the system 60 may be configured to control either: (i) the first and fourth switches 61 , 64 to both be in their electrically conductive state and the second and third switches 62, 63 to be in their electrically non-conductive state, or (ii) the first and fourth switches 61, 64 to both be in their electrically non-conductive state and the second and third switches 62, 63 to be in their electrically conductive state. In this sense, the first and fourth switches 61 , 64 may be operated as a pair (e.g. they may be either electrically conductive together or electrically non-conductive together). Likewise, the second and third switches 62, 63 may be operated as a pair. The two pairs may be operated in an inverse relationship to each other, e.g. so that when one pair is conductive, the other is not.

[0143] Fig. 5b shows the system 60 of Fig. 5a with the first and fourth switches 61 , 64 electrically conductive and the second and third switches 62, 63 electrically non-conductive. Fig. 5c shows the system 60 of Fig. 5a with the first and fourth switches 61 , 64 electrically non-conductive and the second and third switches 62, 63 electrically conductive. In Fig. 5b and 5c, the electrically conductive paths are shown by the thicker lines.

[0144] As shown in Figs. 5b and 5c, by controlling which of switches are electrically conductive, and which are not, the conductive paths between the terminals of the rectifier 66 and the ends of the transformer 67 may be changed. In particular, the apparatus may be configured to control operation of the switches based on the AC waveform / the voltage output from the rectifier 66. This may be split into a first (positive voltage) mode and a second (negative voltage) mode. The positive voltage mode may be aligned with positive voltage output from the rectifier 66, and the negative voltage mode may be aligned with negative voltage output from the rectifier 66. For example, the system 60 (e.g. a controller thereof) may be configured to switch operation of the switches based on these two different voltage outputs from the rectifier 66. For instance, there may be a known frequency associated with the input signal which governs the polarity of the voltage outputs, and the system 60 may be configured to perform switching using same frequency (e.g. the same signal may be used as a switching signal).

[0145] Fig. 5b shows the system 60 in the positive voltage mode. Here, the positive terminal of the rectifier 66 (right-hand side in Fig. 5b) is connected to the first end of the input portion 67a of the transformer 67, and the negative terminal of the rectifier 66 (left-hand side) is connected to the second end of the input portion 67a of the transformer 67. Fig. 5c shows the system 60 in the negative voltage mode. Here, the positive terminal of the rectifier 66 (right-hand side in Fig. 5c) is connected to the second end of the input portion 67a of the transformer 67, and the negative terminal of the rectifier 66 (left-hand side) is connected to the first end of the input portion 67a of the transformer 67.

[0146] Advantageously, this arrangement may enable additional voltage boosting to be provided. For example, the transformer 67 itself may already provide a voltage boost from the input side to the output side, e.g. so that the voltage on the output portion 67b side of the transformer 67 is greater than on the input portion 67a side. Additionally, by switching the electrical connections of the input side of the system 60, this voltage may be further boosted. For example, this voltage may be effectively doubled due to the positive and negative components of the input voltage waveform effectively being summed as a result of the switched connections between rectifier 66 terminals and transformer ends. Additionally, and further advantageously, the inclusion of such a transformer 67 (and its associated inductance) may help to protect against sudden swings towards high current flow. In other words, the inclusion of such a power supply may act as an electrical snubber. For instance, with a transient swing towards a higher current flow (e.g. when approaching electrical arcing), the power supply itself (i.e. the transformer 67) may act to oppose this by dropping the voltage applied. This may act to provide further protection against electrical arcing for the present apparatus.

[0147] As described herein, the apparatus may benefit from having a controllable input electrical power supplied to the vessel 1 (e.g. as described in relation to Fig. 2). During initial conditions (e.g. start-up), this input electrical power may be relatively low, as compared to peak efficiency operation where much higher electrical powers may be used. In some instances, this in input electrical power (at peak efficiencies) may be at a relatively high voltage, such as at around 2.5 kV. The above arrangement described in relation to Figs. 5a to 5c may be of particular utility for providing electrical power to such a vessel 1 , as it may be able to meet the diverse input voltage needs for the vessel 1. That is, the system 60 may be configured to efficiently provide a substantial voltage boost from input to output (vessel 1). As a result, even when taking the input from a relatively low voltage source, such as mains power (e.g. at 230 V), a significant voltage uplift may be applied to get towards the higher voltage limits for the vessel 1. If the vessel voltage requirements are high, then two or more such boosting apparatuses may be included to meet the desired voltage. In other scenarios, a single boosting apparatus may suffice. The transformer 67 may be a non-ferrite transformer. As such, the above system 60 may beneficially facilitate provide the ability to apply high voltage signals to the vessel 1, while requiring a lower voltage input. This may be of particular utility in domestic scenarios, such as in houses. For example, by using an electrical supply system 60 comprising such a voltage boosting apparatus (or a plurality of such apparatuses), a lower voltage input connection, such as mains may be used as the input power source for powering vessel operation (despite the vessel 1 potentially operating at much higher voltages than mains power). This arrangement may therefore facilitate widespread applicability of the above-described vessel technology. Additionally, the electrical supply system 60 may be provided in a smaller form factor than alternative high voltage supply systems. This may also facilitate the implementation of such a vessel 1 in space-limited settings, such as domestic dwellings etc. The electrical supply system 60 of Figs. 5a to 5c may therefore be of significant benefit for providing power to vessels of the present disclosure.

[0148] Alternatives and variants

[0149] In the examples described herein, reference has generally been made to quantities of thermal energy. It will be appreciated in the context of the present disclosure that this is typically the case, where the amount needed is best expressed in terms of the quantity of thermal energy that heated fluid carries. For example, fluid at the same pressure but higher temperature may have higher thermal energy, while still remaining the same quantity of heated fluid (and vice- versa). However, it will be appreciated that an amount (e.g. mass or volume) of heated fluid may be used as an alternative metric. For example, the vessel 1 may be configured to output fluid at a selected temperature and pressure, and the amounts of thermal energy may be represented instead as a quantity of heated fluid at that temperature and pressure. For instance, the demanded amount of thermal energy may be a demanded quantity of heated fluid to be delivered to the work extraction system 80. In the example of a heating system, e.g. central heating for a building, the demand may be for an amount of liquid at a certain temperature to be distributed around that heating system.

[0150] As disclosed herein, the fluid supply system 70 is configured to deliver a selected amount of fluid to the vessel 1 (e.g. as controlled by the controller). For this, the fluid supply system 70 may be configured to implement a selected flow rate (e.g. in grams per second). This sets the amount of fluid (mainly liquid) that is delivered into the vessel 1 , as well as the amount of fluid (mainly heated liquid or gas) that is output from the vessel 1. Typically, the two will be approximately the same during active operation of a vessel 1.

[0151] Likewise, the electrical supply system 60 is configured to deliver a selected amount of input power to the vessel 1 (e.g. as controlled by the controller). For this, the electrical supply system 60 may deliver electrical energy at a selected power level (e.g. the product of applied voltage and current may remain the same, despite fluctuations in the component values). Once this vessel 1 is active and operating in a preferred region of operation, this applied input power may remain relatively constant. It will also be appreciated that, while a particularly advantageous form for the electrical supply system 60 has been described with reference to Figs. 5a to 5c, this should not be considered limiting, as the electrical supply system 60 could take other forms, e.g. other types of such a supply system could be used.

[0152] Reference to COP herein refers to the ratio of thermal energy out (e.g. energy associated with the heated fluid being output from the vessel 1) to input power applied to the first electrode 10. In this context, it will be appreciated that the COP does not take account of other input energy levels, such as those associated with the supply of liquid to the vessel 1 and / or inherent energy levels associated with the liquid in which the plasma is to be generated. During operation of the vessel 1 , e.g. with bubbles of plasma forming within said liquid, energy may be emitted due to energy level transitions occurring within the liquid in the vessel 1. Also, the conditions within the vessel 1 may also facilitate one or more exothermic chemical reactions occurring, e.g. which utilise material carried by the supplied liquid (e.g. dissolved or in suspension therein). For example, the conditions within the vessel 1 may cause one or more Fenton reactions to occur, one or more single-atom catalyst (‘SAC’) reactions to occur, one or more proton hydration reactions to occur and / or substance oxidation reactions. The fluid supplied may contain one or more minerals therein, e.g. transition metals. These may be held in suspension or solution within the fluid supplied to the vessel 1. As a result, thermal energy may be generated as a consequence of input energy components which are not factored into the COP equation (i.e. thermal energy out / electrical energy in), and so it will be appreciated that the COP, as defined by this equation, may exceed one without violating any laws of thermodynamics.

[0153] In the example of Fig. 3 in particular, flow paths are shown between each of the three relevant components: vessel 1, thermal energy store 90, and work extraction system 80. However, it is to be appreciated that the particular structural arrangement connecting these components should not be considered limiting. Thermal energy is to be generated by the vessel 1. Some of this thermal energy may be stored in the thermal energy store 90. Thermal energy is to be used by the work extraction system 80. As such, there need not be a direct connection from the vessel 1 to the work extraction system 80, as the work extraction system 80 could obtain all necessary thermal energy from the thermal energy store 90 (i.e. as an intermediary between the two). Alternatively, there may be a direct connection between the vessel 1 and the work extraction system 80. This may be advantageous for quickly delivering heated fluid (and thermal energy associated therewith) from vessel 1 to work extraction system 80.

[0154] Also, it will be appreciated that Fig. 3 shows a simple schematic of the relationship between these different components. In particular, Fig. 3 shows how thermal energy may flow between different components, but it is to be appreciated that this may be implemented in a number of different ways. The particular choice of implementation may itself vary depending on the use case for the apparatus 100. For example, heated fluid output from the vessel 1 may be delivered directly into the thermal energy store 90 for storage, e.g. where a heated fluid, such as a warm liquid, may be stored for subsequent delivery to the work extraction system 80. In which case, heated fluid could also be delivered directly from the vessel 1 to the work extraction system 80, where needed. As another example, heated fluid output from the vessel 1 may be coupled to the thermal energy store 90 and / or the work extraction system 80 via a heat exchange relationship. In which case, the heated fluid from the vessel 1 may be used to heat another medium (e.g. solid, liquid or gas) stored in the thermal energy store 90 / which is to be used in the work extraction system 80.

[0155] 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, 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. The function of one or more elements shown in the drawings may be integrated into a single functional unit. 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. 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. Any controller described herein may be provided by any control apparatus such as a general purpose processor configured with a computer program product configured to program the processor to operate according to any one of the methods described herein. In addition, the functionality of the controller may be provided by an ASIC, an FPGA, by a configuration of logic gates, or by any other control apparatus. Other examples and variations of the disclosure will be apparent to the skilled addressee in the context of the present disclosure.

Claims

39Claims1. An apparatus comprising: a plasma generating vessel comprising an electrode; a fluid supply system configured to supply fluid to the plasma generating vessel; an electrical supply system coupled to the electrode to apply electrical energy to liquid in the plasma generating vessel to generate one or more bubbles of plasma therein; a thermal energy store configured to store thermal energy from the heated fluid output from the plasma generating vessel; a work extraction system coupled to the thermal energy store; and a controller configured to control the flow of thermal energy between: (i) the plasma generating vessel, (ii) the thermal energy store, and (iii) the work extraction system, based on an indication of a demanded amount of thermal energy by the work extraction system.

2. The apparatus of claim 1, wherein controlling said flow of thermal energy comprises, in the event that the demanded amount of thermal energy is below a lower threshold amount:(i) controlling operation of the vessel to output heated fluid and providing at least some of the thermal energy from said heated fluid to the thermal energy store, or(ii) providing thermal energy from the thermal energy store to the work extraction system.

3. The apparatus of claim 2, wherein step (ii) further comprises stopping or reducing the application of electrical energy to the electrode, and / or stopping or reducing the supply of fluid to the vessel.

4. The apparatus of any preceding claim, wherein controlling said flow of thermal energy comprises: in the event that the demanded amount of thermal energy is above a threshold amount, controlling operation of the vessel to output heated fluid and providing at least some of the thermal energy from said heated fluid to the work extraction system.

5. The apparatus of any preceding claim, wherein the controller is configured to: (i) determine an amount of thermal energy to be output from the vessel based on the indication of the demanded amount of thermal energy by the work extraction system, and (ii) control operation of the apparatus to output the determined amount of heated fluid.

6. The apparatus of claim 5, wherein determining the amount of thermal energy to be output from the vessel comprises: in the event that the demanded amount of thermal energy is at a first value below an upper threshold amount but above a lower threshold amount,40 determining the amount of thermal energy to be output from the vessel to be at or above the upper threshold amount.

7. The apparatus of claim 6, wherein the apparatus is configured to store some or all of the thermal energy from said heated fluid output from the vessel in excess of the first value in the thermal energy store.

8. The apparatus of claim 6 or 7, wherein determining the amount of thermal energy to be output from the vessel comprises: in the event that the demanded amount of thermal energy is at a second value below the lower threshold amount, determining the amount of thermal energy to be output from the vessel to be that associated with dormant or inactive operation of the vessel,9. The apparatus of claim 8, wherein the apparatus is configured to provide thermal energy from the thermal energy store to the work extraction system to meet the second value.

10. The apparatus of any of claims 5 to 9, wherein determining the amount of thermal energy to be output from the vessel comprises: in the event that the demanded amount of thermal energy is at a third value above the upper threshold amount, determining the amount of thermal energy to be output from the vessel to be at or above the third value,11. The apparatus of claim 10, wherein the apparatus is configured to store some or all of the excess thermal energy from the heated fluid output from the vessel in the thermal energy store in the event that the amount of thermal energy output from the vessel is above the third value.

12. The apparatus of any preceding claim, wherein the controller is configured to control the vessel to operate at or above a threshold coefficient of performance, and in the event that the demanded amount of thermal energy would result in vessel operation being under the threshold coefficient of performance, to either: (i) control the vessel to be in a dormant or inactive mode, or (ii) control the vessel to operate at or above the threshold coefficient of performance and to store some of the thermal energy from said heated fluid in the thermal energy store.

13. The apparatus of any preceding claim, wherein the controller is configured to control an input power to be supplied to the electrode by the electrical supply system, and wherein the controller is configured to select an amount of thermal energy to be output from the vessel so that the input power is above a threshold value,4114. The apparatus of claim 13, wherein in the event that the demanded amount of thermal energy corresponds to an input power value below the threshold value, the controller is configured to control operation of the apparatus to either: (i) increase the input power applied to a value at or above the threshold value and store excess thermal energy from said heated fluid in the thermal energy store, or (ii) stop or reduce the input power applied and provide the majority or all of the demanded thermal energy from the thermal energy store.

15. The apparatus of claim 14, wherein the controller is configured to control a flow rate of fluid to be delivered to the vessel by the fluid supply system, and wherein the controller is configured to select: (i) the flow rate of fluid based on the input power, and / or (ii) the input power based on the flow rate of fluid.

16. A method of controlling operation of an apparatus, the apparatus comprising: a plasma generating vessel comprising an electrode, a fluid supply system configured to supply fluid to the plasma generating vessel, an electrical supply system coupled to the electrode to apply electrical energy to liquid in the plasma generating vessel to generate one or more bubbles of plasma therein, a thermal energy store configured to store thermal energy from the heated fluid output from the plasma generating vessel, and a work extraction system coupled to the thermal energy store, and wherein the method comprises: controlling the flow of thermal energy between: (i) the plasma generating vessel, (ii) the thermal energy store, and (iii) the work extraction system, based on an indication of a demanded amount of thermal energy by the work extraction system17. A method comprising: supplying fluid to a plasma generating vessel, wherein the plasma generating vessel comprises an electrode operable to apply electrical energy to liquid in the vessel to generate one or more bubbles of plasma therein; and controlling the flow of thermal energy between: (i) the plasma generating vessel, (ii) a thermal energy store configured to store thermal energy from heated fluid output from the plasma generating vessel, and (iii) a work extraction system, based on an indication of a demanded amount of thermal energy by the work extraction system.

18. An apparatus comprising: a plurality of plasma generating vessels, each comprising an electrode; one or more fluid supply systems configured to supply fluid to the plasma generating vessels; one or more electrical supply systems coupled to the electrodes to apply electrical energy to liquid in the plasma generating vessels to generate one or more bubbles of plasmatherein; a work extraction system coupled to the plasma generating vessels; and a controller configured to select which and / or how many of the plurality of plasma generating vessels are to be active for generating plasma based on an indication of a demanded amount of thermal energy by the work extraction system.

19. The apparatus of claim 18, wherein the controller is configured to select which and / or how many of the plurality of plasma generating vessels are active so that each individual active vessel is operating at or above a threshold efficiency level.

20. The apparatus of claim 19, wherein the controller is configured to control an additional plasma generating vessel to be active in the event that the demanded amount of thermal energy is great enough for each of the existing active vessels and the additional vessel to operate at or above the threshold efficiency level.

21. The apparatus of any of claims 18 to 20, wherein selecting which and / or how many of the plurality of plasma generating vessels to be active comprises: in the event that the demanded amount of thermal energy is below a first threshold amount, controlling at least one of the plasma generating vessels to be in a dormant or inactive mode.

22. The apparatus of claim 21 , wherein selecting which and / or how many of the plurality of plasma generating vessels to operate comprises: in the event that the demanded amount of thermal energy is above the first threshold amount, but below a second, higher, threshold amount, controlling the same number of plasma generating vessels to be active as when operating with the demanded amount of thermal energy below the first threshold amount but operating one or more of the already active plasma generating vessels to output a greater amount of thermal energy.

23. The apparatus of claim 22, wherein selecting which and / or how many of the plurality of plasma generating vessels to operate comprises: in the event that the demanded amount of thermal energy is above the second threshold amount, controlling at least one additional vessel to be active to generate plasma and output heated fluid.

24. The apparatus of any of claims 18 to 23, wherein the controller is configured to: (i) determine an amount of thermal energy to be output from each individual vessel based on the indication of the demanded amount of thermal energy by the work extraction system, and (ii) control operation of the apparatus to output the determined amount of thermal energy.

25. The apparatus of claim 24, wherein determining the amount of thermal energy to be output from each individual vessel comprises: in the event that the demanded amount of thermal energy is at a first value below an upper threshold amount but above a lower threshold amount, determining that some but not all of the plasma generating vessels should be active.

26. The apparatus of claim 25, wherein, in the event that the demanded amount of thermal energy increases from the first value, the controller is configured to operate an additional vessel to be active in the event that the demanded amount of thermal energy is at a value which facilitates any existing active vessels, as well as the additional vessel, to be operating at above a threshold efficiency level.

27. The apparatus of any of claims 24 to 26, wherein in the event that the demanded amount of thermal energy decreases from the first value, the controller is configured to disactivate at least one of the existing active vessels in the event that the demanded amount of thermal energy is at a value which inhibits each of the existing active vessels to be operating at above a threshold efficiency level.

28. The apparatus of any of claims 24 to 27, wherein determining the amount of thermal energy to be output from each individual vessel comprises: in the event that the demanded amount of thermal energy is at a third value above the upper threshold amount, determining that all of the plasma generating vessels should be active.

29. The apparatus of 28, wherein the controller is configured to control an input power to be supplied to the electrode by the electrical supply system and to control a flow rate of fluid to be delivered to the vessel by the fluid supply system; and wherein the controller is configured to select the input power and flow rate for each active vessel based on the amount of thermal energy to be provided for that vessel,30. The apparatus of claim 29, wherein in response to detecting a fault with one of the active vessels, the controller is configured to increase the input power and / or flow rate to other active vessels.

31. The apparatus of any of claims 18 to 30, wherein the apparatus further comprises a thermal energy store configured to store thermal energy from heated fluid output from the plasma generating vessels, and wherein the controller is configured to control the flow of thermal energy between: (i) the plasma generating vessels, (ii) the thermal energy store, and (iii) the work extraction system, based on an indication of a demanded amount of thermal energy by the work extraction system.4432. A method of controlling an apparatus comprising: (i) a plurality of plasma generating vessels, each comprising an electrode, (ii) one or more fluid supply systems configured to supply fluid to the plasma generating vessels, (iii) one or more electrical supply systems coupled to the electrodes to apply electrical energy to liquid in the plasma generating vessels to generate one or more bubbles of plasma therein, and (iv) a work extraction system coupled to the plasma generating vessels, wherein the method comprises: obtaining an indication of a demanded amount of thermal energy by the work extraction system; and selecting which and / or how many of the plurality of plasma generating vessels are to be active for generating plasma based on said indication of a demanded amount of thermal energy by the work extraction system.

33. A method comprising: supplying fluid to one or more of a plurality of plasma generating vessels, wherein each of the plasma generating vessels comprises an electrode operable to apply electrical energy to liquid in that plasma generating vessel to generate one or more bubbles of plasma therein; and selecting which and / or how many of the plurality of plasma generating vessels are to be active for generating plasma based on an indication of a demanded amount of thermal energy by a work extraction system coupled to the plasma generating vessels.

34. An apparatus comprising: a plasma generating vessel comprising an electrode; a fluid supply system configured to supply fluid to the plasma generating vessel; and an electrical supply system coupled to the electrode to apply electrical energy to liquid in the plasma generating vessel to generate one or more bubbles of plasma therein, wherein the electrical supply system comprises a voltage boost apparatus comprising: an input power connection; an output power connection coupled to the electrode; a transformer, wherein the input power connection is coupled to the output power connection via the transformer; and a switching arrangement configured to switch electrical connections between the input power connection and the transformer between: (i) a positive voltage mode, and (ii) a negative voltage mode.

35. The apparatus of claim 34, wherein the input power connection comprises a positive terminal and a negative terminal.4536. The apparatus of claim 35, wherein the switching arrangement is configured to switch the electrical connections between each terminal and the transformer to switch between the positive and negative voltage modes.

37. The apparatus of claim 36, wherein the switching arrangement is configured to: connect: (i) the positive terminal to a first end of the transformer, and (ii) the negative terminal to a second end of the transformer, to operate in the positive voltage mode; and connect: (iii) the positive terminal to the second end of the transformer, and (iv) the negative terminal to the first end of the transformer, to operate in the negative voltage mode.

38. The apparatus of claim 37, wherein the apparatus further comprises: a first switch between the positive terminal and the first end of the transformer; a second switch between the negative terminal and the first end of the transformer; a third switch between the positive terminal and the second end of the transformer; and a fourth switch between the negative terminal and the second end of the transformer.

39. The apparatus of claim 38, wherein the apparatus is configured to control either: (i) the first and fourth switches to be electrically conductive together, or (ii) the second and third switches to be electrically conductive together.

40. The apparatus of claim 38 or 39, wherein the apparatus is configured to control: the first and fourth switches to be electrically conductive and the second and third switches to be electrically non-conductive in the positive voltage mode; and the second and third switches to be electrically conductive and the first and fourth switches to be electrically non-conductive in the negative voltage mode.

41. The apparatus of any of claims 34 to 40, wherein the input power connection comprises an AC input connection and a rectifier coupled to the AC input connection.

42. The apparatus of claim 41, wherein the positive and negative terminals are terminals of the rectifier.

43. The apparatus of any of claims 34 to 43, comprising a plurality of voltage boost apparatuses coupled to the electrode.

44. The apparatus of any of claims 34 to 43, comprising a controller configured to control the switching arrangement to switch between the positive and negative voltage modes.4645. The apparatus of claim 44, wherein the controller is configured to control switching of the switching arrangement based on a frequency of an AC electrical input supplied to the input power connection.

46. The apparatus of claim 45, wherein the controller is configured to control the switching arrangement to operate in a positive voltage mode during a positive portion of the input AC waveform and to operate in a negative mode during a negative portion of the input AC waveform.

47. A method of controlling the supply of electrical energy to the electrode of a plasma generating vessel, wherein the plasma generating vessel comprises an electrode configured to apply electrical energy to liquid in the vessel to generate one or more bubbles of plasma therein, and wherein the method comprises controlling an electrical supply system to: connect, via a transformer, an input power connection to an output power connection coupled to the electrode with electrical connections between the input power connection and the transformer in a positive voltage mode; and connect, via the transformer, the input power connection to the output power connection coupled to the electrode with electrical connections between the input power connection and the transformer in a negative voltage mode.

48. A method comprising: supplying fluid to a plasma generating vessel, wherein the plasma generating vessel comprises an electrode operable to apply electrical energy to liquid in the vessel to generate one or more bubbles of plasma therein; and wherein controlling the application of electrical energy to the electrode comprises: connecting, via a transformer, an input power connection to an output power connection coupled to the electrode with electrical connections between the input power connection and the transformer in a positive voltage mode; and connecting, via the transformer, the input power connection to the output power connection coupled to the electrode with electrical connections between the input power connection and the transformer in a negative voltage mode.

49. A computer program product comprising computer program instructions configured to program an apparatus to implement the method of any of claims 16, 17, 32, 33, 47 and 48.

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