Electrode Carrying Insert for an Energy Cell

Abstract

An electrode carrying insert for an energy cell, the insert comprising: a body having: a proximal region, a distal region, and a sealing region; and an electrode extending within the body from the pro

Description

Technical Field The present disclosure relates to the field of energy cells. In particular, the present disclosure relates to the field of energy cells in which plasma is generated for indirect and direct heating of a fluid. Background 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. Summary 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. In an aspect, there is provided an electrode carrying insert for an energy cell, the insert comprising: a body having: a proximal region, a distal region, and a sealing region; and an electrode extending within the body from the proximal region to the distal region; wherein the insert is insertable into a housing of an energy cell with: the sealing region sealing an opening in the housing through which the body extends from the proximal region outside the housing to the distal region inside the housing, and the electrode configured to apply electrical energy to a fluid inside the housing to generate one or more bubbles of plasma therein. In aspect, there is provided an energy cell comprising: a housing having an opening therein; and an electrode carrier comprising: (i) a body having: a proximal region, a distal region, and a sealing region, and (ii) an electrode within the body; wherein the electrode carrier is coupled to the housing with the sealing member of the electrode carrier sealing the opening in the housing, and with the distal region of the body inside the housing and the proximal region of the body outside the housing; wherein the electrode extends within the body from the proximal region to the distal region and is configured to apply electrical energy to a fluid inside the housing to generate one or more bubbles of plasma therein. Embodiments may enable a ‘completed energy cell’ to be provided using a said electrode carrying insert. This may simplify design constraints for providing the overall cell, as well as manufacturing and / or installation of said cell. For example, the electrode carrying insert may provide a replaceable component, e.g. where multiple electrode carrying inserts may be used in combination with a given energy cell throughout the lifetime of that cell. This may increase longevity for such completed energy cells. The inserts may be manufactured in a more efficient manner as well, e.g. using 3D printing for example. Insertion of a separate electrode carrying insert to provide the completed cell may facilitate easier and more efficient provision of a completed energy cell. The distal region of the body may comprise a member which surrounds the electrode, and wherein the member extends distally from the sealing region. The member may surround the electrode along some, but not all, of the length of the electrode within the housing. A distal end of the electrode may extend beyond a distal end of the member. Apparatuses may further comprise a protective element, such as an electrical shroud, arranged to at least partially surround the distal end of the electrode. At least one of: (i) the protective element, and (ii) the body, may be configured to have a coefficient of thermal expansion similar to, or the same as, a coefficient of thermal expansion of the electrode. The protective element may be coupled to the distal end of the member, optionally wherein said coupling comprises a threaded connection. The member may be narrower at its distal end than at its proximal end. The sealing region may comprise a flange. The flange may be larger than the opening in the housing and arranged to completely circumscribe said opening. A proximal end of the member may be coupled to the flange, and wherein the flange surrounds the proximal end of the member. Apparatuses may further comprise a groove in the flange, wherein the groove is arranged to receive a component of the energy cell within the housing, optionally wherein the component comprises a resistive element. The groove may be configured to hold the component in a fixed spatial arrangement with respect to the electrode. The groove may surround the electrode. The groove may be circular. The electrode may extend distally at a centre point of the circular groove. The electrode may comprise a first portion arranged to be provided inside the housing and a second portion arranged to connect the first portion to a source of electrical energy. The first portion may be different in size and / or shape to the second portion. The sealing region may be configured to seal the opening in the housing in response to pressure from fluid within the internal portion of the housing. The apparatus may include a coupling element configured to secure the insert to the housing. The body may comprise at least one fluid channel arranged to enable fluid to flow therethrough and into the housing. The fluid channel may comprise an aperture in the sealing region. The fluid channel may be configured to provide a turbulent and / or vortical flow of fluid into the housing. The at least one fluid channel may comprise at least one pipe extending distally from the sealing region, optionally wherein said at least one pipe follows an at least partially curved path. The body may be removably insertable into the housing, e.g. to enable multiple different inserts to be used with the housing and / or to enable one insert to be used with multiple different housings. The body may be arranged so that the electrode extends into the housing coaxially with one or more cell electrodes therein. A distal portion of the body may be more thermally resistant than a proximal portion. A distal end of the electrode may extend beyond a distal end of the body. The distal end of the electrode may extend beyond the distal end of the body by a distance selected to provide a colder region within an internal volume of said housing. The distance may be selected to provide a colder region adjacent a proximal end of the cell. A proximal portion of the body may be located in a colder region of the internal volume, and wherein the proximal portion comprises a less thermally resistant material than a distal portion of the body. The distal end of the electrode may extend beyond the distal end of the body by a distance selected so that a line which extends from the distal end of the electrode through the distal end of the body intersects one or more walls of the cell distal of the proximal end of the cell. A solid angle extending from the distal end of the electrode through the distal end of the body may intersects said one or more walls in a plane distal of the proximal end of the cell. The apparatus may comprise one or more components for sealing the proximal end of the cell to the one or more walls of the cell, and wherein said components are located within the colder region of the internal volume. The body may be arranged to permit spraying of electrons from the distal end of the electrode into a distal volume of the cell but to inhibit spraying into a proximal volume, thereby to provide a colder region in the proximal volume. The more thermally resistant portion may be located in a warmer region than the colder region. In an aspect, there is provided a kit of parts comprising: an energy cell comprising a housing having an opening therein; and an electrode carrying insert comprising: a body having: a proximal region, a distal region, and a sealing region; and an electrode extending within the body from the proximal region to the distal region; wherein the insert is insertable into the housing of the energy cell with: the sealing region sealing the opening in the housing through which the body extends from the proximal region outside the housing to the distal region inside the housing, and the electrode configured to apply electrical energy to a fluid inside the housing to generate one or more bubbles of plasma therein. In an aspect, there is provided an energy cell comprising: a housing having a proximal end, a distal end, and one or more walls extending from the proximal end to the distal end to define an internal volume therewithin for receiving a fluid to be heated; and an electrode member extending from the proximal end into the internal volume and comprising: an electrode configured to apply electrical energy to fluid in the internal volume to generate bubbles of plasma therein; and a body which surrounds a proximal region of the electrode within the internal volume; wherein a distal end of the electrode extends beyond a distal end of the body by a distance selected to provide a colder region within a proximal portion of the internal volume; and wherein the colder region intersects the walls of the cell at a location distal of the proximal end of the housing. The distance may be selected to: (i) permit spraying of electrons from the distal end of the electrode into a distal portion of the internal volume, and (ii) inhibit spraying of electrons from the distal end of the electrode into the proximal portion of the internal volume. The distance may be selected so that a line passing from the distal end of the electrode and through the distal end of the body intersects the one or more walls at a location distal of the proximal end. The distance may be selected so that a solid angle passing from the distal end of the electrode and through the distal end of the body intersects the one or more walls in a plane distal of the proximal end. The cell may comprise one or more components for sealing the proximal end of the body to the one or more walls. Said components may be disposed within the proximal portion of the internal volume. A distal portion of the body may comprise a material which is more thermally resistant than a material of a proximal portion of the body. The proximal portion of the body may be located in the colder region. The electrode member may be part of the cell housing or wherein the electrode member is provided by an electrode carrying insert. In an aspect, there is provided an energy cell comprising: a housing comprising one or more walls which define an internal volume of the vessel for receiving a fluid to be heated; and an electrode member disposed within the internal volume and comprising: an electrode configured to apply electrical energy to fluid in the internal volume to generate bubbles of plasma therein; and a body surrounding a proximal region of the electrode within the internal volume, wherein the body comprises a distal portion and a proximal portion, and wherein the distal portion of the body comprises a more thermally resistant material than the proximal portion of the body. A distal end of the electrode may extend beyond a distal end of the body by a distance corresponding to a length of the distal portion of the body. The distal end of the electrode may extend beyond the distal end of the body by a distance selected to provide a colder region in the proximal portion of the internal volume, and wherein the proximal portion of the body is in the colder region. A proximal end of the housing may be located in the colder region. The distal end of the electrode may extend beyond the distal end of the body by a distance selected to inhibit a temperature of fluid adjacent the proximal portion of the body exceeding a threshold value. The distal end of the body may be arranged to inhibit spraying of electrons from the distal end of the electrode into a proximal portion of the internal volume thereby to inhibit a temperature of fluid in the proximal portion of the internal volume exceeding a threshold value. A solid angle extending from the distal end of the electrode through the distal end of the body may intersect the one or more walls at a plane distal of the proximal end. The more thermally resistant material may be for the portion of the member distal of said plane. The proximal portion of the body may be separated from the distal portion by said plane. Figures Some examples of the present disclosure will now be described, by way of example only, with reference to the figures, in which: Fig. 1 is a schematic diagram illustrating an energy cell. Figs. 2a and 2b are schematic diagrams illustrating an electrode carrying insert. Fig. 3 is a schematic diagram illustrating an energy cell with an electrode carrying insert inserted therein. Fig. 4 is a schematic diagram illustrating an electrode carrying insert inserted into a portion of an energy cell. Fig. 5 is a schematic diagram illustrating an energy cell. In the drawings like reference numerals are used to indicate like elements. Specific Description The present disclosure relates to an electrode carrier for an energy cell. The electrode carrier, once inserted into an energy cell, provides one of the electrodes of the energy cell. By applying electrical energy to that electrode (once it is inserted into the cell), bubbles of plasma may occur which generate heat within the energy cell. The electrode carrier is designed so that, once it is inserted into the cell, the internal volume of the cell may be suitably sealed to enable plasma generation therein. The electrode carrier may provide a suitable connection between the internal volume of the cell, where a voltage at the electrode causes generation of bubbles of plasma within the internal volume, and a region outside the cell where the electrode is connected to a source of electrical energy. The electrode carrier may therefore provide an insert for an energy cell, which, when inserted, may complete the cell. That is, once inserted, the combination of the insert and the housing may close off an internal volume of the cell. In other words, with the electrode carrier inserted, the cell may function as intended for generating heated fluid using both the inserted electrode carrier and the remaining part(s) of the cell. An example of an energy cell will first be described with reference to Fig. 1. After this, example electrode carrying inserts will be described with reference to Figs. 2 to 4, wherein Figs. 3 and 4 show example inserts once inserted to provide an energy cell. A further example of an energy cell will then be described with reference to Fig. 5. Fig. 1 shows a schematic diagram of an energy cell 1. The cell is shown in Fig. 1 in a completed without any distinction between an electrode carrying insert and the remainder of the cell. This is to provide context for how a ‘completed cell’ (i.e. a cell with an electrode carrying insert provided therein) will be arranged, and how that completed cell will function. Examples will be described later with reference to Figs. 2 to 4 which make more clear the distinction between cell and insert. As described below, inserts of the present disclosure are designed to enable a resulting completed cell to be arranged and to function in the manner now described with reference to Fig. 1. The cell 1 includes a fluid inlet 54 and a fluid outlet 58. The cell 1 has a housing 50. The housing 50 defines an internal volume 56 of the cell 1. The cell 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 cell 1 may also include a resistive element 40. Although not shown, the cell 1 may be connected to a supply system. The supply system may supply liquid to the cell 1 through the inlet 54. Likewise, although not shown, the cell 1 may be connected to a work extraction system. The work extraction system may extract useable work from heated fluid from the outlet 58. The housing 50 of the cell 1 encapsulates the internal volume 56. The fluid inlet 54 provides a flow path for fluid into the internal volume 56 of the cell 1. The fluid outlet 58 provides a flow path for fluid out from the internal volume 56 of the cell 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 cell 1 may otherwise be sealed by the housing 50. The first electrode 10 is at least partially disposed within the internal volume 56 of the cell 1. The second electrode 20 may also be disposed at least partially within the internal volume 56 of the cell 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 cell 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 is electrically conductive). 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 cell 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, 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). The third electrode 30 is also provided in the internal volume 56 of the cell 1. A first end of the third electrode 30 may be located outside the internal volume 56, and the third electrode 30 may extend form the first end to a second end located within the internal volume 56. The second end of the third electrode 30 may be 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 from outside the opposite end of the housing 50 into the internal volume 56 towards the first end. 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. A resistive element 40 may also be included in the internal volume 56. The resistive element 40 may also 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 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. 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 cells 1 may be provided together, e.g. to increase output as compared to that provided by a single cell. In which case, the cells 1 may be stacked together. The cells 1 may be designed to facilitate more space efficient stacking. For example, the cells 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. 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 cell 1). The fluid outlet 58 may be arranged higher (e.g. above, such as directly above or above and laterally offset from) the fluid inlet 54. 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. 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 may be used. The housing 50 may be formed of multiple different materials. The different materials may be selected based on their photon absorption characteristics. For example, materials may be selected which absorb photons in different wavelength range(s) for which photons are expected within the internal portion 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. 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. The internal volume 56 is arranged to receive liquid to be heated through the fluid inlet 54. The cell 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. The first and second electrodes 10, 20 are configured to provide a current flow path through the internal volume 56 of the cell 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 cell 1. The second electrode 20 may then provide the cathode for carrying current away from the internal volume 56 of the cell 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 presence of fluid in the internal volume 56 may provide a conductive path between the first and second electrode 20. The fluid will provide electrical resistance between the two electrodes 10, 20. The first and second electrode 20 with fluid in the cell 1 may effectively provide a circuit having a capacitance and a resistance. The first and second electrodes 10, 20 are configured to provide a voltage stress to fluid and / or plasma within the internal volume 56. 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 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 cell 1). The tip need not be electrically connected to a component outside of the cell 1. For example, where the third electrode 30 is passive, the provision of an electrical conductor within the housing 1 may provide passive balancing. For example, such a tip could be capable of charging and discharging by itself. 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 cell would be electrically connected to a voltage source (e.g. external to the cell 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 cell 1. That passive exposed portion of electrically conductive material may be arranged to be charged and / or discharged within the cell (e.g. due to internal electrical conditions of the cell). The third electrode 30, when active, may be connected to a voltage source. An exposed portion of the third electrode 30 within the cell 1 may then be connected to the voltage source. 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). The resistive element 40 may be of sufficient resistance to effectively provide an electrical insulator (between the anode and cathode). In operation, a liquid is supplied through the fluid inlet 54 and into the internal volume 56 of the cell 1. In this example, the liquid will be water, but other liquids may be used. For example, the liquid may be any aqueous solution, such as tap water, sea water, ionised water etc. The liquid may be any non-Newtonian liquid. The liquid may be a non-electrically insulating liquid. The liquid may be at least partially electrically resistive (but not fully resistive). The cell 1 will fill up with water. Any gas previously in the cell 1 may be forced out through the fluid outlet 58 of the cell 1. The cell 1 may then be substantially filled with water. 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 cell 1. As a result, some pockets of gas will develop within the liquid in the internal volume 56 of the cell 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. 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 cell 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. 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 giving rise to further increased voltage stress across the bubble. With sufficient voltage stress across the bubble, ionization may occur leading to the formation of plasma within the bubble. Thus, one or more plasma bubbles may form in the liquid in the internal 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 nonNewtonian fluid responses in the liquid in the internal volume 56 of the cell 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. As mentioned above, the breakdown of gas may occur such that a low impedance bridge forms (e.g. the gas resistivity drops), but not as far as a full breakdown in which electrical arcing occurs. In addition to this, thermionic emission may occur within the cell 1. Electron spraying may occur with electrons moving between different electrodes of the cell. 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. The electrodes may be designed to provide a preferential flow for the electron movement. For example, the material of each electrode (and in particular its valence) may be selected to impart this preferential flow of electrons. For example, tungsten may be used for the first electrode as it has a high valence. The electrodes may be arranged to provide a preferential flow from the first electrode 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 parastate to their higher energy ortho-state. Molecules may also move to higher rotational and / or vibrational energy levels, and / or further splitting up of these molecules may occur. As a result, the atoms within each bubble will be at disproportionately high energy levels (e.g. as compared to conventional fluids / the fluid within the internal 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. 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 cell 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 cell 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 cell 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 cell 1 may have somewhat unconventional, or at least lower energy configurations, as compared to the liquid that was provided to the cell 1. This is as a consequence of the plasma generation and subsequent energy release which occurred within the cell 1. In this sense, the cell 1 may operate as a heat pump. That is, the cell 1 is receiving a liquid, such as water (e.g. cold water) and turning this into steam. Although not shown, the cell 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 cell 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 cell. 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 cell 1 may then used in a work extraction system to extract useable work from that heated fluid. In the example described above, the cell 1 is effectively described as comprising a single housing 50, with the different components of the cell 1 being provided as part of the cell 1. The present disclosure relates to the provision of a separate component for providing the first electrode 10 of the cell 1. That separate component is in the form of an electrode insert which is configured to provide part of the resulting cell 1 (the lower part of the cell 1, as shown in Fig. 1). As will be described in more detail below, in addition to providing the first electrode 10 of the cell 1, the insert may also effectively provide a portion of the housing 50 for the cell 1. The insert may also provide the fluid inlet 54 for the cell 1. An example insert will now be described with reference to Figs. 2a and 2b. Fig. 2a shows a cross-section view of an electrode insert 100. Fig. 2a shows the same cross-sectional view as that shown in Fig. 1 for the energy cell 1. Fig. 2b shows the insert 100 of Fig. 2a when viewed in plan (i.e. looking down from above). The electrode insert 100 comprises an electrode 110 and a body 120. The body 120 has a distal region 121, a sealing region 122 and a proximal region 123. The body 120 includes an internal end portion 130, a tapered portion 132 and a flange 134. The flange 134 includes a groove 152 and a fluid channel 154. The body 120 also includes a bushing 136 and an external end portion 138. The insert 100 also includes an earthing element 156. The electrode 110 has an external portion 116 and an internal portion 114. A protective element 140 is also included. The body 120 extends from its proximal region 123 (which is to be located outside the housing 50 of the cell 1) to its distal region 121 (which is to be located inside the housing 50 of the cell 1). The sealing region 122 of the body 120 is located between the proximal and distal regions (to provide sealing of the housing 50 of the cell 1). A central axis of the insert 100 may extend from a proximal end (i.e. outside the housing 50) to a distal end (i.e. inside the housing 50). The flange 134 is located in the sealing region 122 of the body 120. The flange 134 provides a wider region of the body 120. The flange 134 extends radially outward from a central axis of the insert 100. The flange 134 may comprise a distal face and a proximal face. The distal face may face towards the internal volume 56 of the cell 1, and the proximal face may face away from the internal volume 56 of the cell 1. The flange 134 may comprise at least one aperture therein. The aperture extends from a proximal side of the flange 134 to a distal side of the flange 134 to provide the fluid channel 154. The groove 152 may be provided in the distal face of the flange 134. The groove 152 provides a recess within the flange 134 (e.g. in the distal face of the flange 134). The flange 134 may be circular. The groove 152 may be circular. The groove 152 and flange 134 may be arranged concentrically. The groove 152 may be arranged concentrically around the central axis. The flange 134 may also be arranged concentrically around the central axis. The proximal region 123 of the body 120 is located on a proximal side of the flange 134. The bushing 136, earthing element 156 and external end portion 138 are located on a proximal side of the flange 134. The bushing 136 may be arranged concentrically about the central axis of the insert 100 (e.g. as may the external end portion 138). The bushing 136 and / or external carrier may be circular. The external carrier may extend proximally away from the bushing 136. The earthing element 156 may be located on a proximal face of the bushing 136. The earthing element 156 may be a plate. For example, the plate may be annular in shape. The plate may be concentric about the central axis. The external end portion 138 may extend through a central region of the plate. The earthing element 156 may at least partially (e.g. completely) circumscribe the external end portion 138. The external end portion 138 may extend proximally beyond the earthing element 156 (and bushing 136). The bushing 136 and / or earthing element 156 may be electrically connected to the housing 50 of the cell 1 (once the insert 100 is inserted to complete the cell 1) and to an electrical earth, e.g. so as to electrically ground the second electrode 20 which is electrically connected to (e.g. part of) the housing 50. The distal region 121 of the body 120 is located on a distal side of the flange 134. The tapered portion 132 and the internal end portion 130 are located on a distal side of the flange 134. The tapered portion 132 may extend distally from a distal face of the flange 134 to the internal end portion 130 of the body 120. In other words, the tapered portion 132 may connect the flange 134 to the internal end portion 130 of the body 120. The tapered portion 132 may be wider at the flange 134 than at the internal end portion 130. For example, the tapered portion 132 may have a linear taper between its proximal end (at the flange 134) and its distal end (at the internal end portion 130 of the body 120). The internal end portion 130 is narrower than the flange 134 (and narrower than the majority of the tapered portion 132). The tapered portion 132 and / or the internal end portion 130 may be arranged concentrically about the central axis. For example, they may be circular when viewed in plan. The electrode 110 extends along the central axis of the insert 100. The electrode 110 extends from its external portion 116 (on a proximal side of the flange 134) to its internal portion 114 (on a distal side of the body 120). The electrode 110 extends distally beyond the distal end of the body 120. A distal length of electrode 110 extends distally beyond the distal end of the body 120. A portion of said distal length is surrounded (e.g. circumscribed) by the protective element 140. The protective element 140 may be a shroud (e.g. an electrical shroud). The protective element 140 is securable to the distal end of the body 120. For example, this may be a screw fit, such that the protective element 140 may be screwed into the distal end of the body 120 to hold the protective element 140 in place there. The protective element 140 is connected to the body 120. The protective element 140 may be narrower in width than the internal end portion 130 of the body 120. The protective element 140 may be arranged concentrically about the electrode 110. The protective element 140 may be circular. The protective element 140 may extend along some of said distal length, but not all of it. A distal tip of the electrode 110 may extend distally beyond the distal end of the protective element 140. This may provide a distal tip of electrode 110 which is exposed. The electrode carrying insert 100 is configured to be insertable into a housing 50 of an energy cell 1. The insert 100 is configured so that a portion of the insert 100 will effectively provide a portion of the housing 50 of the resulting cell 1 (i.e. once the insert 100 has been inserted). The housing 50 may comprise an opening 52 which the insert 100 is configured to seal. The sealing portion of the body 120 is configured to provide a portion of such housing 50. In other words, the sealing portion of the body 120 is arranged to seal the opening 52 in the housing 50 of the cell 1, e.g. so that the housing 50 and the sealing portion define the internal volume 56 of the cell 1). The electrode 110 is configured to provide the first electrode 10 of the energy cell 1 when the insert 100 is inserted into the housing 50. With the insert 100 inserted, the sealing region 122 will seal the opening 52 in the housing 50 to define the internal volume 56 of the housing 50, and the electrode 110 will provide the first electrode 10 for the cell 1. The cell 1 may therefore be provided by at least two separable components. The insert 100 may be removably insertable into the housing 50 (e.g. so that it may be connected to the housing 50 to provide the cell 1 and removed from the housing 50). The electrode 110 is electrically conductive. The external portion 116 of the electrode 110 is configured to be connected to a source of electrical energy. For example, the external portion 116 of the electrode 110 may be connected to a controlled voltage source. The electrode 110 is configured to electrically conduct from its external portion 116 to the internal portion 114 (and to the distal tip). The controlled voltage source may be configured to control the voltage being applied at the distal tip within the housing 50. Current may therefore flow along the electrode 110 (from the external portion 116 to the internal portion 114). The body 120 is configured to electrically insulate the conductor along at least a portion of the length of the conductor. The body 120 may comprise an electrical insulator. For example, the body 120 may be formed of PEEK (polyether ether ketone) or nylon. Other suitable materials include ceramic materials, such as Aluminium oxide, an epoxy, polycarbonate, silicone, porcelain, PVC, polyethylene and / or EPDM. The body 120 may be 3D printed. The protective element 140 may also be configured to electrically insulate the conductor. For example, the protective element 140 may comprise an electrical shroud. The body 120 and the protective element 140 may electrically insulate the electrode 110 along the majority of its length within the internal volume 56 of the cell 1. For example, the majority of the length of the electrode 110 from the sealing region 122 to its distal tip may be surrounded (e.g. completely circumscribed) by the body 120 and / or the protective element 140. The distal tip of the electrode 110 may be the only portion of electrode 110 which is exposed within the internal volume 56 of the cell 1. The protective element 140 may reduce the turbulence around the distal tip of the electrode 110. For example, this may give rise to a slight capacitive effect occurring with surrounding water. In other words, the insert 100 may be configured to provide a focal point for the application of voltage from the first electrode 10 (i.e. electrode 110) to the fluid within the energy cell 1 (i.e. at the distal tip). Between this distal tip and the sealing region 122, the electrode 110 may be insulated. Fluid adjacent to that portion of the body 120 may be subjected to much lower electrical energy. Fluid in this area may be cooler. The distal tip of the electrode 110 (i.e. the portion of electrode which is exposed within the cell) may be less than 50 mm in length, e.g. less than 40 mm, e.g. less than 35mm, e.g. less than 30 mm, e.g. less than 25 mm, e.g. less than 20 mm, e.g. less than 15 mm, e.g. less than 10 mm, e.g. 5 mm or less. The flange 134 is configured to provide the sealing portion of the body 120. The distal surface of the flange 134 is configured to provide an internal surface of the housing 50 of the cell 1. The groove 152 in the flange 134 may be configured to support an item in the cell 1. In particular, the groove 152 may be configured to hold the resistive element 40 within the cell 1. The groove 152 is configured to circumscribe the central axis (and electrode 110). The groove 152 is arranged concentrically around central axis. The groove 152 may be circular. The centre of the groove 152 may be the central axis. For example, the groove 152 may be configured to hold the resistive element 40 in a fixed orientation relative to the electrode 110 to provide the spatial arrangement described above in relation to Fig. 1. The groove 152 may be arranged to support the resistive element 40 so that the resistive element 40 surrounds the electrode 110 once the resistive element 40 is inserted into the groove 152. For example, with the resistive element 40 being circular and coaxial with the electrode 110. The aperture is arranged to extend through the flange 134 from the proximal side to the distal side to provide the fluid channel 154. The proximal side of the fluid channel 154 (i.e. external to the internal volume 56 of the cell 1) may be configured to receive fluid, such as water, from a fluid supply. For example, a tube may be coupled to the fluid inlet 54 to couple the internal volume 56 of the cell 1 to the fluid supply. In other words, the fluid inlet 54 is configured to provide a passageway for fluid to enter into the internal volume 56 of the cell 1 (with the insert 100 inserted into the cell 1). The body 120 extends from the proximal region (where the body 120 will be outside the internal volume 56 of the housing 50) to the sealing region 122 (where the body 120, i.e. the flange 134, forms part of the housing 50) and through to the distal region 121 (where the body 120 will be inside the internal volume 56 of the housing 50). The body 120 may comprise a one-piece structure. For example, a single piece of material may provide all of the different regions of the body 120. The internal end portion 130 of the body 120 may be uniform in thickness, for example it may be cylindrical. Alternatively, as mentioned above, other shapes may be used. In particular, the shape may be chosen to enable tessellation with that shape. In which case, the internal end portion 130 may correspond to the tessellatable shape to be used for the cell. When circular, the radius of the internal end portion 130 may be constant. The protective element 140 may be connectable into the internal end portion 130 of the body 120. For example, there may be a screw fit between the protective element 140 and the internal end portion 130 of the body 120. The distal end of the body 120 may be coupled to the protective element 140 so that the electrode 110 is surrounded by insulative material (either the body 120 or the protective element 140) in that region. The protective element 140, e.g. the electrical shroud, may be removably insertable into the body 120. For example, the protective element 140 may be a replaceable item, where another protective element 140 could be inserted into the body 120. The protective element 140 may be subject to more material damage than the body 120, and so by having a removable protective element 140, these may be replaced more frequently thus enabling longer life for the insert 100. The protective element 140 and / or the body 120 (e.g. the distal region 121 of the body 120) may have a coefficient of thermal expansion similar to, e.g. the same as, that of the electrode 110. The tapered portion 132 is arranged between the flange 134 and the internal end portion 130 of the body 120. The tapered portion 132 is broader at the flange 134 than at the internal end portion 130 of the body 120. The tapered portion 132 may be circular along its length. The radius may continually decrease from the flange 134 to the internal end portion 130. The body 120 may have a channel extending through its central axis. The electrode 110 is inserted into said channel. The body 120 may be symmetrical about the central axis. The bushing 136 may be arranged for insertion into another opening 52. The earthing element 156 is electrically connectable to an electrical earth. The earthing element 156 may be electrically connected to the housing 50 (e.g. the two may be in electrical contact with each other). The earthing element 156 is configured to direct current away from the housing 50 to the electrical earth. The external end portion 138 of the body 120 is configured to electrically insulate the electrode 110 from the earthing element 156. The external end portion 138 provides an electrical insulator which separates the electrode 110 from the earthing element 156. The proximal region 123 of the body 120 may extend from the flange 134 in a proximal direction (i.e. away from the internal volume 56 of the cell 1). The proximal region 123 may be arranged to electrically insulate the electrode 110 up to the connection between the electrode 110 and the source of electrical energy. The insert 100 may be configured so that, once inserted into the housing 50 of the cell 1, the cell 1 may be arranged to function as described above with reference to Fig. 1. Fig. 2b shows the insert 100 in plan. As can be seen, the body 120 may be symmetrical about a central axis with the different portions being coaxial. The groove 152 may be circular. The electrode 110 may extend in a central region. The electrode 110 may be circular. The flange 134, tapered portion 132 and internal end portion 130 of the body 120 may be circular. The protective element 140, e.g. the shroud, may also be circular and arranged concentrically. Although not shown, there may be a plurality of apertures, e.g. to provide a plurality of fluid inlets. These may be distributed uniformly around the flange 134. For example, the fluid inlets may be located in different portions of the flange 134, e.g. distributed at even angles. Reference will now be made to Fig. 3 to describe the electrode insert 100 as inserted into an energy cell 1. Fig. 3 shows an energy cell 1 with the electrode insert 100 shown in Figs. 2a and 2b inserted into the cell 1. As with the energy cell 1 of Fig. 1, the energy cell 1 of Fig. 3 includes a second electrode 20, a third electrode 30, a resistive element 40 and a housing 50. Inside the housing 50 is the internal volume 56 of the cell 1. The housing 50 includes an opening 52. As shown in Fig. 3, the housing 50 has side wall(s), a top wall and a bottom wall. The opening 52 is in the bottom wall of the housing 50. A portion of the bottom wall may still be included. In Fig. 3, this is shown as lip 53. The opening 52 is the absence of material in the bottom wall of the housing 50 between the lip(s) 53. A contact region 94 is shown in Fig. 3 between the flange 134 and the lip 53. A tube 155 is shown in Fig. 3 for connecting the exterior of the cell 1 to the internal volume 56 through the fluid channel 154 of the body 120. The electrode carrying insert 100 is the same as that shown in Figs. 2a and 2b and so shall not be described again here. The insert 100 is included inside the cell 1. The flange 134 of the insert 100 overlaps the lip 53 of the housing 50. The area of the flange 134 is greater than the area of the opening 52. The flange 134 overlies a portion of the lip 53 to define the contact region 94. Although not shown in Fig. 3, the flange 134 contacts the lip 53 in the contact region 94. In operation, fluid is included in the cell 1, and the cell 1 pressure causes then flange 134 to abut the lip 53 thereby to seal the cell 1 (to define the internal volume 56). For example, both due to the weight of the fluid pushing down on the flange 134 (and onto the lip 53), and also due to the elevated pressure in the internal volume 56 (e.g. due to plasma / steam generation). The flange 134 defines an area which is greater than the area of the opening 52 such that at least a portion of the flange 134 overlies the lip 53. The portion of the flange 134 may comprise a perimeter region of the flange 134. In other words, the sealing region 122 (i.e. the flange 134) of the body 120 is arranged to interact with the lip 53 to seal the opening 52 (e.g. so that fluid in the internal volume 56 cannot escape out through the opening 52). As will be appreciated, the insert 100 may be sized so that it may fit through the opening 52 (e.g. when tilted or sideways). Additionally, or alternatively, at least a portion of the housing 50 may be detachable. For example, the top and / or bottom portion of the housing 50 may be detachable, such as by a selective connection, e.g. by screw fit or other attachment means. The removable portion of the housing 50 may enable the insert 100 to be provided inside the housing 50 with the flange 134 obstructing the opening 52 (e.g. and with the resistive element 40 inserted in the groove 152). The resistive element 40 is provided in the groove 152 of the insert 100. The groove 152 holds the resistive element 40 in its intended spatial arrangement. Although not shown in Fig. 3, a compliant and / or biasing member may be included to interact with the other end of the resistive element 40 to that held in the groove 152. For instance, the resistive element 40 may comprise a relatively brittle or otherwise shatterable material which may shatter under increased stress. The compliant / biasing member may be located between the resistive element 40 and the portion of the housing 50 adjacent to the resistive element 40. As such, this member may act to cushion any interaction between the resistive element 40 and the housing 50 (e.g. to inhibit the element 40 from shattering due to contact therewith). The inclusion of this member may be of particular utility when inserting the electrode carrying insert 100 to provide the cell 1. The electrode 110 of the insert 100 will be arranged in its intended spatial arrangement within the housing 50 once the insert 100 is located in the housing 50. With the insert 100 inserted into the housing 50, the first electrode 10, second electrode 20, third electrode 30 and resistive element 40 will be arranged as described above in relation to Fig. 1 to enable the cell 1 to function as described above. The tube 155 connects a fluid supply to the internal volume 56 to provide fluid thereto. This may therefore provide the inlet 54 shown in Fig. 1 (no outlet is shown in Fig. 3 although it will be appreciated that this will be included). Operation of the cell 1 shown in Fig. 3 will be the same as that described above in relation to Fig. 1, with some of the components being provided by a separate insert 100. Notably, the first electrode 10 as in Fig. 1 will be provided by the electrode 110 of the insert 100. The resistive element 40 will be held by the groove 152 of the insert 100, the fluid inlet 54 is provided by the aperture(s) in the flange 134, and some of the flange 134 / sealing region 122 provides a portion of the housing 50 of the cell 1. Another example of an electrode carrying insert 100 will now be described with reference to Fig. 4. Fig. 4 shows an electrode carrying insert 100. The insert 100 of Fig. 4 is similar to that described above in relation to Figs. 2 and 3, and so similar components will not be described again in detail. For the electrode carrying insert 100 described above in relation to Figs. 2 and 3, the electrode 110 may be providing by a single piece of electrically conductive material (e.g. one continuous block of material). For Fig. 4, the electrode 110 is formed of different portions, which have different properties. In Fig. 4, the electrode 110 comprises a first portion 111 and a second portion 112. For the electrode carrying insert 100 described above in relation to Figs. 2 and 3, the insert 100 may be configured for self-sealing. That is, the insert 100 of Figs. 2 and 3 is arranged to seal the opening 52 in the housing 50 itself in response to fluid being provided in the cell 1. For the insert 100 of Fig. 4, the insert 100 and housing 50 are configured to be coupled to each other, i.e. with the insert 100 coupled to the housing 50 to provide sealing of the internal volume 56. For this, a coupling element 96 and a sealing element 92 are shown in Fig. 4. Fig. 4 also shows an earthing element contact 157 and a lip 153. Also shown in Fig. 4 is a cavity 146, a securing region 144, a limiter 142 and a turbulent pipe 158. The first portion 111 of the electrode 110 is located distally of the second portion 112 of the electrode 110. The first portion 111 is to be located inside the housing 50. The distal tip of the electrode 110 will be provided by the distal end of the first portion 111. The cavity 146 is located in the distal region 121 of the body 120. At least a portion of the electrode 110 is housed within the cavity 146. The proximal end of the first portion 111 of the electrode 110 is housed within the cavity 146. The first portion 111 of the electrode 110 is electrically connected to the second portion 112 of the electrode 110. The connection may be in the cavity 146. For example, the second portion 112 may be attached to the first portion 111 in the cavity 146. The second portion 112 extends through the body 120 to the external portion 116 (e.g. where it is connected to a source of electrical energy). The second portion 112 of the electrode 110 may be thinner than the first portion 111. For example, the second portion 112 may be relatively thin (e.g. and wire-like) in comparison to the first portion 111. The first portion 111 may be much thicker. The first portion 111 may be provided by a bar of electrically conductive material. The second portion 112 may be provided by a portion of electrically conductive wire. The first portion 111 may be the portion of electrode 110 which is housed within the cavity 146 and which extends beyond the distal end of the body 120 (and the protective element 140) to the distal tip. The second portion 112 may the portion of electrode 110 which connects the electrical energy source (e.g. external portion 116) to the first portion 111 of the electrode 110. The second portion 112 may extend through the body 120. The second portion 112 of electrode 110 may be configured to have lower impedance and / or resistance than the first portion 111. The second portion 112 may be configured to provide greater heat dissipation and / or to generate less resistive heating than the first portion 111. For example, the second portion 112 may be configured to electrically connect the first portion 111 of the electrode 110, and in particular the distal tip of the electrode 110, to the source of electrically energy. By utilising a narrower configuration for the second portion 112, less heat may be generated within the body 120 which may avoid the need for cooling of the body 120 (and / or may prevent the body 120 from overheating). For example, the first portion 111 may be a rod or bar of electrically conductive material, such as a metal. The distal tip may comprise a material which is better capable of withstanding stress than a material of other portions of the electrode. For example, the distal tip may comprise Tungsten. The first portion 111 may be provided by two separate materials, e.g. the distal tip may be formed of one material (such as Tungsten) while the remainder of the first portion 111 may be formed of another material (such as stainless steel). This may reduce material costs by only using a more expensive material in the portion which will be immersed in the fluid in the cell (e.g. the distal tip). The second portion 112 of the electrode 110 may be provided by a braid. The second portion 112 may utilise a material selected to avoid overheating within the body 120. For example, the second portion 112 may be provided by a copper braid. The insert 100 and the housing 50 may be configured to be secured to each other. For this, the coupling element 96 may couple a portion of the insert 100 to a portion of the housing 50. The coupling element 96 may comprise a bolt or another attachment fixing element. The insert 100 may comprise an aperture through which the coupling element 96 is to be inserted. A portion of the housing 50 (the lip 53 in Fig. 4) may comprise an aperture through which the coupling element 96 is to be inserted. For example, the coupling element 96 may comprise a bolt which is to extend through the insert 100 and at least a portion of the housing 50. The bolt may be secured in place using one or more nuts. To help illustrate the different components included, in Fig. 4, the insert 100 is shown as not contacting the housing 50, but it will be appreciated that once suitably fastened, the two may be in contact with each other. In other words, the coupling element 96 is configured to selectively couple the insert 100 to the housing 50. The insert 100 and the housing 50 are arranged to be joined together using the coupling element 96. The coupling element 96 may provide a secure connection between the housing 50 and the insert 100 while reducing the stress inflicted upon the insert 100. The coupling element 96 may act to connect the insert 100 to the housing 50 to define the internal volume 56 of the cell 1. The sealing element 92 may be included to facilitate a tighter seal between insert 100 and housing 50. The sealing element 92 may comprise a mechanical sealing member, such as a gasket. For example, the sealing element 92 may comprise an o-ring. The sealing element 92 may be located between the surfaces of the insert 100 and the housing 50 which are brought together (e.g. by the coupling element 96). For example, the sealing element 92 may be compressed by the housing 50 and insert 100 in a gap between the two. In other words, the sealing element 92 is configured to facilitate a greater seal (e.g. a water-tight seal), thereby to ensure the internal volume 56 is sufficiently sealed. The earthing element 156 may have an extension for connecting to the housing 50. This is shown in Fig. 4 as the earthing element contact 157. For example, this may comprise an extension to the material which provides the earthing element 156. The material may extend in a direction towards the housing 50. The earthing element contact 157 may be configured to contact the lip 53 of the housing 50 (e.g. proximal to where the coupling element 96 is connected to the housing 50). The earthing element contact 157 is configured to electrically connect the housing 50 to the electrical earth point to which the earthing element 156 is connected. That way, the earthing element 156 may be configured to provide electrical earthing for the housing 50 of the cell 1. The first portion 111 of the electrode 110 may be received in the cavity 146. The cavity 146 may extend proximally from a distal end of the body 120. The protective element 140 (e.g. an electrical shroud) may be inserted into the distal end of the cavity 146 in the securing region 144. For example, the protective element 140 may be attached to an inside surface of the cavity 146, e.g. there may be a screw thread on the inner surface of the cavity wall for connecting the protective element 140 to the body 120 (e.g. screwing the protective element 140 into the body 120 to secure it thereto). The limiter 142 may comprise a piece of material extending radially outwardly from the protective element 140. The limiter 142 may be configured to abut the distal end of the body 120 (e.g. it may be wider than the cavity 146). The limiter 142 is configured to limit proximal movement of the protective element 140 into the cavity 146 beyond a threshold amount. For example, the limiter 142 may abut the distal end of the body 120 to inhibit further proximal movement of the protective element 140 into the cavity 146. The limiter 142 may be configured to limit the distal tip of the electrode 110 from being exposed by more than a threshold distance in the internal volume 56. The turbulent pipe 158 may comprise a portion of pipe which is sized and / or shaped to provide turbulent flow of liquid into the cell 1. For example, the pipe may be curved and / or it may include one or more internal obstructions / variations in its cross sectional shape which give rise to turbulent flow for liquid proceeding out of the end of the tube 155. In other words, the turbulent tube is arranged to provide a fluid inlet to the cell 1 which causes turbulent flow within the cell 1. Another example energy cell will now be described with reference to Fig. 5. Fig. 5 shows an energy cell 1. The energy cell 1 is similar to the cells described herein and shown in the other Figs., and so repeat aspects of the cell 1 of Fig. 5 will not be described again here. What is shown in particular in Fig. 5 relates to the selection of the exposed length of the first electrode 10 within the internal volume 56 of the cell 1. As shown in Fig. 5, a distal end of the first electrode 10 is exposed within the internal volume 56. As in the other examples described herein, the electrode 10 extends into the internal volume 56 from a proximal end of the housing 50. A body surrounds the electrode 10 along at least some of its length into the internal volume 56 from the proximal end of the housing 50. In the example of Fig. 5, the body is shown as being part of the housing 50, e.g. with the electrode member not provided as a separate insert for a housing (e.g. as in Figs. 2 to 4). However, it will be appreciated that the electrode member may be provided by a separate insert. Likewise, in Fig. 5, the body is shown as being tapered, but it need not be. As shown in Fig. 5, the cell 1 includes an electrode member. The electrode member comprises the electrode 10 as well as a body which surrounds the electrode 10 along the proximal end of the electrode 10 within the internal volume 56. A distal end 115 of the electrode 10 extends beyond a distal end of the body. In Fig. 5, the body comprises two different portions: (i) a distal portion 125, and (ii) a proximal portion 126. The proximal portion 126 is located in an internal volume 56 of the housing 50 towards the proximal end of the housing 50 (the bottom end shown in Fig. 5). The distal portion 125 is located distal to the proximal portion 126 within the internal volume 56 of the housing 50. The distal portion 125 may have one or more different properties to the proximal portion 126. In particular, the distal portion 125 may comprise a more thermally resistant material to the proximal portion 126. The proximal portion 126 may be thicker, e.g. have a larger cross-section (diameter) than the distal portion 125. The distal portion 125 may comprise an electrical shroud. The present inventors have identified that, by selecting the length of the distal end 115 of the electrode 10 which extends beyond the distal end of the body (the distal portion 125), it is possible to control which portions of the internal volume 56 and the housing 50 are heated. In particular, the present inventors have identified that the body which surrounds the electrode, e.g. the distal portion 125, will inhibit spraying of electrons therethrough. In other words, the body is configured to inhibit spraying of electrons from the portion of the electrode 10 which it surrounds into the internal volume 56. The distal end 115 of the electrode 10 is permitted to spray electrons into its surrounding environment (e.g. due to not being surrounded by the body). To demonstrate these different regions, two lines are shown dashed in Fig. 5. The first line 225 is a solid angle line which starts from the distal end 115 of the electrode 10 (e.g. from its perimeter), which passes through the distal end of the distal portion 125 of the body (e.g. from its perimeter), and which extends towards the housing 50 of the cell 1. The first line 225 intercepts an inner surface of the housing 50 at an interception point 227. As will be appreciated, a plane may be defined across the housing which represents the height at which each trajectory from the distal end 115 through the distal end of the distal portion 125 intercepts the housing 50. This is shown by the second line 226 in Fig. 5. The region above the first line 125 receives electrons sprayed from the distal end 115 during operation. In turn, as described above, this region will be subject to heating from this application of electrical energy to the electrode 10. The region below the first line 125 may not receive any (or at least not receive many) sprayed electrons, and so this region will be heated less during operation. As will be appreciated, radiative and conductive heat transfer will still occur for the liquid within the housing. As a result, the volume above the second line will be heated, even if below the first line 225. For lower regions within the internal volume 56, such as the region below the second line 226, there will be much less heating of that liquid, as well as the walls which surround it. The present inventors have identified that, by limiting the exposed length of the distal end 115 of the electrode 10 within the internal volume 56, a colder region may be provided at the proximal end of the internal volume 56. The portion of housing 50 which surrounds this colder region may also be subject to much lower heating. Likewise, the portion of the body (the proximal portion 126) which surrounds the electrode 10 in the colder region of the internal volume 56, as well as the proximal end of the housing 50, will be subject to much lower temperatures in operation. Selecting the exposed length of the distal end 115 of the electrode 10 to provide a colder region within the internal volume may several advantageous effects for the energy cell. Firstly, the proximal portion 126 of the body may be made from a less thermally resistant material than the distal portion 125 of the body. Such a material choice may enable lower cost materials to be used for some of the body, and in turn this may simplify manufacturing options for these components. Secondly, this may improve any securing of the proximal end of the housing to the side wall(s). For example, where the electrode member is an insert which seals an opening in the proximal end of the body (e.g. as described above in relation to Figs. 2 to 4), the connection which secures that insert to the walls of the housing may be more secure and durable when subject to lower temperatures. In other words, the length of the distal end 115 which is exposed within the internal volume 56 may be selected to provide a colder region within the internal volume 56. The colder region may encompass the volume of liquid adjacent to the proximal end of the housing. At least some of the material of the body within the colder region may be formed from a different material to the material of the body in the hotter region. The region where the proximal end of the housing is coupled to the side wall(s) of the housing may be located within the colder region. The distal portion 125 may comprise an electrical shroud. The distal portion 125 may be configured to provide a light block, e.g. it may be substantially opaque. The distal portion 125 may comprise a non-conductive electrical insulator. The distal portion may comprise alumina or a coloured quartz. The distal portion 125 may comprise a chemically resistive material. The proximal portion 125 may be non-porous. Although not shown in Fig. 5, a gap may be present between the electrode 10 and the distal portion 125 of the body. The gap may radially surround the electrode 10, e.g. so that it is interposed between the electrode 10 and the distal portion 125. For example, water and / or plasma may be in said gap in use. The proximal portion 126 may comprise a non-conductive electrical insulator. The proximal portion 126 may be chemically resistant. Any of the cells or electrode inserts disclosed herein may have a distal end having its exposed length selected for the reasons mentioned above. That is, the exposed distal end may have a length selected to provide a colder region within the internal volume 56. At least some of the material used for the housing and / or the electrode member (e.g. its body) may be different in the colder region to in the hotter region. For example, the body of the electrode member may have a more thermally resistant portion and a less thermally resistant portion. The more thermally resistant portion may be arranged for the distal portion of the body (e.g. which will be in the hotter region). Examples described above have generally related to the energy cell 1 shown in Fig. 1. However, it will be appreciated that the cell 1 of Fig. 1 should not be considered limiting. For example, the third electrode 30 need not be included, and / or the resistive element need not be included. For example, any suitable energy cell (such as the cells disclosed in GB 2604853) could be provided in combination with an electrode insert of the present disclosure. It will be appreciated from the discussion above that the examples shown in the figures are merely exemplary, and include features which may be generalised, removed or replaced as described herein and as set out in the claims. With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. In addition, the processing functionality may also be provided by devices which are supported by an electronic device. It will be appreciated however that the functionality need not be divided in this way, and should not be taken to imply any particular structure of hardware other than that described and claimed below. The function of one or more of the elements shown in the drawings may be further subdivided, and / or distributed throughout apparatus of the disclosure. In some examples the function of one or more elements shown in the drawings may be integrated into a single functional unit. 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. Other examples and variations of the disclosure will be apparent to the skilled addressee in the context of the present disclosure.

Claims

1. An electrode carrying insert for an energy cell, the insert comprising:a body having: a proximal region, a distal region, and a sealing region; andan electrode extending within the body from the proximal region to the distal region;wherein the insert is insertable into a housing of an energy cell with: the sealing region sealing an opening in the housing through which the body extends from the proximal region outside the housing to the distal region inside the housing, and the electrode configured to apply electrical energy to a fluid inside the housing to generate one or more bubbles of plasma therein;wherein the body comprises a channel arranged to provide an inlet for the energy cell;wherein said inlet is configured to couple an internal volume of the cell to a supply system such that the internal volume of the cell receives liquid from the supply system through the channel arranged to provide the inlet for the energy cell;wherein the distal region of the body comprises a member which surrounds the electrode, and wherein the member extends distally from the sealing region;wherein the member surrounds the electrode along some, but not all, of the length of the electrode within the housing;wherein a distal end of the electrode extends beyond a distal end of the member; and further comprising a protective element arranged to at least partially surround the distal end of the electrode.

2. An energy cell comprising:a housing having an opening therein; andan electrode carrier comprising: (i) a body having: a proximal region, a distal region, and a sealing region, and (ii) an electrode within the body;wherein the electrode carrier is coupled to the housing with the sealing region of the electrode carrier sealing the opening in the housing, and with the distal region of the body inside the housing and the proximal region of the body outside the housing;wherein the electrode extends within the body from the proximal region to the distal region and is configured to apply electrical energy to a fluid inside the housing to generate one or more bubbles of plasma therein;wherein the body comprises a channel arranged to provide an inlet for the energy cell;wherein said inlet is configured to couple an internal volume of the cell to a supply system such that the internal volume of the cell receives liquid from the supply system through the channel arranged to provide the inlet for the energy cell;wherein the distal region of the body comprises a member which surrounds the electrode, and wherein the member extends distally from the sealing region;wherein the member surrounds the electrode along some, but not all, of the length of the electrode within the housing;wherein a distal end of the electrode extends beyond a distal end of the member; and further comprising a protective element arranged to at least partially surround the distal end of the electrode.

3. The apparatus of any preceding claim, further comprising at least one aperture in the body, wherein said at least one aperture is arranged to provide the channel.

4. The apparatus of any preceding claim, wherein the body comprises a flange, and wherein the channel is provided in the flange.

5. The apparatus of claim 4, wherein the sealing region comprises the flange.

6. The apparatus of claim 4 or 5, wherein the channel is provided by an apertureextending from a proximal side of the flange to a distal side of the flange.

7. The apparatus of any of claims 4 to 6, wherein the channel is provided in a portion of the flange located radially outward from the distal region.

8. The apparatus of any preceding claim, wherein the protective element is coupled to the distal end of the member.

9. The apparatus of any preceding claim, wherein the member is narrower at its distal end than at its proximal end.

10. The apparatus of claim 4, or any claim dependent thereon, wherein the flange is larger than the opening in the housing and arranged to completely circumscribe said opening.

11. The apparatus of claim 4, or any claim dependent thereon, wherein a proximal end of the member is coupled to the flange, and wherein the flange surrounds the proximal end of the member.

12. The apparatus of claim 11, wherein the channel is provided by at least one aperture in the region of the flange which surrounds the proximal end of the member.

13. The apparatus of any preceding claim, where a distal end of the electrode extends beyond a distal end of the body.

14. The apparatus of any preceding claim, wherein the body comprises a plurality of channels, thereby to provide a plurality of inlets to the energy cell.

15. The apparatus of claim 14, wherein a plurality of apertures are provided within the body to provide the plurality of channels.

16. The apparatus of claim 14 or 15, wherein the channels are distributed uniformly around the body.

17. The apparatus of any of claims 14 to 16, as dependent upon claim 4, or any claim dependent thereon, wherein the plurality of channels are provided in the flange of the body, and wherein the channels are distributed uniformly around the flange.

18. The apparatus of any preceding claim, wherein the inlet is arranged to provide turbulent and / or vortical flow of liquid into the internal volume of the vessel.

19. The apparatus of any preceding claim, wherein the channel follows an at least partially curved path.

20. The apparatus of any preceding claim, wherein the body comprises a one-piece structure.

21. The apparatus of any preceding claim, wherein the different regions of the body are provided by a single piece of material.

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