Patent Description:
Typically, the generation of power and/or heating may involve combustion of some sort of fuel. For instance, fossil fuels may be used in a combustion process which heats water to generate steam and/or hot water. Steam may be generated to be used for driving a turbine, and this in turn may be used to generate electricity. Hot water may be generated to be used in heating systems, where that hot water is circulated throughout a building to provide heating to that building. Electricity could also be used to generate warm water, such as in an electric boiler. It may be desirable to provide increased efficiency for such generation of power and/or heating. <CIT> discloses an arc-hydrolysis steam generator apparatus and method. <CIT> discloses electrical power generation systems and methods regarding the same.

Aspects of the invention are set out in the independent claims and optional features are set out in the dependent claims. Aspects of the invention 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 a heating system comprising: a liquid supply system; a cell configured to: receive liquid from the liquid supply system, provide heating thereof, and output heated fluid; a work extraction system configured to extract useable work from heated fluid output from the cell. The cell comprises: (i) a housing arranged to define an internal portion for receiving liquid to be heated, and (ii) a plurality of electrodes configured to apply electrical energy to fluid in the internal portion. The electrodes are configured to apply electrical energy to said fluid in the internal portion to generate one or more bubbles of plasma for releasing energy into said fluid in the internal portion and the housing to provide heating of the fluid in the internal portion.

Embodiments may enable the provision of a high exergy heated fluid from which work is extracted. Work may be extracted from this high exergy heated fluid to provide heating and/or power generation. Embodiments may provide an efficient system for generating heat and/or power. The cell may comprise a plasma cell (e.g. a plasma-generating fuel cell).

The system further comprises a controller configured to: (i) receive a signal indicative of at least one operational parameter of the cell, and (ii) control operation of the heating system based on said operational parameter. The controller may be configured to control operation of the heating system so that heat and/or plasma generation in the cell is above a threshold level. Controlling operation of the heating system may comprise controlling at least one of: (i) the supply of liquid to the cell by the liquid supply system, and (ii) the electrical energy applied by the electrodes. The controller may be configured to control operation to keep at least one operational parameter for the cell within a selected range (e.g. to provide a selected level of performance for the cell).

The controller may be configured to control the supply of liquid to the cell and/or the electrical energy applied by the electrodes based on an obtained indication of demand for heating to be provided by the cell. In the event that the obtained indication of demand indicates increased demand for heating to be provided by the cell, the controller may be configured to increase at least one of: (i) the temperature of liquid supplied to cell, (ii) the pressure of liquid supplied to the cell, (iii) the amount of liquid supplied to the cell, and (iv) the amount of electrical energy applied by the electrodes. For example, controlling such operation may facilitate an increase in the output of the cell (e.g. to provide more heated fluid and/or plasma generation within the cell).

The signal indicative of at least one operational parameter may comprise an indication of a quality and/or quantity of plasma generation within the cell. The controller may be configured to control operation of the heating system so that the quality and/or quantity of plasma generation remains within a selected range. For example, the controller may be configured to provide at least a threshold amount of plasma generation. This threshold amount/selected range for plasma generation may be selected so that sufficient plasma generation is occurring to provide selected heating characteristics for the heating system (e.g. so that the amount of heated fluid generated is within a selected range).

The signal indicative of a quality and/or quantity of plasma generation may comprise an indication of at least one of: (i) a pressure and/or temperature of fluid output from the cell, (ii) an amount and/or type of electromagnetic energy present within the cell, (iii) chatter associated with supply of power to one or more of the electrodes, (iv) a current flow and/or voltage associated with one or more of the electrodes, and (v) fluid flow dynamics within the cell. For example, higher pressures and/or temperatures (e.g. for fluid output from the cell) may indicate increased plasma generation. Likewise, a higher rate of increase for pressure/temperature may indicate greater plasma generation. For example, an increase in any of: electromagnetic activity within the cell, and/or chatter associated with the supply of power may provide an indication of increased plasma generation. For example, sudden changes in current or voltage may provide an indication of any change in plasma generation. Where current begins to increase, this may provide an indication of arcing being about to occur. According to the invention the controller is configured to reduce, or stop, the application of voltage to the first electrode in the event that a change in current exceeds a threshold value (or a rate of change of current exceeds a threshold), e.g. if the current is increasing too much. For example, voltage may be monitored to identify any drops in voltage, e.g. in response to arcing providing decreased resistance to current flow. For example, an indication of increased turbulence for fluid flow within the cell may provide an indication of increased plasma generation.

The controller may be configured to control at least one of: (i) the supply of liquid to the cell based on the electrical energy to be applied by the plurality of electrodes, and (ii) the electrical energy to be applied by the plurality of electrodes based on the supply of liquid to the cell. For example, when increasing the supply of liquid and/or electrical energy, the controller may control the supply of electrical energy/liquid (respectively) in accordance with the change to supply of the other. The change in supply of one may be selected based on the change of supply to the other (e.g. the increase/decrease in one may be selected in proportion to the increase/decrease in supply of the other). The signal indicative of at least one operational parameter may comprise an indication of a temperature associated with at least one of: the cell, the fluid in the cell, and the fluid output from the cell. The controller may be configured to control at least one of: (i) the electrical energy applied by the electrodes, (ii) the supply of liquid to the cell, and (iii) an external heater, to increase the temperature of the cell, the fluid in the cell, and/or the fluid output from the cell in the event that the indication of temperature is below a threshold level. The controller may be configured to increase the electrical energy applied by the electrodes to provide increased heating and/or decrease the flow rate of liquid through the cell in the event that the indication of temperature is below the threshold level.

An internal surface of the housing of the cell may comprise an electromagnetic energy-absorbing material arranged to convert incident photons into heat. At least a portion of the housing may be conductive. For example, the internal surface of the housing may be configured to generate heat in response to photons being incident on said surface. The housing (e.g. its internal surface) may be configured to heat the fluid within the internal portion in response to generating heat from incident photons (e.g. and/or other particles such aselectrons). The housing may be configured to provide conductive heating of the fluid within the internal portion. The housing may be made of metal, e.g. the housing may be made of steel. The housing may be formed of a plurality of different materials. One or more layers or sleeves may be provided to the housing. For example, the cell may include a sleeve located in the internal portion within the housing. The sleeve may be arranged to fit within the internal portion (e.g. it may sit adjacent to the internal portion of the housing). A plurality of such sleeves may be provided. Each sleeve may be arranged to provide different absorption/conduction properties to other regions of the housing/cell. For example, the housing may be made of a first material (e.g. steel), and a sleeve made of a second material (e.g. aluminium) may be inserted within the housing. The housing and/or sleeve may include a coating to further facilitate absorption and/or conduction. For example, a gold coating may be applied.

The liquid supply system may be configured to supply liquid to the cell under pressure. The cell may be arranged to retain fluid in the housing under pressure. For example, the housing may comprise one or more compression devices configured to retain the internal portion of the housing under pressure, and/or the housing may be sufficiently rigid to resist expansion under the pressure applied from inside the internal portion. The liquid supply system may be configured to heat liquid prior to supplying it to the cell. The liquid supply system may be configured to increase heating of liquid prior to supplying it to the cell in the event that heat and/or plasma generation of the cell is below a threshold level. The system may be arranged to provide a variable continuous supply of liquid to the cell.

The plurality of electrodes may comprise: (i) an anode arranged to provide a conductive path for current to be applied to fluid in the internal portion, and (ii) a cathode arranged to provide a conductive path away from the internal portion for current received from the anode through the fluid in the internal portion. The plurality of electrodes may further comprise a balancing electrode arranged to provide an additional conductive path towards or away from fluid in the internal portion. The anode and cathode (and e.g. balancing electrode) may be arranged concentrically with each other. The anode, cathode and balancing electrode may have the same coefficient of thermal expansion. The balancing electrode may be arranged away from the conductive path between the anode and the cathode. For example, the conductive path from the anode to the cathode may be radially outward. The balancing electrode may be offset from anode/cathode in a different direction (e.g. along a longitudinal axis). The balancing electrode may be closer to the anode than the cathode is. For example, the balancing electrode may run substantially perpendicular (e.g. perpendicular) to the current path from anode to cathode (e.g. it may be parallel to the anode).

The cell may comprise a resistive element arranged between the anode and cathode, for example the resistive element may comprise quartz or a bora-silicate glass material (e.g. a high resistance material which can withstand high temperatures and/or pressures). The resistive element may be of sufficient electrical resistance so that it may act as an electrical insulator. The resistive element may be arranged between on the conductive path between anode and cathode, e.g. to provide increased electrical resistance between anode and cathode. For example, the resistive element may be located radially outward from the anode, and radially inward from the cathode (e.g. where the conductive path from anode to cathode extends radially outward).

The system may be configured to provide additional heating to one or more components of the cell (e.g. during a start-up mode). The cell may comprise a heating element to provide such heating. For example, a heater may be located adjacent to the cell, and/or a heating element may be integrated within a part of the cell. A heater may be included in an end cap of the cell (e.g. a cartridge heater may be provided within an end cap of the cell). In some examples, this heating may be provided by a resistive heating element. The resistive heating element may be a part of the cell (e.g. voltage may be applied to a component such as anode or resistive element to provide resistive heating, or to an additional resistive heating element or region of the cell). Such heating may be provided to increase the temperature associated with at least one of: the cell, fluid inside the cell, and fluid output from the cell to the point where the plasma is stimulated. For example, heating may be provided until bubbles being to appear (e.g. gas bubbles).

The liquid supply system may be configured to supply a fluid to the cell, such as water, which at least partially exhibits non-Newtonian nature under circumstances to be expected within the cell. For example, wherein the liquid is configured to resist rapid expansion of plasma within the cell. The system may further comprise a filter apparatus configured to filter fluid output from the cell. The work extraction system may comprise at least one of: (i) a regulator for mass transfer of hot and/or pressurised fluid, (ii) a heat exchanger for transfer of heat to a working fluid, and (iii) a power generation system such as a steam-based power generation system. The heated fluid generated by the cell may itself be used for subsequent applications, or may instead be used for heating one or more other fluids for subsequent applications. For example, heated fluid generated by the cell may be used as a working fluid or heated fluid generated by the cell may be used to heat a separate fluid, which may then be used as a working fluid. The system may comprise a DC voltage source operable to apply a DC voltage to each of the electrodes.

In an aspect, there is provided a system comprising: a cell configured to heat liquid provided thereto, the cell comprising: an inlet for receiving a liquid to be heated, and an outlet for outputting heated fluid; a power management system configured to control application of electrical energy to the cell to control the heating of fluid in the cell; a work extraction system coupled to the outlet and configured to extract useable work from heated fluid output from the cell; and a fluid management system coupled to the inlet of the cell, and configured to: (i) supply liquid to be heated to the cell, and (ii) process heated fluid which has been output by the cell and used by the work extraction system.

The cell may comprise a cell as disclosed herein. The work extraction system may comprise a work extraction system as disclosed herein. The fluid management system may comprise a liquid supply system as disclosed herein, e.g. for supplying liquid to be heated to the cell.

The fluid management system may comprise: (i) a liquid supply coupling for coupling the system to a supply of liquid to be heated, and (ii) a drain coupling for discarding heated fluid which has been output by the cell and used by the work extraction system. The fluid management system may comprise a pump coupled to the liquid supply coupling and the inlet of the cell, wherein the pump is operable to supply liquid to the cell under pressure. The work extraction system may comprise a heat engine. The outlet of the cell may be coupled to a first engine inlet to enable heated fluid output from the cell to drive the engine. The heat engine may be coupled to a generator configured to generate power in response to driving of the engine. The outlet of the cell may also be coupled to a first heat exchanger. A first engine outlet may be coupled to the first heat exchanger so that heated fluid from the cell which has passed through the engine is directed to the first heat exchanger for heating. The first heat exchanger may be coupled to a second engine inlet to enable reheated fluid from the heat exchanger to further drive the engine. The engine may be arranged to be driven at a different ratio for fluid entering through the first and second engine inlets. At least one of the engine and the first heat exchanger may be coupled to a second heat exchanger configured for further extracting heat from the heated fluid output from the cell.

The fluid management system may comprise a filter for filtering heated fluid which output from the cell. The work extraction system may comprise at least one of: a heat management system configured to receive heated fluid which has been output from the cell, and to use said heated fluid as a heat source or in a heat exchanger; and a power generation system configured to receive heated fluid which has been output from the cell, and to use said heated fluid to generate power. The power generation system may be coupled to the power management system to provide generated power thereto. The power management system may comprise an external coupling for coupling to an external source of power. The power management system may be configured to receive power from the external source and/or provide power generated by the power generation system to the external source.

In an aspect, there is provided a method of providing a heated fluid for extracting useable work therefrom, the method comprising: supplying a liquid to be heated to a cell, wherein the cell comprises: (i) a housing arranged to define an internal portion for receiving the liquid to be heated, and (ii) a plurality of electrodes configured to apply electrical energy to fluid in the internal portion; controlling operation of the plurality of electrodes to apply electrical energy to fluid in the internal portion to generate one or more bubbles of plasma; generating heat in the housing proximal to the internal portion in response to the housing receiving incident photons (e.g. and also electrons) associated with plasma bubbles in the internal portion; using the housing to conductively heat fluid in the internal portion.

In an aspect, there is provided a method of controlling operation of a heating system, the heating system comprising a cell comprising: (i) a housing arranged to define an internal portion for receiving liquid to be heated, and (ii) a plurality of electrodes configured to apply electrical energy to fluid in the internal portion, the method comprising: controlling operation of the electrodes to apply electrical energy to fluid in the internal portion to generate one or more bubbles of plasma for releasing energy from the plasma into the fluid in the internal portion and the housing to provide heating of the fluid in the internal portion, wherein controlling operation of the electrodes comprises: receiving a signal indicative of at least one operational parameter associated with the cell and/or a fluid associated therewith; operating in a 'cold-start' mode when the operational parameter indicates heating and/or plasma generation is below a threshold level; and operating in a 'normal' mode when the operational parameter indicates heating and/or plasma generation is above the threshold level; wherein operating in the cold-start mode comprises controlling at least one of: (i) the electrical energy applied by the electrodes, (ii) supply of liquid to the cell, and (iii) operation of an external heater, to increase the temperature of the cell and/or the fluid associated therewith in the event that the operational parameter indicates heating and/or plasma generation is below a threshold level.

Aspects of the present invention may also provide one or more computer program products comprising computer program instructions configured to control a processor to perform any of the methods disclosed herein.

Some examples of the present invention will now be described, by way of example only, with reference to the figures, in which:.

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

Embodiments of the present invention are directed to systems for generating heat and/or power. Such systems may provide heating of a liquid to produce a heated fluid. The heated fluid may then be used for heating purposes and/or for power generation purposes. To generate the heated fluid, liquid may be supplied to a cell. Electrical energy may be applied to liquid held in the cell via one or more electrodes of the cell. The application of this electrical energy to the fluid within the cell causes gas bubbles within the cell to form plasma bubbles. Each bubble of plasma will be a localised region having a higher pressure/temperature than its surrounding fluid. The surrounding fluid may limit expansion of the plasma bubbles so that, as electrical energy is still applied, these bubbles will emit electromagnetic energy. For example, photons may be emitted from atoms (or molecules) within the plasma bubbles. In turn, these emitted photons may heat up the substance on which they are incident. For instance, this may provide heating of the housing of the cell and/or fluid within the cell. In turn, this enables the cell to output a heated fluid for using in a heating and/or power generation system <NUM>. The heated fluid may contain liquid and/or gas, and in some cases, the heated fluid may also contain some plasmatic materials.

An exemplary heating system will now be described with reference to <FIG>.

<FIG> shows a schematic diagram of a heating system <NUM>. The heating system <NUM> includes a liquid supply system <NUM>, a cell <NUM> and a work extraction system <NUM>. The cell <NUM> includes a fluid inlet <NUM> and a fluid outlet <NUM>. The cell <NUM> has a housing <NUM> which defines an internal portion <NUM> of the cell <NUM>. The cell <NUM> also includes a plurality of electrodes, which, as shown, includes a first electrode <NUM> and a second electrode <NUM>. The cell <NUM> may comprise a plasma cell (e.g. a plasma-generating fuel cell).

The housing <NUM> of the cell <NUM> encapsulates the internal portion <NUM>. The fluid inlet <NUM> provides a flow path for fluid into the internal portion <NUM> of the cell <NUM>. The fluid outlet <NUM> provides a flow path for fluid out from the internal portion <NUM> of the cell <NUM>. The internal portion <NUM> of the cell <NUM> may otherwise be sealed by the housing <NUM>. The liquid supply system <NUM> is coupled to the fluid inlet <NUM> of the cell <NUM>. The work extraction system <NUM> is coupled to the fluid outlet <NUM> of the cell <NUM>. The couplings between the liquid supply system <NUM> and the fluid inlet <NUM>, and the work extraction system <NUM> and the fluid outlet <NUM> are shown as an annular flow path. However, it will be appreciated that this is purely for illustrative purposes, and any suitable flow path may be provided). Also, although not shown in the Figs. , the work extraction system <NUM> may also be coupled to the liquid supply system <NUM> (e.g. to facilitate heating and/or pressurising of liquid to be supplied to the internal portion <NUM>).

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

A first end of the first electrode <NUM> is located outside the internal portion <NUM> of the housing <NUM>. A second end of the first electrode <NUM>, distal to the first end, is located within the internal portion <NUM> of the housing <NUM>. The second electrode <NUM> may extend along some, or all, of the length of the internal portion <NUM> of the housing <NUM>. At least one end of the second electrode <NUM> may extend out of the internal portion <NUM> of the cell <NUM>. Although not shown in <FIG> the first and/or second electrode <NUM> may each be coupled to a power supply. For example, each electrode may have one end which extends outside the internal portion <NUM> (e.g. into the housing <NUM>), and this end may be coupled to the power supply. In some examples, the housing <NUM> may provide a ground, and the first electrode <NUM> may be connected to a positive terminal of the power supply.

The housing <NUM> may be cylindrical. The fluid inlet <NUM> is arranged at an opposite end of the housing <NUM> to the fluid outlet <NUM>. The first and second electrode <NUM> extend along an axis extending from the fluid inlet <NUM> to the fluid outlet <NUM> (e.g. a longitudinal axis of the cell <NUM>). The fluid outlet <NUM> may be arranged vertically higher (e.g. above, such as directly above) the fluid inlet <NUM>.

The liquid supply system <NUM> is arranged to supply liquid to the cell <NUM>. Liquid may be provided into the cell <NUM> through the fluid inlet <NUM>. The liquid supply system <NUM> may comprise a coupling to a liquid supply, such as a reservoir of liquid. The liquid supply system <NUM> is configured to control delivery of this liquid to the cell <NUM>. For example, the liquid to be supplied may comprise partly or wholly a fluid which exhibits non-Newtonian behaviour in the environment of the cell <NUM>. The liquid may be water or an aqueous solution.

The work extraction system <NUM> is arranged to receive heated fluid from the cell <NUM>. Heated fluid may be output from the cell <NUM> through the fluid outlet <NUM>. The heated fluid may comprise liquid and/or gas. For example, this may be a combination of gas and liquid - e.g. steam with some water droplets. The fluid outlet <NUM> is arranged to enable flow of this heated fluid out from the cell <NUM> to be used by the work extraction system <NUM>. For example, steam created within the cell <NUM> may rise up and out through the fluid outlet <NUM>. The work extraction system <NUM> is configured to utilise the heated fluid output from the cell <NUM>. The work extraction system <NUM> may be configured to receive this heated fluid, and to use this as part of a supply of heated fluid (e.g. for heating purposes). The work extraction system <NUM> may be configured to receive this heated fluid, and to use this heated fluid for generation of power. For example, this heated fluid may be used to drive a generator, e.g. through use of a steam engine.

The housing <NUM> is configured to encapsulate the internal portion <NUM>. The housing <NUM> is arranged to define the internal portion <NUM> to provide a region in which liquid may be heated. An internal surface of the housing <NUM> (e.g. which faces/defines the internal portion <NUM>) may be configured to generate heat in response to incident photons (for example, the housing <NUM> may be conductive). The internal surface may comprise the region of the housing <NUM> which lies adjacent to the internal portion <NUM>. This may comprise part of the housing <NUM> and/or it may comprise an additional component, such as a layer/film provided there to generate heat in response to incident photons. For example, the internal surface may be configured to absorb electromagnetic energy, such as in the form of visible light. The internal surface is configured to heat up as it receives incident photons. The internal surface is configured to provide heating of fluid within the internal portion <NUM>, e.g. as it heats up from incident photons. The housing <NUM> may be made of a metal, such as steel. The housing <NUM> is configured to retain fluid in the internal portion <NUM> under pressure.

The fluid inlet <NUM>, the internal portion <NUM>, and the fluid outlet <NUM> are arranged to define a flow path for fluid to flow through the internal portion <NUM> of the housing <NUM>. The internal portion <NUM> is arranged to receive liquid to be heated through the fluid inlet <NUM>. The cell <NUM> is arranged to heat this liquid in the internal portion <NUM> to provide a heated fluid. The fluid outlet <NUM> is arranged to provide a flow path for this heated fluid away from the internal portion <NUM>.

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

In operation, the liquid supply system <NUM> supplies a liquid through the fluid inlet <NUM> and into the internal portion <NUM> of the cell <NUM>. In this example, the liquid will be water, but other liquids may be used. The liquid supply system <NUM> operates to supply water to the cell <NUM> so that the cell <NUM> fills up with water. Any gas previously in the cell <NUM> may be forced out through the fluid outlet <NUM> of the cell <NUM>. The cell <NUM> may then be substantially filled with water.

A voltage is applied to the first electrode <NUM> (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. I<NUM>R heating). This process of resistive heating continues as a voltage is applied to the first electrode <NUM>. As the temperature of the water within the internal portion <NUM> rises, microbubbles of gas will start to form within the water in the internal portion <NUM>. These may be steam bubbles forming or bubbles of air being released which were trapped in the water supplied to the internal portion <NUM> of the cell <NUM>. As a result, some pockets of gas will develop within the liquid in the internal portion <NUM> of the cell <NUM>. With continued application of the voltage to the first electrode <NUM>, bubbles of plasma will be generated within the internal portion <NUM> of the housing <NUM>. These bubbles will release energy into the surrounding fluid and the internal surface of the housing <NUM>. In turn this provides heating of the fluid within the internal portion <NUM>.

Without wishing to be bound by theory, by applying the voltage to the first electrode <NUM>, this will charge up the capacitor provided by the first and second electrode <NUM>. As the fluid within the internal portion <NUM> heats up, its permittivity may change, and this may change a capacitance of the cell <NUM> (e.g. between the first and second electrodes <NUM>, <NUM>). For example, when water is used, its permittivity will decrease as it heats up (and then also when it becomes steam). In particular, where microbubbles of gas (e.g. steam) begin to form within the liquid in the internal portion <NUM>, 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 <NUM> (e.g. the capacitance per unit volume in those bubbles may be <NUM>/<NUM>th of that of the surrounding water). During this process, the volumetric energy density for fluid and/or plasma within the internal portion <NUM> 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=<NUM>/<NUM> CV<NUM>). For examples where water is used, the voltage per meter will rise by a factor of approximately √<NUM>.

Without wishing to be bound by theory, with electrical energy still being applied to the first electrode <NUM>, these microbubbles of gas (at lower density than surrounding liquid) will try to rapidly expand into their surroundings. However, the surrounding liquid will resist this expansion, e.g. due to the non-Newtonian nature of the liquid in these conditions. This will cause the microbubbles to rapidly increase in temperature and pressure. In turn, their capacitance will further decrease (e.g. causing an increased dV/dr), thereby giving rise to further increased voltage stress across the bubble. With sufficient voltage stress across the bubble, ionization may occur leading to the formation of plasma within the bubble. Thus, one or more plasma bubbles may form in the liquid in the internal portion <NUM>. The plasma may be at an even lower density than the gas, and so with a voltage still applied to the first electrode <NUM>, 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 portion <NUM> of the cell <NUM>. 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 <NUM>.

Without wishing to be bound by theory, to accommodate this high level of energy within the plasma bubble, 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 portion <NUM>).

Without wishing to be bound by theory, 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 occurs in the visible light spectrum.

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

This heated fluid then passes through the fluid outlet <NUM>. Typically, the heated fluid is in the form of steam, which is generated within the internal portion, and which rises up and out through the fluid outlet <NUM>. The heated fluid is then used in the work extraction system <NUM> to extract useable work from the heated fluid. For instance, this heated fluid may be used for power generation and/or heat distribution.

Further examples of the present invention will now be described with reference to <FIG>.

<FIG> shows a schematic diagram of a heating system <NUM>. As with <FIG>, the heating system <NUM> of <FIG> includes a liquid supply system <NUM>, a cell <NUM> and a work extraction system <NUM>. These components of the heating system <NUM> of <FIG> are similar to those of <FIG>, e.g. features of the heating system <NUM> of <FIG> could be used in combination with features of the heating system <NUM> of <FIG>.

The liquid supply system <NUM> may additionally include a liquid reservoir <NUM>, a heater <NUM> and a pump <NUM>. The cell <NUM> includes fluid inlet <NUM>, fluid outlet <NUM>, and housing <NUM> which defines an internal portion <NUM>. The cell <NUM> includes first electrode <NUM> and second electrode <NUM>. Also, as shown in <FIG>, the cell <NUM> may include a third electrode <NUM> and a resistive element <NUM>. The cell <NUM> may comprise a plasma cell (e.g. a plasma-generating fuel cell).

The heating system <NUM> may also include a power supply <NUM> and a controller <NUM>. A plurality of sensors are shown by black circles to illustrate possible sensing capabilities of the system <NUM>. The sensors shown include a power supply sensor <NUM>, a fluid inlet sensor <NUM>, a first electrode sensor <NUM>, a second electrode sensor <NUM>, and third electrode sensor <NUM>, a fluid outlet sensor <NUM>, and an internal portion sensor <NUM>.

The liquid supply system <NUM> may couple the liquid reservoir <NUM> to the fluid inlet <NUM> of the cell <NUM>. The liquid reservoir <NUM> may be coupled to the fluid inlet <NUM> via the pump <NUM> and/or the heater <NUM> (both are shown in <FIG>). The liquid supply system <NUM> is configured to provide liquid to the internal portion <NUM> of the cell <NUM>. The liquid supply system may supply liquid from a source of liquid, such as the liquid reservoir <NUM> shown in <FIG>, or it may comprise a coupling to a liquid supply, e.g. a mains water supply, for supplying liquid.

The first and second electrode <NUM> may be arranged within the cell <NUM> as described above with reference to <FIG>. Additionally, the third electrode <NUM> is also provided in the internal portion <NUM> of the cell <NUM>. The third electrode <NUM> is optional, and may or may not be included. When included, a first end of the third electrode <NUM> may be located outside the internal portion <NUM>, and the third electrode <NUM> may extend form the first end to a second end located within the internal portion <NUM>. The second end of the third electrode <NUM> may be located proximal to the second end of the first electrode <NUM> within the internal portion <NUM>. The first and third electrodes <NUM>, <NUM> may be parallel (e.g. they may be co-axial). The second and third electrodes <NUM>, <NUM> may be parallel (e.g. coaxial). The first electrode <NUM> may extend from outside a first end of the housing <NUM> into the internal portion <NUM> towards an opposite end of the housing <NUM>. The third electrode <NUM> may extend from outside the opposite end of the housing <NUM> into the internal portion <NUM> towards the first end. The first and third electrodes <NUM>, <NUM> may extend into the internal portion <NUM> so that there is no spatial overlap between these electrodes <NUM>, <NUM> (e.g. their respective second ends do not touch/overlap). The second electrode <NUM> may extend along the length of the internal portion <NUM> from at or outside the first end to at or outside the opposite end. The distance between the second end of the first electrode <NUM> and the second end of the third electrode <NUM> may be less than the smallest distance between the first electrode <NUM> and the second electrode <NUM>. The third electrode <NUM> may be located away from an expected current path between the first and second electrode <NUM>.

A resistive element <NUM> may also be included in the internal portion <NUM>. The resistive element <NUM> may also be cylindrical. The resistive element <NUM> may be arranged to increase the electrical resistance of the conductive path between the first electrode <NUM> (anode) and the second electrode <NUM> (cathode). The resistive element <NUM> may extend around a majority of the internal portion <NUM> (e.g. along a length and width of the internal portion to impede the majority of possible conductive paths from anode to cathode). The resistive element <NUM> may be located between the first/third and second electrodes <NUM>, <NUM>. For example, the resistive element <NUM> may be located radially outward from the first/third electrodes <NUM>, <NUM>, but not as far radially outward than the second electrode <NUM>. The resistive element <NUM> may extend along some or all of the length of the internal portion <NUM>. The resistive element <NUM> may be arranged on a current flow path between the first electrode <NUM> and the second electrode <NUM>, e.g. so that current would need to flow through the resistive element <NUM> to get from the first electrode <NUM> to the second electrode <NUM>. The resistive element <NUM> may extend along one or both of the ends of the internal portion <NUM> (e.g. to reduce the likelihood of a conductive path from anode to cathode not via the resistive element <NUM> being possible).

The power supply <NUM> may comprise a DC supply (e.g. there may be an AC to DC converter for providing DC). The power supply <NUM> may be coupled to one or more components of the heating system <NUM>. <FIG> illustrates a number of these possible couplings with solid lines. For example, these may comprise some form of conductor to provide a conductive coupling from the power supply <NUM> to said component. The power supply <NUM> may be coupled to the first electrode <NUM>, and/or any of the second electrode <NUM>, or third electrode <NUM>. The cell <NUM> may also include a heater, such as a resistive heater (e.g. a cartridge heater). The power supply may also be coupled to the heater. The power supply <NUM> could be coupled to the resistive element <NUM> (e.g. to provide resistive heating), as shown in <FIG>. However, it is to be appreciated that the resistive element need not be coupled to the power supply. Instead, it may be included only to increase resistance between first and second electrodes <NUM>, <NUM>.

The controller <NUM> may be coupled to each of the sensors. The controller <NUM> may also be coupled to one or more of the power supply <NUM>, the heater <NUM> and the pump <NUM>. <FIG> illustrates these couplings with dashed lines. These couplings may be wired or wireless.

The liquid supply system <NUM> is configured to supply liquid to the internal portion <NUM> of the cell <NUM>. The controller <NUM> may be configured to control operation of the liquid supply system <NUM>. For example, the liquid supply system <NUM> may selectively heat (using the heater <NUM>) and/or pressurise (using the pump <NUM>) liquid from the liquid reservoir <NUM> which is to be provided to the internal portion <NUM> of the cell <NUM>. The controller <NUM> may be configured to control operation of the heater <NUM> and/or pump <NUM> to control the temperature and/or pressure of the liquid supplied to the cell <NUM>.

The power supply <NUM> may be configured to apply a voltage to the first electrode <NUM> (e.g. to provide the operation described above with reference to <FIG>). The power supply <NUM> may also be configured to apply a voltage to the third electrode <NUM> (and/or e.g. a heater of the cell <NUM>). The power supply <NUM> may also be coupled to the second electrode <NUM> to receive a current carried away therefrom. The power supply <NUM> may be configured to selectively apply a voltage, e.g. using high voltage DC. The controller <NUM> may be configured to control operation of the power supply <NUM>. For example, the controller <NUM> may be configured to control at least one of: a magnitude of voltage applied by the power supply <NUM>, timing for the voltage supply, and/or the components to which voltage is being applied.

The third electrode <NUM> may be active or passive. When active, a voltage is applied to the third electrode <NUM>. When passive, the third electrode <NUM> may be conductive for receiving current within the internal portion <NUM>, but without receiving power from the power supply <NUM>. The third electrode <NUM> may be configured to provide a balancing electrode (e.g. it may be arranged to balance electric field/current generated within the internal portion <NUM>). The controller <NUM> may be configured to control operation of the power supply <NUM> to selectively control whether (and/or how much) voltage is applied to the third electrode <NUM>.

The resistive element <NUM> may be configured to be of relatively high resistance (e.g. as compared to the resistance of the electrodes and/or fluid within the internal portion <NUM>). The resistive element <NUM> may be of sufficient resistance to effectively provide an electrical insulator (between the anode and cathode).

In examples, the cell includes a heater configured to provide heating in response to application of a voltage thereto, e.g. to provide resistive (I<NUM>R) heating. The heater could be a region of the housing, or a separate component configured to provide resistive heating (e.g. which may be integrated into a part of the housing, such as an end cap). The heater could be arranged to provide heating of the fluid in the internal portion <NUM> and/or the housing <NUM> in response to application of a voltage thereto. The controller <NUM> may be configured to control operation of the power supply <NUM> to selectively control whether (and/or how much) voltage is applied to the heater. In some examples, the heater could be provided by the resistive element <NUM>.

The controller <NUM> may be configured to receive a signal indicative of at least one operational parameter of the operation of the cell <NUM>. The controller <NUM> may be configured to control operation of the heating system <NUM> based on this received signal. For example, the controller <NUM> may be configured to control operation of at least one of the heater <NUM>, the pump <NUM>, and/or the power supply <NUM> based on the received signal. The controller <NUM> may be configured to control the heat and/or pressure of liquid supplied to the internal portion <NUM>.

The controller <NUM> may be configured to control whether and/or how much voltage is applied to one or more of the first electrode <NUM>, the third electrode <NUM> and/or the heater. In other words, the controller <NUM> may be configured to control the supply of liquid to the internal portion <NUM> of the cell <NUM> and/or the electrical energy to be applied by electrodes of the cell <NUM>.

The controller <NUM> may be configured to control operation based on at least one received signal indicative of one or more operational parameters of the cell <NUM>. The signal may be received from one or more of the sensors. It is to be appreciated that the exact nature of the signal received, and/or the sensor from which it is received is not to be considered limiting. Exemplary sensors are shown in <FIG>, which may provide information indicative of one or more operational parameters of the system <NUM>.

The power supply sensor <NUM> may be configured to provide an indication of operation of the power supply <NUM>. The power supply sensor <NUM> may be configured to provide an indication of a magnitude of power (e.g. voltage) being applied, and/or it may provide any relevant feedback on the signal being applied by the power supply <NUM>. For example, the power supply sensor <NUM> may be configured to provide an indication of any chatter associated with the voltage being applied by the power supply <NUM> (e.g. to the first sensor). The fluid inlet sensor <NUM> may be configured to provide an indication of at least one property of the liquid to be supplied to the internal portion <NUM>. For example, this may comprise an indication of a pressure and/or a temperature of the liquid to be supplied. As another example, the fluid inlet sensor <NUM> may be configured to provide an indication of one or more chemical properties of the liquid to be supplied to the internal portion <NUM> (e.g. indicative of the chemical composition of said liquid, such as percentage of impurities/additives etc.). The fluid outlet sensor <NUM> may be similar to the fluid inlet sensor <NUM>. For example, the fluid outlet sensor <NUM> may be configured to provide an indication of a temperature, pressure and/or chemical composition of fluid being output from the cell <NUM>. The fluid outlet sensor <NUM> may be configured to provide an indication of any relevant energy configuration changes to the fluid exiting the cell <NUM> (e.g. whether any additional compositions are present).

The first electrode sensor <NUM>, the first electrode sensor <NUM> and the third electrode sensor <NUM> may be configured to provide an indication of one or more properties of the relevant electrical energy present thereat. The sensors may provide an indication of a voltage and/or current present at the relevant electrode. For example, an electrode sensor may be configured to provide an indication of how current and/or voltage at said electrode varies with time (e.g. to provide an indication of a time derivative for the current/voltage).

The internal portion sensor <NUM> is configured to provide an indication of the conditions within the internal portion <NUM> of the cell <NUM>. The internal portion sensor <NUM> may be located within the internal portion <NUM> of the housing <NUM>, e.g. it may be attached to an internal wall of the housing <NUM> (as shown in <FIG>). Alternatively, the internal portion sensor <NUM> may be located outside the external portion but configured to provide some indication as to the conditions within the internal portion <NUM>. The internal portion sensor <NUM> may be configured to provide an indication of fluid flow dynamics within the internal portion <NUM> - e.g. to provide an indication of whether there is any turbulent flow, and/or how turbulent the flow is. This could include use of a flow meter, a microphone, or any other suitable sensor. The internal portion sensor <NUM> may be configured to provide an indication of electromagnetic energy present inside the internal portion <NUM> (e.g. an indication of the amount and/or type of electromagnetic emission occurring). For example, the internal portion sensor <NUM> may comprise a suitable antenna to detect the presence of such electromagnetic energy/emissions, and/or it may comprise some form of camera (e.g. as part of a fibre optic) configured to obtain an indication of light present in the cell <NUM>. The internal portion sensor <NUM> may be configured to provide an indication of the state of activity occurring inside the cell <NUM>.

In operation, the heating system <NUM> of <FIG> functions in much the same manner as the heating system <NUM> described above with reference to <FIG>. That is, the power supply <NUM> applies electrical energy (e.g. a voltage) to the first electrode <NUM> to heat the fluid in the internal portion <NUM>. This heating is brought about by resistive heating and also heating from incident light emitted from bubbles of plasma within the internal portion <NUM>. Additionally, a capacitance may be provided between the first and third electrode <NUM>, and/or between the second and third electrode <NUM>. This may provide a balancing effect to the electric field within the internal portion <NUM> of the cell <NUM>. The third electrode <NUM> may provide a balancing effect if provided as a floating electrode (e.g. in a passive state) and if a voltage is applied to the third electrode <NUM> (e.g. in an active state).

Additionally, the controller <NUM> may be configured to control operation of the heating system <NUM> according to any of a number of different control loops. Each control loop may provide a feedback loop in which data indicative of an operational parameter of the cell <NUM> is obtained (e.g. from a sensor), and the controller <NUM> controls operation of a component of the heating system <NUM> based on this obtained data. The data may be obtained from any suitable sensor (e.g. any of the sensors shown in <FIG> and described above). The controller <NUM> may control operation of any suitable component of the heating system <NUM>, such as controlling the supply of liquid to the internal portion <NUM> of the cell <NUM> (e.g. controlling the heater <NUM> or the pump <NUM>), and/or controlling the electrical energy to be applied by one or more of the electrodes (e.g. controlling the power supplied by the power supply <NUM>).

Four exemplary control loops will now be discussed. In a first example, operation of the cell <NUM> will be described in a 'normal' mode, where at least one property is monitored and/or regulated to provide increased efficiency for operation of the cell <NUM>. In second and third example, operation of the cell <NUM> will be described for increasing and decreasing cell <NUM> output respectively. In a fourth example, operation of the cell <NUM> will be described when in a 'start-up' mode.

In the first example, operation of the heating system <NUM> is controlled in a normal mode of continued operation. Here, the controller <NUM> is configured to receive a signal indicative of an operational parameter of the cell <NUM>, and the controller <NUM> is configured to control operation of the system <NUM> so that the operational parameter remains within a desired range for performance of the cell <NUM>. The cell <NUM> is designed to provide heated fluid as its output. The operational parameter may therefore provide an indication of the output for the cell <NUM>. For example, the operational parameter may provide an indication of how efficiently the cell <NUM> is performing and/or an indication of the magnitude of heat generation being provided by the cell <NUM> (e.g. it may provide an indication of the amount/temperature of heated fluid being generated by the cell <NUM> per unit time). It will be appreciated in the context of the present disclosure that the cell performance need not be determined per se. , but instead, the controller <NUM> may control operation of the cell <NUM> based on an indicator of cell performance.

The controller <NUM> may be configured to receive an indication of cell performance. The indication of cell performance may provide an indication of the operating state of the cell <NUM>. This may comprise an indication of the amount/temperature of heated fluid being generated by the cell <NUM> and/or an indication of the quality of plasma generation occurring within the cell <NUM>. The indicator may be based on a temperature and/or pressure of heated fluid being generated by the cell <NUM> (e.g. it may be an indication of said temperature and/or pressure). For example, such an indication may be obtained using the fluid outlet sensor <NUM>. The indication may be based on both the temperature/pressure of liquid being provided to the cell <NUM> (e.g. as sensed by the fluid inlet sensor <NUM>) and the temperature/pressure of heated fluid exiting the cell <NUM> (e.g. as sensed by the fluid outlet sensor <NUM>). The indication may be based on an amount of heating being provided by the cell <NUM> (e.g. a difference between inlet and outlet temperatures), and/or a rate of heating being provided by the cell <NUM>.

As an example, the controller <NUM> may be configured to receive a signal indicative of a temperature of the heated fluid leaving the cell <NUM>. In the event that the heated fluid is outside a selected range (e.g. above an upper threshold temperature and/or below a lower threshold temperature), the controller <NUM> may control operation of the heating system <NUM> to increase/decrease the temperature, as appropriate, for the outlet temperature to return to within the selected range. This may further comprise the controller <NUM> determining if the liquid provided to the cell <NUM> is heated by above a threshold amount and/or within a threshold time period. The controller <NUM> may control operation of the heating system <NUM> so that a sufficient amount of heating and/or sufficiently quick heating occurs.

In addition, or as an alternative, to receiving a direct indication of a temperature/pressure of heated fluid leaving the cell <NUM>, the controller <NUM> may receive a signal which is indicative of cell performance. For example, the controller <NUM> may receive a signal indicative of an amount and/or quality of plasma generation occurring within the cell <NUM>. The controller <NUM> may control operation of the heating system <NUM> to so that the quantity and/or quality of plasma generation occurring is within a selected range. In turn, this may act to control the generation of heated fluid by the cell <NUM>, as the generation of plasma within the cell <NUM> ultimately gives rise to heating of the fluid within the cell <NUM>.

The controller <NUM> may be configured to obtain an indication of a property of plasma generation within the cell <NUM> based on a received signal from a sensor. The indication of the property of plasma generation may be determined based on temperature and/or pressure data for fluid entering and/or leaving the cell <NUM>. The amount of plasma generation may be determined based on the amount of heat generation, and/or the speed with which fluid is being heated. For example, quicker/more heating may indicate more plasma generation. The controller <NUM> may be configured to determine that plasma generation is within a selected range in the event that the amount and/or rate of heating by the cell <NUM> is within a selected range.

The amount of plasma generation may be determined based on an obtained indication of the conditions inside the internal portion <NUM> of the housing <NUM> (e.g. using the internal portion sensor <NUM>). An indication that fluid within the internal portion <NUM> is moving turbulently may indicate more plasma generation (e.g. due to more conduction heating being provided by the inner portion of the housing <NUM>, and this giving rise to convection currents). Alternatively, or additionally, an indication that more electromagnetic energy is present (e.g. more light is visible/more electromagnetic waves are being detected) may indicate more plasma generation. The controller <NUM> may be configured to determine that plasma generation is within a selected range in the event that the amount of turbulence and/or electromagnetic energy/emissions is within a selected range.

The amount of plasma generation may be determined based on an obtained indication of current and/or voltage at one of the electrodes. For example, the controller <NUM> may obtain an indication of a voltage being applied to the first electrode <NUM>, and an indication of a resulting current passing through the first electrode <NUM> (e.g. using the first electrode sensor <NUM>). The controller <NUM> may be configured to monitor voltage and current data over time and to determine based on this voltage and current data when a satisfactory plasma is generated. For example, the controller <NUM> may control the power supply <NUM> to increase the voltage applied to first electrode <NUM> over time, and the control may monitor the resulting current. As the voltage increases, the current will also increase initially before holding relatively stable as the voltage continues to increase. Once a threshold voltage is reached, the current will begin to increase, and the rate of increase in current will increase with increased voltage. The controller <NUM> may be configured to detect that satisfactory plasma generation has occurred in the region where the current starts increasing again. For example, the controller <NUM> may be configured to determine satisfactory plasma generation has occurred once the current begins to rise again. The controller <NUM> may then control the power supply <NUM> to no longer raise the voltage applied to the first electrode <NUM>.

The amount of plasma generation may be determined based on an indication of chatter being provided to the power supply <NUM> in response to applying a voltage to the first electrode <NUM>. For example, this may provide an indication of plasma generation occurring in the fuel, e.g. as vibrations occur due to plasma generation. The controller <NUM> may be configured to determine that plasma generation is within a selected range in the event that detected chatter is within a selected range.

The above examples describe operational parameters of the cell <NUM> which the controller <NUM> may be configured to determine and/or receive signals indicative thereof. Based on obtaining an indication of any of these operational parameters, the controller <NUM> may be configured to control operation of the heating system <NUM>. In the event that the obtained indication is outside a selected range (e.g. above an upper threshold value and/or below a lower threshold value), the controller <NUM> may control operation of the system <NUM> so that a value for that parameter is within the selected range. For this, the controller <NUM> may control the liquid supplied to the cell <NUM> and/or the electrical energy applied to the fluid within the cell <NUM>.

The controller <NUM> may be configured to control the liquid supplied to the cell <NUM> so that the at least one operational parameter is within a selected range. Controlling the liquid supply may comprise at least one of: (i) controlling a temperature of liquid supplied to the internal portion <NUM> of the cell <NUM>, (ii) controlling a pressure of liquid supplied to the internal portion <NUM> of the cell <NUM>, and/or (iii) controlling an amount of liquid supplied to the internal portion <NUM> of the cell <NUM> within a selected time window. The controller <NUM> may be configured to control operation of the heater <NUM> and/or the pump <NUM> to control the temperature and/or pressure of the liquid supplied to the cell <NUM>. The fluid inlet <NUM> may comprise one aperture for receiving liquid, or it may comprise a plurality, e.g. to provide a plurality of entry points for liquid to flow into the cell. The controller <NUM> may be configured to control operation of the pump <NUM> to control the flow rate of fluid through the cell <NUM>, e.g. to control how much fluid is delivered to the cell <NUM> per unit time. The liquid supply system <NUM> may be configured to provide a continuous flow of liquid to the cell <NUM>, and the controller <NUM> may control the rate at which liquid is supplied to the cell <NUM>.

In the event that the operational parameter indicates that increased output is needed from the cell (e.g. that the cell <NUM> needs to provide more heating of fluid), the controller <NUM> may control the liquid supply system <NUM> to provide at least one of: (i) liquid to the cell <NUM> at a higher temperature, (ii) liquid to the cell <NUM> under higher pressure, and/or (iii) more liquid to the cell <NUM>. For example, if the operational parameter indicates that plasma generation is below a threshold, the control may increase the heat and/or pressure provided to the cell <NUM>.

The controller <NUM> may be configured to control the electrical energy applied to electrodes of the cell <NUM> so that the at least one operational parameter is within the selected range. This may comprise at least one of: (i) controlling the amount of time for which a voltage is applied to the first electrode <NUM>, (ii) controlling the voltage applied to the first electrode <NUM>, (iii) controlling the voltage applied to the second electrode <NUM>, and/or (iv) controlling the voltage applied to the heater. Where the operational parameter indicates that temperature generation needs to increase and/or plasma generation is below a threshold, the controller <NUM> may control the power supply <NUM> to increase the energy applied. For example, if plasma and/or heat generation is below a threshold value, the controller <NUM> may apply a voltage (or apply a larger voltage) to the heater and/or the first electrode <NUM>.

The controller <NUM> may be configured to control both the electrical energy to be applied by the electrodes of the cell <NUM> and the liquid supply to the cell <NUM> (e.g. the two may be controlled simultaneously). The controller <NUM> may control one in dependence on how it is controlling the other. For example, the controller <NUM> may select how to control the electrical energy to be applied by the electrodes of the cell <NUM> based on how it will control the liquid supply to the cell <NUM> (and/or vice-versa). In the event that the controller <NUM> determines that increased plasma generation is required, the controller <NUM> may increase the voltage applied to the heater and/or first electrode <NUM>, as well as increasing the temperature and/or pressure of water to be provided to the cell <NUM>. In the event that the controller <NUM> determines that increased production of heated fluid is required, the controller <NUM> may increase the voltages applied to the electrodes and/or heater, as well as to increase the amount of liquid supplied to the cell <NUM>.

In the second and third examples, the controller <NUM> is configured to receive a demand signal indicative of a demand on the output from the cell <NUM>. The demand signal may indicate that more or less output is required from the cell <NUM>. For example, this demand may be independent of the efficiency of cell <NUM> - the cell <NUM> may be operating within a threshold range for a relevant operational parameter, but the demand signal may indicate that the output needs to change (e.g. increase or decrease).

In the event that the demand signal indicates less output is required, the controller <NUM> is configured to control the liquid supplied to the cell <NUM> and the electrical energy applied to the electrodes of the cell <NUM>. As the demand decreases, the controller <NUM> will decrease the supply of liquid to the cell <NUM>. For example, the controller <NUM> may decrease the fluid flow rate through the cell <NUM>. The liquid may still be supplied to the cell <NUM> at the same, or similar, temperature and/or pressure. The controller <NUM> may reduce the electrical energy to be applied. For example, the controller <NUM> may decrease the voltage applied to the first electrode <NUM>. The controller <NUM> may still supply the same, or similar, voltage to the third electrode <NUM> and/or heater. The controller <NUM> may still control operation, e.g. as described above, so that plasma generation is within a selected range despite the total output being decreased.

In the event that the demand signal indicates more output is required, the controller <NUM> may control operation in the opposite way. The controller <NUM> may increase the rate that liquid is supplied to the cell <NUM> and the amount of electrical energy applied to the electrodes of the cell <NUM>. The controller <NUM> may be configured to control operation of the cell <NUM> to avoid a flow rate of liquid through the cell <NUM> exceeding a plasma-generation threshold amount at which the flow rate is too high for sufficient plasma generation to occur. The controller <NUM> may still control operation, e.g. as described above, so that plasma generation is within a selected range despite the total output being increased.

In the fourth example, the controller <NUM> is configured to control operation of the system <NUM> in a start-up mode. For example, when the cell <NUM> is first turned on, it may take some time before it can be operated at higher efficiencies. In particular, the housing <NUM> of the cell <NUM> may be colder than it would during use. The controller <NUM> may be configured to determine that start-up operating conditions are to be used. For example, the controller <NUM> may obtain an indication of temperature for relevant components of the system <NUM> (e.g. the housing <NUM>) to determine if the system <NUM> should operate in a start-up mode, and/or the controller <NUM> may determine based on an indication of previous use (e.g. that the system <NUM> has not been used recently) that start-up mode is to be used.

In start-up mode, the controller <NUM> is configured to control operation of the cell <NUM> to provide additional heating. The controller <NUM> may increase the voltage applied to the first electrode <NUM> to provide additional resistive heating. Additionally, or alternatively, the controller <NUM> may apply a voltage to the heater e.g. to provide resistive heating. For example, the controller <NUM> may control operation so that a greater voltage is applied to the heater when in the start-up mode than during normal operation (e.g. no voltage may be applied to the heater during normal operation). For example, the controller <NUM> may be configured to control operation of the heater to provide more heating during start-up (e.g. more heating energy may be used). The controller <NUM> may also control operation of an additional heater, such as a cartridge heater, to provide heating of the cell <NUM>/internal portion <NUM>. The controller <NUM> may control the supply of liquid to the cell <NUM> so that liquid supplied to the cell <NUM> is at a higher temperature and/or pressure and/or the flow rate of fluid through the cell <NUM> is lower when in start-up mode. The controller <NUM> may control the electrical energy applied to the electrodes and/or heater to be higher when in start-up mode.

The controller <NUM> may be configured to monitor at least one operational parameter of the cell <NUM> to determine when to leave start-up mode. For example, while an obtained indication of a temperature associated with the cell <NUM> remains below a threshold temperature value, the controller <NUM> may control operation of the system <NUM> to be in start-up mode. Once this temperature exceeds the threshold temperature value, the controller <NUM> may control operation of the system <NUM> to operate in normal-mode operating conditions. For example, less pre-heating of liquid may occur when in the normal-mode. The controller <NUM> may be configured to determine that sufficient plasma generation is occurring (e.g. in the manner described above), and in response to this, switch to the normal-mode of operation.

Another exemplary cell <NUM> will now be described with reference to <FIG>. The cell <NUM> of <FIG> corresponds closely to that previously described, and so description of relevant components will not be repeated.

<FIG> shows a cell <NUM>. The cell <NUM> includes a first electrode <NUM>, a second electrode <NUM>, a third electrode <NUM> and a resistive element <NUM>. The cell <NUM> also includes a housing <NUM> which defines an internal portion <NUM>, and which has a fluid inlet <NUM> and a fluid outlet <NUM>. The cell <NUM> also includes a first end cap <NUM>, a second end cap <NUM> and a compression device <NUM>. The cell <NUM> may comprise a plasma cell (e.g. a plasma-generating fuel cell).

The internal portion <NUM> extends from a first end of the housing <NUM>, which includes the fluid inlet <NUM>, to a second end of the housing <NUM>, which includes the fluid outlet <NUM>. The internal portion <NUM> may be cylindrical. The housing <NUM> encapsulates the internal portion <NUM> apart from defining the fluid inlet <NUM> and the fluid outlet <NUM>. In this example, the resistive element <NUM> lies adjacent to the internal wall of the housing <NUM> although in other examples, the resistive element <NUM> may be integral with the internal wall or separate from the wall and inside the internal portion <NUM>. The first end cap <NUM> and second end cap <NUM> may also form part of the resistive element <NUM> - e.g. they also provide increased resistance to a conductive path from anode to cathode. The second electrode <NUM> is arranged within (e.g. integral with) the internal wall of the housing <NUM>. The first and third electrode <NUM> are disposed at least partially within the internal portion <NUM>. The first electrode <NUM> extends from outside the first end and into the internal portion <NUM>. The third electrode <NUM> extends from outside the second end and into the internal portion <NUM>. There is a gap between the two in the internal portion <NUM>. The three electrodes and the resistive element <NUM> may be coaxial (e.g. they may be concentric).

The first end cap <NUM> encloses the internal portion <NUM> at the first end. The second end cap <NUM> encloses the internal portion <NUM> at the second end. The end caps <NUM>, <NUM> form part of the housing <NUM> for the internal portion <NUM>. The first end cap <NUM> is non-conducting. The second end cap <NUM> is non-conducting. Each end cap may effectively form part of a resistive barrier for a conductive path from the anode to the cathode (e.g. the end caps may form part of, or work in combination with, the resistive element <NUM>). Each end cap <NUM>, <NUM> includes one or more apertures to enable flow of fluid therethrough. One or both end caps may have an aperture near to its centre. For example, the aperture(s) in the first end cap <NUM> may be located proximal to the first electrode <NUM>. The aperture(s) may be arranged to facilitate flow of liquid into the internal portion <NUM> while inhibiting the likelihood of a conductive path forming from the anode to the cathode through said aperture(s). The first end cap <NUM> may have a plurality of apertures to facilitate multiple different points through which liquid may flow into the internal portion <NUM>. The compression device <NUM> is located within the first end of the housing <NUM> adjacent to the first end cap <NUM>. The compression device <NUM> may comprise any suitable biasing means, such as a spring. Each end of the housing <NUM> may have thicker material, as shown in <FIG>. At least one portion of the housing <NUM> may be connected to electrical ground. As shown in <FIG>, the first end of the housing <NUM> is grounded. One or both of the end caps may include a heating element (e.g. a resistive heater), which may be used to provide heating to liquid within the internal portion <NUM> (e.g. during start-up). For example, the power supply <NUM> may couple to a heater in the end cap (e.g. in the first end cap <NUM>). The controller <NUM> may be configured to control application of power to the heater in the end cap to provide heating.

The first electrode <NUM> may include a conductor extending along the length of the electrode. The conductor may be provided within an insulating body to provide the electrode. An insulating shroud may be provided for at least some of the region of the electrode within the internal portion <NUM> (e.g. the insulating shroud may be provided at the end of the first electrode <NUM> which is disposed in the internal portion <NUM>). For example, the electrode may have a conductor extending along a central axis, where that conductor is radially surrounded by an insulator along the length of the conductor being in the internal portion <NUM> (e.g. it may be along the entire length). The first electrode <NUM> may also include a carrier at its end away from the internal portion <NUM>. The carrier may comprise suitable fixing means, such as a ledge, for attachment to the first end cap <NUM>. The carrier may comprise a sealing means and attachment means for attaching the first electrode <NUM> to the first end cap <NUM> and sealing the internal portion <NUM>. For example, a radially extending flange may provide a sealing face. For example, a screw thread may enable the end cap <NUM> to be secured to the electrode to seal the internal portion <NUM>. A similar arrangement may be provided for the third electrode <NUM>, and e.g. its arrangement with the second end cap <NUM>.

The compression device <NUM> is configured to apply pressure on the first end cap <NUM> towards the internal portion <NUM> of the housing <NUM>. The compression device <NUM> may facilitate retaining the internal portion <NUM> of the housing <NUM> under pressure. The housing <NUM> is arranged to enable the flow of liquid into the internal portion <NUM> through the fluid inlet <NUM> and a flow of steam/liquid out through the fluid outlet <NUM>. The housing <NUM> is arranged to provide structural support to enable the internal portion <NUM> to be held under pressure with fluid therein. For example, the side wall(s) of the housing <NUM> is arranged to withstand radial expansion of the internal portion <NUM>, and the end walls of the housing <NUM> are arranged to withstand longitudinal expansion of the internal portion <NUM>. Operation of the cell <NUM> is similar to that described above with reference to <FIG> and <FIG>, and so shall not be described again here.

Heating systems described herein may find use in larger generation systems. Examples of such larger generating systems will now be described with reference to <FIG> and <FIG>.

<FIG> shows a heat and power generating system <NUM>. The heat and power generating system <NUM> comprises a power management system <NUM>, a cell <NUM>, a heat management system <NUM>, a fluid management system <NUM>, and a power generation system <NUM>. Also shown in <FIG> is a mains coupling <NUM>. The cell <NUM> may comprise a plasma cell (e.g. a plasma-generating fuel cell).

<FIG> shows a block diagram to illustrate the functional interrelationship between the different component systems of the heat and power generating system <NUM>. However, it is to be appreciated that this is intended to demonstrate the functional connections, rather than specific structural connections. It will be appreciated that the structural arrangement of the different component systems may be interlinked (e.g. as will be described later with reference to <FIG>).

As shown in <FIG>, the power management system <NUM> is coupled to the cell <NUM>. The cell <NUM> is coupled to the heat management system <NUM>. The heat management system <NUM> is coupled to each of the power generation system <NUM> and the fluid management system <NUM>. The fluid management system <NUM> is coupled to the cell <NUM>. The power generation system <NUM> is coupled to the power management system <NUM>. This coupling is intended to demonstrate the functional interrelationships between the different component systems. The power management system <NUM> may also be coupled to the mains coupling <NUM> (e.g. as shown in <FIG>).

The power management system <NUM> is configured to control the application of power to the cell <NUM>. The power management system <NUM> may control the electrical energy (e.g. voltage) applied to the first electrode <NUM> of the cell <NUM>. The power management system <NUM> may also control the electrical energy (e.g. voltage) applied to the remaining electrodes and/or the heater of the cell <NUM>. The power management system <NUM> may also control operation of any pump <NUM> and/or heater <NUM> for providing liquid to the cell <NUM> under pressure and/or at a higher temperature. The power management system <NUM> may therefore control the operation of the cell <NUM> to generate heated fluid.

The cell <NUM> is configured to operate as described above (e.g. to apply electrical energy inside its internal portion <NUM> to generate heated fluid).

The heat management system <NUM> is configured to receive the heated fluid generated by the cell <NUM>. The heat management system <NUM> is configured to utilise this heated fluid to provide relevant thermal work. For example, the heat management system <NUM> may be configured to provide heating using this heated fluid, e.g. for heating buildings etc. The heat management system <NUM> may comprise one or more components for providing heat transfer from the heated fluid from the cell <NUM> to another component and/or substance. For example, the heat management system <NUM> may comprise one or more heat exchangers.

The power generation system <NUM> is configured to receive the heated fluid generated by the cell <NUM>. The power generation system <NUM> is configured to utilise this heated fluid to generate power (e.g. electrical energy). <FIG> shows the output of the cell <NUM> being provided to the heat management system <NUM>, and from the heat management system <NUM> to the power generation system <NUM>. However, it will be appreciated in the context of the present disclosure that one of these systems may not be included, or the two systems may be provided by the same components. The power generation system <NUM> may comprise one or more generators to generate electricity based on movement of the heated fluid (e.g. using pressurised gas to drive a turbine to generate electricity). This arrangement may also include some heat management (e.g. to distribute heat to other parts of the power generation system <NUM>. In some examples, the heated fluid may be used for heating purposes and for power generation purposes. The heat management system <NUM> may then control distribution of the heated fluid accordingly (e.g. to control distribution of heated fluid to the power generation system <NUM>). For example, the work extraction system <NUM> described above may comprise such a heat management system <NUM> and/or power generation system <NUM>.

Power generated by the power generation system <NUM> may then be supplied to the power management system <NUM>. For example, this power generated by the power generation system <NUM> may in turn be used by the power management system <NUM> to power the cell <NUM> to provide further power generation. The power management system <NUM> may also be coupled to the mains coupling <NUM> to receive and/or transmit power to the mains. For example, during start-up mode, the power management system <NUM> may obtain all of its power from the mains, but after start-up, at least some of its power may be received from the power generation system <NUM>. After start-up, some of the power generated by the power generation system <NUM> may be provided to the mains coupling <NUM> for distribution elsewhere.

The fluid management system <NUM> is configured to provide liquid to the cell <NUM> (e.g. as described above for the liquid supply system <NUM>). The fluid management system <NUM> is configured to receive fluid which has been output from the cell <NUM>. The fluid management system <NUM> may be configured to process fluid which was heated by the cell <NUM>, and which has since been used by the heat management and/or power generation systems. The heated fluid generated by the cell <NUM> may be at high temperature and/or pressure. The heat management and/or power generation systems are configured to extract useable work from this high temperature/pressure fluid. Once the useable work has been extracted, the fluid may be at much lower temperatures and pressures. For example, it may leave the cell <NUM> as high temperature and pressure gas, and once fully used for work extraction it may be liquid again (e.g. at a lower temperature). The fluid management system <NUM> is configured to process this used fluid. Processing the used fluid may comprise returning it to the environment and/or processing (e.g. filtering) the fluid, e.g. so that it could be used again as a liquid to be provided to the cell <NUM>.

In operation, the power management system <NUM> receives power (e.g. from the mains coupling <NUM> and/or the power generation system <NUM>). The power management system <NUM> applies electrical energy to the cell <NUM> (e.g. to the first electrode <NUM>). The fluid management system <NUM> supplies liquid to the cell <NUM>. The electrical energy applied to the cell <NUM> in turn heats to the liquid provided to the cell <NUM> so that the cell <NUM> outputs a heated fluid. This heated fluid is received by the heat management system <NUM> and/or power management system <NUM>, which extract useable work (e.g. for heating and/or power generation) from the heated fluid. Once this work has been extracted, any power generated by the power generation system <NUM> is provided to the power management system <NUM>. The used fluid is provided to the fluid management, which processes this used fluid. This process may be repeated, e.g. continually, to provide heat and/or power generation.

A more specific example of a heat and power generating system <NUM> will now be described with reference to <FIG>.

<FIG> shows a heat and power generating system <NUM>. The heat and power generating system <NUM> comprises a cell <NUM>. Also included is a power supply <NUM>, a pump <NUM>, and a drain <NUM>. The system <NUM> includes a plurality of heat exchangers, which, as shown in <FIG> includes a first heat exchanger <NUM>, a second heat exchanger <NUM>, a third heat exchanger <NUM> and a fourth heat exchanger <NUM>. The system <NUM> further includes a heat engine <NUM> having a first driving region <NUM> and a second driving region <NUM>, and a generator <NUM>. The cell <NUM> may comprise a plasma cell (e.g. a plasma-generating fuel cell).

The cell <NUM> is connected to receive two inputs (liquid and electricity) and to provide an output (heated fluid). The inputs to the cell <NUM> are shown at the bottom and right of the cell <NUM>, and the output is at the top.

The output of the cell <NUM> is coupled to each of the first heat exchanger <NUM> and the heat engine <NUM>. A flow path for the output may split into two, with one path coupling to the first heat exchanger <NUM> and another path coupling to the heat engine <NUM>. In particular, the output from the cell <NUM> is coupled to the first driving region <NUM> of the heat engine <NUM>. The heat engine <NUM> has a first engine inlet for receiving fluid to drive the engine <NUM> in the first driving region <NUM>. The first driving region <NUM> is also coupled to a first engine outlet for outputting the fluid which has driven the engine <NUM> in the first driving region <NUM>. The first engine outlet is also coupled to the first heat exchanger <NUM>.

The engine <NUM> also includes a second engine inlet and a second engine outlet. The second engine inlet is for receiving fluid to drive the engine <NUM> in the second driving region <NUM>. The second engine outlet is for outputting the fluid which has driven the engine <NUM> in the second driving region <NUM>. The second engine inlet is also coupled to the first heat exchanger <NUM>. For example, fluid may flow from the first engine outlet to the second engine inlet through the first heat exchanger <NUM>. The engine <NUM> is coupled to a generator. Each of the first and second driving regions <NUM>, <NUM> of the engine <NUM> may couple to the generator. The first and second driving regions <NUM>, <NUM> may drive the engine <NUM> at a different ratio. Both may contribute to driving the generator, and thus generating electricity.

The first heat exchanger <NUM> may be coupled to the second heat exchanger <NUM>. The system <NUM> may be configured for heated fluid from the cell <NUM> to flow through the first heat exchanger <NUM> and onto the second heat exchanger <NUM>. The second heat exchanger <NUM> may also be coupled to the third and/or fourth heat exchangers <NUM>, <NUM>.

The power supply <NUM> is coupled to the cell <NUM>. The power supply <NUM> provides an input to the fuel supply (e.g. to provide electrical energy to the electrodes of the cell <NUM>). The power supply <NUM> may include a coupling for receiving power from the mains (e.g. the power supply <NUM> may receive three phase power). The power supply <NUM> may include a converter (e.g. AC to DC) for providing DC output, such as a high voltage DC output. The high voltage DC output may then be supplied to the cell <NUM>, e.g. to be applied to the first electrode <NUM>. The power supply <NUM> may also be coupled to the generator to receive generated electricity therefrom. The power supply <NUM> may receive AC or DC from the generator. Where AC is received, this may be converted to DC (e.g. using the same or a different AC to DC converter). Some of the electricity generated by the generator may be provided to the mains, e.g. for use elsewhere.

The third heat exchanger <NUM> and/or the pump <NUM> may couple to the input for the cell <NUM>. Liquid to be supplied to the cell <NUM> may be heated and/or pressurised using the third heat exchanger <NUM> and/or the pump <NUM>. This may provide the liquid input to the cell <NUM> which is used for generating heated fluid. The heated fluid output from the cell <NUM> is ultimately coupled to a drain <NUM>. For example, the fluid which has passed through both regions <NUM>, <NUM> of the engine <NUM> may be provided to the drain <NUM>. Likewise, fluid which has passed through any of the heat exchangers (e.g. the second, third and/or fourth heat exchanger <NUM>, <NUM>, <NUM>) may then be coupled to the drain <NUM>.

The system <NUM> is arranged to provide multiple uses for the heated fluid generated by the cell <NUM>, e.g. to extract work from the heated fluid in multiple ways. The system <NUM> is configured to provide high temperature, high pressure fluid output from the cell <NUM> to drive the first driving region <NUM> of the engine <NUM>. The generator is configured to generate electricity from this driving of the first driving region <NUM>. The first heat exchanger <NUM> is configured to reheat this fluid which has driven the first driving region <NUM> of the engine <NUM>. The first heat exchanger <NUM> is arranged to exchange heat between the heated fluid from the cell <NUM> and the fluid which has driven the first driving region <NUM> of the engine <NUM>. The system <NUM> is configured to use the re-heated fluid which has driven the first driving region <NUM> of the engine <NUM> to drive the second driving region <NUM> of the engine <NUM>. The second driving region <NUM> of the engine <NUM> is configured to have an easier ratio (e.g. so that less energy is required to drive a rotation) as compared to the first driving region <NUM>. The fluid passing through the second driving region <NUM> may be at a lower pressure than the first driving region <NUM>. The generator is configured to generate electricity in response to driving of the first and/or second driving regions <NUM>, <NUM> of the engine <NUM>.

The system <NUM> is arranged for heated fluid which has passed through the first heat exchanger <NUM> and/or out the second engine outlet to provide further heating use, where relevant. For example, the system <NUM> may be arranged to deliver the heated fluid to one or more of the second, third and/or fourth heat exchangers <NUM>, <NUM>, <NUM> for extracting useable heating work from this heated fluid. Any of these heat exchangers <NUM>, <NUM>, <NUM> may couple to an external component for using such heat. The system <NUM> may be configured to exchange heat from the heated fluid with the liquid to be supplied to the cell <NUM> to provide heating thereof prior to being delivered to the cell <NUM>. The system <NUM> is arranged to discard any remaining fluid using the drain <NUM>.

In operation, liquid is supplied to the cell <NUM>, and electrical energy is applied to the electrodes of the cell <NUM> to generate a heated fluid. The heated fluid leaves the cell <NUM> and flows to both the first heat exchanger <NUM> and the first driving region <NUM> of the engine <NUM>. The heated fluid flows through the first driving region <NUM> to drive the engine <NUM> and generator to generate electricity. This fluid then flows into the first heat exchanger <NUM> where it is re-heated by the heated fluid which travelled directly (e.g. not via the engine <NUM>) to the first heat exchanger <NUM> from the cell <NUM>. The fluid that has travelled through the engine <NUM> is then reheated before flowing through the second engine driving region. This fluid then drives the engine <NUM> and generator to generate electricity. Fluid which has passed through the second driving region <NUM> of the engine <NUM> and/or through the first heat exchanger <NUM> away from the engine <NUM> is then used in further heat exchangers <NUM>, <NUM>, <NUM> to extract more useable heat work from the fluid. This fluid is then discarded using the drain <NUM>.

It will be appreciated in the context of the present disclosure that the examples described herein are not intended to be considered limiting. Alternative and/or additional features may also be included. For example, reference has been made to concentric electrodes, e.g. which are arranged coaxially with a central first electrode <NUM> and a second electrode <NUM> located radially outward form the first electrode <NUM>. However, this arrangement may be reversed. Alternatively, the electrodes need not be arranged concentrically. For example, the two electrodes could be arranged in an alternative fashion, such as being arranged as plate electrodes, e.g. two parallel plates, or as parallel wires or other parallel objections such as spheres.

Reference has been made herein to electrodes of the cell <NUM>. The first electrode <NUM> may provide an anode, the second electrode <NUM> a cathode, and/or the third electrode <NUM> a balancing electrode. It is to be appreciated in the context of the present disclosure that each electrode may provide a conductive path, e.g. each electrode may comprise a conductor extending along a length of the electrode. The anode may comprise a conductor which provides a conductive path from external to the internal portion <NUM> into the internal portion <NUM> to the distal end of the conductor within the internal portion <NUM>. The cathode may comprise a conductor which provides a conductive path from in, or adjacent to, the internal portion <NUM> to away from the internal portion <NUM>. The balancing electrode may comprise a conductor which provides a conductive path into the internal portion <NUM> from external to the internal portion <NUM> or away from the internal portion <NUM> from within the internal portion <NUM>. The first electrode <NUM> may be arranged to pass closer to the third electrode <NUM> than it does to the second electrode <NUM>, e.g. the minimum distance between a point on the first electrode <NUM> and a point on the third electrode <NUM> may be less than that for the first and second electrode <NUM>. For example, the minimum distance between first and third electrodes may be much less than that for the first and second electrodes <NUM>, <NUM>.

Examples described herein relate to use of one cell. However, it is to be appreciated in the context of the present disclosure that multiple cells may be provided. For example, operation of the different cells may be timed to provide a consistent output of heated fluid over time. Operational timing of each cell may be offset so that the total output of heated fluid over time remains relatively constant. For example, it is to be appreciated that each cell may have an output of heated fluid which varies over time, and the multiple cells may have their operations timed so that the output from all of the cells combined is more consistent than for the output of any one cell on its own. The controller <NUM> may be configured to control the supply of liquid to each cell, and/or the application of electrical energy to the electrodes to provide consistent output of heated fluid. For example, one or more sensors may be used for each cell to determine operational parameters thereof, such as its output of heated fluid.

It is to be appreciated that the supply of liquid to the cell <NUM> may happen continuously over time or only in discrete time periods. The controller <NUM> may be configured to control whether or not liquid is delivered to the cell <NUM>. For example, the cell <NUM> may comprise a fluid inlet valve operable to control whether fluid can flow into the internal portion <NUM> or not, and/or operation of the pump <NUM> may be controlled to either deliver liquid to the cell <NUM> or not. There may be a continuous turnover of fluid within the cell <NUM>, e.g. fluid is continually being provided to the cell <NUM> and heated fluid is continuously leaving the cell <NUM> (e.g. as a gas through the fluid outlet <NUM>). There may be discrete time periods for fluid input so that one unit of liquid is delivered to the cell <NUM> (e.g. enough to fill the cell <NUM>), then no further liquid is provided while electrical energy is applied to the electrodes to provide heated fluid, e.g. once all the fluid has been heated sufficiently for release through the fluid outlet <NUM>. Then, another unit of liquid may be provided to the cell <NUM>. It is to be appreciated that for this mode of operation, multiple different cells being operated together may comprise timing operation so that while unit is being delivered to one cell, another cell is applying electrical energy to the fluid in its cell. It will be appreciated that multiple different cells (e.g. more than <NUM>) may be used with timings all offset from each other, e.g. so that when one is nearly finishing heating, another is mid-heating, and another is just starting heating etc..

The internal surface of the housing <NUM> has been described as being an electromagnetic energy-absorbing surface. This may be a property of the material used to provide the housing <NUM>, e.g. steel, and/or a coating may be provided on the internal surface to facilitate absorption of electromagnetic energy (e.g. from photon emissions). It is to be appreciated that absorbing electromagnetic energy may comprise receiving incident photons (e.g. in the visible light spectrum) and in response to said photons being incident on the surface, generating heat. It will also be appreciated that electrons or other particles (e.g. charged particles emitted from the plasma/plasma-cooling process) may also be incident on the internal surface of the housing <NUM>. The internal surface of the housing <NUM> may also be configured to generate heat in response to such incident particles. For example, resistive heating may be provided in response to electron flow through the internal surface.

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.

Claim 1:
A heating system (<NUM>) comprising:
a liquid supply system (<NUM>);
a cell (<NUM>) configured to: receive liquid from the liquid supply system (<NUM>), provide heating thereof, and output heated fluid;
a work extraction system (<NUM>) configured to extract useable work from heated fluid output from the cell (<NUM>); and
a controller (<NUM>);
wherein the cell (<NUM>) comprises: (i) a housing (<NUM>) arranged to define an internal portion (<NUM>) for receiving liquid to be heated, and (ii) a plurality of electrodes including a first electrode (<NUM>) configured to apply electrical energy to fluid in the internal portion (<NUM>);
wherein the first electrode (<NUM>) is configured to apply electrical energy to said fluid in the internal portion (<NUM>) to generate one or more bubbles of plasma for releasing energy into said fluid in the internal portion (<NUM>) and the housing (<NUM>) to provide heating of the fluid in the internal portion; the system is characterized in that
the controller (<NUM>) is configured to reduce or stop applying a voltage to the first electrode (<NUM>) in the event that a change in current or a rate of change in current exceeds a threshold value.