ENERGY STORAGE AND CONVERSION

Abstract

A device for converting energy of a fluid to electrical energy is disclosed. The device comprises a pressure vessel having an inlet port for a fluid. A pair of charge collecting electrodes is spaced apart from each other along a collection direction and disposed within the pressure vessel. An electric field generator is configured to generate an electric field in the pressure vessel along a field direction to separate charged species in the fluid. Other disclosed devices provide a current flow delay to encourage charge build up or illumination with electromagnetic radiation. Yet other devices are arranged for fluid flow rather than pressure. Also disclosed is a system comprising any one of the disclosed devices and related methods. The disclosure may find application, for example, in providing a source of energy for an electric vehicle.

Claims

1. A device for converting energy of a fluid to electrical energy, the device comprising: a pressure vessel having an inlet port for a fluid and configured to retain pressurised fluid from the inlet port in the pressure vessel; a pair of charge collecting electrodes spaced apart from each other along a collection direction and disposed within the pressure vessel; and an electric field generator configured to generate an electric field in the pressure vessel along a field direction to separate charged species in the fluid.

2. A device according to claim 1, wherein the electric field is an ionising electric field to ionise the fluid.

3. A device according to claim 1, wherein the electric field generator comprises a pair of field generating electrodes spaced apart along the field direction and disposed on either side of the flow chamber.

4. A device according to claim 3, wherein the field generating electrodes are electrically isolated from the pressure vessel.

5. A device according to wherein the field and collection directions are substantially parallel.

6. A device according claim 1, wherein the pressure vessel comprises a partition between the collection electrodes sealing the pressure vessel into a first portion connected to the inlet port and comprising one of the collection electrodes and a second portion connected to a further inlet port and comprising another one of the collection electrodes.

7. A device according claim 1 comprising a current delay arrangement for delaying current flow from the collection electrode until an amount of charge has built up on the collection electrode.

8. A device according to claim 7, wherein the current delay arrangement comprises a further pressure vessel sealed around a portion of the collection electrode protruding out of the pressure and a further electrode disposed in the further pressure vessel wherein respective free ends of the collection electrode and further electrode define a spark gap therebetween.

9. A device according to claim 1, wherein the device comprises a single charge collection electrode instead of a pair of charge collection electrodes.

10. A device according to claim 1 comprising a source of electromagnetic radiation for irradiating a pressurised fluid inside the pressure vessel.

11. A device as claimed in claim 6, wherein the source of electromagnetic radiation is configured to generate electromagnetic radiation in a wavelength range of 120NM to 820NM.

12. A method of converting energy of a pressurised fluid to electric energy, the method comprising: causing the pressurised fluid to maintain a pressure inside a pressure vessel; applying an electric field to the pressurised fluid in the pressure vessel, thereby separating positive and negative species of the fluid along the field direction with one of the positive and negative charged species; collecting at least a fraction of one or each of the positive and negative charged species at a respective current collector; and drawing a current from one of the current collectors to provide electrical energy to a load.

13. A method according to claim 12 comprising ionising the fluid by applying the electric field to the flowing fluid to produce an ionised fluid comprising the negative and positive charged species.

14. A method according to claim 13, wherein ionising the fluid comprises generating a plasma.

15. A method according to claim 13, wherein ionising the fluid comprises causing a discharge, for example a dark or corona discharge.

16. A method according to claim 12, the method comprising delaying current flow from the current collector or current collectors until an amount of charge has built up on the current collectors.

17. A method according to claim 16, wherein delaying current flow comprises delaying current flow until a spark occurs in a spark gap between a free end of the current collector or collectors protruding outside the pressure vessel and a respective current receiving electrode.

18. A method according to claim 12, the method comprising irradiating the pressurised fluid with electromagnetic radiation while causing the pressurised fluid to maintain a pressure in the pressure vessel.

19-28. (canceled)

29. A method of converting energy of a pressurised fluid to electric energy, the method comprising: causing the pressurised fluid to flow through a flow chamber along a flow direction, thereby converting the potential energy to kinetic energy of the flowing fluid; applying a pulsed electric field to the fluid flowing in the flow chamber with an electric field generator; collecting at least a fraction of one or each of the positive and negative charged species at a respective current collector; and drawing a current from one of the current collectors to provide electrical energy to a load.

30-35. (canceled)

36. A device according to claim 1, wherein the fluid is a gas, for example air, Argon or Neon.

37-40. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Embodiments are now described by way of example and illustration with reference to the accompanying drawings in which like reference numerals refer to like elements and in which:

[0041] FIG. 1 illustrates an embodiment of an energy storage and conversion system using fluid flow;

[0042] FIG. 2 illustrates an alternative embodiment of an energy storage and conversion system;

[0043] FIG. 3 illustrates an electric vehicle including the system of FIG. 1 or 2;

[0044] FIG. 4 illustrate a method of converting fluid energy to electrical energy;

[0045] FIG. 5 illustrates a further embodiment of an energy storage and conversion system;

[0046] FIG. 6 illustrates a simplified circuit diagram of the further embodiment;

[0047] FIGS. 7 to 10 illustrate yet further embodiments of an energy storage and conversion system.

DETAILED DESCRIPTION OF EMBODIMENTS

[0048] With reference to FIG. 1, a system 2 for converting energy stored in a compressed fluid comprises an energy conversion device 4 connected to a reservoir 6 of compressed fluid, for example a compressed fluid container. The fluid is in some embodiments a gas, for example an inert gas such as Argon or Neon. A flow chamber 8 comprises a fluid inlet port 10 connected to the reservoir 6 by a conduit 12 at one end and a fluid exhaust port 14 at another, opposed end. Respective current collecting mesh electrodes 15 are provided at each end so that fluid flow from/through the inlet and exhaust ports 10, 14 flows through the mesh electrodes. In some embodiments, the ports extend through or are flush with their respective electrode 15. In some embodiments, other electrode geometries may be employed, for example a ring electrode around the respective port or disposed adjacent to it, a point electrode disposed adjacent its respective port, etc. The electrodes 15 may be configured the same or may each be different from the other with any combination of the disclosed or other geometries.

[0049] A pair of field generating electrodes 16 is spaced apart with the flow chamber 8 in between, with each electrode adjacent a respective one of the inlet and exhaust ports 10, 14. A dielectric material 18 is disposed between each field generating electrode 16 and an adjacent end of the flow chamber 8. In some embodiments, the dielectric material 18 is a solid, in other embodiments it is air or any other suitable dielectric. The field generating electrodes 16 are thus electrically isolated form the flow chamber 8. In some embodiments, the conduit 12 connects to the flow chamber 8 through the dielectric material 18 and/or an exhaust conduit 20 is connected to the exhaust port 14 through the dielectric material 18. The exhaust conduit 20 is in some embodiments connected fluidically to the surrounding atmosphere, directly or indirectly through an exhaust ion trap.

[0050] A high voltage, current limited supply 22 is connected to the field generating electrodes 16 to generate an electric field of sufficient strength inside the flow chamber 8 to separate charged species in the fluid. In some embodiments, the field is of sufficient strength to ionise the fluid. For example, the potential difference applied between the field generating electrodes by the supply may be such as to generate a field strength of 6000V/cm or larger to ionise Argon as the flowing fluid. A lower field strength is required for some fluids, such as Neon (600 V/cm) while a higher field strength would be required for other fluids, for example air (30 kV/cm). The supply 22 is fed from a source 24 of electrical energy, for example a dc source such as a battery, for example a 12V battery. In some embodiments, the supply 22 is configured to limit current so as to draw less than 2 A from the battery (or other source of input current) in some embodiments. In some embodiments, the current in the circuit connected to the supply (output current) may also be limited, for example to less than 2 A. In some embodiments, the output current was found to be limited by the breakdown current when the chamber 8 is filled with air and a spark occurs, which in some embodiments was found to be in a range around 50 too 100 mA. In some embodiments, the input voltage to the supply may vary, for example between 9 and 12V. In some embodiments, the supply 22 and source 24 are replaced with a high voltage capacitor that has previously been charged up by any suitable source.

[0051] A step-down converter 26 is connected to one, in some embodiments the lower potential one, in others the higher potential one (as illustrated), of the charge collecting electrodes 15 to step the potential difference between the electrodes 6 down to a required working voltage for a load 28 connected to the step down converter 26 in order to draw current from the step down converter 26 and hence the device 4. The load 28 is connected between the charge collecting electrode 15 in question and, in some embodiments, one side of the load and the corresponding current collecting electrode are connected to ground. In other embodiments the load 28 is connected between the charge collecting electrodes 15 in a floating arrangement. In some embodiments, the load 28 is connected between ground and one of the charge and the other one of the charge collecting electrodes is also connected to ground.

[0052] In some specific embodiments, the charge collecting electrodes 15 have an area of 1 cm.sup.2 and are spaced 1.6 cm apart, with the field generating electrodes having an area of 5 cm.sup.2 and spaced 7 cm apart. The flow chamber has a length of 7 cm and an internal volume of 34 cm.sup.3, with the flow rate at 0.1 ml/minute (1.7×10.sup.−3 ml/s) by the flow resistance of conduits and ports 10, 12, 14, 20, and in particular by a relatively small flow cross-section/relatively high hydrodynamic resistance of the exhaust port 14, for a pressure in the reservoir of 10 bar.

[0053] With reference to FIG. 2, in some embodiments, now described with reference to like reference numerals for like elements, the device 4 is arranged similarly to the device 4 described above with reference to FIG. 1 but with the field and collection electrodes 15, 16 replaced with combined field and collection electrodes 17 disposed within the flow chamber 8 at respective ends of the flow chamber 8 and connected to the supply 22. In some specific embodiments, the electrodes 17 are configured as a tubular electrode, with each electrode having its axis aligned along a common direction. In some embodiments, the inlet and exhaust ports 10, 14 are disposed in a side of a respective one of the electrodes 17. In some embodiments, the supply 22 is configured to prevent or strongly limit current corresponding to electrons flowing into a positive terminal of the supply 22, for example by means of a diode associated with the positive terminal of the supply 22.

[0054] The combined field and collection electrodes 17 are connected to respective terminals of the supply 22. The step down converter 26 is connected to one of the electrodes 17 in parallel with the supply 22 (which limits or blocks current flows from that electrode 17 back to the supply as described above) and the load 28 is connected to the step down converter 26. Specifically, the step down converter 26 and load 28 are connected between the electrodes 17. In some embodiments, one side of the load and one of the electrodes 17 are connected to ground. In some embodiments, the load is connected between one of the electrodes 17 (for example the lower potential one) and ground, with the other one of the electrodes 17 connected to ground to complete the circuit.

[0055] With reference to FIG. 3, an electric vehicle 30, for example an electric car, incorporates the reservoir 6 connected to an energy conversion device 4 as described above. The energy conversion device 4 is connected to the supply 22 and the load 28 as described above. The load 28 is an electric motor coupled to a drive train 32 of the vehicle for causing movement of the vehicle, for example driving wheels of the vehicle. In some embodiments, the energy stored in the pressurised fluid 6 in the reservoir is the sole source of energy to cause locomotion of the vehicle. The reservoir 6 is, in some embodiments, removably connected to the device 4 and can be exchanged against a full reservoir when empty. In other embodiments, the reservoir 6, whether removable/exchangeable or not, can be refilled with pressurised fluid through a refill port in the electric vehicle 30.

[0056] A controller 33 receives inputs from one or more of a vehicle driver interface (for example demand speed or torque), the load/motor 28 (for example current demand, actual current) and the reservoir 6 (for example pressure in the reservoir, as measured by pressure and/or flow sensors associated with the reservoir, for example) and controls the supply 22, specifically the voltage across electrodes 16 or 17, as the case may be, and a valve (not shown) regulating the flow of fluid from the reservoir 6 to the device 4. The controller 33, in accordance with specific embodiments controls the applied voltage and flow based on a suitable control law, for example using negative feedback to regulate current, flux, torque output or speed of the motor. For example, the field strength (i.e. voltage applied to electrodes 15/17) may be controlled based on power demand, with the field strength being increased with power demand. It will be appreciated that a suitable controller implementing a suitable control law is, in some embodiments, incorporated as described with reference to FIG. 3 in the embodiments of FIGS. 1 and 2, i.e. irrespective of the specific application. Of course, it will be appreciated that the specific control law implemented, and the sensed or received and controlled quantities will vary from one application to the next.

[0057] With reference to FIG. 4, a method of operating the energy storage and conversion system is now described. Fluid flow from the reservoir 6 to the device 4 is caused at step 34 and at step 36 an electric field is applied to electrodes 16/17 to separate charged species in the fluid. In some embodiments, there is no or substantially no fluid flow and the kinetic energy is thought to be mainly provided by thermal motion due to pressure, and in such embodiments (described further below), pressure is applied to the chamber 8 by filling it with fluid under pressure with an exhaust closed or no exhaust present and keeping the chamber 8 connected to a source of pressurised fluid, for example the reservoir 6, or isolating the chamber from the reservoir. In embodiments in which the fluid is a gas, the gas is ionised by the electric field. For example, in some embodiments, the electric field cause a dark or a corona discharge in the gas. In some embodiments, the fluid is caused to flow along the direction of the electric field, depending on the geometry of the device 4. At step 38, the charged species (either inherent in the fluid or generated by ionisation, for example gas ions and electrons), are collected by the collection electrodes 16. The charged species may be affected differentially by the fluid flow due to, for example, the mobility of each species and/or the arrangements of electrodes relative to the flow. As a result, one of the charged species may preferentially leave the device 4 through the exhaust port 20 and the other one of the charged species may preferentially be collected by a corresponding electrode 15/17, as the case may be. As a result, due to the flow of fluid, the potential difference between electrodes 15/17 may be increased beyond that which it is would be otherwise and the corresponding excess charge can be drawn as current by the load 28 to do electrical work at step 40.

[0058] As described above, either or both of the fluid flow at step 34 (for example via a valve) or applied electric field at step 36 (for example via a voltage setting for the supply 22) may be controlled on the basis of one or more sensed or received parameters, in some embodiments. A sensed parameter may be indicative of energy dissipated by the load and a received parameter may be indicative of energy demand by the load. Control may further be based on sensed parameters like the pressure in the reservoir 6. Additionally, the voltage by the supply 22 is controlled, for example as described above based on power demand, to provide a field strength sufficient to ionise the fluid in the case of embodiments in which the fluid is a gas and for the device 4 to be able to supply the power demanded. The voltage may in some embodiments vary with time. For example, in some embodiments, a higher voltage is initially provided by the supply 22 until a discharge occurs in the gas and/or a plasma is generated and the voltage is then reduced to a lower level sufficient to maintain the discharge or plasma. Control of the field strength may be based on feedback, a time protocol or both to achieve efficient use of the fluid and meeting power demands.

[0059] The flow rate may be controlled to be substantially constant to the extent achievable, for example as the pressure inside the reservoir 6 varies and/or based demand or actual power dissipated in the load (or a related measure—see above). The controller may, in some embodiments, respond to power demand/power dissipated by increasing the flow rate and/or supply voltage. In addition or alternatively, in some embodiments the controller controls the pressure inside the flow chamber 8, for example in response to a signal from a pressure sensor inside the flow chamber 8. Flow rate and/or pressure may be controlled by controlling the flow resistance of the inlet conduit and port 12, 10 on the one hand and/or the flow resistance of the exhaust conduit and port 14, 20 on the other hand. For example, in some embodiments, a throttle valve may be provided in either or both of the conduits 12, 14 and/or the ports 10, 20 may have a variable aperture. In some embodiments, the throttle valve and/or variable aperture, as the case may be, are under the control of the controller, for example to control flow rate and/or pressure as described above.

[0060] It will be appreciated that the described control aspects are applicable to all embodiments described, including those described above with reference to FIG. 1, 2 or 3, as well as the further embodiments relating to flowing fluids below.

[0061] In some embodiments, the direction of flow and the field direction may point in generally opposite directions (i.e. have a negative scalar product). In these embodiments, the positive charged species is biased to move in different directions by the electric field and the flow. In the case of an ionised gas as working fluid, this means that the positive ions in the gas are in effect blown away from their corresponding capture electrode 16/17 by the flow and may thus be removed from the device 4 efficiently, while the higher mobility electrons are less affected by the fluid flow and in any case are biased towards their respective capture electrode 16/17 by the fluid flow. In some embodiments, however, the relative orientation of fluid flow and electric field may be reversed.

[0062] The performance of the specific embodiment described above with reference to FIG. 1 was characterised by way of illustration by varying the input voltage of the supply 22 between 9 and 12 Volt for a fixed flow rate of 0.1 ml/minute, a reservoir pressure of 10 bar and supply current of 2 A and two loads, which resulted in a varying power dissipated in the load above a threshold input voltage. The output voltage of the supply was pulsed with a maximum voltage amplitude of approximately 30 kV at the threshold input voltage and approximately 45 kV at the maximum supply input voltage of 12V. Some results are presented in the following table:

TABLE-US-00001 Threshold Power dissipated Power dissipated Load supply voltage at thresh. voltage at max voltage (Ohm) (V) (W) (W) 10 9.6 6.4 40 4.7 9.7 13.6 340

[0063] With reference to FIG. 5, in some embodiments of the system 2, the collection electrodes 10, 14 are tungsten, for example thoriated tungsten, rods disposed through wall of the flow chamber 8, for example a quartz chamber or a glass/silica chamber and the wall seals around the collection electrodes. It will be appreciated that any non-conducting material that can withstand the pressures and temperatures involved in each embodiment can be used and, similarly, any suitable electrode material can be used. The inlet 12 and outlet 20 are oriented relative to the chamber 8 to provide fluid flow substantially diagonally across the chamber 8. Only the chamber 8 and its components are illustrated in FIG. 5, the remaining components are omitted for clarity and are, in some embodiments, as described above with reference to FIG. 1. A simplified circuit diagram in which the device 4 is represented by a voltage source with positive and negative poles corresponding to the collection electrodes 10, 14, is illustrated in FIG. 6.

[0064] In some embodiment, for example any of the embodiments described above, the applied electric field is pulsed at step 36, that is the output voltage of the supply 22 is pulsed to produce a pulsed waveform of electric field strength/potential difference between electrodes 16 that comprises a sequence of pulsed. For example, the pulses may have a complex shape, such as a large pulse with smaller pulses each side, with a pulse width of 1 ms and a cycle time of 4 ms. It will be appreciated that other pulse-shapes, such as a substantially top-hat shape, a sinc shape, a bell shape or any other suitable shape may be employed. In some embodiments, additionally or alternatively, the chamber 8, for example in particular the collector electrodes, may be irradiated with electromagnetic radiation in the wavelength range of 120NM to 820NM, for example UV light to facilitate ionisation in the chamber 8. In such embodiments, a corresponding radiation/light source (not shown) is disposed in relation to the chamber 8 to irradiate the chamber accordingly.

[0065] Using the embodiment described with reference to FIG. 5, a one-minute experimental run of gas flow (neon gas) through the chamber 8 with a pulsed applied electric field were run with the following experimental parameters and result:

TABLE-US-00002 Pulsed applied electric field Potential Resistor Flow Gas Measured Calculated Calculated Input diff. Value rate Pressure Voltage Vrms Current rms Power rms Power (kV) (ohms) (L/m) (Bar) (V) (A) (W) (W) 50.0 0.10 0.2 10 6.4 64 410 6.0

[0066] The potential difference corresponds to the pulsed potential difference across the electrodes 16 and hence the pulsed output of the source 22 (with a wave form as described in the specific example above and a maximum amplitude of 50 kv, rms 4 kv), the resistor value is the value of the load/measurement resistor illustrated in FIG. 6, where a Root Mean Square Voltage over the run is measured using an oscilloscope, with RMS current and power values calculated based on the value of the load resistor. The input power is the power fed to the supply 22 to generate the potential difference. The flow rate (litres per minute) and gas pressure refer to the flow rate and pressure of the gas in inside the chamber 9. It can be seen that the calculated RMS power dissipated in the load exceeds the input power, with the difference in power believed to be provided by the kinetic energy of the flow of pressurised ionised gas.

[0067] Corresponding data for a constant applied electric field, with otherwise unchanged experimental parameters, is presented in the following table:

TABLE-US-00003 Constant applied electric field Potential Resistor Flow Gas Measured Calculated Calculated Input diff. Value rate Pressure Voltage Vrms Current rms Power rms Power (kV) (ohms) (L/m) (Bar) (V) (A) (W) (W) 50.0 0.10 0.2 10 2.4 24 58 1.5

[0068] It can be seen that a pulsed application of the electric field may facilitate better extraction of energy from the pressurised gas flow with a ratio of calculated power dissipated across the load to electric input power of 68 for a pulsed applied field and 39 for the constant applied field.

[0069] With reference to FIG. 7, in one variant of the above embodiments, only a single collection electrode 14 is disposed within the chamber 8 and may be connected to a load in a floating or earth-connected manner.

[0070] With reference to FIG. 8, in some variants applicable to all embodiments described above and below, a means for delaying onset of current flow to enable more charge build-up on the collection electrodes 10, 14 is provided. Specifically, in some embodiments, the free ends 50 of the collection electrodes 10, 14 are enclosed in a respective further chamber 52 sealed to the chamber 8 and filled with an inert gas with low breakdown voltage, for example Neon, through a further respective inlet 54. A further respective electrode 56, for example a tungsten electrode, is disposed sealingly through the wall of the chamber 32 in juxtaposition with the free ends 30 to define a spark gap between each free end 30 and the corresponding further electrode 56. The further electrodes 36 are connected to the remaining system 2 (not shown) en lieu of the collection electrodes 10, 14.

[0071] As fluid flows through the chamber 8 while being ionised by the applied electric field, charge accumulates on the collection electrodes 10, 14 until a potential difference between the collection electrodes 10,14 exceeds the breakdown voltage of the inert gas in the further chambers 32 across the spark gap, at which point a discharge occurs and current flows through the further electrodes 36 as long as the spark is maintained. In this way, it will be seen that current flow is delayed until sufficient charge has built up on the electrodes 10,14 to cause a spark. Of course, it will be understood that any other way of delaying the onset of current flow can also be employed in related embodiments, for example using a voltage triggered relay or switch, a diode or timed switch in place of the spark gap.

[0072] As briefly mentioned above, energy stored in a pressurised fluid may be converted to electrical energy also by mainly or exclusive application of pressure to a fluid, as such.

[0073] Flow-based embodiments described above can be converted to pressure-based embodiments by blocking the exhaust 20, either permanently or removably, for example using a stop-cock. In some embodiments, illustrated in FIG. 9, the chamber 8 is modified by removing the exhaust 20 entirely, so that the chamber 8 is in fluidic communication only through the inlet 12.

[0074] An experimental one-minute run of pressure-based energy conversion was carried out using the embodiment of FIGS. 5 and 6 with the exhaust 20 blocked off and experimental parameters and results are presented in the following table for a pulsed electric field (with the same parameters described above for the flow-based experiment).

[0075] At the beginning of the run the chamber was filled with Neon gas at a pressure of 10 bar and the chamber was then sealed from the gas supply. Over the run a decline in pressure was observed, believed to be due to energy conversion, since the pressure was substantially constant over a similar time-period without drawing current from the collector.

TABLE-US-00004 Pulsed applied electric field Initial Final Potential Resistor Gas Gas Measured Calculated Calculated Input diff. Value Pressure Pressure Voltage Vrms Current rms Power rms Power (kV) (ohms) (Bar) (Bar) (V) (A) (W) (W) 50.0 0.10 10 <0.1 6.4 64 360 6.0

[0076] The calculated rms power is calculated over the whole one minute run and therefore averages over the change in pressure during the run.

[0077] As for the flow embodiments described above, the pressure embodiments can equally be operated with a pulsed or constant applied field, with otherwise unchanged experimental parameters. Experimental parameters and results are presented in the following table.

TABLE-US-00005 Constant applied electric field Initial Final Potential Resistor Gas Gas Measured Calculated Calculated Input diff. Value Pressure Pressure Voltage Vrms Current rms Power rms Power (kV) (ohms) (Bar) (Bar) (V) (A) (W) (W) 50.0 0.10 10 <0.1 6.4 64 40 1.5

[0078] As can be seen, a similar trend as for the flow-based experiments discussed above can be observed. For completeness it can be noted that the lower input power is due to a different power source being used and lower current drawn by the supply to maintain the constant field as opposed to continually charging and discharging the field electrodes.

[0079] As described above, any flow-based embodiment can be converted in to a pressure-based embodiment by stopping the exhaust 20. In some embodiments, illustrated in FIG. 9, the chamber 8 is modified by removing the exhaust 20 entirely, so that the chamber 8 is in fluidic communication only through the inlet 12, with other components of the device 4 remaining unchanged in some embodiments. In some other embodiments, illustrated in FIG. 10, a partition 58, for example a quartz window, sealingly partitions the chamber 8 into two portions, each one comprising one of the collections electrodes 10, 14 and the exhaust 20 is connected as a further inlet 12 so that each portion of the chamber 8 has a respective inlet 12 connected to a source of pressurised fluid and pressure is maintained independently in each portion of the chamber 8, with other components of the device 4 remaining unchanged in some embodiments. In some embodiments the chamber is made as a unitary workpiece comprising the chamber wall and partition 58.

[0080] Specific embodiments have been described above by way of example to illustrate aspects of the disclosure. It will be understood that the scope of the invention is set out in the appended claims. Many modifications and different combinations of features will be apparent to a person having ordinary skill in the art, for example as set out above, which are within the scope of the claims. Further, it will be appreciated that the order of steps of the method embodiments can be changed as suitable and that some or all of the steps may indeed be carried out in fully or partially overlapping relationship in time. Equally, features of the various embodiments described above may be combined as appropriate. Some of the embodiments are based on fluid flow, while others are based on an applied pressure, with no or minimal flow. It will be understood that, as applicable, any feature described with respect to a flow based embodiment is also applicable to any pressure based embodiments and vice versa. Where the present invention makes reference to charged, positive and negative respectively, species, each species may correspond to a single type of entity (e.g. singly charged positive gas ions and electrons, respectively) or each may comprise sub-species, for example positively charged gas ions with different respective charges. Similar considerations apply to embodiments in which the liquid is a solution with respective ions inion.

[0081] For the avoidance of doubts, some aspects and embodiments are set out in the following list of items:

[0082] 1. A device for converting kinetic energy of a fluid to electrical energy, the device comprising: [0083] a flow chamber having an inlet port for a fluid and an exhaust port for the fluid; [0084] a pair of charge collecting electrodes spaced apart from each other along a collection direction and disposed within the flow chamber; and [0085] an electric field generator configured to generate an electric field in the flow chamber along a field direction to separate charged species in the fluid, wherein a flow path for the fluid between the inlet port and the exhaust port has a flow direction with a component along the collection direction and a component along the field direction.

[0086] 2. A device according to item 1, wherein the electric field is an ionising electric field to ionise the fluid.

[0087] 3. A device according to item 1 or 2, wherein the electric field generator comprises a pair of field generating electrodes spaced apart along the field direction and disposed on either side of the flow chamber.

[0088] 4. A device according to item 3, wherein the field generating electrodes are electrically isolated from the flow chamber.

[0089] 5. A device according to any preceding item, wherein the field and flow directions are substantially parallel.

[0090] 6. A device according to any preceding item, wherein the collection and flow directions are substantially parallel.

[0091] 7. A device according to any preceding item, wherein the charge collecting electrodes are centred on an axis coinciding with at least a portion of the flow path.

[0092] 8. A device according to any preceding item, wherein the flow path passes through the charge collecting electrodes.

[0093] 9. A device according to any preceding item, wherein the charge collecting electrodes are mesh electrodes.

[0094] 10. A system for converting kinetic energy of a fluid to electric energy, the system comprising: [0095] a device as itemed in any preceding item; [0096] a current limited voltage supply to generate the ionising electric field; and [0097] a load connected to one of the charge collecting electrodes.

[0098] 11. A system according to item 10 comprising a connector for connecting the inlet port to a container containing pressurised fluid.

[0099] 12. A system according to item 11, wherein the container is removably connected to the connector to enable an empty container to be replaced with a fresh container containing pressurised fluid.

[0100] 13. A system according to any one of items 10 to 12 comprising a controller to regulate a rate of flow of the fluid.

[0101] 14. A system according to item 13, wherein the controller is configured to receive a quantity indicative of energy dissipated by the load and to regulate a rate of flow of the fluid as a function of the quantity indicative of energy dissipated by the load.

[0102] 15. A system according to item 13 or 14, wherein the controller is configured to receive a quantity indicative of energy demand by the load and to regulate a rate of flow of the fluid as a function of the quantity indicative of energy demand by the load.

[0103] 16. A system according to any one of items 10 to 15, wherein the load is an electric motor.

[0104] 17. A system according to item 16, wherein the electric motor is installed in an electric vehicle, for example an electric or hybrid car, bicycle, tricycle, ship, train or airplane.

[0105] 18. A system according to any one of items 10 to 15, wherein the load comprises an electricity supply network, for example a utility substation or an electricity supply network of one or more commercial or residential units.

[0106] 19. A method of converting potential energy of a pressurised fluid to electric energy, the method comprising: [0107] causing the pressurised fluid to flow through a flow chamber along a flow direction, thereby converting the potential energy to kinetic energy of the flowing fluid; [0108] applying an electric field to the fluid flowing in the flow chamber, the electric field having a field direction with a component along the flow direction, thereby separating positive and negative species of the fluid along the field direction with one of the positive and negative charged species being biased to move in a direction having a component in the flow direction and the other one of the positive and negative charged species being biased to move in a direction having a component in a direction opposite the flow direction; [0109] collecting at least a fraction of one or each of the positive and negative charged species at a respective current collector; and [0110] drawing a current from one of the current collectors to provide electrical energy to a load.

[0111] 20. A method according to item 19 comprising ionising the fluid by applying the electric field to the flowing fluid to produce an ionised fluid comprising the negative and positive charged species.

[0112] 21. A method according to item 20, wherein ionising the fluid comprises generating a plasma.

[0113] 22. A method according to item 20 or 21, wherein ionising the fluid comprises causing a discharge, for example a dark or corona discharge.

[0114] 23. A method according to any one of items 19 to 22, the method comprising sensing a quantity indicative of energy dissipated by the load and regulating a rate of flow of the fluid and/or as a function of the quantity indicative of energy dissipated by the load.

[0115] 24. A method according to any one of items 19 to 23, the method comprising receiving a quantity indicative of energy demand by the load and regulating a rate of flow of the fluid as a function of the quantity indicative of energy demand by the load.

[0116] 25. A device, system or method according to any preceding item, wherein the scalar product of the flow direction and the field direction is negative.

[0117] 26. A device, system or method according to any one of item 1 to 24, wherein the scalar product of the flow direction and the field direction is positive.

[0118] 27. A device, system or method according to any preceding item, wherein the fluid is a gas, for example air, Argon or Neon.

[0119] 28. A device, system or method according to any preceding item, wherein the fluid is an inert gas.

[0120] 29. A device for converting kinetic energy of a fluid to electrical energy, the device comprising:

[0121] a flow chamber having an inlet port for a fluid and an exhaust port for the fluid;

[0122] a pair of charge collecting electrodes spaced apart from each other along a collection direction and disposed within the flow chamber; and

[0123] an electric field generator configured to generate an electric field in the flow chamber along a field direction to separate charged species in the fluid.

[0124] 30. A method of converting potential energy of a pressurised fluid to electric energy, the method comprising:

[0125] causing the pressurised fluid to flow through a flow chamber along a flow direction, thereby converting the potential energy to kinetic energy of the flowing fluid;

[0126] applying an electric field to the fluid flowing in the flow chamber with an electric field generator;

[0127] collecting at least a fraction of one or each of the positive and negative charged species at a respective current collector; and

[0128] drawing a current from one of the current collectors to provide electrical energy to a load.

[0129] 31. The device according to item 29 or method according to item 30, wherein the electric field generator comprises a pair of field generating electrodes spaced apart along the field direction and disposed on either side of the flow chamber and wherein the field generating electrodes are electrically isolated from the flow chamber.

[0130] In any of these items, the applied electric field may be a pulsed electric field, and/or the flow chamber may be irradiated with electromagnetic radiation, for example UV light or electromagnetic radiation within one or more wavelength in a range of 120NM to 820NM. Additionally, or alternatively, the current flow may be delayed in any of the items, to enable an amount of charge to build up on the electrode(s) before current flows. In addition, or in alternative, to all, some or any of these variations, the pair of charge collecting electrodes may be replaced with a single charge collecting electrode in all items.

[0131] In any of the items above, the device or system may be configured to limit flow rates in and/or out of the flow chamber or pressure vessel to less than 0.1 ml/minute, for example less than 9×10{circumflex over ( )}−2 ml/minute, less than 8×10{circumflex over ( )}−2 ml/minute or less than 7×10{circumflex over ( )}−2 ml/minute, or may, more generally be configured to cause fluid to flow through the pressure vessel or flow chamber at a flow rate different from 0.1 ml/minute, for example 9×10{circumflex over ( )}−2 ml/minute, 8×10{circumflex over ( )}−2 ml/minute or 7×10{circumflex over ( )}−2 ml/minute, as well as a flow rate higher than 0.1 ml/minute, for example 0.5 ml/minute or higher, 1 ml/minute or higher, 0.051/minute or higher, 0.1 ml/minute or higher or 0.2 ml/minute or higher. Equally, the device and/or system may be configured to operate at specific pressure, for example a pressure different from 10 bar, such as more than 10 bar, for example 11 bar or more or 12 bar. The pressure may be less than 10 bar, for example 9 bar or less, 8 bar or less, 7, 6 or 5 bar or less and in any of these cases, the pressure may be more than 1 bar, more than 2 bar, more than 3 bar or more than 4 bar. In some embodiments, the flow rate is substantially zero. For example, in some embodiments, the inlet port is the only fluidic communication path to and from the pressure vessel. It will be appreciated that the corresponding method items may operate accordingly.