Cryogenic cooling system

Abstract

The invention relates to a mobile cryogenic cooling system comprising: o at least one compressor (1a, 2a) to compress a cryogenic gas and at least one radiator (1b, 2b) to cool the compressed cryogenic gas, o at least one expansion valve (4), o a heat exchanger (5) suitable for being connected to a cooling apparatus, o two regenerators (7, 8), suitable for exchanging heat energy between the compressed cryogenic gas and the expanded cryogenic gas downstream of the heat exchanger (5), characterised in that it comprises at least one intermediate heat exchanger (10), cooled by a cooling device (14), and in that the intermediate heat exchanger (10) is arranged so as to cool the cryogenic gas from the first regenerator (7) before the cryogenic gas flows into the second regenerator, the expansion valve (4) being arranged downstream of the second regenerator so as to cool the gas to a cryogenic temperature.

Description

[0001] CRYOGENIC COOLING SYSTEM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a mobile cryogenic cooling system.

[0004] STATE OF THE ART

[0005] A Turbo-Brayton type cooling system uses compression, cooling, and expansion processes to achieve cooling by adiabatic expansion of a gas initially at room temperature.

[0006] Such a cooling system may have several compression levels by successive compressors. Each compression causes the compressed gas to heat up. In general, the gas compression is carried out at ambient temperature and a radiator or other cooling device is used downstream of each compressor so as to cool the compressed gas to a temperature close to ambient temperature, by dissipating energy from the compressed gas. The compressed gas is then significantly cooled in a recuperative exchanger and then reaches its minimum temperature by an expansion downstream of said recuperative exchanger. The gas can therefore be used for the intended application, for example the cooling of a superconducting device such as a propulsion engine, or the liquefaction of another gas such as hydrogen.

[0007] During use, the gas temperature increases as a result of heat exchange with the device to be cooled. The gas is then reused as a cold source to cool the compressed gas in the recuperator exchanger and its temperature increases to a value close to ambient temperature. In general, the gas is directly reintroduced into the successive compression system.

[0008] For the cooling of electric propulsion systems using superconducting elements, efficient heat exchangers are required for heat exchange between a low temperature of about 20K and a high temperature that is slightly above the temperature of the system environment, which is typically around 290K on the ground and can drop to about 220K for an aircraft at altitude.

[0009] For the condensation or liquefaction of hydrogen from cold hydrogen vapor, the low temperature is 205 K, requiring recovery exchangers that are also very efficient.

[0010] Figure 1 illustrates such a cooling system. After the compression steps in compressors 1a and 2a, the compressed gas is cooled to room temperature by radiators 1b and 2b. The gas is then cooled to a temperature of approximately 20-25 K by passing through a counterflow heat exchanger 3 in duct 3a. After this passage, the gas is expanded in an expansion member 4 which is typically an expansion turbine. At the outlet of the expansion member 4, the gas reaches a temperature of 17-18 K and is therefore suitable for cooling an application 50 such as a superconducting engine to 20 K.

[0011] After the heat exchange 55 in the exchanger 5, the gas temperature becomes close to 20K. Via the conduit 3b, the gas is returned to the recovery exchanger 3, in which it is used to cool the compressed gas to ambient temperature in the conduit 3a. During this last step, said gas is reheated to a temperature close to ambient temperature and can be reintroduced into the successive compression process from the compressor 1a.

[0012] Such cooling systems are heavy and very bulky. Even for relatively short cooling times, such as a short flight, the required system has a significant footprint and mass because it requires the same components as a system designed for long-term cooling. In addition, the power consumption of such systems is high.

[0013] STATEMENT OF THE INVENTION

[0014] An aim of the invention is to design a lighter and less bulky mobile cryogenic cooling system, having reduced electrical consumption, comprising: o at least one compressor for compressing a cryogenic gas and at least one radiator arranged downstream of said compressor for cooling the compressed cryogenic gas, o at least one expander for expanding the compressed cryogenic gas, o a heat exchanger adapted to be coupled to an apparatus to be cooled by the expanded cryogenic gas, o two recovery exchangers, adapted for an exchange of thermal energy between the compressed cryogenic gas upstream of the expander and the expanded cryogenic gas downstream of the heat exchanger, characterized in that it comprises at least one intermediate heat exchanger, cooled by a cooling device,and in that the intermediate heat exchanger is arranged so as to cool the cryogenic gas coming from the first exchanger-recuperator before the passage of said cryogenic gas into the second exchanger-recuperator, the expander being arranged downstream of said second exchanger-recuperator so as to cool said gas to a cryogenic temperature.,

[0015] Such a system is versatile in the sense that its mass and volume can be adapted to the duration of use. It is thus possible to design a system with a minimum mass and volume for a target temperature and a known duration of use. The system also allows for local adaptation to constraints, because the intermediate exchanger can be cooled by different cold sources.

[0016] In some embodiments, the cooling device comprises a cryogenic fluid providing heat exchange with the intermediate heat exchanger. Thus, the weight and size can be adapted according to the duration of use, such as the duration of a flight for an application in an aircraft, by limiting the volume of cryogenic fluid to the volume required for the duration of use of the system. Advantageously, the cryogenic fluid is nitrogen or methane.

[0017] In other embodiments, the cooling device comprises at least one Turbo-Brayton type cryocooler, a Stirling cycle based cryocooler or a pulse tube.

[0018] Advantageously, the efficiency of the first recovery exchanger is lower than the efficiency of the second recovery exchanger.

[0019] Preferably, the heat exchanger is adapted to cool an apparatus to a temperature between 17 K and 50 K and more preferably between 17 K and 20 K.

[0020] Advantageously, the radiators comprise fixing elements adapted to hold said heat exchanger on an external wall of an aircraft or are thermally connected to a structure cooled by the external environment of said aircraft.

[0021] The invention also relates to an electrically powered vehicle or aircraft using at least one superconducting element comprising a cryogenic cooling system as described above, said cooling system being arranged so as to thermally couple the heat exchanger to the at least one superconducting element to be cooled. Preferably, the radiators are arranged on an external wall of said vehicle or aircraft or in heat exchange with the external environment of said vehicle or aircraft.

[0022] Advantageously, said electrically powered vehicle or aircraft comprises a fluidic connector capable of fluidly connecting the cold source to a source of cryogenic fluid to cool the heat exchanger to a cryogenic temperature. Advantageously, said electrically powered vehicle or aircraft further comprises a cryogenic fluid reservoir arranged in said vehicle or aircraft, said cryogenic fluid being in fluidic connection with the intermediate heat exchanger to cool said heat exchanger to a cryogenic temperature.

[0023] The invention also relates to a hydrogen liquefaction installation, comprising a vehicle, a container or an aircraft, a cryogenic cooling system as described above, arranged in said vehicle, container or aircraft, said installation being arranged so as to thermally couple the heat exchanger to a source of hydrogen to be liquefied or to a superconducting element. In certain embodiments, said hydrogen liquefaction installation comprises a cryogenic fluid tank arranged in said vehicle or container or aircraft, said tank being in fluid connection with the intermediate heat exchanger to cool said intermediate heat exchanger to a cryogenic temperature using the cryogenic fluid.In other embodiments, the hydrogen liquefaction installation comprises a connector adapted to establish a fluid connection between the intermediate heat exchanger and a cryogenic fluid tank outside said vehicle, container or aircraft, to cool said intermediate heat exchanger to a cryogenic temperature.

[0024] The invention also relates to a cryogenic cooling method, comprising the following steps: o one or more steps of compressing a cryogenic gas in a compressor and a step of cooling said compressed gas by a radiator after each compression step, o passing said gas through a first heat exchanger-recuperator so as to cool the compressed gas to a first temperature, o passing the gas downstream of the first heat exchanger-recuperator into an intermediate heat exchanger, cooled by a cooling device, so as to cool the gas coming from the first heat exchanger-recuperator to an intermediate temperature lower than the first temperature, o passing said gas downstream of the intermediate heat exchanger into a second heat exchanger-recuperator, so as to cool the gas coming from the intermediate heat exchanger to a second temperature lower than the intermediate temperature,o the expansion of said gas in an expansion member so as to cool said gas to a cryogenic temperature lower than the second temperature, o the use of said gas for cooling a device to be cooled, o the passage of said gas downstream of the device to be cooled in the second exchanger-recoverer and the first exchanger-recoverer by recovering the thermal energy of the compressed gas in the circuit.,

[0025] BRIEF DESCRIPTION OF THE FIGURES

[0026] Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings, in which:

[0027] Figure 1 is a schematic view of a cryogenic cooling system of the conventional Turbo-Brayton type. Figure 2 is a schematic view of a cryogenic cooling system according to the invention.

[0028] Figure 3 illustrates the application of a cryogenic cooling system according to the invention in an aircraft.

[0029] Figure 4 shows in detail the cooling system of Figure 3.

[0030] Figure 5 illustrates the application of a cryogenic cooling system according to the invention in a mobile container.

[0031] DETAILED DESCRIPTION OF EMBODIMENTS

[0032] Cooling system structure

[0033] Figure 2 is a schematic view of a cryogenic cooling system according to the invention. The system is mobile in the sense that it is arranged in a means of transport such as a vehicle, a trailer, or an aircraft, and / or can be easily embarked in such a means of transport. For example, the system can be installed in a container configured to be transported by a vehicle. The system comprises one or more radiators 1b, 2b each located at the outlet of a respective compressor 1a, 2a. The system further comprises two heat exchangers 7 and 8. Each heat exchanger comprises a cooling duct 7a, 8a downstream of the radiator(s) 1b, 2b and upstream of one or more expansion valves 4, and a recovery duct 7b, 8b in heat exchange with the cooling duct 7a, 8a of the respective heat exchanger 7, 8. The expander is for example an expansion turbine or a Joule-Thompson type expander.To increase the efficiency of the system, several regulators can be arranged in series or in parallel.

[0034] An intermediate heat exchanger 10 is arranged between the cooling duct 7a of the first recovery exchanger 7 and the cooling duct 8a of the second recovery exchanger 8.

[0035] The intermediate heat exchanger provides a cold environment allowing, by heat exchange, the gas to be cooled downstream of the cooling duct 7a of the first recovery exchanger 7 and upstream of the cooling duct 8a of the second recovery exchanger 8. By "cold", is meant in the present text that the zone or element concerned is at a cryogenic temperature, that is to say a temperature typically lower than 150 K.

[0036] As an illustrative and non-limiting example, the intermediate heat exchanger 10 may be a cryorefrigerator of the Turbo-Brayton type or a cryorefrigerator based on the Stirling cycle or a pulsed tube, or a combination of several cryorefrigerators of the same type or of different types. Alternatively, the intermediate heat exchanger 10 may be an exchanger in fluid connection 12 with a cooling fluid in a tank 14, or immersed in a bath of cooling fluid. In this case, the cryogenic fluid circulates so as to use the heat capacity of said cryogenic fluid for cooling the gas downstream of the cooling conduit 7a of the first recovery exchanger 7 and upstream of the cooling conduit 8a of the second recovery exchanger 8.Advantageously, the cryogenic fluid is a cryogenic liquid having high cryogenic power due to its latent heat, such as liquid nitrogen or liquid methane. In some embodiments, the intermediate heat exchanger is a combination of a cryorefrigerator and a device cooled using a cryogenic fluid.

[0037] A heat exchanger 5, arranged downstream of the expander(s) 4, allows the heat exchange 55 with the application 50. The application is, by way of illustration and not limitation, a superconducting engine for example in an aircraft, or a hydrogen cooling or liquefaction system.

[0038] Said heat exchanger 5 is fluidically connected to the recovery conduit 8b of the second exchanger-recoverer 8, which is in turn fluidically connected to the recovery conduit 7b of the first exchanger-recoverer 7.

[0039] A conduit capable of reintroducing the gas into the compressor 1a is arranged downstream of the recovery conduit 7b of the first exchanger-recoverer 7.

[0040] How the cooling system works

[0041] In order to cool an application 50, a cryogenic gas included in the system is compressed in the compressors 1a and 2a, such compression producing heating of said gas. Preferably, said cryogenic gas is helium. Alternatively, the gas may be a mixture of helium and neon, or hydrogen, or a mixture of hydrogen and neon, or a mixture of the three fluids mentioned. After each compression step, the compressed gas is cooled to a temperature close to the ambient temperature of the system by a radiator 1b or 2b. The ambient temperature is typically around 290K on the ground and may drop to around 220K for an aircraft at altitude.

[0042] The compressed gas is then cooled to a first low temperature, for example 90 K, by passing through the recovery exchanger 7 in the conduit 7a. The gas is then cooled by the intermediate heat exchanger 10 to an intermediate temperature, for example 80 K.

[0043] The gas downstream of the intermediate exchanger is cooled to a second low temperature, for example 22 K, by passing through the recovery exchanger 8 in the conduit 8a. The intermediate temperature is lower than the first low temperature and higher than the second low temperature. After this passage, the gas is expanded in the expansion valve(s) 4. At the outlet of the expansion valve(s) 4, the gas reaches its minimum temperature (lower than 20 K) and is conducted into the exchanger 5 thermally connected to the intended application 50.

[0044] After the heat exchange 55 in the exchanger 5, the temperature of the gas becomes close to the application temperature 50. Via the conduit 8b, the gas is returned to the second recovery exchanger 8, in which it is used to cool the compressed gas to the intermediate temperature in the conduit 8a. Then, via the conduit 7b, the gas is returned to the first recovery exchanger 7, in which it is used to cool the compressed gas to ambient temperature in the conduit 7a. During this last step, said gas is reheated to a temperature close to ambient temperature and can be reintroduced into the process of successive compressions from the compressor 1a.

[0045] Applications

[0046] As an illustrative and non-limiting example, the system can be used for cooling the superconducting components of an engine, for example for the propulsion of an aircraft.

[0047] Such an aircraft engine may include components, for example electromagnetic coils, made of superconducting material, allowing an increase in the power of the machine. These components must be maintained at a temperature below the lowest critical temperature of the superconducting components during the operation of the engine.

[0048] The system can also be used to cool a superconducting generator or any other superconducting system, for example a cable or a current limiter. In this case, the temperature of the cryogenic gas at the inlet of the exchanger 5 is typically close to 20 K. The system is therefore capable of cooling the superconducting element to a temperature between 20 and 50 K.

[0049] Figure 3 illustrates an aircraft 90 equipped with a turbo-generator 95 to be cooled, two superconducting motors to be cooled, and a cooling system 91 according to the invention. The aircraft 90 comprises a tank 92 containing a cryogenic liquid, for example liquid methane at 110K, intended to cool the turbo-generator 95 used to generate the electrical energy necessary for the operation of the aircraft. This liquid methane is further used to cool the intermediate heat exchanger of the cooling system 91.

[0050] The cooling system 91 comprises two radiators 98 at the outlet of the two compressors. The radiators 98 are arranged close to the wall 97 allowing thermal contact with the air outside the aircraft, which represents a temperature of approximately 220 K at altitude. Alternatively, a heat exchanger can be used to establish thermal contact between the outside air and the radiators 98.

[0051] Referring to Figure 4, the cryogenic liquid in the tank 92 is used for cooling the intermediate heat exchanger of the cooling system 91, and then used for cooling the turbo-generator 95 for the production of electrical energy. The cooling ducts 99 of the generator 95 and the cooling ducts 96 of the superconducting motors are cooled by the cooling system 91 to a temperature close to 20 K.

[0052] Alternatively, the system can be used for liquefaction or reliquefaction of hydrogen or cooling of liquid hydrogen during storage. Liquefaction means a process of changing hydrogen from a gaseous state to a liquid state from hydrogen at room temperature, i.e. at a temperature of approximately 280-300 K, which involves cooling the hydrogen and then liquefying it. Reliquefaction or condensation means a process of changing hydrogen from a gaseous state to a liquid state from cold vapors that have just been generated by evaporation of a portion of the liquid hydrogen and are still cold, i.e. at a temperature close to that of liquid hydrogen. Reliquefaction or condensation therefore only involves liquefying the hydrogen without going through a cooling phase because the vapors are already cold.Subcooling means a process of cooling liquid hydrogen to a temperature below the liquefaction temperature.

[0053] For the liquefaction, re-liquefaction or subcooling of hydrogen, the temperature of the cryogenic gas at the inlet of the exchanger 5 is 17-35K. Said gas is therefore capable of liquefying hydrogen at a temperature between 20 and 35K, or of subcooling liquid hydrogen at a temperature between 20 and 30K. The heat exchanger 5 must be adapted to operate at a temperature between 17K and 35K and more advantageously between 17K and 25K.

[0054] During storage of hydrogen at cryogenic temperature, continuous cooling is maintained to limit pressure build-up in the storage tank and prevent hydrogen loss through evaporation. Alternatively, cooling can be applied intermittently at regular intervals, by allowing the pressure in the tank to build up to a limit pressure and then initiating cooling to reduce the pressure.

[0055] Hydrogen can be used to power a fuel cell or a hydrogen combustion engine, also in aeronautical applications. A cooling system can thus be used in aeronautics for simultaneous cooling of a quantity of hydrogen and superconducting components. Uses and advantages

[0056] The intermediate heat exchanger 10 is used to cool the cryogenic gas during its flow at high pressure to an intermediate temperature, higher than the cold temperature required by the application. The first heat exchanger-recuperator 7 is used to lower the temperature upstream of the intermediate heat exchanger. The more additional cooling the intermediate heat exchanger 10 provides, the less cooling power the first heat exchanger-recuperator requires, and vice versa. The power of the first heat exchanger-recuperator and the intermediate heat exchanger 10 can therefore be adjusted according to the constraints of the environment in which the cooling system is used.

[0057] The first heat exchanger 7 can therefore be considerably less bulky and less heavy than a heat exchanger in a known cooling system as described above, providing the same cold temperature. The second heat exchanger 8 is used downstream of the intermediate heat exchanger 10 at a temperature closer to that required by the application. With regard to the second heat exchanger 8, a lower cooling power than in a known system is sufficient to obtain the desired cooling. The electrical consumption of each compressor 1a, 2a downstream of the first heat exchanger 7 is reduced.

[0058] The second heat exchanger-recuperator 8 can therefore be considerably less bulky and less heavy than a heat exchanger-recuperator in a known cooling system providing the same cold power at the same cold temperature.

[0059] Thanks to the intermediate heat exchanger 10, the flow rate of the cooling cycle can be reduced by a factor of approximately 2 or 3 compared to a known cooling system, to obtain an identical transmitted power at the level of the exchanger 5.

[0060] For example, for a cold temperature of 20 K at a given power, the volume and mass of each heat exchanger-recuperator can be reduced by a factor of between 4 and 5 compared to that of an exchanger-recuperator in a known cooling system and the electrical consumption of each compressor is reduced by a factor of between 3 and 4.

[0061] Even considering the need for two heat exchangers and an intermediate heat exchanger, a system according to the invention allows a reduction in mass and size and simultaneously a reduction in electrical consumption depending on the components used compared to a known cooling system.

[0062] The second heat exchanger-recuperator 8 requires a certain level of efficiency in order to reach the second low temperature which is for example approximately 20 K. Advantageously, the first heat exchanger-recuperator 7 has a lower efficiency which is generally sufficient for cooling to the first low temperature and makes it possible to size the first heat exchanger-recuperator in a lighter and less bulky manner.

[0063] In particular, when cooling is to be carried out for a limited period, for example a short flight, the intermediate heat exchanger can be supplied with a limited quantity of cryogenic fluid, cooled before the flight by a ground system. The mass and size of the cooling system can thus be sized according to the required cooling duration.

[0064] Cooling of limited duration can thus be carried out during a journey by vehicle, transport of a container for example by a boat or a vehicle, or a flight by aircraft. In this case, said vehicle, container or aircraft comprises a cooling system in which at least part of the cooling of the intermediate heat exchanger 10 is carried out by a cryogenic fluid. The vehicle, container or aircraft further comprises a tank adapted to store a quantity of cryogenic fluid sufficient for the planned journey. Advantageously, the vehicle, container or aircraft further comprises a connector capable of fluidically connecting the cold source to a source of cryogenic fluid on the ground. The tank can thus be filled before the journey or flight in order to cool the heat exchanger to a cryogenic temperature during the journey or flight.Thus, the total mass of the cooling system is minimized depending on the cryogenic temperature used and the duration of the flight.

[0065] In other cases, the cryogenic cooler is arranged in a mobile container, which can be arranged on board a vehicle or aircraft. Cooling is carried out when said container is at rest. Cooling of the intermediate heat exchanger can be carried out using a cold source arranged at a fixed location. For example, the intermediate heat exchanger is fluidically connected to a liquid nitrogen storage tank. This solution also makes it possible to minimize the total mass of the system intended for transport.

[0066] Figure 5 illustrates the cooling system arranged in a mobile container 60 mounted on a truck. The cooling system can be connected to an external electricity source 63 and to an external tank 62 filled with a cryogenic fluid, for example liquid nitrogen. Thus, the cooling system can be designed to be less bulky and less heavy than a known cooling system, and can be powered by electricity and cryogenic liquid sources available at the place of its use. The system can be used for the liquefaction or re-liquefaction of liquid hydrogen in a tank 61, or for any other cryogenic application.

[0067] Table 1 illustrates the consumption, mass and requirement of cryogenic fluid in the case of different cooling systems providing a power of 1 kW at a temperature of 20K. This table only considers the main loop of the cooling system, in which the cryogenic gas circulates, and not the secondary loop which, in the invention, provides the cooling power required for the intermediate heat exchanger.

[0068] Table 1] A known turbo-Brayton type cooling system (first line of the table) providing such a power of 1 kW at a temperature of 20K has a mass of 1000 kg and a power consumption of 200 kW.

[0069] According to a first alternative provided by the invention (second line of the table), the same cooling power can be obtained at a temperature of 20K by using a cooling system comprising an intermediate heat exchanger cooled by a turbo-Brayton type machine providing a power of 5 kW at 80K. The electrical consumption of the main loop of such a system is 135 kW and its mass is approximately 580 kg. The assembly consisting of the main loop and the secondary loop has a lower electrical consumption and mass than those of the known system. It is thus possible to design lighter systems, which allows them to be carried on board an aircraft and a vehicle and also to save fuel for applications on board an aircraft or vehicle.

[0070] According to a second alternative provided by the invention (third row of the table), the same cooling power of 1 kW at a temperature of 20K can be obtained by using a cooling system comprising an intermediate heat exchanger cooled by liquid nitrogen providing a power of 5 kW at 80K. The power consumption of the main loop of the cooling system is 60 kW and the mass of the system is 250 kg. The power consumption of the secondary loop is 75 kW. The assembly consisting of the main loop and the secondary loop has a lower power consumption and mass than those of the known system. During operation, the system also consumes approximately 82 kg of liquid nitrogen per hour. For example, for a flight lasting 3 hours, this corresponds to a mass of liquid nitrogen of 246 kg, and a mass of the cooling system comprising this quantity of liquid nitrogen of 446 kg.For shorter flight durations, the system requires a smaller amount of cooling fluid such as liquid nitrogen and therefore has an even lower mass and footprint. This allows for the design of modular, lighter, and more compact cooling systems for shorter flight durations.

[0071] Moreover, in the case of use in a vehicle or aircraft, the radiators 1a and 1b may be arranged in thermal contact with the external environment of the aircraft, for example on an external wall of the aircraft using fastening elements adapted to hold the radiators 1a and 1b on such a wall during flight. Alternatively, the radiators 1a and 1b may be arranged on a heat-conducting wall in thermal contact with the external environment, or in thermal contact using slots, grilles or other openings allowing an exchange with the air outside the vehicle or aircraft.

[0072] This embodiment is very advantageous for use in an aircraft traveling at altitude. For example, at an altitude of 10 km from the ground, the temperature outside the aircraft can drop to approximately 220 K. Moving from an ambient temperature around 300 K to an environment such as the exterior of an aircraft, the cooling requirements to obtain the intermediate temperature decrease. For aeronautical applications, the cooling system according to the invention therefore allows for greater savings in weight and size.

[0073] For the example of a cooling system providing 1 kW of power at a cold temperature of 20K using an intermediate heat exchanger with a power of 5kW at an intermediate temperature of 80K, a drop in ambient temperature from 300K at ground level to 220K at 10 km altitude results in a drop in the cooling requirement by the intermediate heat exchanger to 2.5 kW for an intermediate temperature of 80K. In the case where liquid nitrogen is used to cool the intermediate heat exchanger, the liquid nitrogen consumption is reduced by a factor of 2.

[0074] Moreover, superconducting aircraft engines are generally sized for flight phases requiring maximum engine power, particularly the takeoff phase. The cryogenic cooler is then sized for the maximum engine power. When the aircraft is in the cruise or landing phase, the engine and cryogenic cooling system power are lower. The cooling provided by the intermediate heat exchanger can therefore be adapted, and, if necessary, its cryogenic fluid requirement. Such an adaptation further reduces the mass and size of the cooling system by more precisely adapting the quantity of fluid used for intermediate cooling.

Claims

DEMANDS 1. A mobile cryogenic cooling system comprising: at least one compressor (1a, 2a) for compressing a cryogenic gas and at least one radiator (1b, 2b) arranged downstream of said compressor for cooling the compressed cryogenic gas, at least one expansion valve (4) for expanding the compressed cryogenic gas, a heat exchanger (5) adapted to be coupled to a device to be cooled by the expanded cryogenic gas, two heat recovery exchangers (7, 8) adapted for the exchange of thermal energy between the cryogenic gas compressed upstream of the expansion valve (4) and the cryogenic gas expanded downstream of the heat exchanger (5), characterized in that it comprises at least one intermediate heat exchanger (10), cooled by a cooling device (14), and in that the intermediate heat exchanger (10) is arranged so as to cool the cryogenic gas from the first heat recovery exchanger (7) before the passage of said cryogenic gas into the second heat recovery exchanger.the expansion valve (4) being arranged downstream of said second heat exchanger-recuperator so as to cool said gas to a cryogenic temperature.

2. System according to claim 1, wherein the cooling device comprises a cryogenic fluid ensuring heat exchange with the intermediate heat exchanger (10).

3. System according to claim 2, wherein the cryogenic fluid is nitrogen or methane.

4. System according to claim 1, wherein the cooling device comprises at least one Turbo-Brayton type cryo-refrigerator, a Stirling cycle based cryo-refrigerator or a pulsed tube.

5. System according to any one of the preceding claims, wherein the efficiency of the first recuperating exchanger (7) is less than the efficiency of the second recuperating exchanger (8).

6. System according to any one of the preceding claims, wherein the heat exchanger (5) is adapted to cool a device to a temperature between 17 K and 50 K and more advantageously between 17 K and 20 K.

7. System according to any one of the preceding claims, wherein the radiators (1b, 2b) have fastening elements adapted to hold said heat exchanger (5) on an external wall of an aircraft or are thermally connected to a structure cooled by the external environment of said aircraft.

8. Electrically propelled vehicle or aircraft using at least one superconducting element comprising a cryogenic cooling system according to any one of the preceding claims, said cooling system being arranged so as to thermally couple the heat exchanger (5) to the at least one superconducting element to be cooled.

9. Vehicle or aircraft according to claim 8, in which the radiators (1b, 2b) are arranged on an external wall of said vehicle or aircraft or in heat exchange with the external environment of said vehicle or aircraft.

10. Vehicle or aircraft according to any one of claims 8-9, comprising a fluidic connector capable of fluidly connecting the cold source to a cryogenic fluid source to cool the heat exchanger to a cryogenic temperature.

11. Vehicle or aircraft according to any one of claims 8-10, comprising a cryogenic fluid reservoir arranged in said vehicle or aircraft, said cryogenic fluid being in fluidic connection with the intermediate heat exchanger (10) to cool said heat exchanger to a cryogenic temperature.

12. Hydrogen liquefaction installation, comprising a vehicle, container or aircraft, a cryogenic cooling system according to any one of claims 1-7 arranged in said vehicle, container or aircraft, said installation being arranged so as to thermally couple the heat exchanger to a source of hydrogen to be liquefied or in superconducting form.

13. Hydrogen liquefaction installation according to claim 12, comprising a cryogenic fluid reservoir arranged in said vehicle, container, or aircraft, said reservoir being in fluidic connection with the intermediate heat exchanger (10) for cool said intermediate heat exchanger (10) to a cryogenic temperature using the cryogenic fluid.

14. Hydrogen liquefaction installation according to claim 12, comprising a connector adapted to establish a fluidic link between the intermediate heat exchanger (10) and a cryogenic fluid reservoir outside said vehicle, container or aircraft, to cool said intermediate heat exchanger (10) to a cryogenic temperature.

15. Cryogenic cooling process, comprising the following steps: one or more steps of compressing a cryogenic gas in a compressor (1a, 2a) and a step of cooling said compressed gas by a radiator (1b, 2b) after each compression step, passing said gas through a first heat exchanger (7) so as to cool the compressed gas to a first temperature (Ti), passing the gas downstream of the first heat exchanger (7) into an intermediate heat exchanger (10), cooled by a cooling device (14), so as to cool the gas from the first heat exchanger to an intermediate temperature (Tj) lower than the first temperature (Ti), passing said gas downstream of the intermediate heat exchanger (10) into a second heat exchanger (8), so as to cool the gas from the intermediate heat exchanger (10) to a second temperature (T2) lower than the intermediate temperature (Ti),the expansion of said gas in an expansion device (4) so ​​as to cool said gas to a cryogenic temperature (T, c ) lower than the second temperature (T2), the use of said gas for the cooling of a device (50) to be cooled, the passage of said gas downstream of the device to be cooled (50) in the second heat exchanger (8) and the first heat exchanger (7) recovering the thermal energy of the compressed gas in the circuit.

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