REGENERATIVE CRYOGENIC MACHINE

Abstract

The application relates to a cryogenic machine of the regenerative type, comprising: a pressure oscillator, at least one cold finger (20) in fluid connection with the pressure oscillator,

wherein the pressure oscillator comprises a centrifugal compressor (1) and a fluid distribution member (12) configured to alternately distribute high-pressure and low-pressure working fluid from the centrifugal compressor into said cold finger.

Claims

1. A cryogenic machine of a regenerative type, comprising: a pressure oscillator, at least one cold finger in fluid connection with the pressure oscillator, wherein the pressure oscillator comprises a centrifugal compressor and a fluid distribution member configured to alternately distribute high-pressure and low-pressure working fluid from the centrifugal compressor into said cold finger.

2. The cryogenic machine according to claim 1, wherein the compression ratio of the centrifugal compressor is between 1.1 and 1.5.

3. The cryogenic machine according to claim 1, wherein the operating frequency of the pressure oscillator is greater than 10 Hz.

4. The cryogenic machine according to claim 1, wherein the centrifugal compressor is arranged between a buffer tank called low-pressure buffer tank and a buffer tank called high-pressure buffer tank, the fluid distribution member being configured to selectively put in fluid connection the cold finger and one of the low-pressure and high-pressure buffer tanks.

5. The cryogenic machine according to claim 1, wherein the fluid distribution member comprises a rotary valve or a linear distribution valve.

6. The cryogenic machine according to claim 1, comprising a cold finger of a pulsed gas tube type including a pulse tube, an exchanger and a phase shifter.

7. The cryogenic machine according to claim 1, comprising a cold finger of a Stirling type including an expansion piston.

8. The cryogenic machine according to claim 1, wherein the fluid distribution member is configured to be fluidly actuated by the working fluid or mechanically by an outer actuator.

9. The cryogenic machine according to claim 7, wherein the fluid distribution member is configured to be actuated by a control rod of the expansion piston of the cold finger.

10. The cryogenic machine according to any of claim 1, containing helium as working fluid.

11. The cryogenic machine according to claim 1, comprising several cold fingers, each cold finger being fluidly connected to one or several centrifugal compressors.

12. The cryogenic machine according to claim 4, further comprising a circuit for circulating working fluid from the high-pressure buffer tank to the low-pressure buffer tank, so as to cool a part offset from the cold finger and mechanically decoupled from said cold finger.

13. A spacecraft comprising a cryogenic machine according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0047] Other characteristics and advantages will emerge from the following detailed description, with reference to the appended drawings, in which:

[0048] FIG. 1 is a block diagram of a cryogenic machine of the pulsed air tube type according to the state of the art;

[0049] FIG. 2 is a block diagram of another cryogenic machine of the pulsed air tube type according to the state of the art;

[0050] FIG. 3 is a block diagram of a cryogenic machine of the Stirling type according to the state of the art;

[0051] FIG. 4 is a block diagram of a cryogenic machine of the pulsed gas tube type according to one embodiment;

[0052] FIG. 5 is a block diagram of a cryogenic machine of the Stirling type according to one embodiment;

[0053] FIG. 6 is a block diagram of a cryogenic machine of the Stirling type according to another embodiment;

[0054] FIG. 7 is a block diagram of a cryogenic machine of the pulsed gas tube type integrating a thermal switch function according to one embodiment.

[0055] Naturally, these figures are given for illustrative purposes only.

[0056] Identical reference signs from one figure to the other refer to identical elements or fulfill the same function.

DETAILED DESCRIPTION OF EMBODIMENTS

[0057] FIG. 4 is a block diagram of a cryogenic machine of the pulsed air tube type according to one embodiment. The reference signs identical to those of FIG. 1 refer to identical elements or elements fulfilling the same function. These elements will therefore not be described again in detail.

[0058] Particularly, the cold finger 20 is similar to that of existing machines, for example to that of FIG. 1 or to that of FIG. 2.

[0059] The oscillator 1 comprises a centrifugal compressor fluidly coupled on the one hand to a buffer tank 10 called low-pressure buffer tank and a buffer tank 11 called high-pressure buffer tank. In the present text, the terms “low-pressure” and “high-pressure” are relative terms, a low pressure being lower than a high pressure.

[0060] The oscillator further comprises a fluid circuit connecting the cold finger to each of the buffer volumes 10, 11.

[0061] The oscillator finally comprises a fluid distribution member 12 arranged in the fluid circuit, making it possible to selectively and alternately put the cold finger in fluid connection with the buffer tank 10 or the buffer tank 11.

[0062] This distribution member 12 can be advantageously a rotary valve or a linear actuator, but any other type of actuator could be used as long as it allows alternately distributing the high-pressure and low-pressure gas in the cold finger. For example, each buffer tank could be fitted with a respective valve, said valves being configured to open or close depending on the phase of the operating cycle of the machine.

[0063] By buffer tank, it is meant that the volume of the tanks 10 and 11 is large enough compared to the volume of the fluid circuit which connects the tanks and the cold finger so that the pressure generated by the centrifugal compressor in the said tanks 10, 11 remains substantially constant. These tanks can be possibly eliminated if the volume of the fluid circuit ensures this function or if the performance of the cold finger is not impacted by this pressure fluctuation.

[0064] For helium, for example, a compression ratio between 1.1 and 1.5 will be sought to replace the pressure oscillator with a centrifugal compressor and a fluid distribution member. This compression ratio is completely compatible with the compression ratio generated by a centrifugal compressor. The pressure oscillator can therefore be directly replaced by a centrifugal compressor coupled to a fluid distribution member.

[0065] In practice, conventional coolers are filled at an average pressure from 20 to 40 bars. Then, the pressure oscillates due to the pressure oscillator around this average pressure with an amplitude from +/− 2 to 5 bars. The average pressure and the amplitude of the pressure wave are parameters specific to each cooler.

[0066] The operating frequency of the pressure oscillator is advantageously greater than or equal to 10 Hz.

[0067] The operation of the proposed cryogenic machine is as follows.

[0068] In a first phase of the cycle, the cold finger 20 is in fluid connection with the high-pressure buffer tank 11 via the valve 12. The working fluid passes through the first exchanger 2, the regenerator 3 and the second exchanger 4 towards the tube 5. The working fluid switches from the ambient temperature T1 to the cryogenic temperature T2; the heat of the working fluid transferred to the regenerator 3 is accumulated therein.

[0069] In the tube 5, the working fluid undergoes adiabatic compression.

[0070] Under the effect of the compression of the fluid in the tube 5, part of the fluid is pushed towards the buffer tank 8 through the inertance 7.

[0071] In a second phase of the cycle, the valve 12 is actuated so as to interrupt the fluid connection between the cold finger and the high-pressure buffer tank 11 to establish a fluid connection between the cold finger and the low-pressure tank 10.

[0072] The working fluid undergoes adiabatic expansion in the tube 5. Part of the fluid is drawn from the buffer tank 8 towards the tube 5 through the inertance 7. The working fluid passes through the second heat exchanger 4 and the regenerator 3, which restores the stored heat via the first heat exchanger 2.

[0073] Contrary to the case where the compressor is a volumetric compressor such as the piston illustrated in FIGS. 1 and 2, the centrifugal compressor allows decoupling the compression area from the cold finger. Indeed, the pressure wave can be transmitted over a sufficiently long distance and does not depend on the volume of fluid between the compressor and the cold finger.

[0074] Consequently, the oscillator is not necessarily aligned with the cold finger as represented in FIG. 4, but can be arranged at another location in the machine, depending on the space constraints encountered.

[0075] The same operating principle is applicable to a machine comprising a Stirling cold finger, as illustrated in FIG. 5.

[0076] In this machine, the centrifugal compressor 1 and the fluid distribution member are similar to those already described with reference to FIG. 4.

[0077] Furthermore, the regenerator 3 and the expander 9, which form the cold finger 20 of the machine, are similar to those of FIG. 3.

[0078] As explained above, the centrifugal compressor allows decoupling the compression area from the cold finger. Indeed, the pressure wave can be transmitted over a sufficiently long distance and does not depend on the volume of fluid between the compressor and the cold finger.

[0079] Consequently, the compressor is not necessarily aligned with the cold finger as represented in FIG. 3, but can be arranged at another location in the machine, depending on the space constraints encountered.

[0080] It is also possible to couple the fluid distribution member with the driving of the expansion piston 9 as shown in FIG. 6. In this embodiment, the cold finger is of the coaxial type, the expansion piston 9 being arranged in the regenerator 3.

[0081] In other embodiments, regardless of the type of cold finger, the fluid distribution member can be actuated fluidly by the working fluid or mechanically by an outer actuator.

[0082] In some embodiments, it is possible to couple several cold fingers, of the same type or of different types (pulsed air tube, Stirling, Gifford-McMahon, etc.) to an oscillator or several oscillators each comprising a centrifugal compressor and one or several fluid distribution members.

[0083] This coupling is furthermore independent from the configuration of the cold fingers, which can be for example in line, coaxial, with active expander, with inertance, alpha, beta, with free piston, etc. Consequently, the figures should not be construed as limiting the invention to a particular cold finger configuration.

[0084] In addition, the oscillator(s) can be offset from the cold finger(s).

[0085] The oscillator therefore allows forming a wide variety of regenerative cryogenic machines, with great freedom of choice in the arrangement of the different components.

[0086] Referring to FIG. 7, it is also possible to integrate in the cryogenic cooler, an integrated “thermal link” function that allows: [0087] offsetting the cold finger 20 to a position away from the part to be cooled which is represented by the exchanger 50; [0088] mechanically decoupling the cold finger 20 from the part to be cooled, making it possible to simplify the cold finger and its integration into the application using the cryogenic machine; [0089] offering a thermal switch function linked to the inherent operation of the cryogenic cooler.

[0090] This thermal link function is performed by using the pressure difference between the buffer tanks 10 and 11 to ensure circulation of working fluid from the high-pressure buffer tank to the low-pressure buffer tank.

[0091] The working fluid is cooled to a cold temperature close to T2 by a countercurrent exchanger 40, then to the temperature T2 on an exchanger integrated into the cold exchanger 4. The cold working liquid is then offset at a distance ranging from a few centimeters to several meters to cool the part to be cooled via the exchanger 50. The working fluid is heated in the exchanger 50 and then returns to the countercurrent exchanger 40 to be re-injected into the low-pressure tank buffer 10.

[0092] The secondary fluid circuit 51 and 52 constituting the thermal link can be made with small-dimensioned tubes making it possible to limit the mass of the system, to lower the stiffness of the tubes (in order to ensure mechanical decoupling between the components) or to limit the losses by conductions along these tubes.

[0093] This thermal link is therefore passive in the sense that, when the cooler is operating, the circulation of working fluid is effective and so is the thermal coupling. Conversely, if the cryogenic cooler is stopped, there is no thermal coupling.

[0094] This is then referred to as thermal switch, having a thermal coupling/decoupling function. This function is particularly useful for systems integrating several cold fingers (case of a spacecraft in particular integrating a nominal cooler and a redundant cooler). The non-operating cold fingers are then thermally decoupled from the part to be cooled and thus do not cause heat losses.

[0095] Although the cold finger 20 represented in FIG. 7 is of the pulsed gas tube type, it goes without saying that any other type of cold finger could be used in connection with this thermal switch.