EP4025845B1 - Regenerative cryogenic machine - Google Patents

Description

Technical area

The invention relates to a cryogenic machine of the regenerative type (eg pulsed gas tube, Stirling, Gifford-McMahon, etc.).

State of the art

There are different types of cryogenic machines. These cryogenic machines are classified into two types: regenerative chillers and regenerative chillers.

Recuperative coolers (Joule-Thomson or inverse Brayton cycles) are based on a continuous flow of the working fluid, usually a gas, which is compressed and expanded, the expansion taking place continuously in an orifice for the Joule-Thomson cycle or in a turbine for the Brayton cycle. The term “recovery” comes from the fact that an exchanger, generally against the current, is used to recover the enthalpy of the cold gas coming from the expansion to pre-cool the hot gas coming from the compressor.

For regenerative chillers, the flow of the working fluid is reciprocating. Gas compression and expansion take place cyclically at a frequency of a few Hertz for so-called “low frequency” coolers and at several tens of Hertz for so-called “high frequency” coolers.

• Les figures 1 et 2 sont des schémas de principe d'une machine cryogénique régénérative de type tube à gaz pulsé fonctionnant à haute fréquence (c'est-à-dire au-delà de 20Hz).
• La figure 3 est un schéma de principe d'une machine cryogénique régénérative de type Stirling fonctionnant à haute fréquence.

As with recuperative coolers, the enthalpy of the cold gas from the expansion must be recovered. However, it is not possible to use an exchanger in the case of cyclic operation. A regenerator is then used to perform this function. The regenerator makes it possible to transfer the enthalpy from the cold gas to the hot gas between two cycles. The regenerator also implements thermal storage to ensure this heat transfer at two different instants. EP 1 158 256 A discloses a regenerative-type cryogenic machine comprising a piston compressor for generating alternating pressure and mass flow throughout the pulse tube refrigerator.

• THE figures 1 and 2 are block diagrams of a pulsed gas tube type regenerative cryogenic machine operating at high frequency (i.e. above 20Hz).
• There picture 3 is a block diagram of a Stirling-type regenerative cryogenic machine operating at high frequency.

The diagrams of figures 1 to 3 represent the general topology of these coolers, that is to say in a schematic configuration called “in line” of the cold fingers. In other embodiments, the topology of these cold fingers can also be “U” shaped or coaxial, while keeping the same operating principle and the same components.

The machine comprises an oscillator 1' and a cold finger 20 in fluidic connection with the oscillator. The machine contains a working fluid, usually helium.

Oscillator 1' is in the form of a piston moving back and forth schematized by the bidirectional arrow, thus generating a pressure wave in the working fluid. We speak of a "pressure oscillator" because the to-and-fro movement of the piston makes it possible to generate a pressure oscillation and not a pressure difference as in recuperative machines.

The cold finger 20 (which may in particular be of the pulsed gas tube, Stirling or Gifford-McMahon type) allows the production of the cooling effect.

In the case of a pulsed gas tube (cf. figures 1 and 2 ), the cold finger comprises a first heat exchanger 2, a regenerator 3, a second heat exchanger 4, a pulse tube 5, a third heat exchanger 6, and a phase shift system 7, 8 or 9.

When the piston moves to the right of the picture 1 or 2 , the working fluid is compressed and passes through the first heat exchanger 2 and the regenerator 3. The regenerator having a high specific heat and being thermally insulated from the outside of the machine, the temperature of the working fluid passes from a first temperature T1, which is generally the ambient temperature to which the machine is exposed, to a second temperature T2 lower than T1. The second temperature is a cryogenic temperature, that is to say typically below 120K. During this phase, the working fluid yields energy to the regenerator 3 which stores it due to its high specific heat.

The working fluid enters the pulse tube 5 through the second heat exchanger 4. In the tube 5, which is thermally insulated from the outside of the machine, the working fluid undergoes compression and successive adiabatic expansion at the operating frequency of the oscillator 1'.

The compression work is evacuated at the end of the pulse tube 5, in a third heat exchanger 6 operating at ambient temperature while at the other end of the pulse tube 5, the expansion makes it possible to lower the temperature of the gas in the second exchanger 4, reaching a cryogenic temperature.

This thermal decoupling effect on either side of the cold finger is ensured by a phase shift system 7, 8 or "phase shifter" in English. This system provides the necessary phase shift between the pressure wave and the flow in the cold finger so that the expansion takes place at the level of the cold exchanger 4. The phase shift system generally consists of an inertance 7 and a buffer tank 8. The inertance has a small passage section compared to that of the pulse tube 5, and the buffer tank 8 has a high volume compared to that of the tube and the inertance; consequently, the pressure within the buffer tank 8 is substantially constant.

In some cases, as shown in the figure 2 , this phase shift system is in the form of an expander piston 9, similar to the pressure oscillator 1' but of different volume and power.

After the expansion phase producing the cooling effect, the working fluid passes through the regenerator 3 in the opposite direction and this time it is the regenerator which transfers the energy stored during the compression to the working fluid cooled during the expansion.

In the case of a Stirling cooler (cf. picture 3 ), the general configuration is similar to that of the pulsed gas tube, except that the cold finger 20 uses an expansion valve mechanical 9 to ensure the expansion of the working fluid. In other words, the pulse tube 5, the exchanger 6 and the phase shift system 7, 8 are eliminated in the case of a Stirling cold finger.

In both cases, and in general for all regenerative machines, the pressure oscillator is a critical element for the aspects: cost, performance, size, mass, reliability...

Furthermore, it is difficult to deport the oscillator from the cold finger because the addition of volume in the system causes the amplitude of the pressure wave and the flow rate to drop and thus lowers the cooling capacity.

Finally, these pressure oscillators use linear motors to create the reciprocating motion of the piston. This type of engine has several major drawbacks.

On the one hand, even if they are mechanically balanced, these motors generate extremely problematic vibrations for space applications. They then require binding ancillary systems and complex, disabling and costly control electronics.

On the other hand, these oscillators are difficult to extrapolate to high powers. Indeed, beyond a few hundred Watts, the size, mass and cost of these oscillators become problematic and infeasible in some cases.

Brief description of the invention

An object of the invention is to remedy the aforementioned drawbacks and in particular to design a cryogenic machine in which the generation of the pressure oscillation is carried out by means that are less costly, more reliable and generate less vibration than the existing oscillators. Furthermore, said machine must be able to be used in a high or low power cooler.

• un oscillateur de pression,
• au moins un doigt froid en liaison fluidique avec l'oscillateur de pression, ladite machine étant caractérisée en ce que l'oscillateur de pression comprend un compresseur centrifuge et un organe de distribution fluidique configuré pour distribuer alternativement du fluide de travail à haute pression et à basse pression du compresseur centrifuge dans ledit doigt froid.

To this end, the invention proposes a cryogenic machine of the regenerative type, comprising:

• a pressure oscillator,
• at least one cold finger in fluidic connection with the pressure oscillator, said machine being characterized in that 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.

The use of a centrifugal compressor coupled to a fluid distribution member instead of a linear motor pressure oscillator has several advantages.

On the one hand, the centrifugal compressor does not generate vibrations, which is particularly advantageous in the space field and in all applications where vibrations would risk disturbing the operation of devices.

On the other hand, the transmission of the pressure wave does not depend on the volume between the compressor and the cold finger, the compressor can be offset from the cold finger, which allows greater freedom in the design of the machine and in particular greater compactness, which is particularly sought after for on-board applications.

Finally, such a compressor is reliable and can be upgraded according to the power required.

It is also possible to couple several cold fingers (for example Stirling and/or pulsed gas tube) on the same compressor.

• le taux de compression du compresseur centrifuge est compris entre 1,1 et 1,5 ;
• la fréquence de fonctionnement de l'oscillateur de pression est supérieure à 1 0Hz ;
• le compresseur centrifuge est agencé entre un réservoir tampon dit à basse pression et un réservoir tampon dit à haute pression, l'organe de distribution fluidique étant configuré pour sélectivement mettre en liaison fluidique le doigt froid et l'un des réservoirs tampons à basse et haute pression :
• l'organe de distribution fluidique comprend une vanne rotative ou une vanne de distribution linéaire ;
• la machine comprend un doigt froid de type tube à gaz pulsé incluant un tube à pulsation, un échangeur et un système de déphasage ;
• la machine comprend un doigt froid de type Stirling incluant un piston détendeur ;
• l'organe de distribution fluidique est configuré pour être actionné fluidiquement par le fluide de travail ou mécaniquement par un actionneur externe ;
• l'organe de distribution fluidique est configuré pour être actionné par la tige de commande du piston détendeur du doigt froid ;
• la machine contient de l'hélium en tant que fluide de travail ;
• la machine comprend plusieurs doigts froids, chaque doigt froid étant connecté fluidiquement à un ou plusieurs compresseurs centrifuges ;
• la machine comprend en outre un circuit de circulation de fluide de travail du réservoir tampon à haute pression vers le réservoir tampon à basse pression, de sorte à refroidir une pièce déportée vis-à-vis du doigt froid et découplée mécaniquement dudit doigt froid.

According to optional but advantageous characteristics of the invention, possibly combined when technically possible:

• the compression ratio of the centrifugal compressor is between 1.1 and 1.5;
• the operating frequency of the pressure oscillator is greater than 10Hz;
• the centrifugal compressor is arranged between a so-called low-pressure buffer tank and a so-called high-pressure buffer tank, the fluidic distribution member being configured to selectively put the cold finger in fluidic connection and one of the low- and high-pressure buffer tanks:
• the fluid distribution member comprises a rotary valve or a linear distribution valve;
• the machine comprises a cold finger of the pulse gas tube type including a pulse tube, an exchanger and a phase shift system;
• the machine comprises a Stirling-type cold finger including an expansion piston;
• the fluid distribution member is configured to be actuated fluidically by the working fluid or mechanically by an external actuator;
• the fluid distribution member is configured to be actuated by the control rod of the cold finger expansion piston;
• the machine contains helium as the working fluid;
• the machine comprises several cold fingers, each cold finger being fluidically connected to one or more centrifugal compressors;
• the machine further comprises a working fluid circulation circuit from the high-pressure buffer tank to the low-pressure buffer tank, so as to cool a part remote from the cold finger and mechanically decoupled from said cold finger.

Another object of the invention relates to a spacecraft comprising a cryogenic machine as described above.

Brief description of figures

• La figure 1 est un schéma de principe d'une machine cryogénique de type tube à air pulsé selon l'état de la technique ;
• La figure 2 est un schéma de principe d'une autre machine cryogénique de type tube à air pulsé selon l'état de la technique ;
• La figure 3 est un schéma de principe d'une machine cryogénique de type Stirling selon l'état de la technique ;
• La figure 4 est un schéma de principe d'une machine cryogénique de type tube à gaz pulsé selon un mode de réalisation de l'invention ;
• La figure 5 est un schéma de principe d'une machine cryogénique de type Stirling selon un mode de réalisation de l'invention ;
• La figure 6 est un schéma de principe d'une machine cryogénique de type Stirling selon un autre mode de réalisation de l'invention ;
• La figure 7 est un schéma de principe d'une machine cryogénique de type tube à gaz pulsé intégrant une fonction d'interrupteur thermique selon un mode de réalisation de l'invention.

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

• There figure 1 is a block diagram of a cryogenic machine of the pulsed air tube type according to the state of the art;
• There picture 2 is a block diagram of another cryogenic machine of the pulsed air tube type according to the state of the art;
• There picture 3 is a block diagram of a Stirling-type cryogenic machine according to the state of the art;
• There figure 4 is a block diagram of a cryogenic machine of the pulse gas tube type according to one embodiment of the invention;
• There figure 5 is a block diagram of a Stirling-type cryogenic machine according to one embodiment of the invention;
• There figure 6 is a block diagram of a Stirling-type cryogenic machine according to another embodiment of the invention;
• There figure 7 is a block diagram of a cryogenic machine of the pulsed gas tube type integrating a thermal switch function according to one embodiment of the invention.

Naturally, these figures are given for illustrative purposes only.

The identical reference signs from one figure to another designate identical elements or fulfilling the same function.

Detailed description of embodiments

There figure 4 is a block diagram of a cryogenic machine of the pulsed air tube type according to one embodiment of the invention. The reference signs identical to those of the figure 1 designate elements that are identical or perform the same function. These elements will therefore not be described again in detail.

In particular, the cold finger 20 is similar to that of existing machines, for example to that of the figure 1 or to that of picture 2 .

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

The oscillator further comprises a fluidic circuit connecting the cold finger to each of the buffer volumes 10, 11.

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

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

By buffer tank, it is meant that the volume of the tanks 10 and 11 is large enough with respect to the volume of the fluidic 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 reservoirs may optionally be eliminated if the volume of the fluidic circuit makes it possible to perform this function or if the performance of the cold finger is not impacted by this pressure fluctuation.

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 fluidic distribution device. This compression ratio is completely compatible with the compression ratio generated by a centrifugal compressor. It is therefore possible to directly replace the pressure oscillator by a centrifugal compressor coupled to a fluid distribution member.

In practice, conventional coolers are filled to an average pressure of 20 to 40 bar. Then the pressure oscillates due to the pressure oscillator around this average pressure with an amplitude of +/- 2 to 5 bar. The average pressure and the amplitude of the pressure wave are parameters specific to each chiller.

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

The operation of the proposed cryogenic machine is as follows.

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

In tube 5, the working fluid undergoes adiabatic compression.

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 inertia 7.

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

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

Unlike the case where the compressor is a volumetric compressor such as the piston illustrated on the figures 1 and 2 , the centrifugal compressor makes it possible to decouple the compression zone 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.

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

The same principle of operation is applicable to a machine comprising a cold Stirling finger, as illustrated in the figure 5 .

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

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

As explained above, the centrifugal compressor makes it possible to decouple the compression zone 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.

Therefore, the compressor is not necessarily aligned with the cold finger as shown in the picture 3 , but can be arranged at another location in the machine, depending on the size constraints encountered.

It is also possible to couple the fluid distribution member with the drive of the expander piston 9 as shown in the figure 6 . In this embodiment, the cold finger is of the coaxial type, the expander piston 9 being arranged in the regenerator 3.

In other embodiments, regardless of the type of cold finger, the fluid distribution member can be actuated fluidically by the working fluid or mechanically by an external actuator.

In certain 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 more fluid distribution members.

This coupling is moreover independent of 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. Accordingly, the figures should not be construed as limiting the invention to any particular cold finger configuration.

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

The oscillator according to the invention therefore makes it possible to form a wide variety of regenerative cryogenic machines, with great freedom of choice in the arrangement of the various components.

• de déporter le doigt froid 20 à une position éloignée de la pièce à refroidir qui est représentée par l'échangeur 50 ;
• de découpler mécaniquement le doigt froid 20 de la pièce à refroidir, permettant de simplifier le doigt froid et son intégration dans l'application utilisant la machine cryogénique ;
• d'offrir une fonction d'interrupteur thermique liée au fonctionnement inhérent du refroidisseur cryogénique.

With reference to the figure 7 , it is also possible to integrate in the cryogenic cooler, an integrated "thermal link" function allowing:

• to move the cold finger 20 to a position remote from the part to be cooled which is represented by the exchanger 50;
• to mechanically decouple 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;
• to provide a thermal switch function related to the inherent operation of the cryocooler.

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.

The working fluid is cooled to a cold temperature close to T2 by a counter-current exchanger 40, then to temperature T2 on an exchanger integrated into the cold exchanger 4. The cold working liquid is then deported 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 counter-current exchanger 40 to be re-injected into the buffer tank 10 at low pressure.

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

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.

We then speak of a 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 one). The non-functioning cold fingers are then thermally decoupled from the part to be cooled and thus do not cause heat losses.

Although the cold finger 20 represented on the figure 7 either 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.

Claims (13)

1. A cryogenic machine of the regenerative type, comprising : -
   a pressure oscillator,

   - at least one cold finger (20) in fluid connection with the pressure oscillator, said machine being characterized in that 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.
2. The machine of claim 1, wherein the compression ratio of the centrifugal compressor (1) is between 1.1 and 1.5.
3. The machine of claim 1, wherein the operating frequency of the pressure oscillator is greater than 10Hz.
4. The machine according to any of claims 1, 2 or 3, wherein the centrifugal compressor (1) is arranged between a so-called low-pressure buffer tank (10) and a so-called high-pressure buffer tank (11), the fluidic distribution member (12) being configured to selectively put the cold finger and one of the low-pressure and high-pressure buffer tanks (10, 11) in fluidic connection.
5. The machine of any of claims 1 to 4, wherein the fluidic distribution member (12) comprises a rotary valve or a linear distribution valve.
6. The machine according to one of the claims 1 to 5, comprising a cold finger of the pulsed gas tube type including a pulsation tube (5), an exchanger (6) and a phase shifting system (7, 8).
7. The machine according to one of the claims 1 to 6, comprising a Stirling-type cold finger including an expansion piston (9).
8. The machine of any of claims 1 to 7, wherein the fluidic distribution member (12) is configured to be actuated fluidically by the working fluid or mechanically by an external actuator.
9. The machine of claim 7, wherein the fluidic distribution member is configured to be actuated by the control rod of the cold finger expansion piston (9).
10. The machine according to any of claims 1 to 9, containing helium as a working fluid.
11. The cryogenic machine of any of claims 1 to 10, comprising a plurality of cold fingers, each cold finger being fluidly connected to one or more centrifugal compressors.
12. The cryogenic machine according to one of claims 1 to 11 in combination with claim 4, further comprising a circuit (40, 50, 51, 52) for circulating working fluid from the buffer tank (11) at high pressure to the buffer tank (10) at low pressure, so as to cool a part offset from the cold finger (20) and mechanically decoupled from said cold finger (20).
13. A spacecraft comprising a cryogenic machine according to any of claims 1 to 12.

Images