CLOSED CYCLE CRYOGEN RECIRCULATION SYSTEM AND METHOD

Abstract

There is provided refrigeration system (1) and method for remote cooling of a thermal load having a first portion (27) and a second portion (25). The system comprises a cold source (4) having a first cooling stage (5) and a second cooling stage (6), the temperature of the first cooling stage being higher than the temperature of the second cooling stage. The system also comprises a cryogen circuit for circulation of a cryogen flow in a closed cycle, the closed cycle being thermally coupled to the cold source. The system further comprises a compressor (7) for compressing and circulating the cryogen flow in the cryogen circuit. The cryogen circuit comprises a first conduit for thermally connecting the first cooling stage of the cold source to the first portion of the thermal load so as to cool said first portion towards the temperature of the first cooling stage, and a second conduit for thermally connecting the second cooling stage of the cold source to the second portion of the thermal load so as to cool said second portion to wards the temperature of the second cooling stage. The cryogen flow in the system is a sub-cooled or saturated liquid, two phase, saturated or overheated, supercritical gas helium flow.

Claims

1. A refrigeration system (1) for remote cooling of a thermal load having a first portion (27) and a second portion (25), the system comprising: a cold source (4) having a first cooling stage (5) and a second cooling stage (6), the temperature of the first cooling stage being higher than the temperature of the second cooling stage; a cryogen circuit for circulation of a cryogen flow in a closed cycle, the closed cycle being thermally coupled to the cold source; and a compressor (7) for compressing and circulating the cryogen flow in the cryogen circuit, wherein the cryogen circuit comprises a first conduit for thermally connecting the first cooling stage of the cold source to the first portion of the thermal load so as to cool said first portion towards the temperature of the first cooling stage, and a second conduit for thermally connecting the second cooling stage of the cold source to the second portion of the thermal load so as to cool said second portion towards the temperature of the second cooling stage, and wherein the cryogen flow is a sub-cooled or saturated liquid, two phase, saturated or overheated, supercritical gas helium flow.

2. A refrigeration system (1) according to claim 1, wherein the first portion (27) of the thermal load is a thermal shield.

3. A refrigeration system (1) according to claim 1, wherein the second portion (25) of the thermal load is a superconducting magnet.

4. A refrigeration system (1) according to claim 1, wherein the system further comprises a transfer line (24) in which one or both of the conduits are located, and wherein the transfer line has low thermal loss.

5. A refrigeration system (1) according to claim 1, wherein the first (5) and second (6) cooling stages and the first and second conduits of the closed cycle cryogen circuit are all connected in series.

6. A refrigeration system (1) according to claim 1, wherein the cold source is a cryocooler.

7. A refrigeration system (1) according to claim 1, wherein the cold source is contained in a cryostat that is separate and independent from a cryostat of the thermal load.

8. A refrigeration system (1) according to claim 7, wherein the cryostat comprises an actively cooled thermal shield (3).

9. A refrigeration system (1) according to claim 1, wherein the system further comprises at least one heat exchanger.

10. A refrigeration system (1) according to claim 1, wherein the system comprises means for performing a Joule-Thompson expansion step (18).

11. A refrigeration system (1) according to claim 1, wherein the system can also act as a liquefier.

12. A method for cooling remotely a thermal load using a refrigeration system (1), the method comprising: selecting the temperature of a first cooling stage (5) of a cold source (4) of the system to be higher than the temperature of a second cooling stage (6); circulating a cryogen flow in a closed cycle around the cryogen circuit of the refrigeration system, the closed cycle being thermally coupled to the cold source, the cryogen circuit comprising a first conduit for thermally connecting the first cooling stage of the cold source to a first portion (27) of the thermal load so as to cool said first portion towards the temperature of the first cooling stage, and a second conduit for thermally connecting the second cooling stage of the cold source to a second portion (25) of the thermal load so as to cool said second portion towards the temperature of the second cooling stage; and compressing the flow in the cryogen circuit using a compressor (7) of the refrigeration system, wherein the cryogen flow is a sub-cooled or saturated liquid, two phase, saturated or overheated, supercritical gas helium flow.

Description

BRIEF DESCRIPTIONS OF DRAWINGS

[0026] Certain embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0027] FIG. 1 is a schematic diagram of a refrigeration system and a load to be cooled according to the present invention;

[0028] FIG. 2 is a schematic diagram of a refrigeration system according to the present invention; and

[0029] FIG. 3 is a schematic diagram of another refrigeration system according to the present invention.

DETAILED DESCRIPTION OF DRAWINGS

[0030] Reference will now be made to FIG. 1, which is a schematic diagram of a system according to the present invention. FIG. 1 shows a refrigeration system (1) and a thermal load (25, 27) to be cooled, each being installed separately in two separate cryostats (2) The cold source (4), which in this case may be a cryocooler, cools the cryogen to the required temperature, and then the cryogen is delivered to the thermal shield (25) and to the load (27) through a pipe system (26, 28). A low-loss transfer line (24) is also shown.

[0031] FIG. 2 illustrates the refrigeration system (1) in more detail. This is one of the many possible configurations, which can vary according to the cooling requirements. This particular configuration could be considered as the baseline of more complex configurations potentially resulting in higher performances. An example of those more complex configurations is presented in FIG. 3. The refrigeration system (1) in FIG. 2 consists of a pre-cooling refrigerator and a cryogen circuit. The two systems are thermally coupled to each other. Most of the components are inside a vacuum chamber or cryostat (2) and, where necessary, some of them are also thermally protected by an actively cooled thermal shield against undesired thermal radiation (3).

[0032] The pre-cooling refrigerator consists in this case of a commercial 2-Stage (5, 6) cryocooler (4) (GM-type, Stirling type, Pulse Tube type, or other) or any other suitable refrigeration system. The first cooling stage (5) has a temperature that is higher than the temperature of the second cooling stage (6).

[0033] There is also shown in FIG. 2 a compressor (7) (or gas pump) at room temperature, a pipe system (8, 9) for the cryogen and various heat exchangers (10, 11, 12, 13, 15, 16, 17).

[0034] The cryogen circuit starts with a compressor (7) at room temperature, which is used to circulate the cryogen. The cryogen circulates through a pipe system, which consists of the feed pipeline (8) and the return pipeline (9). The feed pipeline (8) starts in the flow direction at the compressor (7), goes through different heat exchangers (10, 11, 12, 15, 16, 17) and ends at the feed through connection (23) to the thermal load. Correspondingly, the return pipeline (9) starts at the feed through connection (23) from the thermal load, goes through different heat exchangers (13, 12, 11) and ends at the compressor (7).

[0035] The compressor (7) compresses and moves the cryogen gas through pipe runs. The first heat exchanger (10) re-cools the cryogen gas back from room temperature. Subsequently a group of heat exchangers (11-13) transport the cryogen heat from the feed pipeline (8) to the return pipeline (9). The cryogen is additionally cooled in the feed pipeline (8) by the cryocooler (4) at the heat exchangers on the first (15, 16) and second stage (17). After the cryogen is being pre-cooled in the feed pipeline (8), it flows towards the feed through connection (23) to the thermal load.

[0036] The cryogen can be taken at two different stages of the refrigeration process simultaneously, allowing its use at least at two different temperatures, or in case of need, at intermediate temperatures at temperature levels between ambient and first stage, or temperatures between first and second stage. Additional pipes and connections may be needed for this functionality. The following description focuses on the two stage configuration, however, other configurations comprising more stages are also conceivable. The cryogen at a higher temperature will be delivered over a pipe system to the thermal shield (25) of the load, while the colder cryogen will go to the load (27). In both cases, the cryogen will return to the refrigeration system (1) after being used in order to provide a closed cycle system.

[0037] Depending on the configuration of the refrigeration system (1) and the chosen cryogen, the system can be set up to provide a mass flow of a cryogen as any one of a sub-cooled or saturated liquid, two phase, saturated or overheated, supercritical gas helium flow. Therefore, the sensible heat (the cryogen is gaseous or supercritical and changes its temperature at the load to be cooled) or the latent heat (the liquid cryogen evaporates and therefore it does not change his temperature) of the cryogen can be used for refrigeration. After the cryogen refrigerates the load it returns to the compressor (7) through the return pipeline (9), thus closing the cycle.

[0038] FIG. 3 illustrates the refrigeration system (1) in a more complex configuration and potentially with a higher performance than in FIG. 2. As mentioned before, the many possible configurations of the system can vary according to the cooling necessities. However, some basic principles presented in FIG. 2 remain the same in FIG. 3. In this particular case, the refrigeration system (1) consists of a pre-cooling refrigerator, a cryogen circuit comprising a Joule Thompson (JT) expansion step and a transfer line (24). Most of the components are inside a vacuum chamber or cryostat (2) and some of them are also thermally protected by an actively cooled thermal shield (3) against undesired thermal radiation.

[0039] The pre-cooling refrigerator consists in this case of a commercial 2-Stage (5, 6) cryocooler (4) or any other suitable refrigeration system (see above). The JT refrigerator includes a compressor (7) at room temperature, a pipe system (8, 9) for the cryogen, various heat exchangers (10-17) and a Joule Thompson (JT) expansion device (18). In addition, in order to reduce flow impedances and to accelerate cool down, several bypass valves (19-22) can be installed in case of necessity.

[0040] The JT refrigerator starts with a compressor (7) at room temperature, which is used to compress and circulate the cryogen. The cryogen circulates through a pipe system, which consists of the feed pipeline (8) and the return pipeline (9). The feed pipeline (8) starts in the flow direction at the compressor (7), goes through various heat exchangers and valves (10-12, 15, 23, 16-18) and ends at the feed through connection (23) to the load. Correspondingly, the return pipeline (9) starts at the feed through connection (24) from the load, goes through different heat exchangers (14-11) and ends at the compressor (7).

[0041] For remote cooling, a transfer system is required. This may comprise an optimized transfer line (24) which delivers the cryogen to the thermal loads. The optimization consists of minimizing the losses on all lines, and in particular in the cold circuit. This allows a more efficient integration into the overall system.

[0042] After the compression of the cryogen gas, the first heat exchanger (10) cools the cryogen back from room temperature. Afterwards a group of heat exchangers (11-14) transport the cryogen heat from the feed pipeline (8) to the return pipeline (9). The cryogen is additionally cooled in the feed pipeline (8) by the cryocooler (4) at the heat exchangers on the first (15, 16) and second stage (17). After the cryogen is being pre-cooled in the feed pipeline (8), it flows through the JT expansion device (18).

[0043] The cryogen can be taken at two different stages of the refrigeration process simultaneously, allowing his use at two different temperatures. The cryogen at a higher temperature will be delivered over a pipe system to the loads thermal shield (25), while the colder cryogen will go to the load (27). In both cases, the cryogen will return to the refrigeration system (1) after being used, in order to provide a closed cycle system.

[0044] Depending on the configuration of the refrigeration system (1) and the chosen cryogen, the system can be set up to provide a mass flow of either sub-cooled or saturated liquid, two phase, saturated or overheated, supercritical gas. Therefore, the sensible heat (the cryogen is gaseous and changes his temperature) and/or the latent heat (the liquid cryogen evaporates and therefore it does not change his temperature) of the cryogen can be used for refrigeration. After the cryogen refrigerates the load it returns to the compressor (7) through the return pipeline (9), closing the cycle.

[0045] When the entire system is switched on, the cryogen starts circulating and the cryocooler (4) starts cooling down from room temperature. During this period of time, the bypass-valves can be opened (19-22) in case of necessity. Consequently, the cryogen can bypass some components (13, 14, 18), reducing the overall pressure losses. Once the cool down process is finished, the bypass-valves (19-22) can be closed again.

KEY

[0046] 1. Refrigeration system [0047] 2. Cryostat or vacuum chamber [0048] 3. Thermal Shield of the Cryogen Recirculation System [0049] 4. Cryocooler [0050] 5. First stage of cryocooler [0051] 6. Second stage of cryocooler [0052] 7. Compressor [0053] 8. Feed pipeline [0054] 9. Return pipeline [0055] 10. Heat exchanger 1 (HX1) [0056] 11. Heat exchanger 2 (HX2) [0057] 12. Heat exchanger 3 (HX3) [0058] 13. Heat exchanger 4 (HX4) [0059] 14. Heat exchanger 5 (HX5) [0060] 15. Heat exchanger at the first stage before going to the thermal shield of the load (HX1stA) [0061] 16. Heat exchanger at the first stage after going to the thermal shield of the load (HX1stB) [0062] 17. Heat exchanger at the 2nd Stage (HX2nd) [0063] 18. JT expansion device [0064] 19. Bypass-valve for Heat Exchanger 4 (HX4) at the feed side [0065] 20. Bypass-valve for Heat Exchanger 5 (HX5) at the feed side [0066] 21. Bypass valve for JT expansion device [0067] 22. Bypass-Valve for Heat Exchanger 4 and 5 (HX4 and HX5) at the return side [0068] 23. Feed through connection for the transfer lines [0069] 24. Transfer line [0070] 25. Thermal Shield of the load [0071] 26. Pipe system for the thermal shield of the load [0072] 27. Load [0073] 28. Load pipe system [0074] 29. Thermal shield of the transfer line