Joule-Thomson refrigerator

Abstract

A JT refrigerator (18) is provided with: a pre-cooling refrigerator (20) provided with a second pre-cooling stage (27); a refrigerant circuit (40) that is provided with a second heat exchanger (42b) and a second refrigerant pipe (44b) that extends from the second heat exchanger (42b) and that is cooled by the second pre-cooling stage (27); and a first heat transfer path (48a) provided separately from the second refrigerant pipe (44b) and connecting the second pre-cooling table (27) and the second heat exchanger (42b) such that the second pre-cooling table (27) can conduct and cool the second heat exchanger (42b).

Description

Technical Field

[0001] The present invention relates to a Joule - Thomson (JT) refrigerator. Background Art

[0002] Conventionally, a JT refrigerator is known, which includes: a JT valve that cools a refrigerant gas by using JT expansion; and a precooling refrigerator, such as a Gifford - McMahon (GM) refrigerator or the like, that precools the refrigerant gas supplied to the JT valve. Cooling of the refrigerant gas by JT expansion in the JT valve requires the refrigerant gas to be pre - cooled to a temperature below the inversion temperature at which the JT coefficient becomes zero.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid - Open No. 2003 - 214719 Summary of the Invention

[0006] Technical Problem to be Solved by the Invention

[0007] When starting the JT refrigerator, a temperature - lowering operation is required, that is, cooling the JT refrigerator from the ambient temperature (for example, a normal temperature of about 300 K) to a target ultra - low temperature. The refrigerant gas supplied to the JT valve is cooled from the ambient temperature to a temperature below the inversion temperature by the temperature - lowering operation. The temperature - lowering operation is merely a preparation for ultra - low temperature cooling of a desired object to be cooled using the JT refrigerator, and thus it is desired that the time required for it be as short as possible.

[0008] One exemplary object of an embodiment of the present invention is to shorten the temperature - lowering time of the JT refrigerator.

[0009] Means for Solving the Technical Problem

[0010] According to an embodiment of the present invention, the JT refrigerator includes: a precooling refrigerator having a precooling stage; a refrigerant circuit having a heat exchanger and a refrigerant pipe that extends from the heat exchanger and is cooled by the precooling stage; and a heat conduction path that is separately provided from the refrigerant pipe and is used to connect the precooling stage and the heat exchanger so that the precooling stage can conductively cool the heat exchanger.

[0011] Advantageous Effects of the Invention

[0012] According to the present invention, the temperature - lowering time of the JT refrigerator can be shortened. Brief Description of the Drawings

[0013] Figure 1 It is a diagram schematically showing an ultra - low temperature cooling device according to the embodiment.

[0014] Figure 2 This is a diagram schematically showing an exemplary structure of a heat conduction path according to an embodiment.

[0015] Figure 3 This is a diagram schematically showing a modification example of the heat conduction path according to an embodiment. Detailed Embodiment

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and drawings, the same or equivalent components, parts, and processes are denoted by the same reference numerals, and repeated descriptions are appropriately omitted. The proportions or shapes of the respective parts shown in the drawings are simply set for the sake of explanation, and are not to be construed restrictively unless otherwise specifically stated. The embodiments are examples and do not limit the scope of the present invention in any way. All features or combinations thereof described in the embodiments are not necessarily essential features or combinations thereof of the invention.

[0017] Figure 1 This is a diagram schematically showing a cryogenic cooling device 10 according to an embodiment. The cryogenic cooling device 10 includes a vacuum vessel 12, a radiation shield 14, and a JT cooler 18 for cooling an object to be cooled 16.

[0018] The vacuum vessel 12 can be, for example, a cryostat and is configured to provide a cryogenic vacuum environment inside. The vacuum vessel 12 is made of a metal material such as stainless steel or other suitable high-strength materials to withstand the surrounding pressure (e.g., atmospheric pressure). Inside the vacuum vessel 12, a radiation shield 14, a low-temperature part of the JT cooler 18, and the object to be cooled 16 are arranged.

[0019] The radiation shield 14 is arranged to surround the low-temperature part of the JT cooler 18 and the object to be cooled 16 inside the vacuum vessel 12, and suppresses the intrusion of radiant heat from the vacuum vessel 12 into the JT cooler 18 and the object to be cooled 16. The radiation shield 14 is made of a high-thermal-conductivity metal material such as copper (e.g., pure copper). An insulating material such as a multi-layer insulating material can be arranged between the vacuum vessel 12 and the radiation shield 14.

[0020] The object to be cooled 16 can be, for example, a superconducting device such as a superconducting coil, a measuring device that operates better at cryogenic temperatures, or other devices used at cryogenic temperatures. Alternatively, the object to be cooled 16 can be a cryogenic fluid such as liquid helium, and the JT cooler 18 can be used for the recondensation of the vaporized cryogenic fluid.

[0021] The JT cooler 18 includes a precooling cooler 20 and a refrigerant circuit 40. The refrigerant circuit 40 includes a JT valve 30 and a final heat exchanger 32. The refrigerant flowing through the refrigerant circuit 40 is precooled by the precooling cooler 20, further cooled by JT expansion in the JT valve 30, and supplied to the final heat exchanger 32. The object to be cooled 16 is cooled by exchanging heat with the final heat exchanger 32. The cooled refrigerant is recovered from the final heat exchanger 32, boosted in pressure by a compressor described later, precooled again by the precooling cooler 20, and supplied to the JT valve 30. Thus, the refrigerant circulates in the refrigerant circuit 40. The JT cooler 18 can cool the final heat exchanger 32 to a temperature range of, for example, about 4K or lower than 4K (e.g., 1K to 4K), and thus can cool the object to be cooled 16 to this temperature range.

[0022] As an example, the precooling cooler 20 is a two-stage GM cooler. The precooling cooler 20 includes a first compressor 21 and an expander 22 also called a cold head. The expander 22 includes a drive unit 23, a first cylinder block 24, a first precooling stage 25, a second cylinder block 26, and a second precooling stage 27. The first compressor 21 is disposed in the surrounding environment (e.g., room temperature and atmospheric pressure environment), that is, outside the vacuum vessel 12. The expander 22 is disposed in the vacuum vessel 12 as follows: the drive unit 23 is disposed outside the vacuum vessel 12, and the cylinder block and the precooling stage are disposed inside the vacuum vessel 12.

[0023] The first cylinder block 24 connects the first precooling stage 25 to the drive unit 23, whereby the first precooling stage 25 is structurally supported by the drive unit 23. The second cylinder block 26 connects the second precooling stage 27 to the first precooling stage 25, whereby the second precooling stage 27 is structurally supported by the first precooling stage 25. The first cylinder block 24 and the second cylinder block 26 extend coaxially, and the drive unit 23, the first cylinder block 24, the first precooling stage 25, the second cylinder block 26, and the second precooling stage 27 are arranged in a straight line in sequence. Typically, the first precooling stage 25 and the second precooling stage 27 are made of a highly thermally conductive metal material such as copper (e.g., pure copper), and the first cylinder block 24 and the second cylinder block 26 are made of other metal materials such as stainless steel.

[0024] A first displacer and a second displacer (not shown) are disposed in the first cylinder block 24 and the second cylinder block 26 respectively in a reciprocable manner. A first regenerator and a second regenerator (not shown) are respectively assembled on the first displacer and the second displacer. And the drive unit 23 has a drive mechanism such as a motor (not shown) for reciprocating the first displacer and the second displacer. The drive mechanism includes a flow path switching mechanism that switches the flow path of the refrigerant gas so as to periodically repeat the supply of the refrigerant gas into the expander 22 and the discharge therefrom. Usually, the refrigerant gas of the precooling cooler 20 is helium, but other appropriate gases can also be used.

[0025] The first compressor 21 is configured to recover the refrigerant gas from the expander 22, boost the pressure of the recovered refrigerant gas, and supply the refrigerant gas to the expander 22 again. The circulation of the refrigerant gas between the first compressor 21 and the expander 22 is carried out by a suitable combination of pressure change and volume change of the refrigerant gas in the expander 22, thereby constituting a thermodynamic cycle (e.g., GM cycle) that generates cold, and the expander 22 can provide ultra-low temperature cooling.

[0026] The first pre-cooling stage 25 is cooled to the first cooling temperature, and the second pre-cooling stage 27 is cooled to the second cooling temperature lower than the first cooling temperature. The first cooling temperature can be selected from the temperature range of 50K or more and 150K or less, for example. The second cooling temperature can be selected from the temperature range of 10K or more and 25K or less, for example.

[0027] The radiation shield 14 is in physical contact with the first pre-cooling stage 25 and thermally connected, or thermally connected to the first pre-cooling stage 25 via a heat transfer component. Therefore, the radiation shield 14 is cooled to the first cooling temperature by the first pre-cooling stage 25.

[0028] In addition to the JT valve 30 and the final heat exchanger 32, the refrigerant circuit 40 further includes a second compressor 41, a heat exchanger group 42, and refrigerant supply pipes 44 and refrigerant recovery pipes 46 connecting these components. Usually, the refrigerant gas circulating in the refrigerant circuit 40 is helium, but other suitable gases can also be used. In addition, the refrigerant circuit 40 is not limited to the specific structure described herein, and various typical structures can be appropriately adopted.

[0029] The second compressor 41 is configured to boost the pressure of the refrigerant gas recovered from the refrigerant recovery pipe 46 and transport it to the refrigerant supply pipe 44. For ease of understanding, Figure 1 the direction of refrigerant flow is shown by an arrow in the figure. The second compressor 41 serves as a refrigerant source for circulating the refrigerant in the refrigerant circuit 40. The second compressor 41 is arranged outside the vacuum vessel 12.

[0030] In the refrigerant circuit 40, the heat exchanger group 42 is arranged between the second compressor 41 and the final heat exchanger 32. The heat exchanger group 42 is composed of a series of countercurrent heat exchangers (42a to 42c). In this embodiment, it has a three-stage structure including the first heat exchanger 42a, the second heat exchanger 42b, and the third heat exchanger 42c. The first heat exchanger 42a is arranged between the vacuum vessel 12 and the radiation shield 14, that is, in the space inside the vacuum vessel 12 and outside the radiation shield 14. The second heat exchanger 42b, the third heat exchanger 42c, and the final heat exchanger 32 are arranged inside the radiation shield 14.

[0031] The first heat exchanger 42a cools the refrigerant gas at a high temperature (e.g., normal temperature (e.g., about 300 K)) flowing from outside the vacuum container 12 into the vacuum container 12. The second heat exchanger 42b further cools the refrigerant cooled by the first heat exchanger 42a and the first pre-cooling stage 25. The third heat exchanger 42c further cools the refrigerant cooled by the second heat exchanger 42b and the second pre-cooling stage 27.

[0032] The refrigerant supply pipe 44 connects the discharge side of the second compressor 41 to the refrigerant inlet of the final heat exchanger 32, and the refrigerant recovery pipe 46 connects the refrigerant outlet of the final heat exchanger 32 to the suction side of the second compressor 41. The refrigerant supply pipe 44 has the high-pressure side flow paths of the first heat exchanger 42a, the second heat exchanger 42b, and the third heat exchanger 42c respectively, and the refrigerant recovery pipe 46 has the low-pressure side flow paths of the first heat exchanger 42a, the second heat exchanger 42b, and the third heat exchanger 42c respectively. In each heat exchanger, the refrigerant flowing through the high-pressure side flow path can be cooled by heat exchange between the high-pressure side flow path and the low-pressure side flow path. The high-pressure side flow path and the low-pressure side flow path may also be referred to as the high-temperature side flow path and the low-temperature side flow path respectively.

[0033] Moreover, the refrigerant supply pipe 44 includes a first refrigerant pipe 44a and a second refrigerant pipe 44b. These refrigerant pipes are made of a highly heat-conductive metal material such as copper (e.g., pure copper), for example.

[0034] The first refrigerant pipe 44a extends from the first heat exchanger 42a via the first pre-cooling stage 25 to the second heat exchanger 42b. The first refrigerant pipe 44a connects the high-pressure side flow path of the first heat exchanger 42a to the high-pressure side flow path of the second heat exchanger 42b. The first refrigerant pipe 44a is thermally connected to the first pre-cooling stage 25, and the refrigerant flowing through the first refrigerant pipe 44a is cooled by the first pre-cooling stage 25. The first refrigerant pipe 44a may be fastened to the first pre-cooling stage 25 in a state of being wound around the outer peripheral surface of the first pre-cooling stage 25.

[0035] The second refrigerant pipe 44b extends from the second heat exchanger 42b via the second pre-cooling stage 27 to the third heat exchanger 42c. The second refrigerant pipe 44b connects the high-pressure side flow path of the second heat exchanger 42b to the high-pressure side flow path of the third heat exchanger 42c. The second refrigerant pipe 44b is thermally connected to the second pre-cooling stage 27, and the refrigerant flowing through the second refrigerant pipe 44b is cooled by the second pre-cooling stage 27. The second refrigerant pipe 44b may be fastened to the second pre-cooling stage 27 in a state of being wound around the outer peripheral surface of the second pre-cooling stage 27.

[0036] The JT valve 30 is disposed between the last heat exchanger (the 3rd heat exchanger 42c in this example) of the heat exchanger group 42 in the refrigerant supply pipe 44 and the final heat exchanger 32. The high-pressure side flow path of the 3rd heat exchanger 42c is connected to the refrigerant inlet of the final heat exchanger 32 via the JT valve 30. In this embodiment, the JT valve 30 is a fixed throttle orifice. However, the JT valve 30 may also be a variable throttle orifice capable of adjusting the opening degree.

[0037] During the steady-state operation of the JT refrigerator 18, the refrigerant flows through the refrigerant circuit 40 as follows. The high-pressure refrigerant compressed by the 2nd compressor 41 is first supplied to the high-pressure side flow path of the 1st heat exchanger 42a. The high-pressure refrigerant flowing through the high-pressure side flow path of the 1st heat exchanger 42a exchanges heat with the returning low-pressure refrigerant flowing through the low-pressure side flow path of the 1st heat exchanger 42a and is cooled. The high-pressure refrigerant cooled in the 1st heat exchanger 42a flows into the 1st refrigerant pipe 44a.

[0038] The high-pressure refrigerant flowing through the 1st refrigerant pipe 44a is cooled by the 1st precooling stage 25 of the precooling refrigerator 20 and sent to the high-pressure side flow path of the 2nd heat exchanger 42b. The high-pressure refrigerant flowing through the high-pressure side flow path of the 2nd heat exchanger 42b exchanges heat with the returning low-pressure refrigerant flowing through the low-pressure side flow path of the 2nd heat exchanger 42b and is cooled. The high-pressure refrigerant cooled in the 2nd heat exchanger 42b flows into the 2nd refrigerant pipe 44b.

[0039] The high-pressure refrigerant flowing through the 2nd refrigerant pipe 44b is cooled by the 2nd precooling stage 27 of the precooling refrigerator 20 and sent to the high-pressure side flow path of the 3rd heat exchanger 42c. The high-pressure refrigerant flowing through the high-pressure side flow path of the 3rd heat exchanger 42c exchanges heat with the returning low-pressure refrigerant flowing through the low-pressure side flow path of the 3rd heat exchanger 42c and is cooled. Thus, the high-pressure refrigerant is cooled to a temperature at which the JT effect can be expected (i.e., a temperature below the inversion temperature) and is sent to the JT valve 30.

[0040] This cooled high-pressure refrigerant becomes a misty gas-liquid mixed state of low-pressure refrigerant due to the Joule-Thomson effect when passing through the JT valve 30 and generates a cooling capacity within the temperature range of the liquefied refrigerant. The misty low-pressure refrigerant is sent to the final heat exchanger 32. As described above, when the refrigerant is helium, the final heat exchanger 32 can be cooled to the liquid helium temperature range. The final heat exchanger 32 can cool the object to be cooled 16 to this temperature by exchanging heat with the object to be cooled 16.

[0041] When the final-stage heat exchanger 32 is cooled, the mist-like low-pressure refrigerant evaporates and thus gasifies again. In the JT valve 30, the unliquefied refrigerant and the refrigerant gasified due to evaporation return to the low-pressure side flow path of the third heat exchanger 42c. The low-pressure refrigerant sequentially flows through the third heat exchanger 42c, the second heat exchanger 42b, and the first heat exchanger 42a in the refrigerant recovery pipeline 46. At this time, as described above, the low-pressure refrigerant heats up while cooling the high-pressure refrigerant in each heat exchanger (42c, 42b, 42a). In this way, the low-pressure refrigerant that has returned to room temperature leaves the vacuum container 12, is recovered to the second compressor 41, and is compressed again.

[0042] In this way, the ultra-low temperature cooling device 10 can cool the object to be cooled 16 to a temperature lower than the second cooling temperature of the precooling refrigerator 20, for example, a desired temperature of about 4K or lower than 4K (for example, 1K to 4K).

[0043] When the JT refrigerator 18 is started, the JT refrigerator 18 is cooled from the ambient temperature (for example, room temperature of about 300K) to the target ultra-low temperature (for example, the lowest achievable temperature lower than 4K). This initial cooling is also called the temperature reduction operation. The refrigerant gas supplied to the JT valve 30 is cooled from the ambient temperature to a temperature below the inversion temperature through the temperature reduction operation. The temperature reduction operation is only a preparation for ultra-low temperature cooling of the object to be cooled 16 using the JT refrigerator 18, so it is expected that the required time is as short as possible.

[0044] The JT valve 30 is designed to achieve the optimal JT flow rate at ultra-low temperatures. Therefore, at the initial stage of temperature reduction when the refrigerant gas temperature is high, the flow rate of the refrigerant gas that can pass through the JT valve 30 may be quite small. This may significantly increase the time required for temperature reduction.

[0045] When the JT valve 30 is a variable throttle orifice, at the start of temperature reduction, the opening of the JT valve 30 is set larger than the optimal opening at ultra-low temperatures to ensure a large flow rate, and then the opening of the JT valve 30 is reduced as the cooling progresses, thereby shortening the temperature reduction time. However, this measure is time-consuming and laborious. For example, it may be necessary for a technician to perform the appropriate opening adjustment operation of the JT valve 30. And when the JT valve 30 is a fixed throttle orifice, this measure cannot be adopted (as a result, compared with the case of a variable throttle orifice, it may take more than twice the time to cool the JT refrigerator 18 to the lowest achievable temperature (for example, about 4K)).

[0046] In a JT refrigerator of the prior art design, generally, in order to avoid heat intrusion from the precooling refrigerator into the JT refrigerant circuit during normal operation, the heat exchangers of the precooling refrigerator and the JT refrigerant circuit are configured not to be thermally connected to each other. The precooling stage of the precooling refrigerator is supported on the surrounding structure by a heat insulating material such as fiber reinforced plastic, and there is substantially no heat conduction path from the precooling stage to the heat exchanger.

[0047] This embodiment aims to use the precooling refrigerator 20 to shorten the time required for temperature reduction. The JT refrigerator 18 includes a heat conduction path 48 that connects at least one precooling stage in the precooling refrigerator 20 to at least one heat exchanger in the heat exchanger group 42, so that the precooling refrigerator 20 can conductively cool at least one heat exchanger. The heat conduction path 48 can connect the second precooling stage 27 to at least one of the second heat exchanger 42b and the third heat exchanger 42c, so that the second precooling stage 27 can conductively cool at least one of the second heat exchanger 42b and the third heat exchanger 42c.

[0048] For example, the JT refrigerator 18 can include a first heat conduction path 48a that connects the second precooling stage 27 to the second heat exchanger 42b, so that the second precooling stage 27 can conductively cool the second heat exchanger 42b. And, alternatively or in addition, the JT refrigerator 18 can include a second heat conduction path 48b that connects the second precooling stage 27 to the third heat exchanger 42c, so that the second precooling stage 27 can conductively cool the third heat exchanger 42c.

[0049] In order to avoid heat load conduction from the high-temperature part to the low-temperature part of the JT refrigerator 18 after the temperature reduction operation is completed and the JT refrigerator 18 is operating normally, the heat conduction path 48 is set such that the temperature difference between its two ends is as small as possible during the normal operation of the JT refrigerator 18. The heat conduction path 48 can be set such that during the normal operation of the JT refrigerator 18, the temperature difference between the two ends of the heat conduction path 48 is, for example, less than 5K or less than 3K.

[0050] As an example, as Figure 1 shown, the first heat conduction path 48a can be connected to the low-temperature side of the second heat exchanger 42b. In an exemplary JT refrigerator 18, it is expected that the low-temperature side of the second heat exchanger 42b and the second precooling stage 27 of the precooling refrigerator 20 are at substantially the same temperature (e.g., around 12K) during the normal operation of the JT refrigerator 18.

[0051] On the other hand, assume that the high-temperature side of the second heat exchanger 42b has substantially the same temperature as the first pre-cooling stage 25 of the pre-cooling refrigerator 20. Assuming that the first heat conduction path 48a connects the high-temperature side of the second heat exchanger 42b to the second pre-cooling stage 27 of the pre-cooling refrigerator 20, during the normal operation of the JT refrigerator 18, a temperature difference equivalent to the temperature difference between the first pre-cooling stage 25 and the second pre-cooling stage 27 will be generated at both ends of the first heat conduction path 48a, which will increase the heat load of the second pre-cooling stage 27 and may have an adverse effect on the refrigeration performance of the JT refrigerator 18.

[0052] For the same reason, as Figure 1 shown, the second heat conduction path 48b can be connected to the low-temperature side of the third heat exchanger 42c. Alternatively, or additionally, the second heat conduction path 48b can also be connected to the high-temperature side of the third heat exchanger 42c.

[0053] The refrigerant pipes (e.g., the first refrigerant pipe 44a or the second refrigerant pipe 44b) constituting the refrigerant circuit 40 are structurally connected to the pre-cooling stage and the heat exchanger, but since the cross-sectional area perpendicular to the pipe axis direction is quite small, sufficient heat conduction to shorten the cooling time cannot be achieved.

[0054] Therefore, the heat conduction path 48 is provided separately from the refrigerant pipes constituting the refrigerant circuit 40. That is, the first heat conduction path 48a is provided separately from the second refrigerant pipe 44b, and the second pre-cooling stage 27 and the second heat exchanger 42b are thermally connected to each other. The second heat conduction path 48b is provided separately from the second refrigerant pipe 44b, and the second pre-cooling stage 27 and the third heat exchanger 42c are thermally connected to each other.

[0055] The heat conduction path 48 is formed by one or more heat conduction components. Such heat conduction components are made of a metal material with a high heat conduction coefficient such as copper (e.g., pure copper or copper alloy) or aluminum (e.g., pure aluminum or aluminum alloy) or other high heat conductivity materials. The heat conduction components can be made of a material with a higher heat conduction coefficient than stainless steel (e.g., SUS304), for example.

[0056] Figure 2 is a diagram schematically showing an exemplary structure of the heat conduction path according to the embodiment. As shown in the figure, the first heat conduction path 48a has a table extension member 50 and a heat conduction plate 52 as an example of the heat conduction component.

[0057] The table extension member 50 is a cylindrical (e.g., cylindrical) heat conduction component made of a high heat conductivity material (e.g., pure copper), one end of which is thermally connected to the second pre-cooling stage 27 and the other end is thermally connected to the heat conduction plate 52. For example, the flange formed at one end of the table extension member 50 can be fixed to the second pre-cooling stage 27 by fastening components such as bolts, and the flange formed at the other end of the table extension member 50 can be fixed to the heat conduction plate 52.

[0058] The heat conducting plate 52 is a flat heat conducting component made of a high heat conductivity material (e.g., aluminum alloy). The table extension component 50 and the low temperature end of the second heat exchanger 42b are thermally connected through the heat conducting plate 52. The table extension component 50 and the second heat exchanger 42b can be arranged on the same side of the heat conducting plate 52 and fixed on the same surface of the heat conducting plate 52.

[0059] The second heat exchanger 42b can have a typical structure with a cylindrical housing. The second heat exchanger 42b can include a mandrel coaxially arranged inside the housing and a pipe wound around the outer peripheral surface of the mandrel and arranged in a cylindrical cavity between the mandrel and the housing. This pipe can be used as the high pressure side flow path of the second heat exchanger 42b, and the cylindrical cavity can be used as the low pressure side flow path of the second heat exchanger 42b.

[0060] As shown in the figure, the second refrigerant pipe 44b and the refrigerant recovery pipe 46 penetrate through the end plate on the low temperature side of the housing of the second heat exchanger 42b. As referred to Figure 1 above, the second refrigerant pipe 44b is connected to the high pressure side flow path of the second heat exchanger 42b, and the refrigerant recovery pipe 46 is connected to the low pressure side flow path of the second heat exchanger 42b. Moreover, the second refrigerant pipe 44b is installed on the second pre-cooling table 27 in a wound manner so as to be able to perform heat exchange with the second pre-cooling table 27.

[0061] Although not shown in Figure 2 , similarly, the third heat exchanger 42c can also be thermally connected to the second pre-cooling table 27 via the heat conducting plate 52 and the table extension component 50. The third heat exchanger 42c can also have a cylindrical outer shape similar to that of the second heat exchanger 42b, and its low temperature end is fixed to the heat conducting plate 52. As an exemplary configuration, the third heat exchanger 42c can be arranged in parallel with the second heat exchanger 42b and, with respect to Figure 2 the paper surface of, be arranged in front of or behind the second heat exchanger 42b.

[0062] As described above, according to the embodiment, the second heat exchanger 42b and the third heat exchanger 42c are connected to the second pre-cooling table 27 of the pre-cooling refrigerator 20 through the heat conducting path 48. During the temperature reduction operation, in addition to using the refrigerant gas circulating in the refrigerant circuit 40, conduction cooling via the heat conducting path 48 can also be used to promote the cooling of the heat exchanger group 42 of the JT refrigerator 18. Therefore, the temperature reduction time of the JT refrigerator 18 can be shortened.

[0063] According to the verification of the present inventor, in the existing design without the heat conducting path 48, it takes about 24 hours to reduce the temperature. In contrast, in the embodiment with the heat conducting path 48, the temperature reduction can be completed in about 12 hours.

[0064] Figure 3 This is a diagram schematically showing a modified example of the heat conduction path according to the embodiment. As shown in the figure, the third heat exchanger 42c can be thermally connected to the second precooling stage 27 through the second heat conduction path 48b. However, in addition to heat conduction components (for example, the stage extension member 50 and the heat conduction plate 52), the second heat conduction path 48b can also include a thermal resistance element 60. The second heat conduction path 48b can connect the second precooling stage 27 and the third heat exchanger 42c via the thermal resistance element 60.

[0065] The thermal resistance element 60 can be a spacer made of a metal material or other material with a lower thermal conductivity than the heat conduction components, and the third heat exchanger 42c can be fixed to the heat conduction plate 52 in such a way that the thermal resistance element 60 is clamped between its low-temperature end and the heat conduction plate 52. For example, when the heat conduction components are made of copper or aluminum as described above, the thermal resistance element 60 can be made of stainless steel (for example, SUS304).

[0066] As shown in the figure, a refrigerant supply pipe 44 and a refrigerant recovery pipe 46 are connected to the end plate on the low-temperature side of the housing of the third heat exchanger 42c. As referred to Figure 1 above, the refrigerant supply pipe 44 is connected to the high-pressure side flow path of the third heat exchanger 42c, and the refrigerant recovery pipe 46 is connected to the low-pressure side flow path of the third heat exchanger 42c. Also, the refrigerant supply pipe 44 is connected to the JT valve 30.

[0067] In this way, during the temperature reduction operation, the cooling of the third heat exchanger 42c can also be promoted by conduction cooling from the second precooling stage 27 through the second heat conduction path 48b, shortening the temperature reduction time of the JT refrigerator 18.

[0068] On the other hand, during the normal operation of the JT refrigerator 18, a certain temperature difference may occur between the low-temperature end of the third heat exchanger 42c and the second precooling stage 27. For example, the low-temperature end of the third heat exchanger 42c is cooled to about 5K, while the second precooling stage 27 is cooled to about 12K as described above. At this time, the second precooling stage 27 becomes a heat source relative to the third heat exchanger 42c, and the heat entering the third heat exchanger 42c from the second precooling stage 27 through the second heat conduction path 48b may reduce the refrigeration performance of the JT refrigerator 18.

[0069] However, in this embodiment, since the thermal resistance element 60 is provided on the second heat conduction path 48b, the heat input to the third heat exchanger 42c via the second heat conduction path 48b that may occur during the normal operation of the JT refrigerator 18 can be restricted. Therefore, the above problems can be alleviated or prevented.

[0070] In addition, when necessary, a thermal resistance element 60 may also be provided on the first heat conduction path 48a. The first heat conduction path 48a can connect the second precooling stage 27 and the second heat exchanger 42b via the thermal resistance element 60.

[0071] As described above, the present invention has been described based on the embodiments. Those skilled in the art should understand that the present invention is not limited only to the above-described embodiments, various design changes can be made and various modifications can exist, and such modifications are also within the scope of the present invention. The various features described in association with a certain embodiment can also be applied to other embodiments. The new embodiments generated by combination have the effects of the respective embodiments combined.

[0072] The precooling refrigerator 20 is not limited only to the GM refrigerator. The precooling refrigerator 20 can also be other forms of cryogenic refrigerators such as a pulse tube refrigerator and a Stirling refrigerator.

[0073] In the above-described embodiment, the case where the heat exchanger group 42 has the first to third heat exchangers has been exemplified, but the heat exchanger group 42 can also have other multi-stage structures. For example, the JT refrigerator 18 can, for example, have an additional heat exchanger (i.e., the fourth heat exchanger) between the third heat exchanger 42c and the final heat exchanger 32.

[0074] The above-described JT valve 30 can also be disposed between the last heat exchanger (i.e., the fourth heat exchanger) of the heat exchanger group 42 in the refrigerant supply pipe 44 and the final heat exchanger 32. Alternatively, the JT refrigerator 18 can also adopt a two-stage JT expansion method, and the first JT valve can be disposed between the third heat exchanger 42c and the fourth heat exchanger in the refrigerant supply pipe 44, and the second JT valve can be disposed between the fourth heat exchanger and the final heat exchanger 32 in the refrigerant supply pipe 44.

[0075] The JT refrigerator 18 can also include a third heat conduction path that connects the second precooling stage 27 and the fourth heat exchanger so that the second precooling stage 27 can conductively cool the fourth heat exchanger. The third heat conduction path can also be composed of a stage extension member 50 and a heat conduction plate 52, like the first heat conduction path 48a and the second heat conduction path 48b. That is, the fourth heat exchanger can also be thermally connected to the second precooling stage 27 via the heat conduction plate 52 and the stage extension member 50.

[0076] According to the embodiment, the present invention has been described using specific statements, but the embodiment only shows one aspect of the principle and application of the present invention. Within the scope not departing from the idea of the present invention defined by the claims, the embodiment can have many modifications and configuration changes.

[0077] Industrial Applicability

[0078] The present invention can be applied to the field of Joule - Thomson refrigerators.

[0079] Symbol Explanation

[0080] 10 - Ultra - low temperature cooling device, 18 - JT refrigerator, 20 - Pre - cooling refrigerator, 25 - First pre - cooling stage, 27 - Second pre - cooling stage, 30 - JT valve, 32 - Final heat exchanger, 40 - Refrigerant circuit, 42 - Heat exchanger group, 42a - First heat exchanger, 42b - Second heat exchanger, 42c - Third heat exchanger, 44a - First refrigerant pipe, 44b - Second refrigerant pipe, 48 - Heat conduction path, 48a - First heat conduction path, 48b - Second heat conduction path, 50 - Stage extension part, 52 - Heat conduction plate, 60 - Thermal resistance element.

Claims

1. A Joule-Thomson refrigerator, characterized in that, Comprising: A precooling refrigerator having a precooling stage; A refrigerant circuit having a heat exchanger and refrigerant piping that extends from the heat exchanger and is cooled by the precooling stage; And A heat conduction path that is provided separately from the refrigerant piping and connects the precooling stage and the heat exchanger so that the precooling stage can conductively cool the heat exchanger.

2. The Joule-Thomson refrigerator according to claim 1, wherein The precooling refrigerator has a cylinder extending from the precooling stage, The heat conduction path includes: A first heat conduction member that is thermally connected to the precooling stage and extends from the precooling stage toward the side opposite to the cylinder; and A second heat conduction member that thermally connects the first heat conduction member and the heat exchanger.

3. The Joule-Thomson refrigerator according to claim 1, wherein The precooling refrigerator has a first precooling stage and a second precooling stage cooled to a temperature lower than that of the first precooling stage, The refrigerant circuit has a first heat exchanger, a second heat exchanger, and a third heat exchanger. The second heat exchanger further cools the refrigerant cooled by the first heat exchanger, and the third heat exchanger further cools the refrigerant cooled by the second heat exchanger. The refrigerant piping extends from the second heat exchanger via the second precooling stage to the third heat exchanger, The heat conduction path connects the second precooling stage to at least one of the second heat exchanger and the third heat exchanger so that the second precooling stage can conductively cool at least one of the second heat exchanger and the third heat exchanger.

4. The Joule-Thomson refrigerator according to claim 3, wherein The heat conduction path connects the second precooling stage to the second heat exchanger so that the second precooling stage can conductively cool the second heat exchanger.

5. The Joule-Thomson refrigerator according to claim 3, wherein The precooling refrigerator has a cylinder connecting the second precooling stage and the first precooling stage, The heat conduction path includes: A stage extension member that is thermally connected to the precooling stage and extends from the precooling stage toward the side opposite to the cylinder; And A heat conduction plate that thermally connects the stage extension member to at least one of the second heat exchanger and the third heat exchanger.

6. The Joule-Thomson refrigerator according to claim 5, wherein At least one of the second heat exchanger and the third heat exchanger and the stage extension member are arranged on the same side of the heat conduction plate.

7. The Joule-Thomson refrigerator according to claim 1, wherein The heat conduction path includes a thermal resistance element.

8. The Joule-Thomson refrigerator according to claim 2, wherein The heat conduction path has a thermal resistance element between the heat exchanger and the second heat conduction member, The thermal conductivity of the thermal resistance element is less than the thermal conductivity of the second heat conduction member.

9. The Joule-Thomson refrigerator according to claim 3 or 4, wherein The heat conduction path connects the second precooling stage and the third heat exchanger via a thermal resistance element.

10. The Joule-Thomson refrigerator according to claim 5 or 6, characterized in that the heat conduction path is provided with a thermal resistance element between the third heat exchanger and the heat conduction plate, and the thermal conductivity of the thermal resistance element is less than the thermal conductivity of the heat conduction plate.

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