Heat exchanger, refrigerator, and sintered body

Abstract

The heat exchanger (18) includes: a low-temperature side flow path (32) through which low-temperature liquid helium flows; a high-temperature side flow path (30) through which high-temperature liquid helium flows; and a heat conduction part (36) that conducts heat from the high-temperature side flow path (30) to the low-temperature side flow path (32). The heat conduction part (36) has: a partition member that separates the high-temperature side flow path (30) and the low-temperature side flow path (32); and a thermal resistance reduction part (40) that reduces the thermal resistance between the partition member and the liquid helium. The thermal resistance reduction part (40) has: a porous body having nano-sized pores; and metal fine particles having a higher thermal conductivity than the porous body.

Description

Technical Field

[0001] The present disclosure relates to a heat exchanger used in a refrigerator. Background Art

[0002] Hitherto, as a refrigerator for achieving an extremely low temperature of 100 mK or less, a 3 He- 4 He dilution refrigerator is known. The lowest temperature and cooling capacity that can be achieved by such a dilution refrigerator largely depend on the performance of the heat exchanger. The heat exchanger of the dilution refrigerator uses a so-called 3 He dilute phase (D phase: 3 He concentration of about 6.4%) to cool the 3 He concentrated phase (C phase: 3 He concentration of about 100%) flowing into the mixing chamber as a cooling unit.

[0003] Therefore, the key lies in how to effectively transfer the heat of the 3 He concentrated phase to the 3 He dilute phase. For example, in order to improve heat conduction, the following heat exchanger has been proposed: that is, a heat exchanger in which a metal plate that separates the concentrated phase and the dilute phase is formed of a silver plate having a high thermal conductivity, and a disk made of sintered silver is arranged so as to sandwich the silver plate (see Patent Document 1).

[0004] (Prior Art Documents)

[0005] (Patent Documents)

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-74774 Summary of the Invention

[0007] (Problems to be Solved by the Invention)

[0008] However, since 3 He used in the above-described dilution refrigerator is very scarce and expensive, reducing its usage helps to cut costs and miniaturize the device. In addition, since the performance of the dilution refrigerator largely depends on the performance of the heat exchanger, it is required to further improve the heat conduction of the heat exchanger of the refrigerator.

[0009] The present disclosure is made in view of such circumstances, and one of the exemplary objects thereof is to provide a technique for further improving the heat conduction of the heat exchanger of a refrigerator.

[0010] (Measures for Solving the Problems)

[0011] To solve the above problems, a heat exchanger according to one aspect of the present disclosure includes: a low-temperature side flow path through which low-temperature liquid helium flows; a high-temperature side flow path through which high-temperature liquid helium flows; and a heat conduction portion that conducts heat from the high-temperature side flow path to the low-temperature side flow path. The heat conduction portion has: a metal component that separates the high-temperature side flow path and the low-temperature side flow path; and a thermal resistance reduction portion that reduces the thermal resistance between the metal component and the liquid helium. The thermal resistance reduction portion has: a porous body having nano-sized pores; and metal fine particles having a higher thermal conductivity than the porous body.

[0012] (Effects of the Invention)

[0013] According to the present disclosure, it is possible to further improve the heat conduction of the heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 FIG. is a schematic diagram showing a schematic structure of a dilution refrigerator according to the present embodiment.

[0015] Figure 2 FIG. is a schematic diagram showing a schematic structure of a heat exchanger according to the present embodiment.

[0016] Figure 3 FIG. is a schematic diagram showing a main part of a thermal resistance reduction portion according to the present embodiment.

[0017] Figure 4 FIG. is a schematic diagram schematically showing a schematic structure of a porous body according to the present embodiment.

[0018] Figure 5 FIG. is a schematic diagram showing a schematic structure of a mixing chamber according to the present embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] A heat exchanger according to one aspect of the present disclosure includes: a low-temperature side flow path through which low-temperature (e.g., 3 low He concentration) liquid helium flows; a high-temperature side flow path through which high-temperature (e.g., 3 high He concentration) liquid helium flows; and a heat conduction portion for conducting heat from the high-temperature side flow path to the low-temperature side flow path. The heat conduction portion has: a metal component that separates the high-temperature side flow path and the low-temperature side flow path; and a thermal resistance reduction portion that reduces the thermal resistance between the metal component and the liquid helium. The thermal resistance reduction portion has: a porous body having nano-sized pores; and metal fine particles having a higher thermal conductivity than the porous body.

[0020] According to this aspect, compared with the case where only metal fine particles are fixed to the metal component, the thermal resistance reduction portion is composed of metal fine particles having a higher thermal conductivity and a porous body having a large specific surface area, so that the thermal resistance between the metal component and the liquid helium can be reduced. Therefore, it is possible to further improve the heat conduction from the high-temperature side flow path to the low-temperature side flow path.

[0021] The thermal resistance reduction part can also be a sintered body of a porous body and metal particles. Thereby, the contact area with liquid helium is increased by the porous body to reduce the Kapitza resistance, and the heat conduction between the porous body and the metal component is carried out by metal particles having a higher thermal conductivity than the porous body, so that the thermal resistance between the metal component and liquid helium can be reduced.

[0022] The thickness of the thermal resistance reduction part can be in the range of 1 to 1000 μm, more preferably in the range of 1 to 500 μm, and most preferably in the range of 1 to 200 μm. Thereby, while including a porous body having pores of a certain degree of nano size, the thermal resistance of the entire thermal resistance reduction part can be reduced.

[0023] The porous body can be particles having through-holes formed on the surface as pores. Thereby, the helium outside the porous body particles and the helium in the pores can be in direct contact for heat conduction.

[0024] The through-holes on the surface of the porous body particles can have a diameter in which helium can exist in a liquid form inside. Thereby, heat conduction between the same liquid helium can be carried out in the through-holes. In addition, the through-hole means a hole that is continuous from the opening formed on the surface of the porous body to the inside of the porous body, and the entrance or exit can be blocked by metal particles.

[0025] The pores of the porous body only need to have a diameter that satisfies the following conditions: Even if a solid-state helium (e.g., 4 He) layer is formed on the inner wall, helium (e.g., 3 He) can exist in a liquid form in the central part of the pores, and the diameter in which helium (e.g., 3 He) liquids can be connected and exist. Specifically, the average pore diameter of the porous body can be in the range of 2 to 30 nm.

[0026] The porous body can be silicate particles having an average particle size in the range of 50 to 20000 nm. Thereby, it is possible to balance a large specific surface area that contributes to reducing the Kapitza resistance and shortening the heat conduction distance through the silicate component of the porous body that affects the thermal resistance.

[0027] The specific surface area of the porous body can be 600 m 2 / g or more. Thereby, the Kapitza resistance at the interface between the porous body and liquid helium can be reduced.

[0028] The metal particles can be silver particles having an average particle size in the range of 50 to 100000 nm. Thereby, the metal particles surround the porous body and are fixed to the metal component as a sintered body.

[0029] Another aspect of the present disclosure is a refrigerator. The refrigerator may include: the above-described heat exchanger; a mixing chamber in which 3 a dilute phase of He and 3 a concentrated phase of He are formed, and which has an inflow path for 3 He liquid to flow into the 3 concentrated phase of He and an outflow path for 3 He liquid to flow out from the 3 dilute phase of He to the low-temperature side flow path; a fractionation chamber having an inflow path for 3 He liquid flowing in the low-temperature side flow path, for selectively separating 3 He in the form of vapor from the 4 mixture of He liquid and 3 He liquid; and a cooling passage for liquefying the 3 He separated in the fractionation chamber and returning it to the high-temperature side flow path.

[0030] Another aspect of the present disclosure is a sintered body. The sintered body is a sintered body of a porous body having nano-sized pores and metal particles having a higher thermal conductivity than the porous body. Adsorbed inside the pores of the porous body are 4 He and 3 He. Thus, the thermal resistance of the sintered body can be made sufficiently small.

[0031] According to this aspect, since further improvement in heat conduction of the heat exchanger can be provided, improvement in refrigeration performance and miniaturization of the entire refrigerator can be achieved.

[0032] In addition, any combination of the above-described components and conversion of the expressions of the present disclosure among methods, apparatuses, systems, etc. are also effective as aspects of the present disclosure.

[0033] Hereinafter, aspects for implementing the present disclosure will be described in detail with reference to the drawings and the like. In addition, in the description of the drawings, the same elements are denoted by the same reference numerals, and repeated descriptions are appropriately omitted. In addition, the structures described below are examples and do not limit the scope of the present disclosure.

[0034] (Dilution refrigerator)

[0035] The dilution refrigerator of the present embodiment is a representative refrigerator that achieves an extremely low temperature of 100 mK or less. Figure 1 FIG. is a schematic diagram showing a schematic structure of the dilution refrigerator of the present embodiment. The dilution refrigerator 10 includes: a mixing chamber 16 in which 3 a dilute phase of He (hereinafter, appropriately referred to as "dilute phase") 12 and 3 a concentrated phase of He (hereinafter, appropriately referred to as "concentrated phase") 14 can be formed; a heat exchanger 18 for3 Liquid He exchanges heat with the liquid He flowing out of the mixing chamber 16 3 and the liquid He 4 and the mixture of liquid He; a fractionation chamber 20 for selectively separating 3 He in the form of vapor from 3 the liquid He and 4 the mixture of liquid He; a 1K storage chamber 22 for storing 1K liquid helium. The fractionation chamber 20 has an inlet 20b for the mixture flowing in the cryogenic side flow path 32 to flow in. The mixing chamber 16, the heat exchanger 18, the fractionation chamber 20, and the 1K storage chamber 22 are arranged in a vacuum-insulated cryostat 24.

[0036] Next, the operation of the dilution refrigerator 10 will be described. 3 Liquid He and 4 the mixture of liquid He undergo phase separation at a low temperature below 0.87K. Therefore, in the mixing chamber 16, 3 liquid He and 4 the mixture of liquid He separate into 3 a concentrated phase 14 of nearly 100% liquid He and a dilute phase 12 in which about 6.4% of 4 liquid He is mixed in 3 liquid He and coexist.

[0037] Since the density of the concentrated phase 14 is less than that of the dilute phase 12, it floats on top of the dilute phase 12. When 3 liquid He in the concentrated phase 14 dissolves into the dilute phase 12, cooling corresponding to the entropy difference occurs. The dilution refrigerator 10 is a refrigerator that utilizes the entropy difference between these two phases, the concentrated phase and the dilute phase.

[0038] If the temperature of the fractionation chamber 20 is set below 0.8K, only 3 He is selectively evaporated due to the difference in vapor pressure. By using a vacuum pump outside the cryostat 24 connected to the discharge path 26 of the fractionation chamber 20 to suck, 3 He can be selectively separated and taken out in the form of vapor S from the dilute phase 20a.

[0039] As a result, the concentration of 3 He in the dilute phase 20a in the fractionation chamber 20 decreases, creating a concentration difference with the dilute phase 12 in the mixing chamber 16. Thereby, 3 He in the dilute phase 12 in the mixture 16 moves toward the fractionation chamber 20, and the concentration of 3 He in the dilute phase 12 decreases, so 3He is dissolved in the dilute phase 12. At this time, cooling occurs and the temperature of the dilute phase 12 in the mixing chamber 16 further decreases.

[0040] The 3 vapor S of He evaporated in the fractionation chamber 20 is recovered and compressed by an external pump, and then returns to the mixing chamber 16 again from the supply path 28. The 3 vapor S of He supplied from the supply path 28 can be precooled by 4.2K 4 He and is further cooled and liquefied in the 1K storage chamber 22. In the present embodiment, the passage from the supply path 28 through the 1K storage chamber 22 to the high-temperature side flow path 30 serves as a cooling passage 29 for 3 liquefying He and returning it to the high-temperature side flow path 30. The liquefied 3 He exchanges heat with the 3 He passing through the low-temperature side flow path 32 of the heat exchanger 18 during the process of passing through the high-temperature side flow path 30 of the heat exchanger 18, and is further cooled, and returns to the concentrated phase 14 from the inflow path 34 of the mixing chamber 16.

[0041] As described above, the dilution refrigerator 10 of the present embodiment continuously obtains an extremely low temperature of 1K to a few mK through the 3 circulation of He, and thus can be expected to be applied to various fields requiring extremely low temperature cooling such as semiconductor detectors and quantum computers. In addition, reducing the usage amount of expensive 3 He and miniaturizing the device without reducing the cooling performance are also important for the popularization of the dilution refrigerator.

[0042] (Heat exchanger)

[0043] The present inventor focused on the heat exchanger, which is one of the structures that greatly affects the performance of such a dilution refrigerator. In particular, a new technique for improving the heat conduction from the high-temperature side flow path 30 to the low-temperature side flow path 32 has been developed.

[0044] Figure 2 FIG. is a schematic diagram showing the schematic structure of the heat exchanger of the present embodiment. The heat exchanger 18 of the present embodiment includes a low-temperature side flow path 32, a high-temperature side flow path 30, and a heat conduction portion 36 inside the container 31. Among them, the low-temperature side flow path 32 allows 3 liquid helium with a low He concentration (about 6.4%) to flow through, the high-temperature side flow path 30 allows 3 liquid helium with a high He concentration (about 100%) to flow through, and the heat conduction portion 36 is used to conduct heat H from the high-temperature side flow path 30 to the low-temperature side flow path 32.

[0045] The high-temperature side flow path 30 has a supply for being precooled in the 1K storage chamber 22 and the fractionation chamber 20 3The inflow path 30a for the inflow of He, and for the 3 outflow path 30b for the outflow of He. The low-temperature side flow path 32 mainly has 3 an inflow path 32a for He to flow into the dilute phase 12 of the mixing chamber 16, and for the 3 He that has taken heat H from the 3 He to flow out through the outflow path 32b toward the dilute phase 20a of the fractionation chamber 20. The heat conduction part 36 has a plate-like metal part 38 that serves as a partition member separating the high-temperature side flow path 30 and the low-temperature side flow path 32, and a thermal resistance reduction part 40 that reduces the thermal resistance between the metal part 38 and liquid helium. The metal part 38 is made of a material with a high thermal conductivity such as copper or silver. As the partition member, in addition to metal, it can also be made of a material with a high thermal conductivity such as diamond.

[0046] In heat exchange in the temperature range of about 100 mK or lower using the dilution refrigerator 10, the Kapitza thermal resistance generated at the interface between a solid surface such as the metal part 38 and liquid helium becomes one of the main reasons for the degradation of heat exchange performance. Therefore, one solution is to fix metal particles of silver and copper, which have a good thermal conductivity and can increase the interface area as much as possible, to the surface of the metal part 38. However, the present inventor has developed a thermal resistance reduction part 40 that can achieve a thermal conductivity that cannot be achieved by metal particles alone through the combination of multiple functional parts.

[0047] (Thermal resistance reduction part)

[0048] Figure 3 FIG. is a schematic diagram showing the main part of the thermal resistance reduction part 40 of the present embodiment. Although Figure 3 shows a structure centered on one nanoporous body, of course, there may also be multiple nanoporous bodies and metal particles in the thermal resistance reduction part 40.

[0049] As Figure 3 shown, the thermal resistance reduction part 40 of the present embodiment has: a porous body 42 having pores with a nanoscale size; and metal particles 44 having a thermal conductivity higher than that of the porous body 42. In this way, the thermal resistance reduction part 40 is composed of metal particles 44 with a relatively high thermal conductivity and a porous body 42 with a large specific surface area, whereby the thermal resistance between the metal part 38 and liquid helium can be reduced compared to the case where only the metal particles 44 are fixed to the metal part 38. Therefore, the heat conduction from the high-temperature side flow path 30 to the low-temperature side flow path 32 can be further improved.

[0050] In addition, the thermal resistance reduction part 40 is a sintered body of a porous body 42 and metal fine particles 44 fixed to the metal member 38. Thus, the contact area with liquid helium is increased by the porous body 42 to reduce the Kapitza thermal resistance. Moreover, the heat conduction between the porous body 42 and the metal member 38 is carried out via the metal fine particles 44 having a higher thermal conductivity than the porous body 42, whereby the thermal resistance between the metal member 38 and liquid helium can be reduced.

[0051] (porous body)

[0052] Figure 4 FIG. is a schematic diagram schematically showing the schematic structure of the porous body 42 of the present embodiment. The porous body 42 is a nanoporous body (mesoporous silica) composed of silicate or the like, and a plurality of nano-sized pores 42a are regularly formed therein. Therefore, the specific surface area of the porous body 42 is 600 to 1300 m 2 / g, which is more than three orders of magnitude larger than the specific surface area (about 1 m 2 / g) of metal fine particles such as silver. The thermal resistance caused by the Kapitza effect decreases in inverse proportion to the interface area. Therefore, by performing heat conduction between the metal member 38 and liquid helium through the porous body 42, the Kapitza thermal resistance at the interface between the metal member 38 and liquid helium can be reduced. In addition, even a small heat conduction part 36 can ensure a sufficient interface area, so that miniaturization of the device can be achieved.

[0053] In addition, from the viewpoint of the specific surface area, it is preferable that the average pore diameter D of the pores 42a is small. However, according to the research and analysis of the present inventors, it has been found that in the pores 42a of the porous body 42 having a pore diameter larger than about 2 nm in contact with liquid helium, solid helium (mainly 4 He) is adsorbed on the pore wall surface 42b. In addition, the thickness C of the solid layer 46 formed by the solid helium at this time is about 0.6 nm. Since the average interparticle distance of liquid helium is about 0.4 nm, when the pore diameter is 1.5 nm or less, the entire pore will be filled with solid helium.

[0054] The measured value of the pore diameter D of the porous body 42 of the present embodiment obtained by the Barrett-Joyner-Halenda (BJH) method is about 3.9 nm. Therefore, the cylindrical region with a diameter of 2.7 nm inside the solid layer 46 is filled with the 3 He liquid L' contained in the dilute phase 12 or the concentrated phase 14. Since 3 the diameter of the cylindrical region of the He liquid L' is sufficiently larger than the particle spacing of about 0.4 nm of liquid helium, the same heat conduction properties as those of the helium liquid L located around the porous body 42 can be expected. The liquid helium L located around the porous body 42 and the3 The liquid He L' is directly connected to the other liquid through the through-holes on the surface of the porous body particles.

[0055] Inside the pore 42a 3 The thermal resistance caused by the Kapitza thermal resistance between the He liquid L' and the pore wall surface of the porous body is inversely proportional to the total area of the pore wall surface. Due to the huge specific surface area of the porous body 42, even a small heat exchanger can achieve a large area, thus reducing the thermal resistance caused by the Kapitza thermal resistance. In this way, the heat conduction between the liquid helium L around the porous body 42 and the silicate component of the porous body 42 becomes good.

[0056] In this way, the pore 42a of the porous body 42 has 3 a diameter in which He can exist in liquid form inside, and in addition, the pore 42a is a through-hole. Thus, the heat conduction at both ends of the pore 42a can be effectively achieved through the He liquid L'. In addition, the outside of the granular porous body 42 and the He liquid L' inside the pore 42a are directly connected to enable heat conduction. 3 3

[0057] In addition, preferably, the average pore diameter D of the porous body 42 is set such that the diameter of the cylindrical shape in the central part of the pore 42a of the He liquid L' is sufficiently larger than the particle spacing of about 0.4 nm of the liquid helium. In this case, considering the thickness of 0.6 nm of the solid layer 46 of solid He, at least the pore diameter D needs to be 1.6 nm or more, preferably 2 nm or more, and from the viewpoint of the specific surface area, 30 nm or less is more preferable. Thus, in the central part of the pore 42a, a He liquid L' with a diameter sufficiently larger than 0.4 nm can exist. 3 4 3

[0058] When the porous body 42 is a silicate particle, if the average particle diameter is too large, the thermal resistance of the porous body 42 itself will become large. In addition, if the average particle diameter is too small, it is difficult to adjust the average pore diameter D to an appropriate range. Therefore, the porous body 42 of the present embodiment is a silicate particle with an average particle diameter in the range of 50 to 20,000 nm, and considering the thermal resistance of the components of the porous body 42, etc., a silicate particle with an average particle diameter in the range of 100 to 500 nm is preferred. Thus, it is possible to balance the large specific surface area contributing to the reduction of the Kapitza thermal resistance and the shortening of the heat conduction distance of the silicate component of the porous body affecting the thermal resistance. In addition, examples of the silicate particles applicable to the porous body 42 include FSM-16, MCM-41, etc.

[0059] ​​​​​The metal fine particles 44 of the present embodiment are silver fine particles having an average particle diameter in the range of 50 to 100,000 nm. Thus, the metal fine particles 44 with good heat conduction surround the porous body 42 and are fixed to the metal member 38 as a sintered body.

[0060] The thickness of the thermal resistance reducing portion 40 of the present embodiment is in the range of 1 to 500 μm. Thus, a certain amount of the metal fine particles 44 surround the porous body 42 having nano-sized pores, and the thermal resistance generated by the metal fine particles 44 between the metal member 38 and the liquid helium is reduced. In addition, the thickness of the thermal resistance reducing portion 40 may be in the range of 1 to 1000 μm, and most preferably in the range of 1 to 200 μm.

[0061] Thus, in the dilution refrigerator 10 of the present embodiment, since the heat conduction of the heat exchanger 18 is further improved, an improvement in refrigeration performance and miniaturization of the entire refrigerator can be achieved.

[0062] (Performance evaluation)

[0063] Regarding the above-described sintered structure of the nanoporous body and silver, evaluation was performed by measuring the ultra-low temperature specific heat of He and He adsorbed on the nanoporous body. The specific heat measurement was performed by the quasi-adiabatic heat pulse method, and a heater and a thermometer were installed on the specific heat container. By analyzing the time change of the container temperature after applying a heat pulse, the relaxation time until the adsorbed helium and the container reached the same temperature was measured. As a result, it was confirmed that: up to a temperature of 26 mK, the relaxation time was shorter than the response time of about 5 seconds of the thermometer, and the thermal resistance was sufficiently small. 4 He and 3 He.

[0064] Therefore, a step-type heat exchanger having the thermal resistance reducing portion 40 of the present embodiment was fabricated and installed on a helium dilution refrigerator for operation. A dilution refrigerator that operates with only a tube-in-tube heat exchanger installed without a step-type heat exchanger reaches a minimum temperature of about 35 mK when He is continuously circulated at about 20 μmol / sec, and reaches 20 mK in the case of single-shot (a method of stopping the circulation of He and only performing recovery for cooling). On the other hand, when the heat exchanger of the present embodiment is installed on this dilution refrigerator, the minimum temperature reaches 20.6 mK in the case of continuous circulation and 8.6 mK in the case of single-shot. Thus, the dilution refrigerator of the present embodiment has improved the achievable minimum temperature and demonstrated the effectiveness of the thermal resistance reducing portion 40 including the porous body 42. 3 He 3 He

[0065] In addition, the above-mentioned thermal resistance reducing portion 40 is not only used in the heat exchanger 18, but can also be used in the heat conduction portion of the mixing chamber 16. Figure 5 FIG. is a schematic diagram showing a schematic structure of the mixing chamber 16 of the present embodiment. The mixing chamber 16 includes a container 48, and the container 48 is formed with an inflow path 34 for 3 He liquid to flow from the high-temperature side flow path 30 into the concentrated phase 14, and an outflow path 52 for 3 He liquid to flow out from the dilute phase 12 to the low-temperature side flow path 32.

[0066] The thermal resistance reducing portion 40 is disposed inside the bottom 48a of the container 48. Thereby, the thermal resistance between the liquid helium in the dilute phase 12 and the bottom 48a can be reduced, and the cooling performance when the bottom 48a is used as the cooling surface S can be improved.

[0067] As described above, the present disclosure has been described based on the embodiments. Those skilled in the art can understand that this embodiment is an example, and various deformation examples can be generated by combining each component and each processing procedure, and these deformation examples all fall within the scope of the present invention.

[0068] (Industrial Applicability)

[0069] The refrigerator of the present disclosure can be used for cooling devices that need to operate at extremely low temperatures. For example, it can be used for cooling quantum computers and semiconductor detectors.

[0070] (Explanation of Reference Numerals)

[0071] 10: Dilution refrigerator; 12: Dilute phase; 14: Concentrated phase; 16: Mixing chamber; 18: Heat exchanger; 20: Fractionation chamber; 20a Dilute phase; 20b: Inflow path; 22: 1K storage chamber; 24: Cryostat; 26: Discharge path; 28: Supply path; 29: Cooling passage; 30: High-temperature side flow path; 30a: Inflow path; 30b: Outflow path; 31: Container; 32: Cryostat; 32a: Inflow path; 32b: Outflow path; 34: Inflow path; 36: Heat conduction portion; 38: Metal component; 40: Thermal resistance reducing portion; 42: Porous body; 42a: Pore; 42b: Pore wall surface; 44: Metal particles; 46: Solid layer; 48: Container; 48a: Bottom; 52: Outflow path.

Claims

1. A heat exchanger, characterized in that, Comprising: A low-temperature side flow path through which low-temperature liquid helium flows; A high-temperature side flow path through which high-temperature liquid helium flows; And A heat conduction part that conducts heat from the high-temperature side flow path to the low-temperature side flow path, The heat conduction part has: A partition member for partitioning the high-temperature side flow path and the low-temperature side flow path; and A thermal resistance reduction part for reducing the thermal resistance between the partition member and the liquid helium, The thermal resistance reduction part has: a porous body having nano-sized pores; and metal fine particles sintered on the outer periphery of the porous body so as to surround the porous body, and the thermal conductivity of the metal fine particles is higher than that of the porous body, The porous body is formed of a material different from that of the metal fine particles.

2. The heat exchanger according to claim 1, characterized in that, The thermal resistance reduction part is a sintered body of the porous body and the metal fine particles.

3. The heat exchanger according to claim 1 or 2, characterized in that, The thickness of the thermal resistance reduction part is in the range of 1 to 1000 μm.

4. The heat exchanger according to claim 1 or 2, characterized in that, The porous body is a particle having through holes formed on its surface as the pores.

5. The heat exchanger according to claim 4, characterized in that, The through holes have a diameter that allows helium to exist in a liquid form inside them.

6. The heat exchanger according to claim 1 or 2, characterized in that, The average pore diameter of the porous body is in the range of 2 to 30 nm.

7. The heat exchanger according to claim 1 or 2, characterized in that, The porous body is a silicate particle having an average particle size in the range of 50 to 20000 nm.

8. The heat exchanger according to claim 1 or 2, characterized in that, The specific surface area of the porous body is 600 m 2 / g or more.

9. The heat exchanger according to claim 1 or 2, characterized in that, The metal fine particles are silver fine particles having an average particle size in the range of 50 to 100000 nm.

10. A refrigerator, characterized in that, Comprising: The heat exchanger according to any one of claims 1 to 9; Mixing chamber, inside of which is formed 3 a dilute He phase and 3 a concentrated He phase, and having an inlet path for 3 He liquid to flow from the high-temperature side flow path into the 3 concentrated He phase, and an outlet path for 3 He liquid to flow out from the 3 dilute He phase to the low-temperature side flow path; A fractionation chamber having an inlet passage for inflow of He liquid flowing in the low-temperature side flow path and configured to selectively separate He in vapor form from a mixture of He liquid and He liquid; and 3 He liquid to flow in, and for 3 selectively separating He in vapor form from 4 a mixture of He liquid and 3 He liquid; and A cooling passage that liquefies the 3 He separated in the fractionation chamber and returns it to the high-temperature side flow path.

11. A sintered body, characterized in that, The sintered body is a sintered body of a porous body having nano-sized pores and metal fine particles sintered on the outer periphery of the porous body so as to surround the porous body, The thermal conductivity of the metal fine particles is higher than that of the porous body, The interior of the micropores adsorbs 4 He and 3 He. The porous body is formed of a material different from that of the metal fine particles.

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