JP2024058079A - Heat transfer member connection structure for cryogenic device and cryogenic device - Google Patents

Abstract

To make it possible to reduce the contact thermal resistance of a connection part of a heat transfer member.SOLUTION: In a heat transfer member connection structure of a cryogenic device, a superconducting coil 11 is conduction-cooled to a cryogenic temperature via a second heat transfer member 16 by a cryogenic refrigerator 12. The second heat transfer member 16 comprises a low-temperature side heat transfer member 17 connected to the cryogenic refrigerator, and a high-temperature side heat transfer member 18 connected to the superconducting coil. A convex part 23 is formed in one of the high-temperature side heat transfer member and the low-temperature side heat transfer member, and a hole 24 having a shape following the shape of the convex part is formed in an end part 27 of the other. Under the same temperature condition of the high-temperature side heat transfer member 18 and the low-temperature side heat transfer member 17 at the time of manufacturing, the internal diameter of the hole 24 is set equal to or smaller than the external diameter of the convex part 23. The convex part is fitted into the hole by heating or cooling, and thereby the high-temperature side heat transfer member 18 and the low-temperature side heat transfer member 17 are connected.SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to a heat transfer member connection structure of a cryogenic device that uses a cryogenic refrigerator to conductively cool objects such as superconducting coils to cryogenic temperatures via a heat transfer member, and a cryogenic device having a heat transfer member to which the connection structure is applied.

Conventionally, cryogenic devices using a conduction cooling system have been developed that utilize a cryogenic refrigerator capable of cooling to extremely low temperatures of 77K or less to conduct heat to objects to be cooled, such as superconducting coils, by solid-state thermal conduction of heat transfer members made of good thermal conductors.

In this cooling method, flexible heat transfer materials are used in part to alleviate thermal stress caused by differences in thermal contraction between the cylinder of the cryogenic refrigerator and the structural materials, and multiple heat transfer materials are connected by bolting or welding to form a thermal path from the object to be cooled to the cooling stage of the cryogenic refrigerator.

As shown in FIG. 6, at the connection points between the heat transfer members, there are minute irregularities on the surface of the connection between the low-temperature side heat transfer member 101 and the high-temperature side heat transfer member 102 in the heat transfer member 100, which creates minute gaps 103 on the contact surface between the low-temperature side heat transfer member 101 and the high-temperature side heat transfer member 102, and these gaps 103 impede heat conduction. For this reason, the connection points of the heat transfer members 100 may have contact thermal resistance greater than the thermal resistance of the heat transfer member 100.

In general, contact thermal resistance tends to decrease inversely proportional to the actual contact area or pressure. Therefore, an effective method for reducing contact thermal resistance is to reduce the gap 103 and increase the actual contact area. To achieve this, a method is used in which sufficient surface pressure is applied to plastically deform the fine irregularities on the surface, or, as shown in Figure 7, a contact heat transfer medium 104 such as thermally conductive grease or a soft metal sheet for promoting heat transfer is placed on the contact surface to fill the gap 103 and increase the actual contact area.

JP 2010-192253 A Japanese Patent No. 5520740

Bolt fastening is a common method for connecting heat transfer members. In addition, Patent Document 1 discloses a structure in which two members with different thermal shrinkage rates are connected by a fitting structure, and Patent Document 2 discloses a structure in which a heat shrink ring with a large thermal shrinkage rate is placed on the outer side of the fitting structure to connect the members.

In the heat transfer of the connection between the low-temperature heat transfer member 101 and the high-temperature heat transfer member 102 in the heat transfer member 100, as described above, the heat flow is restricted by the gap 103 caused by the minute unevenness of the contact surface, resulting in contact thermal resistance. In order to reduce this contact thermal resistance, a contact heat transfer medium 104 such as thermally conductive grease or a soft metal sheet can be placed on the contact surface to fill the gap 103, thereby reducing the contact thermal resistance. However, in the extremely low temperature range, the thermal conductivity of the contact heat transfer medium 104 is extremely small compared to the heat transfer member 100 made of high-purity aluminum or copper, and therefore the contact heat transfer medium 104 cannot exert a sufficient effect.

Another method for reducing contact thermal resistance is to apply strong surface pressure to reduce the gap 103 by promoting deformation of the fine irregularities on the contact surface. However, in the usual case of applying pressure by fastening a bolt, the pressure is applied only to the periphery of the bolt hole, known as the Letschel cone of influence. As a result, as shown in Figure 8, undulations are generated in the low-temperature side heat transfer member 101 and the high-temperature side heat transfer member 102, which are made of aluminum or copper, and as a result, only the periphery of the bolt 105 is in contact, creating the problem of not being able to reduce contact thermal resistance.

In addition, in the fitting structure of Patent Document 1, no surface pressure is applied to the joint at room temperature, which increases thermal resistance and, in some cases, poses the risk of separation. In the fitting structure of Patent Document 2, a heat shrink ring is used for fastening, but similarly, clearance occurs at room temperature, increasing contact thermal resistance.

The embodiment of the present invention has been made in consideration of the above circumstances, and aims to provide a heat transfer member connection structure for a cryogenic device and a cryogenic device that can reduce the contact thermal resistance of the connection part of the heat transfer member.

The heat transfer member connection structure of a cryogenic device in an embodiment of the present invention is a heat transfer member connection structure of a cryogenic device in which a cryogenic refrigerator conducts and cools an object to be cooled to a cryogenic temperature via a heat transfer member, the heat transfer member having a low-temperature side heat transfer member connected to the cryogenic refrigerator and a high-temperature side heat transfer member connected to the object to be cooled, a convex portion is formed on one end of the high-temperature side heat transfer member and the low-temperature side heat transfer member, and a concave portion having a shape that conforms to the shape of the convex portion is formed on the other end, and the inner diameter of the concave portion is set to be equal to or smaller than the outer diameter of the convex portion under the same temperature conditions of the high-temperature side heat transfer member and the low-temperature side heat transfer member during manufacture, and the convex portion is fitted into the concave portion by heating or cooling to connect the high-temperature side heat transfer member and the low-temperature side heat transfer member.

The cryogenic device in the embodiment of the present invention is characterized by having a cryogenic refrigerator, a heat transfer member that is configured by applying the heat transfer member connection structure of the cryogenic device described in the embodiment and thermally connects the cryogenic refrigerator and the object to be cooled, and a vacuum container that stores the cryogenic refrigerator, the object to be cooled, and the heat transfer member.

According to an embodiment of the present invention, it is possible to reduce the contact thermal resistance of the connection part of the heat transfer member.

1 is a schematic cross-sectional view showing an overall configuration of a cryogenic device having a heat transfer member to which a heat transfer material connection structure for a cryogenic device according to a first embodiment is applied. FIG. 2 is a cross-sectional view showing the heat transfer member of FIG. 1 . 3 is a cross-sectional view showing a modified example of the heat transfer member of FIG. 2; FIG. 13 is a cross-sectional view showing a heat transfer member to which a heat transfer member connection structure for a cryogenic device according to a second embodiment is applied. FIG. 13 is a graph showing the thermal expansion coefficient of materials including a base material constituting a heat transfer member to which the heat transfer member connection structure of the cryogenic device according to the third embodiment is applied. FIG. 4 is a conceptual diagram illustrating minute gaps in the contact surface of a heat transfer member. FIG. 13 is a conceptual diagram showing a state in which a contact heat transfer medium is interposed between contact surfaces of heat transfer members. 6 is a conceptual diagram illustrating undulations that occur when heat transfer members are joined by bolt fastening.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[A] First embodiment (FIGS. 1 to 3)
Fig. 1 is a schematic cross-sectional view showing the overall configuration of a cryogenic device having a heat transfer member to which the heat transfer material connection structure for a cryogenic device according to the first embodiment is applied. The cryogenic device 10 shown in Fig. 1 conducts and cools a superconducting coil 11 and a heat shield 14, which are objects to be cooled, to a cryogenic temperature of 77K or less by a cryogenic refrigerator 12, and is configured with a vacuum vessel 13, the cryogenic refrigerator 12, the heat shield 14, a first heat transfer member 15, and a second heat transfer member 16.

The vacuum vessel 13 supports the cryogenic refrigerator 12 and houses the heat shield 14, with the superconducting coil 11 housed within this heat shield 14. The cryogenic refrigerator 12 is a Gifford-McMahon (GM) refrigerator or a pulse tube refrigerator, etc., and has a first cooling stage 21 that generates cold at about 20K to 50K, and a second cooling stage 22 that generates cold at about 3K to 30K. The first cooling stage 21 is disposed within the vacuum vessel 13, and the second cooling stage 22 is disposed within the heat shield 14.

The first heat transfer member 15 thermally connects the first cooling stage 21 of the cryogenic refrigerator 12 to the heat shield 14 as the object to be cooled, and the heat shield 14 is conductively cooled to a cryogenic temperature (approximately 20K to 50K) by the first cooling stage 21 via the first heat transfer member 15. The second heat transfer member 16 thermally connects the second cooling stage 22 of the cryogenic refrigerator 12 to the superconducting coil 11 as the object to be cooled, and the superconducting coil 11 is conductively cooled to a cryogenic temperature (approximately 3K to 30K) by the second cooling stage 22 via the second heat transfer member 16.

In the following, in the first to third embodiments, the configuration and effects of the second heat transfer member 16 will be described, but the first heat transfer member 15 may also have a similar configuration to the second heat transfer member 16, in which case the first heat transfer member 15 will also have the same effects as the second heat transfer member 16.

The second heat transfer member 16 is configured to include a low-temperature side heat transfer member 17 that is thermally connected to the second cooling stage 22 of the cryogenic refrigerator 12, and a high-temperature side heat transfer member 18 that is thermally connected to the superconducting coil 11. As shown in FIG. 2, a convex portion 23 is formed on one of the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18, for example, on the high-temperature side heat transfer member 18, and a hole 24 is formed as a concave portion on the other of the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18, for example, on the end portion 27 (described later) having rigidity of the low-temperature side heat transfer member 17. The concave portion is not limited to a hole that penetrates the end portion 27 as shown in FIG. 2, but may be a hole 25 that hollows out, for example, the bottom portion of the end portion 27 as shown in FIG. 3. These holes 24 and holes 25 are formed in a shape that follows the shape of the convex portion 23 of the high-temperature side heat transfer member 18, for example, a shape that fits the convex portion 23.

The protrusions 23 in the high-temperature side heat transfer member 18 are preferably formed by machining the base material of the high-temperature side heat transfer member 18, but the protrusions 23 may be manufactured as a separate member from the main body of the high-temperature side heat transfer member 18, and the protrusions 23 may be joined to the main body of the high-temperature side heat transfer member 18 by welding or fastened with bolts or the like. The base material constituting the high-temperature side heat transfer member 18 including the protrusions 23 is preferably a material with high thermal conductivity, especially at extremely low temperatures, and for example, pure aluminum (purity 99.5% or more) containing high-purity aluminum (purity 99.99% or more) or pure copper (purity 99.9% or more) containing high-purity copper (purity 99.96% or more) is used.

The low-temperature side heat transfer member 17 is constructed by joining, for example, a rigid end 27 to one end of a flexible member 26 and an end 28 to the other end. The flexible member 26 is provided to relieve thermal stress caused by the difference in thermal contraction between the cryogenic refrigerator 12 and the object to be cooled, the superconducting coil 11, and is constructed from multiple foils or thin wires. The end 28 of the low-temperature side heat transfer member 17 is attached to the second cooling stage 22 of the cryogenic refrigerator 12.

The base material constituting the flexible member 26 is preferably a material with high thermal conductivity at cryogenic temperatures, such as a foil or thin wire of pure aluminum (purity 99.5% or more) containing high purity aluminum (purity 99.99% or more), a foil or thin wire of pure copper (purity 99.9% or more) containing high purity copper (purity 99.96% or more), or a foil or thin wire made of carbon fiber. The flexible member 26 may also be formed by using foils or thin wires of the above-mentioned aluminum, copper, and carbon fiber in parallel.

The base material constituting the ends 27 and 28 of the low-temperature side heat transfer member 17 is also preferably a material with high thermal conductivity at extremely low temperatures, such as pure aluminum (purity 99.5% or more) containing high-purity aluminum (purity 99.99% or more), or pure copper (purity 99.9% or more) containing high-purity copper (purity 99.96% or more).

By the way, under the same temperature conditions of the high-temperature side heat transfer member 18 and the low-temperature side heat transfer member 17 during the manufacture of the second heat transfer member 16 at room temperature, the inner diameter of the hole 24 or hole 25 of the low-temperature side heat transfer member 17 is set to a dimension equal to or smaller than the outer diameter of the protruding portion 23 of the high-temperature side heat transfer member 18. Then, the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 are connected by fitting the protruding portion 23 into the hole 24 or hole 25 by heating or cooling, and the second heat transfer member 16 is manufactured. In other words, the protruding portion 23 of the high-temperature side heat transfer member 18 is cooled to a low temperature, and the outer diameter of the protruding portion 23 is reduced by thermal contraction, and the protruding portion 23 is fitted into the hole 24 or hole 25 of the low-temperature side heat transfer member 17. Alternatively, the end 27 of the low-temperature side heat transfer member 17 is heated, and the inner diameter of the hole 24 or hole 25 is enlarged by thermal expansion, and the protrusion 23 of the high-temperature side heat transfer member 18 is fitted into this hole 24 or hole 25.

Therefore, the hole 24 or hole 25 of the low-temperature side heat transfer member 17, which serves as the connection part of the second heat transfer member 16, and the protrusion 23 of the high-temperature side heat transfer member 18 are in a state where uniform pressure is applied to the side (outer peripheral surface) of the protrusion 23 due to thermal stress of the end 27 of the low-temperature side heat transfer member 17. As a result, the end 27 of the low-temperature side heat transfer member 17 and the protrusion 23 of the high-temperature side heat transfer member 18 are connected without using bolts, welding, soldering, etc.

As configured as above, the first embodiment provides the following advantages (1) and (2).
(1) The high-temperature side heat transfer member 18 and the low-temperature side heat transfer member 17 constituting the second heat transfer member 16 have a protrusion 23 on one side (e.g., the high-temperature side heat transfer member 18) and a hole 24 or a hole 25 formed in an end 27 of the other side (e.g., the low-temperature side heat transfer member 17) in a shape that conforms to the shape of the protrusion 23, and under the same temperature conditions during the manufacture of the second heat transfer member 16, the inner diameter of the hole 24 or the hole 25 is set to be equal to or smaller than the outer diameter of the protrusion 23. Then, the high-temperature side heat transfer member 18 and the low-temperature side heat transfer member 17 are connected by fitting the protrusion 23 into the hole 24 or the hole 25 by heating or cooling, thereby manufacturing the second heat transfer member 16.

Therefore, when the high-temperature side heat transfer member 18 and the low-temperature side heat transfer member 17 are connected, even before cooling by the cryogenic refrigerator 12, uniform pressure due to thermal stress acts on the contact surface between the connecting portion, the protrusion 23, and the hole 24 or hole 25, so that a sufficient contact area can be secured at the contact surface, and contact thermal resistance can be reduced. As a result, the temperature difference between the cryogenic refrigerator 12 and the superconducting coil 11 can be maintained low.

(2) The second heat transfer member 16 is manufactured by fitting the protrusion 23 of the high-temperature side heat transfer member 18 into the hole 24 or hole 25 of the low-temperature side heat transfer member 17 by heating or cooling to connect the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18. Therefore, in the second heat transfer member 16, a uniform pressure due to thermal stress acts on the contact surface between the protrusion 23 and the hole 24 or hole 25, which is the connection part, in all temperature ranges during operation of the cryogenic refrigerator 12. As a result, the second heat transfer member 16 can reduce the contact thermal resistance of the contact surface at the connection part in all temperature ranges during operation of the cryogenic refrigerator 12 without causing the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 to fall off.

[B] Second embodiment (FIG. 4)
4 is a cross-sectional view showing a heat transfer member to which the heat transfer member connection structure of the cryogenic device according to the second embodiment is applied. In the second embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

The second heat transfer member 32 (Fig. 4) of the cryogenic device 30 (Fig. 1) of the second embodiment differs from the first embodiment in that a flexible metal plating layer (metal plating layer 33) with a Mohs hardness of less than 2.9 is provided on at least a portion of the outer peripheral surface of the protrusion 23 of the high-temperature side heat transfer member 18 and the inner peripheral surface of the hole 24 or hole 25 (e.g. hole 24) of the low-temperature side heat transfer member 17.

The softer the base material, the greater the micro contact area and the lower the contact thermal resistance. When the high-temperature side heat transfer member 18 and the low-temperature side heat transfer member 17 in the second heat transfer member 32 are made of aluminum, for example, the Vickers hardness is about 200 to 300 MPa, and the Mohs hardness, which is a guide to the surface hardness, is 2.9. The metal plating layer 33 is preferably made of a material that is at least softer than aluminum, and examples of such materials include gold, silver, tin, and indium. In the second embodiment, the metal plating layer 33 is formed of indium, which has a Vickers hardness of about 9 MPa and a Mohs hardness of 1.2, which is the softest, but gold, silver, tin, and the like may be used instead of indium. The metal plating layer 33 is preferably formed by electrolytic plating, but may also be deposited by ultrasonic soldering or cold spray.

As configured as described above, the second embodiment achieves the same effects as the first embodiment (1) and (2), and also achieves the following effect (3).

(3) In the second heat transfer member 32, the inner diameter of the hole 24 or hole 25 of the low-temperature side heat transfer member 17 is set to be equal to or smaller than the outer diameter of the protrusion 23 of the high-temperature side heat transfer member 18 under the same temperature conditions at room temperature during manufacture, and the protrusion 23 is fitted into the hole 24 or hole 25 by heating or cooling, thereby connecting the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 to manufacture the second heat transfer member 32. As a result, pressure due to thermal stress is generated on the inner circumferential surface of the hole 24 or hole 25 of the low-temperature side heat transfer member 17 and the outer circumferential surface of the protrusion 23 of the high-temperature side heat transfer member 18, which are in contact with each other.

The metal plating layer 33 provided on these contact surfaces is deformed more than the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 due to the pressure caused by the thermal stress before the start of cooling by the cryogenic refrigerator 12, and can fill minute gaps in the contact surfaces. As a result, the contact thermal resistance of the contact surface between the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 in the second heat transfer member 32 (the hole 24 or hole 25 and the protrusion 23) can be further reduced.

[C] Third embodiment (FIG. 5)
5 is a graph showing the thermal expansion coefficient of materials including a base material constituting a heat transfer member to which the heat transfer member connection structure of the cryogenic device according to the third embodiment is applied. In the third embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

The second heat transfer member 42 (Figs. 2 and 3) of the cryogenic device 40 (Fig. 1) of the third embodiment differs from the first embodiment in that the protrusion 43 of the high-temperature side heat transfer member 18 is made of pure copper (purity of 99.9% or more), and the rigid end 47 in which the hole 24 or hole 25 of the low-temperature side heat transfer member 17 is formed is made of pure aluminum (purity of 99.5% or more).

As shown in FIG. 5, it is known that the thermal expansion coefficient (thermal contraction coefficient) of aluminum is greater than that of copper. By forming the rigid end 47 of the low-temperature side heat transfer member 17 from aluminum, which has a large thermal expansion coefficient, this end 47 tends to thermally contract by about 0.1% (1‰) more than the convex portion 43 of the high-temperature side heat transfer member 18 when the second heat transfer member 42 is cooled by the operation of the cryogenic refrigerator 12. For this reason, when the second heat transfer member 42 is cooled by the operation of the cryogenic refrigerator 12, thermal stress greater than that at room temperature is generated at each contact surface between the hole 24 or hole 25 of the end 47 of the low-temperature side heat transfer member 17 and the convex portion 43 of the high-temperature side heat transfer member 18.

As configured above, the third embodiment provides the same effects as the effects (1) and (2) of the first embodiment, as well as the following effect (4).

(4) The convex portion 43 of the high-temperature side heat transfer member 18 in the second heat transfer member 42 is made of pure copper, and the end portion 47 of the low-temperature side heat transfer member 17 is made of pure aluminum, which has a larger thermal expansion coefficient (thermal contraction coefficient) than pure copper. Therefore, when the convex portion 43 is fitted into the hole 24 or hole 25 of the end portion 47, the pressure due to thermal stress on the contact surface between the hole 24 or hole 25 and the convex portion 43 is larger due to thermal contraction of the end portion 47 made of pure aluminum when the second heat transfer member 42 is cooled by operating the cryogenic refrigerator 12 than when the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 are connected to manufacture the second heat transfer member 42 at room temperature. As a result, when the cryogenic refrigerator 12 is operating, the contact thermal resistance of the contact surface of the connection portion between the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 in the second heat transfer member 42 (the hole 24 or hole 25 and the convex portion 43 of the end portion 47) can be further reduced.

Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, changes, and combinations can be made without departing from the gist of the invention. Furthermore, such substitutions, changes, and combinations are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

10... cryogenic device, 11... superconducting coil (object to be cooled), 12... cryogenic refrigerator, 13... vacuum vessel, 14... heat shield (object to be cooled), 15... first heat transfer member, 16... second heat transfer member, 17... low-temperature side heat transfer member, 18... high-temperature side heat transfer member, 23... convex portion, 24... hole (recess), 25... hole (recess), 27... end, 30... cryogenic device, 32... second heat transfer member, 33... metal plating layer, 40... cryogenic device, 42... second heat transfer member, 43... convex portion, 47... end

Claims (5)

A heat transfer member connection structure for a cryogenic device that conductively cools an object to a cryogenic temperature via a heat transfer member using a cryogenic refrigerator,
the heat transfer member includes a low-temperature side heat transfer member connected to the cryogenic refrigerator and a high-temperature side heat transfer member connected to the object to be cooled,
a convex portion is formed on one end of the high-temperature side heat transfer member and the low-temperature side heat transfer member, and a concave portion having a shape that conforms to the shape of the convex portion is formed on an end of the other end of the high-temperature side heat transfer member and the low-temperature side heat transfer member,
an inner diameter of the recess is set to be equal to or smaller than an outer diameter of the protrusion under the same temperature condition of the high-temperature side heat transfer member and the low-temperature side heat transfer member during manufacture;
A heat transfer member connection structure for a cryogenic device, characterized in that the high-temperature side heat transfer member and the low-temperature side heat transfer member are connected by fitting the convex portion into the concave portion by heating or cooling. The heat transfer member connection structure for a cryogenic device according to claim 1, characterized in that at least one of the protrusion and the end where the recess is formed is made of pure aluminum or pure copper. The heat transfer member connection structure for a cryogenic device according to claim 1 or 2, characterized in that a plating layer of a metal having a Mohs hardness of less than 2.9 is provided on at least a portion of the outer peripheral surface of the protrusion and the inner peripheral surface of the recess. The heat transfer member connection structure for a cryogenic device according to claim 1, characterized in that the protrusion is made of pure copper, and the end portion where the recess is formed is made of pure aluminum. A cryogenic refrigerator,
A heat transfer member that is configured by applying the heat transfer member connection structure for a cryogenic device according to claim 1 or 4 and thermally connects the cryogenic refrigerator and an object to be cooled;
a vacuum vessel for accommodating the cryogenic refrigerator, the object to be cooled, and the heat transfer member,

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