Heat insulation support device and heat insulation support method

Abstract

A heat insulation support device for supporting a member includes a hollow outer cylindrical body and a plurality of inner cylindrical bodies. Each of the plurality of inner cylindrical bodies is supported by the inner surface of the outer cylindrical body and regulates the position of the member. The thermal shrinkage rate of the plurality of inner cylindrical bodies is equal to or less than the thermal shrinkage rate of the outer cylindrical body.

Description

Thermal insulation support device and thermal insulation support method

[0001] The present invention relates to a thermal insulation support device and a thermal insulation support method.

[0002] Cooling devices that generate extremely low temperatures below the boiling point of helium (approximately 4 K), and containers for storing and transporting liquid cryogenic materials, have a nested structure of multiple containments (containers). Specifically, in one example, a container whose outer surface is in contact with the room temperature environment (approximately 300 K) is cooled to about 50 K, and then another container is placed inside this cooled container and its interior is further cooled to about 4 K, and so on. This multi-stage temperature setting achieves an extremely low temperature environment where the interior reaches as low as 0.0007 K. The interiors of such containers are shielded with radiation shields to reduce the intrusion of radiant heat and heat conducted through various structures.

[0003] Heat that enters each temperature stage is removed by various cooling mechanisms, and by maintaining the temperature to be achieved in each temperature stage (or the temperature difference with adjacent temperature stages), an extremely low temperature state is created and maintained inside.

[0004] Therefore, the thermal conductivity of the physical structures placed between each temperature stage is designed to be as low as possible (this is called an adiabatic support mechanism).

[0005] J.Tuttle, et al., Vibration-heating in ADR Kevlar suspensionsystems, IOP Conf. Ser.: Mater.Sci. Eng. 755 012015 (DOI:10.1011 / 1757-899X / 755 / 1 / 012015), 2019

[0006] However, there are cooling mechanisms such as pulse tube refrigerators and GM (Gifford-McMahon) refrigerators that generate relatively large mechanical vibrations. When using such cooling mechanisms, if the adiabatic support mechanism is not sufficiently robust, the low-temperature container and search device will vibrate relative to the high-temperature container immediately outside. This can generate frictional heat, making it impossible to maintain the desired low temperature, or cause a shift in the relative position between the sample and the search device, making high-precision measurements impossible. Even with cooling mechanisms that do not have vibration-generating mechanisms, such as pulse tube refrigerators and GM refrigerators, if the adiabatic support mechanism is not sufficiently robust, vibrations from the ground or the building itself can be transmitted, leading to difficulties such as being unable to maintain the desired low temperature or being unable to perform high-precision measurements.

[0007] In other words, the thermal insulation support mechanism requires not only thermal insulation but also mechanical robustness. However, thermal insulation and mechanical strength are contradictory, so it is not easy to achieve both when the gap between each temperature stage is narrow. In one example of a conventional cooling system, the radiant shields corresponding to each temperature stage are cylindrical in shape, and the gap between the bottom surface of one radiant shield and the inner bottom surface of the outer radiant shield is 10 to 15 mm. In such cases, the thermal insulation support mechanism is often omitted at the expense of vibration heat generation.

[0008] In the example disclosed in Non-Patent Document 1, an inner radiation shield is suspended and pulled within an outer radiation shield using Kevlar®, which is a twisted aramid fiber. Since Kevlar has a sufficiently high tensile strength (3 GPa at room temperature), the cross-sectional area of ​​the twisted yarn can be reduced while maintaining mechanical strength, and thermal insulation can also be maintained. However, because Kevlar has a negative thermal shrinkage rate in the length direction, it stretches in the direction of losing tension at low temperatures. Therefore, Non-Patent Document 1 discloses a stopper mechanism to maintain sufficient tension even in low-temperature environments.

[0009] Thus, using Kevlar requires a complex configuration such as a stopper mechanism, making attachment and detachment difficult, and its use is challenging when the gap between each temperature stage is narrow.

[0010] Alternatively, using Kevlar that has been heat-treated while under stress beforehand can maintain sufficient tension in low-temperature environments without the need for a complex stopper mechanism. However, in this case, the tension decreases over time due to repeated thermal cycles between room temperature and low temperatures, making it unsuitable for use in locations where maintenance is not easy.

[0011] This invention has been made in view of the above circumstances, and one of its objectives is to provide a thermal insulation support device and thermal insulation support that are easy to attach and detach, reduce the need for maintenance, and have sufficient mechanical strength and thermal insulation properties.

[0012] One aspect of the present invention relates to a thermal insulation support device for supporting a member, having a hollow cylindrical outer body and a plurality of inner cylinders, wherein each of the plurality of inner cylinders is supported by the inner surface of the outer body and restricts the position of the member, and the thermal shrinkage rate of the plurality of inner cylinders is less than or equal to the thermal shrinkage rate of the outer body.

[0013] Another aspect of the present invention relates to a thermal insulation support method, the thermal insulation support method comprising the steps of: arranging a portion of a plurality of inner cylinders between the inner surface of a hollow cylindrical outer cylinder and a member to be supported; and elastically deforming the remaining inner cylinders among the plurality of inner cylinders so as to be supported by the inner surface of the outer cylinder and to restrict the position of the member, thereby press-fitting them between the inner surface and the member, wherein the thermal shrinkage rate of the plurality of inner cylinders is less than or equal to the thermal shrinkage rate of the outer cylinder.

[0014] According to the present invention, a support device is provided that is easy to attach and detach, and has sufficient mechanical strength and heat insulation, even in locations with narrow gaps between adjacent temperature stages or limited installation space. Furthermore, its mechanical strength does not decrease even after repeated thermal cycles, reducing or eliminating the need for maintenance.

[0015] This is a schematic perspective view showing an example of a thermal insulation support according to an embodiment of the present invention. This is a schematic cross-sectional view showing an example of use of a thermal insulation support according to an embodiment of the present invention. This is an explanatory diagram showing an example of a thermal insulation support device according to an embodiment of the present invention.

[0016] Embodiments of the present invention will be described with reference to the drawings. Note that the sizes and proportions of the parts in the following description and illustrations are examples or exaggerated for illustrative purposes and do not represent the actual sizes or proportions.

[0017] An example of an embodiment of the present invention is a thermal insulation support 30 (hereinafter simply referred to as a support) formed of a thermal insulation material with relatively low thermal conductivity, and as illustrated in Figure 1, it has a hollow cylindrical shape and is elastically deformable in a plane (XY plane) perpendicular to the axial direction (direction along the central axis, the Z-axis direction in Figure 1).

[0018] As illustrated in Figure 2, a plurality of support members 30 are arranged inside a container 10 whose interior is cooled. The plurality of support members 30 support a preferably cylindrical or cylindrical member 20 to be supported inside the container 10 and restrict the movement of the member 20 inside the container 10. The container 10 has a cylindrical or other tubular shape and is understood as an outer cylinder. The support members 30 have a cylindrical or other tubular shape and are understood as inner cylinders. Figure 2 is a schematic cross-sectional view showing an example of a support structure in which the member 20 is supported by a plurality of support members 30 inside the container 10, broken at a plane perpendicular to the axial direction (Z-axis direction) of the support member 30 (XY plane with the axial direction as the normal). In one example, the plurality of support members 30 are connected to or exposed to the high-temperature side of the container 10, and the member 20 is connected to or exposed to the low-temperature side. Note that the expressions "high-temperature side" and "low-temperature side" are relative expressions. That is, the high-temperature side is hotter than the low-temperature side.

[0019] In one example, a base (for example, a flange-shaped portion) that can be connected to a high-temperature structure (a temperature stage structure on the high-temperature side) may be formed at at least one end of the container 10. Also, a base (for example, a disc-shaped portion with a diameter slightly larger than the outer diameter of the member 20) that can be connected to a low-temperature structure (a temperature stage structure on the low-temperature side) may be formed at at least one end of the member 20. The container 10 may be connected to or exposed to the high-temperature side, and the member 20 may be connected to or exposed to the low-temperature side.

[0020] In this example, the support body 30 is disposed between the inner surface of the container 10 and the outer surface of the member 20, sandwiched by the container 10 and the member 20. From another perspective, the member 20 is held in a gap formed by the plurality of support bodies 30 by the plurality of support bodies 30, and its movement inside the high-temperature side container 10 is restricted.

[0021] In the example of the present embodiment, so that the movement restriction of the member 20 inside the container 10 is effective even at low temperatures, the support body 30 has a linear thermal expansion coefficient ΔL / L 30 that needs to be formed of a material satisfying the following inequality.

[0022] 2r (ΔL / L ３０ ) ≤ R (ΔL / L １０ ) - a (ΔL / L ２０ ) (1) Here, ΔL / L １０ : Linear thermal expansion coefficient of the container (outer cylindrical body) 10 from a predetermined temperature T １０ to room temperature (where ΔL > 0 in the case of expansion) ΔL / L ２０ : Linear thermal expansion coefficient of the member 20 from a predetermined temperature T ２０ to room temperature ΔL / L ３０ : Linear thermal expansion coefficient of the support body (inner cylindrical body) 30 from a predetermined temperature T ３０ to room temperature r: Outer radius of the support body R: Inner radius of the container a (= R - 2r): Outer radius of the member 20.

[0023] Note that T ３０ is a temperature distributed between T １０ and T ２０ , and is specifically determined by the thermal conductivity of the support body, the amount of heat flowing therethrough, and the position within the support body.

[0024] As an example, the container 10 is formed of a material with relatively high thermal conductivity in a low-temperature environment, such as copper or aluminum, and the linear thermal expansion coefficient of such a material from 0K to room temperature is 0.33% (copper) to 0.41% (aluminum).

[0025] The support 30 is formed from a material such as polyamide-imide (PAI) filled with glass fibers. The linear thermal expansion coefficient of PAI itself at room temperature is 31 ppm / °C, and the linear thermal expansion coefficient from 0 K to room temperature is 0.45%. In other words, at low temperatures, it shrinks slightly more than the copper and aluminum mentioned above. However, it is known that glass fiber-filled PAI (hereinafter referred to as GF-PAI), which is PAI filled with, for example, 30 volume percent of glass fibers, has its linear thermal expansion coefficient at room temperature halved to 16 ppm / °C. Based on this, calculations show that the linear thermal expansion coefficient of GF-PAI from 0 K to room temperature is approximately 0.14%, which is considerably smaller than that of copper and aluminum, and satisfies equation (1).

[0026] Furthermore, GF-PAI has very high mechanical strength, with a bending strength of 333 MPa at room temperature.

[0027] Furthermore, the thermal conductivity of PAI itself is 11.5 × 10⁻¹⁰ at 0.3 K or less. －５ T ２．５８ With a low W / K·cm, PAI is one of the materials with exceptionally low thermal conductivity among known materials. Furthermore, due to its high temperature index (=2.58), its low thermal conductivity becomes more pronounced at lower temperatures. Therefore, PAI is suitable as an insulating support. Polyether ether ketone (PEEK), which has relatively similar low-temperature properties to PAI, is known to have its temperature index increased and its thermal conductivity below 1K further reduced when filled with 30% by volume of glass fiber. Therefore, it can be said that the thermal conductivity of GF-PAI at low temperatures is sufficiently low.

[0028] Thus, GF-PAI is a suitable material for the support 30 as an insulating material with a linear thermal expansion coefficient that is sufficiently small compared to the components of the cooling structure, high mechanical strength, and exceptionally low thermal conductivity at low temperatures among known materials.

[0029] For example, a hollow cylindrical support 30 can be formed using GF-PAI (a material in which 30 volume percent of glass fiber is packed into polyamide-imide, such as Solvay's Torlon 5030). However, this is just one example, and a material in which 12 volume percent of graphite powder is packed into polyamide-imide (such as Solvay's Torlon 4301) may also be used. On the other hand, compared to these materials, a material in which 40 wt% of graphite powder is packed into polyimide (such as DuPont's Vespel SP22) has a temperature of 2.21 × 10⁻¹⁰ at 0.3 K or below. －５ T ２．１５ Because it has a low thermal conductivity of W / K·cm, it is a typical low-temperature insulating material, but its tensile strength at room temperature is only 52 MPa, and its linear thermal expansion coefficient from 0K to room temperature is 0.64%, which is higher than that of copper and aluminum, so it is not suitable as a material for the support 30. [Example of support use] Such a support 30 can be used, for example, as follows: Three support 30s of the same shape and material are placed inside a cylindrical (hollow cylindrical) container 10 with an inner radius R, and a cylindrical or cylindrical member 20 with an outer radius a is supported thereby. In this case, if the value of the inner radius R of the container 10 is determined, the outer radius a of the member 20 and the outer radius r of the support 30 are automatically determined as follows.

[0030]

[0031] In this example, the support 30 is made into a hollow cylindrical shape, and its practical outer radius r' is made slightly larger than r. Alternatively, the practical outer radius a' of the member 20 is made slightly larger than a. In this way, the shape of each support 30 is slightly compressed and deformed from a perfect circle in the direction of the contact point between the container 10 and the member 20, and the member 20 is mechanically and stably fixed to the container 10 by their internal stresses. The material and shape of the container 10 and the columnar or cylindrical member 20 are set so that their mechanical strength is sufficiently greater than that of the hollow cylindrical support 30. In this way, when considering deformation during implementation, only the deformation of the support 30 needs to be considered.

[0032] In this example, when the support 30 is placed at room temperature, multiple support 30s are inserted between the member 20 and the inner surface of the container 10. At this time, the last support 30 to be inserted is pressed between the member 20 and the inner surface of the container 10 while being flattened in the XY plane perpendicular to the axial direction (Z-axis direction), so that the member 20 is in contact with each of the three support 30s at three points. In addition, each support 30 is in contact with the inner surface of the container 10 at one point. In this state, since Figure 2 is an XY cross-sectional view, the points where the support 30, the high-temperature side container 10, and the member 20 are in contact are labeled as "contact points." However, in reality, the line segment extending in the axial direction including the contact point, i.e., the "tangent line," or, considering the deformation of the circular cross-section of the support 30, the "contact surface" is a rectangle with a very small width. It should be noted that a film or the like may be placed between the container 10 and the multiple support 30s, as long as it does not contradict the spirit of the present invention. Furthermore, a film or the like may be placed between the multiple support bodies 30 and the member 20.

[0033] As the inside of the container 10 and the members 20 are cooled to their respective predetermined temperatures, the amount of thermal contraction of the support 30 is smaller than the difference between the amount of thermal contraction of the container 10 and the amount of thermal contraction of the members 20 (components of the cooling structure). Therefore, each support 30 deforms further in the direction connecting the contact point with the container 10 and the contact point with the members 20. This deformation generates additional internal stress, fixing the members 20 more firmly to the container 10 than at room temperature, further suppressing relative vibration and reducing frictional heat caused by vibration.

[0034] Heat transfer between the inner wall of the container 10 and the member 20 occurs only through the contact points between the support 30 and the inner wall of the container 10, and between the support 30 and the member 20. Furthermore, since the thermal conductivity of the support 30 is sufficiently low, the heat transfer between the container 10 and the member 20 is sufficiently small.

[0035] In the arrangement shown in Figure 2, the thickness t (difference between the outer radius and the inner radius) and the length h in the z-axis direction (see Figure 1) of the support 30 should be such that the support 30 is elastically deformable in the XY plane (i.e., even if it is deformed flat, it will try to return to its original shape). The specific values ​​of t and h can be determined experimentally.

[0036] The three cylindrical supports 30 of this support mechanism may generally be N (N is an integer of 3 or more) supports 30 having the same shape and material. Also in this case, each support 30 is in contact with the inner periphery of the container 10 having an inner radius R and the member 20 having an outer radius a at two opposing points, and is in contact with two adjacent supports 30 at the other two points, thereby restricting the relative vibration of the member 20 with respect to the container 10. In the case of N pieces, the outer radius a of the member 20 and the outer radius r of the supports 30 are generally defined by the following equations.

[0037]

[0038] Equations (2) and (3) correspond to the cases where N=3 in Equations (4) and (5), respectively. However, as N increases, the thermal conductivity between the container 10 and the member 20 increases, leading to deterioration of the thermal insulation performance, and in addition, it becomes difficult to evenly press-fit the supports 30 between the member 20 and the inner surface of the container 10. Therefore, the configuration with N=3 or 4 has high practicability. [Support Device] Using the supports 30 described so far, the support device 40 illustrated in FIG. 3 can be configured. The support device 40 includes the container 10 coupled to the high-temperature side structure H, the member 20 coupled to the low-temperature side structure L, and a plurality of supports 30 that support the member 20 inside the container 10. Note that in FIG. 3, a part of the outer periphery of the container 10 is cut away to show the internal structure. In addition, the member 20 may be coupled to the low-temperature side structure L via a coupling portion J that is coupled to the low-temperature side structure L.

[0039] The support device 40 may be, for example, placed inside a solenoid-type superconducting magnet that is thermally anchored to the high-temperature structure. The inner circumference of the bobbin of this superconducting magnet is considered to be the inner circumference of the container 10. Alternatively, a member 20 (whose outer radius a' is equal to or slightly larger than a, as previously described) which is coupled to the magnetic refrigerant L for the adiabatic demagnetizing refrigerator, which is the low-temperature structure, may be placed concentrically with the cylindrical inner circumference (inner radius R) of the container 10. Three support bodies 30 (whose outer radius r' is equal to or slightly larger than r, as previously described) may be pressed into the space between the inner circumference of the container 10 and the outer circumference of the member 20, deformed within an elastically deformable range so that their outer circumferences are in contact with each other and with the outer circumference of the member 20. Here, a and r are defined by equations (2) and (3).

[0040] With this support device 40, even when the radial spatial gap between different temperature stages is narrow, the support 30 can be used to support the member 20 connected to the lower temperature side. Experimentally, it has been confirmed that vibration-induced heat generation can be reduced and the total heat inflow can be stabilized. In other words, this embodiment provides a support device that is space-saving and combines high thermal insulation performance with mechanical strength. Furthermore, it has been confirmed that even when a device supported by the support device 40 is used repeatedly, the thermal insulation performance of the support device 40 does not change, reducing or eliminating the need for maintenance.

[0041] A polymer clay, for example, may be placed between the container 10 and the structure to which it is joined, and / or between the member 20 and the structure to which it is joined.

[0042] 10 High-temperature side container, 20 Member, 30 Support, 40 Support device.

Claims

1. A thermal insulation support device having a hollow cylindrical outer body and a plurality of inner cylindrical bodies for supporting a member, wherein each of the plurality of inner cylindrical bodies is supported by the inner surface of the outer body and restricts the position of the member, and the thermal contraction rate of the plurality of inner cylindrical bodies is less than or equal to the thermal contraction rate of the outer body.

2. The thermal insulation support device according to claim 1, characterized in that each of the plurality of inner cylindrical bodies is in contact with the outer cylindrical body.

3. The thermal insulation support device according to claim 1 or 2, characterized in that each of the plurality of inner cylindrical bodies is in contact with the member.

4. The thermal insulation support device according to any one of claims 1 to 3, characterized in that the plurality of inner cylindrical bodies are arranged between the inner surface and the member in an elastically deformed state.

5. The thermal insulation support device according to any one of claims 1 to 4, characterized in that the outer cylindrical body is coupled to the high-temperature side structure, and the member is coupled to the low-temperature side structure.

6. The heat insulating support device according to claim 5, characterized in that the outer cylindrical body is provided with a base that can be connected to the high-temperature side structure, and the member is provided with a base that can be connected to the low-temperature side structure.

7. The temperature T of the outer cylindrical body １０ linear thermal expansion coefficient from to room temperature is ΔL / L １０ , the temperature T of the member ２０ linear thermal expansion coefficient from to room temperature is ΔL / L ２０ , the temperature T of the inner cylindrical body ３０ linear thermal expansion coefficient from to room temperature is ΔL / L ３０ , where the outer radius of the support body is r and the inner radius of the outer cylindrical body is R, 2r(ΔL / L ３０ ) ≦ R (ΔL / L １０ ) - a (ΔL / L ２０ ) is satisfied, The heat insulating support device according to any one of claims 1 to 6.

8. A thermal insulation support method comprising the steps of: positioning a portion of a plurality of inner cylinders between the inner surface of a hollow cylindrical outer cylinder and a member to be supported; and elastically deforming the remaining inner cylinders among the plurality of inner cylinders so as to be supported by the inner surface of the outer cylinder and to restrict the position of the member, wherein the thermal shrinkage rate of the plurality of inner cylinders is less than or equal to the thermal shrinkage rate of the outer cylinder.

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