Regenerator for cryogenic refrigeration machine and cryogenic refrigeration machine

Abstract

To reduce pressure loss in a regenerator for a cryogenic refrigeration machine that uses a helium gas for a cold storage material.SOLUTION: A regenerator for a cryogenic refrigeration machine includes a stranded pipe 50 formed by stranding a plurality of pipes 52 capable of storing a helium gas. The stranded pipe 50 may be wound into a coil shape with such as honeycomb winding. A cryogenic refrigeration machine including such the regenerator for a cryogenic refrigeration machine may be provided.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a regenerator for a cryogenic refrigerator and a cryogenic refrigerator using the regenerator. [Background technology]

[0002] Helium gas is known to have a large specific heat capacity compared to various other materials at extremely low temperatures below about 10 K. Therefore, it has been proposed to use helium gas as a regenerator in cryocoolers such as Gifford-McMahon (GM) refrigerators that provide cooling to such extremely low temperatures. Such cryocoolers incorporate a regenerator, for example, a tube filled with helium gas wound like a solenoid coil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-16137 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have studied the above-mentioned cryogenic refrigerators using helium gas as a regenerator material and have recognized the following problem. In such cryogenic refrigerators, the helium gas tubes are wound so that they are closely adjacent to each other between the turns of the coil. However, in a regenerator wound in this way, the closeness of the tubes makes the working gas flow path for the working gas of the cryogenic refrigerator narrow and long, and as a result, the pressure loss of the working gas in the regenerator tends to be large. The increased pressure loss can reduce the refrigeration capacity of the cryogenic refrigerator.

[0005] An exemplary object of an embodiment of the present invention is to reduce pressure loss in a regenerator for a cryogenic refrigerator that uses helium gas as a regenerator material. [Means for solving the problem]

[0006] According to one aspect of the present invention, a regenerator for a cryogenic refrigerator includes a twisted tube in which a plurality of tubes capable of accommodating helium gas are twisted together.

[0007] According to one aspect of the present invention, a regenerator for a cryogenic refrigerator includes a tube capable of accommodating helium gas, the tube being wound into a coil shape by honeycomb winding.

[0008] According to one aspect of the present invention, a cryogenic refrigerator includes the regenerator for a cryogenic refrigerator according to any one of the above aspects. Effect of the Invention

[0009] According to the present invention, it is possible to reduce pressure loss in a regenerator for a cryogenic refrigerator that uses helium gas as a regenerator material. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating a schematic diagram of a cryogenic refrigerator according to an embodiment; [Diagram 2] 1 is a diagram illustrating a schematic diagram of a cryogenic refrigerator according to an embodiment; [Diagram 3] FIG. 4 is an enlarged schematic view showing a part of a cross section of a low-temperature side of a second-stage regenerator in the embodiment. [Figure 4] FIG. 2 is a perspective view illustrating a twisted tube constituting a low-temperature side regenerator according to the embodiment. [Diagram 5] FIG. 4 is a diagram illustrating a helium gas regenerator according to a comparative example. [Figure 6] FIG. 11 is a perspective view showing a helium gas regenerator according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processes are given the same reference numerals, and duplicated descriptions are omitted as appropriate. The scale and shape of each part shown in the drawings are set for convenience in order to facilitate the description, and are not to be interpreted as being limiting unless otherwise specified. The embodiments are merely examples, and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0012] 1 and 2 are schematic diagrams illustrating a cryogenic refrigerator 10 according to an embodiment. The cryogenic refrigerator 10 is, as an example, a two-stage Gifford-McMahon (GM) refrigerator. FIG. 1 shows the exterior of the cryogenic refrigerator 10, and FIG. 2 shows the internal structure of the cryogenic refrigerator 10.

[0013] The cryogenic refrigerator 10 includes a compressor 12 and an expander 14. The compressor 12 is configured to recover the working gas of the cryogenic refrigerator 10 from the expander 14, pressurize the recovered working gas, and supply the working gas again to the expander 14. The working gas, also called a refrigerant gas, is typically helium gas, although other suitable gases may be used.

[0014] The expander 14 includes a refrigerator cylinder 16, a displacer assembly 18, and a refrigerator housing 20. The refrigerator housing 20 is coupled to the refrigerator cylinder 16, thereby forming an airtight container that houses the displacer assembly 18. Note that the internal volume of the refrigerator housing 20 may be connected to the low pressure side of the compressor 12 and maintained at low pressure.

[0015] The refrigerator cylinder 16 has a first cylinder 16a and a second cylinder 16b. The first cylinder 16a and the second cylinder 16b are, for example, members having a cylindrical shape, and the second cylinder 16b has a smaller diameter than the first cylinder 16a. The first cylinder 16a and the second cylinder 16b are arranged coaxially, and the lower end of the first cylinder 16a is rigidly connected to the upper end of the second cylinder 16b.

[0016] The displacer assembly 18 has a first displacer 18a and a second displacer 18b. The first displacer 18a and the second displacer 18b are, for example, cylindrical members, and the second displacer 18b has a smaller diameter than the first displacer 18a. The first displacer 18a and the second displacer 18b are arranged coaxially.

[0017] The first displacer 18a is accommodated in the first cylinder 16a, and the second displacer 18b is accommodated in the second cylinder 16b. The first displacer 18a can reciprocate in the axial direction along the first cylinder 16a, and the second displacer 18b can reciprocate in the axial direction along the second cylinder 16b. The first displacer 18a and the second displacer 18b are connected to each other and move together.

[0018] In this document, in order to explain the positional relationship between the components of the cryogenic refrigerator 10, for convenience, the side closer to the top dead center of the axial reciprocating motion of the displacer will be referred to as "top" and the side closer to the bottom dead center as "bottom." The top dead center is the position of the displacer where the volume of the expansion space is maximum, and the bottom dead center is the position of the displacer where the volume of the expansion space is minimum. During operation of the cryogenic refrigerator 10, a temperature gradient occurs in which the temperature decreases from the top to the bottom in the axial direction, so the top side can also be called the high temperature side and the bottom side the low temperature side.

[0019] The first displacer 18a accommodates the first regenerator 26. The cylindrical body of the first displacer 18a serves as a first regenerator container extending in the axial direction. The first regenerator 26 is formed by filling the body of the first displacer 18a with a wire mesh such as copper or other suitable first regenerator material. The upper and lower lids of the first displacer 18a may be provided as separate members from the body of the first displacer 18a, and the upper and lower lids of the first displacer 18a may be fixed to the body by suitable means such as fastening or welding, thereby accommodating the first regenerator material in the first displacer 18a.

[0020] Similarly, the second displacer 18b accommodates the second regenerator 28. The cylindrical body of the second displacer 18b serves as a second regenerator container extending in the axial direction. The upper and lower lids of the second displacer 18b may be provided as separate members from the body of the second displacer 18b, and the upper and lower lids of the second displacer 18b may be fixed to the body by an appropriate means such as fastening or welding, thereby accommodating the second regenerator material in the second displacer 18b.

[0021] The second regenerator 28 includes at least two types of regenerator materials, which are stacked in the axial direction of the second displacer 18b. As shown in Fig. 2, the second regenerator 28 includes a high-temperature side regenerator 28a and a low-temperature side regenerator 28b. To increase the refrigeration capacity of the second stage of the cryogenic refrigerator 10, regenerator materials having large specific heats at different temperatures are selected for these regenerators.

[0022] For example, the high-temperature side regenerator 28a may be made of a regenerator material having a relatively high volumetric heat capacity at the high-temperature side of the second displacer 18b, for example, in a temperature range of 10K to 50K or at least a part thereof. The regenerator material forming the high-temperature side regenerator 28a may have a higher volumetric heat capacity than copper, which is a regenerator material typically used in the first displacer 18a, in this temperature range or at least a part thereof. The regenerator material forming the high-temperature side regenerator 28a may also have a higher volumetric heat capacity than the regenerator material forming the low-temperature side regenerator 28b in this temperature range or at least a part thereof. The high-temperature side regenerator 28a may be made of a non-magnetic metal material, such as bismuth, zinc, or an alloy thereof.

[0023] The low-temperature side regenerator 28b may be formed of a regenerator material having a relatively high volume specific heat at a temperature on the low-temperature side of the second displacer 18b, for example, in a temperature range of 1K to 10K or at least a part of the range (for example, 4K). In this embodiment, helium gas is used for the low-temperature side regenerator 28b. Therefore, the low-temperature side regenerator 28b includes a tube 52 (see Figs. 3 and 4) capable of accommodating helium gas. At least one end of the tube 52 may be open. Thereby, the working gas (i.e., helium gas) of the cryogenic refrigerator 10 supplied into the second regenerator 28 in accordance with the operation of the cryogenic refrigerator 10 may be introduced into the tube 52. Alternatively, a tube filled with helium gas in advance and closed at both ends may be used. Details of an exemplary configuration of such a helium gas regenerator will be described further below with reference to Figs. 3 and 4.

[0024] Referring to FIG. 2, the displacer assembly 18 forms an upper chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the refrigerator cylinder 16. For heat exchange with a desired object or medium to be cooled by the cryogenic refrigerator 10, the expander 14 includes a first cooling stage 33 and a second cooling stage 35. The upper chamber 30 is formed between the upper cover of the first displacer 18a and the upper part of the first cylinder 16a. The first expansion chamber 32 is formed between the lower cover of the first displacer 18a and the first cooling stage 33. The second expansion chamber 34 is formed between the lower cover of the second displacer 18b and the second cooling stage 35. The first cooling stage 33 is fixed to the lower part of the first cylinder 16a so as to surround the first expansion chamber 32, and the second cooling stage 35 is fixed to the lower part of the second cylinder 16b so as to surround the second expansion chamber 34.

[0025] The first regenerator 26 is connected to the upper chamber 30 through a working gas passage 36a formed in the upper lid of the first displacer 18a, and is connected to the first expansion chamber 32 through a working gas passage 36b formed in the lower lid of the first displacer 18a. The second regenerator 28 is connected to the first regenerator 26 through a working gas passage 36c formed from the lower lid of the first displacer 18a to the upper lid of the second displacer 18b. The second regenerator 28 is also connected to the second expansion chamber 34 through a working gas passage 36d formed in the lower lid of the second displacer 18b.

[0026] A first seal 38a and a second seal 38b may be provided so that the working gas flow between the first expansion chamber 32, the second expansion chamber 34 and the upper chamber 30 is guided to the first regenerator 26 and the second regenerator 28, instead of through the clearance between the refrigerator cylinder 16 and the displacer assembly 18. The first seal 38a may be attached to an upper cover of the first displacer 18a so as to be disposed between the first displacer 18a and the first cylinder 16a. The second seal 38b may be attached to an upper cover of the second displacer 18b so as to be disposed between the second displacer 18b and the second cylinder 16b.

[0027] The expander 14 also includes a pressure switching valve 40 and a drive motor 42. The pressure switching valve 40 is accommodated in the refrigerator housing 20, and the drive motor 42 is attached to the refrigerator housing 20.

[0028] As shown in FIG. 2, the pressure switching valve 40 includes a high-pressure valve 40a and a low-pressure valve 40b, and is configured to generate periodic pressure fluctuations in the refrigerator cylinder 16. The working gas discharge port of the compressor 12 is connected to the upper chamber 30 via the high-pressure valve 40a, and the working gas intake port of the compressor 12 is connected to the upper chamber 30 via the low-pressure valve 40b. The high-pressure valve 40a and the low-pressure valve 40b are configured to selectively and alternately open and close (i.e., when one is open, the other is closed). High-pressure (e.g., 2 to 3 MPa) working gas is supplied from the compressor 12 to the expander 14 through the high-pressure valve 40a, and low-pressure (e.g., 0.5 to 1.5 MPa) working gas is collected from the expander 14 to the compressor 12 through the low-pressure valve 40b. For ease of understanding, the flow direction of the working gas is indicated by arrows in FIG. 2.

[0029] The drive motor 42 is provided to drive the reciprocating motion of the displacer assembly 18. The drive motor 42 is connected to a displacer drive shaft 44 via a motion conversion mechanism 43, such as a Scotch yoke mechanism. The motion conversion mechanism 43 is housed in the refrigerator housing 20, as is the pressure switching valve 40. The displacer drive shaft 44 extends from the motion conversion mechanism 43 through the refrigerator housing 20 into the upper chamber 30 and is fixed to the upper cover of the first displacer 18a. A third seal 38c is provided to prevent leakage of the working gas from the upper chamber 30 to the refrigerator housing 20 (which may be maintained at a low pressure as described above). The third seal 38c may be attached to the refrigerator housing 20 so as to be disposed between the refrigerator housing 20 and the displacer drive shaft 44.

[0030] When the drive motor 42 is driven, the rotational output of the drive motor 42 is converted into axial reciprocating motion of the displacer drive shaft 44 by the motion conversion mechanism 43, and the displacer assembly 18 reciprocates in the axial direction inside the refrigerator cylinder 16. In addition, the drive motor 42 is connected to the high pressure valve 40a and the low pressure valve 40b so as to selectively and alternately open and close these valves.

[0031] When the compressor 12 and the drive motor 42 are operated, the cryogenic refrigerator 10 generates periodic volume fluctuations and synchronous pressure fluctuations of the working gas in the first expansion chamber 32 and the second expansion chamber 34, thereby forming a refrigeration cycle, and the first cooling stage 33 and the second cooling stage 35 are cooled to a desired cryogenic temperature. The first cooling stage 33 can be cooled to a first cooling temperature in the range of, for example, about 30 K to about 80 K. The second cooling stage 35 can be cooled to a second cooling temperature lower than the first cooling temperature, for example, 1 K to 10 K. The second cooling temperature may be the liquid helium temperature of about 4.2 K or a temperature lower than that.

[0032] Fig. 3 is a schematic enlarged view of a part of a cross section of the low-temperature side regenerator 28b of the second regenerator 28 according to the embodiment. Fig. 3 shows a part of a cross section of the low-temperature side regenerator 28b in a plane including the central axis of the expander 14, as in Fig. 2. For ease of understanding, a working gas flow 48 of the cryogenic refrigerator 10 passing through the second regenerator 28 is shown by a double-headed arrow in Fig. 3. Fig. 4 is a schematic perspective view of a twisted tube 50 constituting the low-temperature side regenerator 28b according to the embodiment.

[0033] The low-temperature side regenerator 28b includes a twisted tube 50 in which a plurality of tubes 52 capable of accommodating helium gas are twisted together. As shown in FIG. 4, in this example, three tubes 52 are twisted together. The number of tubes 52 forming the twisted tube 50 is arbitrary, and may be two or four or more. The tube 52 is hollow so that helium gas can be accommodated therein, and at least one end is open. The inner diameter of the tube 52 may be, for example, 10 to 20 μm, and the outer diameter may be, for example, 30 μm or less or 40 μm or less. The tube 52 may be formed of, for example, a metal material such as copper (for example, pure copper such as oxygen-free copper or tough pitch copper) or other material having high thermal conductivity.

[0034] The twisted tube 50 is wound in a coil shape. The low-temperature side regenerator 28b includes a core 54, and the twisted tube 50 is wound around the core 54. The twisted tube 50 is wound around the core 54, for example, by solenoid winding. Alternatively, the twisted tube 50 may be wound around the core 54 by other appropriate winding methods. By winding the twisted tube 50 in a coil shape, the length of the twisted tube 50 can be increased in the second regenerator 28, and pressure fluctuations in the tube 52 that may occur due to pressure fluctuations in the second regenerator 28 during operation of the cryogenic refrigerator 10 can be reduced. This leads to suppressing a decrease in the refrigeration capacity of the cryogenic refrigerator 10.

[0035] For ease of understanding, a circle enveloping the outer circumference of the three tubes 52 forming the twisted tube 50 is drawn in dashed lines in Fig. 3. The tubes 52 extend in a spiral shape within this enveloping circle 56. Therefore, as shown in Fig. 3, gaps 58 are formed between the twisted tubes 50 wound in a coil shape around the core material 54.

[0036] FIG. 5 is a schematic diagram of a helium gas regenerator 60 according to a comparative example. The helium gas regenerator 60 includes a core material 62 and a single tube 64 capable of accommodating helium gas therein and wound around the core material 62 in a coil shape. In this comparative example, instead of a twisted tube, a normal single tube is wound around the core material 62 in a coil shape. As shown in the figure, the single tube 64 is wound so that the turns of the coil are closely adjacent to each other. Therefore, in the helium gas regenerator 60, the closeness of the single tubes 64 narrows and lengthens the working gas flow path for the working gas passing through the helium gas regenerator 60, and as a result, the pressure loss of the working gas in the regenerator tends to increase. The increase in pressure loss can reduce the refrigeration capacity of the cryogenic refrigerator.

[0037] In contrast, in the embodiment, referring again to Fig. 3, during operation of the cryogenic refrigerator 10, the working gas flow 48 passing through the second regenerator 28 can flow through the gap 58. The gap 58 can reduce the pressure loss of the second regenerator 28. When the working gas flow 48 flows through the gap 58, it can exchange heat with the helium gas in each tube 52 of the twisted tube 50, thereby allowing the second regenerator 28 to perform a regenerative function.

[0038] Fig. 6 is a perspective view showing a schematic diagram of a helium gas regenerator 70 according to another embodiment. The helium gas regenerator 70 includes a tube 72 capable of accommodating helium gas, and the tube 72 is wound into a coil shape by honeycomb winding. Here, the tube 72 may be the twisted tube 50 described with reference to Figs. 3 and 4. Alternatively, the tube 72 may be a single tube 64 instead of the twisted tube 50. The helium gas regenerator 70 may be used as the low-temperature side regenerator 28b of the second regenerator 28 described with reference to Figs. 1 and 2.

[0039] Honeycomb winding, like solenoid winding, is one of the well-known methods of winding coils. Solenoid winding is a method in which the upper layer of coil wire is wound so that it is almost parallel to the lower layer of coil wire, whereas honeycomb winding is a method in which the upper layer of coil wire is wound at an angle to the lower layer of coil wire. Honeycomb winding allows for larger gaps between the wires compared to solenoid winding. Also, with honeycomb winding, the gap between the wires can be adjusted by adjusting the winding angle.

[0040] 6, the working gas of the cryogenic refrigerator 10 can flow through the gaps between the pipes 72, similarly to the second regenerator 28 according to the embodiment described with reference to Figs. 1 to 4. The pressure loss in the helium gas regenerator 70 can be reduced.

[0041] The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, that various design changes are possible, that various modifications are possible, and that such modifications are also within the scope of the present invention. Various features described in relation to one embodiment can also be applied to other embodiments. A new embodiment resulting from a combination has the combined effects of each of the combined embodiments.

[0042] In the above embodiment, the twisted tube 50 is formed by twisting together a plurality of tubes 52. However, in some embodiments, the twisted tube 50 may be used instead of the tube 52. That is, the regenerator may include a bundle of twisted tubes 50 in which a plurality of twisted tubes 50 are twisted together. Such a bundle of twisted tubes 50 may be wound into a coil, for example, by honeycomb winding or by other winding methods such as solenoid winding. The bundle of twisted tubes 50 is thicker than a single twisted tube 50, and therefore has the advantage that it may be easier for workers to wind the bundle during manufacturing.

[0043] Also, it is not essential for the present invention to wind the stranded tube 50 or the bundle of stranded tubes 50 in a coil shape. For example, in one embodiment, the regenerator may include a bundle of multiple straight stranded tubes 50. Alternatively, in one embodiment, the regenerator may include stranded tubes 50 woven into a net shape.

[0044] In the above embodiment, the GM refrigerator is taken as an example, but the present invention is not limited thereto. In some embodiments, the cryocooler 10 may be other types of cryocooler, such as a Solvay refrigerator, a Stirling refrigerator, a pulse tube refrigerator, etc.

[0045] The present invention has been described using specific terms based on the embodiments, but the embodiments merely show one aspect of the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiments without departing from the spirit of the present invention as defined in the claims. [Explanation of symbols]

[0046] 10 cryogenic refrigerators, 50 twisted tubes, 52 tubes.

Claims

1. A regenerator for a cryogenic refrigerator, comprising a twisted tube formed by twisting together a plurality of tubes capable of accommodating helium gas.

2. 2. The regenerator for a cryogenic refrigerator according to claim 1, wherein the twisted tube is wound in a coil shape.

3. 3. The regenerator for a cryogenic refrigerator according to claim 2, wherein the twisted tube is wound by a honeycomb winding.

4. A tube capable of containing helium gas is provided, The regenerator for a cryogenic refrigerator is characterized in that the tube is wound into a coil shape by honeycomb winding.

5. A cryogenic refrigerator comprising the regenerator for a cryogenic refrigerator according to any one of claims 1 to 4.

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