Regenerator for a cryo-cooler with helium as a working gas and as a heat-storing material, method for producing such a regenerator, and cryo-cooler with such a regenerator

Abstract

Regenerator (1) for a cryo-cooler with helium as a working gas and as a heat-storing medium, with at least one cell (2) with cell walls (4) which enclose a cavity (6) that has a number of sub-cavities (6-i). The sub-cavities (6-i) are connected to one another by way of at least one connecting channel (12) and, with the exception of the at least one connecting channel (12) to other sub-cavities (6-i), are enclosed by the cell walls (4). The cavity (6) of the at least one cell (2) is filled with helium gas as a heat-storing material. The regenerator also has flow channels (10) for helium as the working gas, which are formed between the individual sub-cavities (6-i) and have a pressure-equalizing opening in the form of a capillary (8), which passes through the cell walls (4) and forms a permanently open connection between the helium as the working gas outside the cavity (6) and the helium as the heat-storing material inside the cavity (6). In their interior, the sub-cavities (6-i) have supporting elements (14), which provide mutual support for the cell walls (4) delimiting a sub-cavity (6-i).

Description

[0001] The invention relates to a regenerator for cryogenic coolers with helium as working gas according to claim 1, a method for producing such a regenerator and a cryogenic cooler provided with such a regenerator according to the independent claims.

[0002] Helium is frequently used as a working gas in cryogenic coolers. Helium has a comparatively high heat capacity in the temperature range from 2K to 20K, comparable to the heat capacity of rare earth compounds in this temperature range. Therefore, it has been proposed to use helium as a regenerator material. Helium-filled, closed hollow bodies made of glass or metal are known as regenerator structures from US 2012 / 0304668 A1, DE 10319510 A1, DE 102005007627 A1, CN 104197591 A, DE 19924184 A1, and US 4359872 A. This basic idea has not yet led to a finished product. Furthermore, helium-filled spheres lead to wear, which reduces the service life of the cryogenic cooler. The basic problem with these well-known closed hollow bodies containing helium is the complex process of filling the hollow bodies with helium under excess pressure.Due to the overpressure, the wall thickness of the hollow bodies must be increased, which leads to a deterioration of the heat transfer resistance.

[0003] In the article "Heat Capacity Characterization of a 4K Regenerator with Non-Rare Earth Material" in Cryocoolers 19, International Cryocooler Conference, Inc., Boulder, CO, 2016, a structure with adsorbent material capable of absorbing helium is proposed as a regenerator for cryogenic coolers. The design of the regenerator is complex and laborious, and there is a risk that parts of the adsorbent material will be entrained by the working gas flow. The entrained adsorbent particles would drastically reduce the lifetime of a cryogenic cooler with such a regenerator.

[0004] JP H07318181 discloses a regenerator in which the helium-filled hollow bodies are sealed by thermal shrinkage. CN 104 197 591 A discloses a regenerator with cuboid-shaped cells filled with helium as a heat storage material. The cells are sealed after filling and therefore have no pressure equalization openings. JP S62-233688A discloses a regenerator that uses metal as the heat storage material for storing heat; helium is not used as a heat storage material.

[0005] JP2011190953A discloses a regenerator with tubes open on both sides, containing helium as a heat storage material. The helium-filled tubes thus have pressure equalization openings, allowing pressure equalization between the interior of the tubes and the helium working gas during operation of the cooler or regenerator. A disadvantage of this regenerator is that neighboring cells filled with helium as a heat transfer material lie on top of one another, and the overlapping sections of the cell walls cannot contribute to heat exchange. This limits the functionality of this known regenerator.

[0006] WO 2018 / 104410 A1 discloses a regenerator designed for helium as a working gas and heat storage material. The known regenerator comprises a cavity with several sub-cavities that are tubular and interconnected. Flow channels for the working gas helium are formed between the sub-cavities. A pressure equalization opening in the form of a capillary that penetrates the cell walls creates a permanently open connection between the working gas helium outside the cavity and the heat storage material helium inside the cavity. The thinner the cell walls, the better the heat transfer between the working gas helium and the heat storage material helium through the cell walls. However, a certain thickness of the cell walls is required so that they do not break or tear due to pressure fluctuations during operation of the regenerator.

[0007] It is therefore an object of the present disclosure, based on WO 2018 / 104410 A1, to provide a regenerator with helium as working gas and heat storage material, which enables more effective heat transfer through the cell walls compared to WO 2018 / 104410 A1.

[0008] US2019323737A1 discloses a regenerator according to the preamble of claim 1; and a method for manufacturing said regenerator by 3D printing.

[0009] This problem is solved by the features of independent claims 1 and 11.

[0010] The subclaims relate to further advantageous embodiments of the disclosure.

[0011] Preferred embodiments of the disclosure are described below with reference to the drawings.

[0012] It shows: Fig. 1 a perspective sectional view of a first embodiment of the regenerator according to the invention, and Fig. 2a perspective sectional view of a second embodiment of the invention

[0013] The Figures 1 and 2show two embodiments of the disclosure in the form of a columnar regenerator 2 with a round cross-section, wherein only one half of the regenerator 2 is shown in each case. The regenerator 2 comprises a cell 2 with cell walls 4 that enclose a cavity 6 with partial cavities 6-i. The cell walls 4 are penetrated by a pressure equalization opening in the form of a capillary 8. The cell 2 has a circular cross-section and is arranged in a tubular flow channel for the working gas helium. The interior of the cavity 6 is filled with helium as a heat storage material during operation. The partial cavities 6-i form planar structures parallel to the longitudinal axis of the cell 2. Parallel slot-shaped flow channels 10 for helium as the working gas are formed between the planar partial cavities 6-i.The partial cavities 6-i are interconnected in the edge region of the columnar regenerator 2 by a connecting channel 12 and, together with the partial cavities 6-i, form the cavity 6. The individual, flat, parallel partial cavities 6-i extend over the entire height or length of the columnar cell 2 and are formed by two spaced-apart, flat cell walls 4-1, sealed in the edge region by strip-shaped cell walls 4-2. The slot-shaped flow channels 10, which completely penetrate the cell 2, are arranged between the individual partial cavities 6-1.

[0014] Support elements 14 are provided inside the partial cavities 6-1, which support the flat cell walls 4-1 against each other. In the first embodiment according to Fig. 1The support elements 14 are designed as small cuboids distributed throughout the interior of the partial cavities 6-i. The support elements 14 can also be columnar or rounded and spherical.

[0015] In the second embodiment according to Fig. 2 The support elements are strip-shaped and extend away from the strip-shaped cell walls 4-2, creating a meandering channel. The strip-shaped support elements 14 are provided with blind-hole-shaped slots (not shown) that are accessible to the working gas helium. This allows thermal stresses occurring during 3D printing to be absorbed in an accordion-like manner, preventing cracks in the material. List of reference symbols:

[0016] 1Regenerator 2Cell 4Cell wall 4-1Flat cell walls 4-2Strip-shaped cell walls 6Cavity 6-iPartial cavity 8Capillary 10Flow channel for working gas 12Circular connecting channel 14Support elements

Claims

1. A regenerator (1) for a cryocooler with helium as working-gas and heat-storing medium, comprising at least one cell (2) with cell walls (4) enclosing a cavity (6) having several sub-cavities (6-1), wherein the sub-cavities (6-i) are interconnected via at least one connecting passage (12) and, with the exception of the at least one connecting passage (12) to other sub-cavities (6-i), are enclosed by the cell walls, wherein the cavity (6) of the at least one cell (2) is filled with helium gas as heat-storing material, flow passages (10) for the working-gas helium formed between the individual sub-cavities (6-i), and a pressure-equalizing opening in the form of a capillary (8) which penetrates the cell walls (4) and forms a permanently open connection between the working-gas helium outside the cavity (6) and the heat-storing material helium inside the cavity (6), characterized in that the sub-cavities (6-i) have supporting elements (14) in their interior which support the cell walls (4) bounding a sub-cavity (6-i) against each other.

2. The regenerator (1) according to claim 1, characterized in that the sub-cavities are tubular due to the arrangement and shape of the supporting elements and by the shape of the cell walls.

3. The regenerator (1) according to claim 1 or 2, characterized in that the sub-cavities (6-i) are meander-shaped due to the arrangement and shape of the supporting elements (14) and the shape of the cell walls.

4. The regenerator (1) according to any of the preceding claims, characterized in that the supporting elements (14) are strip-shaped and extend away from the cell walls into the sub-cavities (6-i).

5. The regenerator (1) according to claim 4, characterized in that the strip-shaped supporting elements (14) are provided with a slit in the form of a blind hole which is accessible to the working-gas helium.

6. The regenerator (1) according to any of preceding claims 2 to 5, characterized in that the sub-cavities (6-i) have a rectangular cross-section.

7. The regenerator (1) according to any of preceding claims 2 to 5, characterized in that the sub-cavities (6-i) have a rounded cross-section.

8. The regenerator (1) according to any of preceding claims 6 or 7, characterized in that the flow passages (10) between the sub-cavities (6-i) have a rectangular cross-section.

9. The regenerator (1) according to any of the preceding claims, characterized in that the at least one cell (2) is formed as a disk with a circular cross-section, and that the connecting passage (12) connecting the sub-cavities (6-i) is arranged in an edge section of the disk-shaped cell (2).

10. The regenerator (1) according to any of the preceding claims, characterized in that the outside of the cell walls (4-i) in the flow passages (10) for the working-gas helium has swirl structures.

11. A method of manufacturing a regenerator (1) according to any of the preceding claims, wherein the regenerator (1) is produced via 3D printing.

12. The method according to claim 11, characterized in that the sub-cavities (6-i) have openings after 3D printing which are subsequently closed.

13. A cryocooler in the form of a Stirling, Gifford-McMahon or pulse tube cooler with at least one regenerator, characterized by a regenerator (1) according to any of preceding claims 1 to 10.

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