Magnetocaloric module for very low temperature magnetic refrigeration

Abstract

The application discloses a magnetic heat module for extremely low-temperature magnetic refrigeration, which comprises a shell, a heat conduction assembly, a heat conduction part and magnetic material. The shell is internally provided with a sealed cavity, and the lateral wall of the shell is provided with an opening communicating with the sealed cavity. The heat conduction assembly comprises a plurality of heat conduction sheets, each of which is axially installed in the sealed cavity, and the planes of each of the heat conduction sheets are parallel to each other. A plurality of flow-through holes are formed in the heat conduction sheets, and the flow-through holes are located in the sealed cavity. One or more fractal structures are arranged in each of the flow-through holes, and the fractal structures are one-level or multi-level fractal structures. The heat conduction part is connected to the end of the heat conduction assembly and at least partially located outside the shell for heat conduction. The magnetic material is arranged in the gap formed by the heat conduction sheets. The magnetic heat module for extremely low-temperature magnetic refrigeration can ensure good heat conduction performance while occupying a smaller volume of magnetic material.

Description

Technical Field

[0001] This invention relates to the field of cryogenic thermal insulation and demagnetization refrigeration technology, and in particular to a magnetothermal module for cryogenic magnetic refrigeration. Background Technology

[0002] Extremely low temperatures refer to temperatures below 1K. Extremely low temperature adiabatic demagnetization refrigeration is independent of gravity and scarce materials. 3 With advantages such as high efficiency and intrinsic strength, it is widely used in space projects and ground laboratories. The magnetocaloric module is the source of cooling energy for cryogenic adiabatic demagnetizing refrigerators. The magnetocaloric module consists of magnetic materials and a heat transfer structure. Utilizing the magnetocaloric effect of magnetic materials—releasing heat to the outside during excitation and absorbing heat from the outside during demagnetization—by controlling changes in the magnetic field and the on / off state of a thermal switch, heat is released to the heat sink during excitation and absorbed from the object being cooled during demagnetization, thus achieving cooling. Since the magnetic material needs to be placed within the magnetic field of a magnet, and the internal space of the magnet is limited, and the objects to be cooled vary in shape and size, making direct heat exchange with the magnetic material difficult, and the objects to be cooled usually need to be placed outside the magnetic field to avoid electromagnetic interference, a heat transfer structure is needed to transfer the cooling energy generated during the demagnetization process to the object being cooled. In addition, the temperature rises during the excitation process of the magnetic material, requiring the heat generated by the magnetic material to be transferred to the heat sink through the heat transfer structure.

[0003] In the temperature range of 10 mK to 1 K, commonly used magnetic materials are mostly paramagnetic salt crystals containing coordinated water. Commonly used magnetic materials in this temperature range include FAA (Fe(SO4)2NH4·12H2O, iron ammonia vanadium), CPA (CrK(SO4)2·12H2O, chromium potassium vanadium), and CMN (Ce2Mg3(NO3)). 12 ·24H2O, cerium magnesium nitrate, etc. These magnetic materials have poor thermal conductivity below 1K. Taking CPA as an example, its thermal conductivity is approximately 10 at 100mK. -2 W·m -1 ·K -1 Therefore, it is impossible to directly utilize the thermal conductivity of the magnetic material itself to transfer internal cold to the outside. Under high temperatures or mechanical shocks, paramagnetic salt crystals are prone to dehydration, causing magnetic material failure. For example, FAA dehydrates at 35°C. Therefore, it is impossible to enhance heat transfer by grinding the magnetic material into powder and mixing it with powder of a high thermal conductivity material. When the magnetic material in the magnetocaloric module is a paramagnetic salt containing coordinated water, considering its poor thermal conductivity and easy dehydration failure, the heat transfer structure is often placed in a saturated solution of the magnetic material, and the magnetic material is grown on the heat transfer structure to enhance the heat transfer of the magnetic material.

[0004] There are two types of heat transfer structures in existing technology:

[0005] The first type is made of a bundle of metal wires (usually copper or gold wires, or other highly thermally conductive materials). Several metal wires are manually threaded onto a threading frame designed according to the dimensions of the magnetic material. After threading, the ends of the metal wires are welded to an external heat transfer structure to exchange heat with the outside environment. To minimize eddy current heating in a changing magnetic field while meeting the stress requirements of the metal wires, the wire diameter should be as small as possible; to ensure uniform distribution of the metal wires within the magnetic material for maximum heat exchange, the number of metal wires should be as large as possible. For example, the magnetothermal module in the Astro-E project uses a heat transfer structure containing 4500 gold wires with a diameter of 0.2mm.

[0006] The second method uses wire-cut heat-conducting metal rods. A relatively thick copper rod with a diameter similar to that of the magnetic material is wire-cut into multiple thin copper rods, leaving one end of the thick rod uncut. The thin copper rods are evenly distributed within the magnetic material. Since the thin copper rods in contact with the magnetic material are integrated with the heat transfer structure, welding is unnecessary, avoiding the risk of thermal resistance caused by poor welding processes.

[0007] In existing technologies, the enhanced heat transfer structure using metal wires presents several challenges. First, the ends of the metal wire bundle need to be welded to other heat transfer structures (such as thermally conductive copper rods) to exchange heat. The welded sections of hundreds or thousands of metal wires to these structures exhibit significant thermal resistance at extremely low temperatures, resulting in a large temperature difference between the wire bundle and the copper rod, leading to a loss of cooling capacity in the refrigerator. Second, the large number of metal wires necessitates manual threading and fabrication. Furthermore, to prevent wire breakage due to uneven thermal stress at low temperatures, the tension of each wire must be kept as consistent as possible. Finally, to ensure uniform distribution of the metal wires within the magnetic material, the wires must be kept parallel to each other and avoid contact.

[0008] In the existing technology, the enhanced heat transfer structure obtained by wire cutting has two main drawbacks. First, due to the limitations of the wire cutting process, the diameter of the thin copper rod is larger than that of the metal wire. Within a limited volume, the excessive volume of the heat transfer structure will encroach on the volume of the magnetic material, resulting in a reduction in the amount of magnetic material used and thus a decrease in the maximum total cooling capacity of the refrigerator. Second, the relatively large diameter of the thin copper rod obtained by wire cutting makes the eddy current heating effect generated in the changing magnetic field more significant, leading to a greater loss of cooling capacity. Summary of the Invention

[0009] To address at least one of the problems mentioned in the background section, the present invention aims to provide a magnetothermal module for extremely low temperature magnetic refrigeration.

[0010] This invention is achieved through the following technical solution:

[0011] A magnetocaloric module for ultra-low temperature magnetic refrigeration includes:

[0012] A housing, wherein a sealed cavity is provided inside the housing, and an opening communicating with the sealed cavity is provided on the side wall of the housing;

[0013] A heat-conducting component includes several heat-transfer sheets, each of which is axially mounted in the sealed cavity. The planes of each heat-transfer sheet are parallel to each other. Several flow holes are formed on the heat-transfer sheets, which are located in the sealed cavity. Each flow hole is also provided with one or more fractal structures, which are single-level or multi-level fractal structures.

[0014] A heat-conducting element, which is connected to the end of the heat-conducting assembly and is at least partially located outside the housing for heat conduction;

[0015] A magnetic material is disposed in the gaps formed by the heat transfer sheets.

[0016] Optionally, the flow holes are elongated, and each flow hole is evenly distributed on the heat transfer sheet at horizontal, vertical, or oblique intervals.

[0017] Optionally, the fractal structure includes a first fractal piece and a second fractal piece. One end of the first fractal piece is fixed to one end of the flow hole, forming a first angle between the first fractal piece and the heat transfer sheet. A first fractal hole is formed on the first fractal piece. One end of the second fractal piece is fixed to the other end of the first fractal hole, forming a second angle between the second fractal piece and the first fractal piece. The first angle and the second angle are both between zero and 180 degrees.

[0018] Optionally, the fractal structure includes a third fractal plate, a fourth fractal plate, and a fifth fractal plate. One end of the third fractal plate is fixed to one end of the flow hole, forming a third angle between the third fractal plate and the heat transfer sheet. One end of the fourth fractal plate and the fifth fractal plate are fixed side by side to the other end of the third fractal plate, forming a fourth angle between the fourth fractal plate and the third fractal plate, and forming a fifth angle between the fifth fractal plate and the third fractal plate. The third, fourth, and fifth angles are all between 0 and 180 degrees.

[0019] Optionally, the fractal structure includes a sixth fractal piece and a seventh fractal piece. One end of the sixth fractal piece is fixed to one end of the flow hole, forming a sixth angle between the sixth fractal piece and the heat transfer sheet. The other end of the sixth fractal piece is provided with a concave groove. One end of the seventh fractal piece is fixed in the concave groove at the other end of the sixth fractal piece, forming a seventh angle between the seventh fractal piece and the sixth fractal piece. Both the sixth and seventh angles are between zero and 180 degrees.

[0020] Optionally, the housing includes an outer shell and end caps, the opening is provided on the side wall of the outer shell, and the end caps are provided at each end of the outer shell to form the sealed cavity inside the outer shell, and at least a portion of the heat-conducting element is located outside the end caps.

[0021] Optionally, the end cap opposite to the sealed cavity is provided with the heat-conducting element, and the end facing the receiving cavity is provided with a plurality of radially spaced positioning grooves. The ends of a plurality of heat transfer sheets are respectively fitted into the positioning grooves, so that the heat-conducting element is connected to the heat transfer sheets through the end cap for heat conduction.

[0022] Optionally, the end cap has a central hole, and the ends of the plurality of heat transfer sheets are connected to each other to form the heat conductor. The heat conductor passes through the central hole so that at least a portion of the heat conductor is located on the outer low-temperature adhesive of the end cap.

[0023] Optionally, it also includes a support frame installed in the sealed cavity, with a plurality of the heat transfer sheets passing through the support frame, the support frame being close to the heat conductor, and the heat conductor and the central hole being sealed by a low-temperature adhesive.

[0024] Optionally, the end cap is snapped into the outer shell, the cross-sectional shape of the outer contour of the end cap corresponds to the cross-sectional shape of the inner contour of the outer shell, and a low-temperature adhesive is provided on the outer side of the end cap.

[0025] The beneficial effects of this invention are as follows: The magnetocaloric module for ultra-low temperature magnetic refrigeration in this invention, compared with the magnetocaloric module structure of metal wire bundles, is directly connected to the external heat exchange object, reducing the thermal resistance caused by poor welding quality; the assembly of heat transfer plates is relatively easy, requiring only manual installation of a few heat transfer plates to achieve heat exchange performance, and there is no need to specifically control the tension of each wire, which saves labor costs far compared to threading hundreds or thousands of metal wires; it can increase the heat transfer area of ​​the heat transfer plates in the magnetic material, improving the temperature uniformity of the magnetic material; compared with the magnetocaloric module made by wire cutting, the thickness of the heat transfer plates is thinner, and the resulting magnetocaloric module heat transfer structure can ensure good heat transfer performance while occupying less magnetic material volume, improving the temperature uniformity of the magnetic material; because the thickness of the heat transfer plates is extremely small and they do not form conductive paths with each other, the losses caused by eddy current heating are smaller. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of a magnetocaloric module for ultra-low temperature magnetic refrigeration according to an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of a heat transfer sheet for a magnetocaloric module for ultra-low temperature magnetic refrigeration according to an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the structure of a heat transfer sheet for a magnetocaloric module for ultra-low temperature magnetic refrigeration according to another embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram of the structure of a heat transfer sheet for a magnetocaloric module for ultra-low temperature magnetic refrigeration according to another embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram of a magnetocaloric module for ultra-low temperature magnetic refrigeration according to another embodiment of the present invention;

[0032] Among them, 1. shell; 2. heat-conducting component; 3. magnetic material; 4. support frame; 41. flow hole; 11. outer shell; 12. end cap; 13. positioning groove; 14. low temperature adhesive; 21. heat transfer sheet; 22. flow hole; 23. fractal structure; 24. heat-conducting component; 231. first fractal piece; 232. second fractal piece; 233. third fractal piece; 234. fourth fractal piece; 235. fifth fractal piece; 236. sixth fractal piece; 237. seventh fractal piece; 238. first fractal hole. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0034] The following is for reference Figure 1-5 The present invention will specifically describe a magnetocaloric module for ultra-low temperature magnetic refrigeration according to an embodiment of the present invention.

[0035] like Figure 1-5 As shown, a magnetocaloric module for ultra-low temperature magnetic refrigeration according to an embodiment of the present invention includes a housing 1, a heat-conducting component 2, a heat-conducting element 24, and a magnetic material 3. The housing 1 has a sealed cavity, and the side wall of the housing 1 has an opening communicating with the sealed cavity. The heat-conducting component 2 includes a plurality of heat-transferring sheets 21, each heat-transferring sheet 21 being axially mounted in the sealed cavity. The planes of each heat-transferring sheet 21 are parallel to each other. A plurality of flow holes 22 are formed on the heat-transferring sheet 21, and the flow holes 22 are located in the sealed cavity. Each flow hole 22 also has one or more fractal structures 23, and the fractal structures 23 are single-level or multi-level fractal structures 23. The heat-conducting element 24 is connected to the end of the heat-conducting component 2 and is at least partially located outside the housing 1 for heat conduction. The magnetic material 3 is disposed in the gaps formed by each heat-transferring sheet 21.

[0036] It should be noted that the shell 1 needs to be selected based on the type of magnetic material, using a material that does not react with the magnetic material, is not prone to cracking at extremely low temperatures, and has little or no eddy current heating in a magnetic field; G10 glass fiber (hereinafter referred to as G10) is preferred. When the shell 1 is made of metal, it can have a grooved design to reduce eddy current heating. The heat transfer sheet 21 needs to be selected based on the type of magnetic material, using a material with high thermal conductivity that does not react with the magnetic material; copper or gold is preferred. The thickness of the heat transfer sheet 21 should not be too thick. The heat transfer sheet 21 has a thickness of 0.01 to 2 mm; the width of the largest heat transfer sheet 21 is approximately equal to the inner diameter of the housing 1, ensuring that it can be smoothly installed into the housing 1; since the pipe interface provided during the growth of the magnetic material varies, the opening on the housing 1 for the flow of the magnetic material solution is not shown in the figures. After the growth of the magnetic material is completed, the magnetothermal module is removed from the magnetic material solution, and the opening is sealed with low-temperature adhesive, so that the magnetic material is in the completely sealed cavity.

[0037] It should be noted that the installation method of the flow hole 22 and the fractal structure 23 can use a convenient connection. In this embodiment, preferably, the material in the flow hole 22 is not completely removed. When processing the flow hole 22, the shape of the flow hole 22, the position of the incomplete cut on the heat transfer sheet 21, and the position of the cut are changed. When processing the material in the flow hole 22, different fractal structures 23 are obtained by bending them out in different quantities, directions, angles, and lengths. Cutting is performed on the incompletely cut and bent sheet, and smaller sheets are bent out to achieve multi-level fractals. The bending direction and angle of the fractal structure 23 on the heat transfer sheet 21 can have various forms. Preferably, the bent fractal sheet should be kept as parallel as possible to the magnetic field lines of the magnetic field under actual working conditions to reduce eddy current heating. Magnetic field lines should be avoided from passing through the bent fractal sheet as much as possible, especially from passing through the bent fractal sheet perpendicularly. This facilitates the flow of the magnetic material 3 solution, expands the contact area between the magnetic material 3 and the heat transfer sheet 21, and makes the temperature within the magnetic material 3 more uniform. Therefore, the magnetocaloric module for ultra-low temperature magnetic refrigeration in this invention, compared to the magnetocaloric module structure of metal wire bundles, directly connects to the external heat exchange object, reducing thermal resistance caused by poor welding quality; the assembly of the heat transfer sheets is easier, requiring only manual installation of a few sheets to achieve heat exchange performance, and there is no need to specifically control the tension of each wire, saving labor costs far compared to threading hundreds or thousands of metal wires; it can increase the heat transfer area of ​​the heat transfer sheets in the magnetic material, improving the temperature uniformity of the magnetic material; compared to magnetocaloric modules made by wire cutting, the heat transfer sheets are thinner, and the resulting magnetocaloric module heat transfer structure can ensure good heat transfer performance while occupying less volume of the magnetic material, improving the temperature uniformity of the magnetic material; because the thickness of the heat transfer sheets is extremely small and they do not form conductive paths with each other, the losses caused by eddy current heating are even smaller.

[0038] like Figure 2 As shown, in one embodiment, the flow holes 22 are elongated, and each flow hole 22 is evenly distributed on the heat transfer sheet 21 at horizontal, vertical, or oblique intervals. This facilitates the flow of the magnetic material 3 solution, promotes the growth of the magnetic material 3, and ensures that the magnetic material 3 uniformly fills the space inside the sealed cavity and makes full and tight contact with the heat transfer sheet 21.

[0039] like Figure 2As shown, in one embodiment, the fractal structure 23 includes a first fractal piece 231 and a second fractal piece 232. One end of the first fractal piece 231 is fixed to one end of the flow hole 22, so that a first included angle is formed between the first fractal piece 231 and the heat transfer sheet 21. A first fractal hole 238 is provided on the first fractal piece 231. One end of the second fractal piece 232 is fixed to the other end of the first fractal hole 238, so that a second included angle is formed between the second fractal piece 232 and the first fractal piece 231. The first included angle and the second included angle are both between zero and 180 degrees.

[0040] It should be noted that, in this embodiment, preferably, the thin sheet inside the hole is not completely cut away during the opening process. Instead, it is bent out and further processed by cutting holes to form a fractal structure 23. That is, the first fractal piece 231 is the material in the flow hole 22, and the second fractal piece 232 is the material in the first fractal hole 238. This enhances the heat transfer between the heat transfer structure and the magnetic material 3, making the internal temperature of the magnetic material 3 more uniform and reducing eddy current heat. Figure 3 As shown, in another embodiment, the fractal structure 23 includes a third fractal piece 233, a fourth fractal piece 234, and a fifth fractal piece 235. One end of the third fractal piece 233 is fixed to one end of the flow hole 22, forming a third angle between the third fractal piece 233 and the heat transfer sheet 21. One end of the fourth fractal piece 234 and the fifth fractal piece 235 are fixed side-by-side to the other end of the third fractal piece 233, forming a fourth angle between the fourth fractal piece 234 and the third fractal piece 233. The fifth fractal piece 235 and the third fractal piece 233 form a fifth angle. The third, fourth, and fifth angles are all between 0 and 180 degrees. Therefore, a two-dimensional fractal structure 23 can be obtained through simple processing of the fractal structure 23, which can increase the heat transfer area of ​​the heat transfer sheet 21 in the magnetic material 3 while reducing manual labor.

[0041] like Figure 4As shown, in another embodiment, the fractal structure 23 includes a sixth fractal piece 236 and a seventh fractal piece 237. One end of the sixth fractal piece 236 is fixed to one end of the flow hole 22, forming a sixth angle between the sixth fractal piece 236 and the heat transfer sheet 21. The other end of the sixth fractal piece 236 is provided with a concave groove. One end of the seventh fractal piece 237 is fixed in the concave groove at the other end of the sixth fractal piece 236, forming a seventh angle between the seventh fractal piece 237 and the sixth fractal piece 236. Both the sixth and seventh angles are between 0 and 180 degrees. Therefore, by simply processing the fractal structure 23, the surface area of ​​the heat transfer sheet 21 can be increased, the magnetic material 3 can be more uniformly distributed, and the heat transfer efficiency can be improved.

[0042] like Figure 1 and 5 As shown, in one embodiment, the housing 1 includes an outer shell 11 and an end cap 12. The opening is provided on the side wall of the outer shell 11, and the end cap 12 is provided at the end of the outer shell 11 to form the sealed cavity within the outer shell 11. At least a portion of the heat-conducting element 24 is located outside the end cap 12.

[0043] like Figure 1 As shown, in one embodiment, the end cap 12 is provided with the heat-conducting element 24 at one end away from the sealed cavity, and a plurality of radially spaced positioning grooves 13 are provided at the end facing the receiving cavity. The ends of a plurality of heat transfer sheets 21 are respectively fitted into the positioning grooves 13, so that the heat-conducting element 24 is connected to the heat transfer sheets 21 through the end cap 12 for heat conduction.

[0044] like Figure 5 As shown, in another embodiment, the end cap 12 has a central hole at its center, and the ends of the plurality of heat transfer sheets 21 are connected to each other to form the heat conductor 24. The heat conductor 24 passes through the central hole such that at least a portion of the heat conductor 24 is located outside the end cap 12.

[0045] like Figure 5 As shown, in another embodiment, a support frame 4 is also included, which is installed in the sealed cavity. A plurality of the heat transfer sheets 21 pass through the support frame 4. The support frame 4 is close to the heat conductor 24. The heat conductor 24 and the central hole are sealed by a low-temperature adhesive 14.

[0046] It should be noted that multiple flow holes 41 can be provided on the support frame 4 to allow the solution to flow.

[0047] In one embodiment, the end cap 12 is snapped into the outer shell 11, the cross-sectional shape of the outer contour of the end cap 12 corresponds to the cross-sectional shape of the inner contour of the outer shell 11, and a low-temperature adhesive 14 is provided on the outer side of the end cap 12.

[0048] It should be noted that the gaps between the end cap 12 and the heat transfer sheet 21, as well as the gaps between the end cap 12 and the outer shell 11, are sealed by the low-temperature adhesive 14. When using the low-temperature adhesive for sealing, the operation must be carried out before the adhesive has cured, and depending on the type of low-temperature adhesive used, a certain amount of time must be allowed for the adhesive to fully cure and achieve a seal. This creates a sealed cavity within the magnetothermal module, isolating the magnetic material 3 from the outside environment and preventing the magnetic material 3 from dehydrating and failing during operation.

[0049] In the description of the embodiments of the present invention, it should be understood that the terms "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0050] Furthermore, the terms "first" and "another" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" or "several" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0051] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0052] In the description of this specification, references to terms such as "an embodiment," "an example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0053] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A magnetocaloric module for ultra-low temperature magnetic refrigeration, characterized in that, include: A housing, wherein a sealed cavity is provided inside the housing, and an opening communicating with the sealed cavity is provided on the side wall of the housing; A heat-conducting component includes several heat-transfer sheets, each of which is axially mounted in the sealed cavity. The planes of each heat-transfer sheet are parallel to each other. Several flow holes are formed on the heat-transfer sheets, which are located in the sealed cavity. Each flow hole is also provided with one or more fractal structures, which are single-level or multi-level fractal structures. A heat-conducting element, which is connected to the end of the heat-conducting assembly and is at least partially located outside the housing for heat conduction; A magnetic material, wherein the magnetic material is disposed in the gaps formed by the heat transfer sheets; The flow holes are elongated strips, and each flow hole is evenly distributed on the heat transfer sheet at horizontal, vertical, or diagonal intervals. The fractal structure includes a first fractal piece and a second fractal piece. One end of the first fractal piece is fixed to one end of the flow hole, so that a first included angle is formed between the first fractal piece and the heat transfer sheet. A first fractal hole is formed on the first fractal piece. One end of the second fractal piece is fixed to the other end of the first fractal hole, so that a second included angle is formed between the second fractal piece and the first fractal piece. The first included angle and the second included angle are both between zero and 180 degrees.

2. The magnetocaloric module for ultra-low temperature magnetic refrigeration according to claim 1, characterized in that, The fractal structure includes a third fractal plate, a fourth fractal plate, and a fifth fractal plate. One end of the third fractal plate is fixed to one end of the flow hole, forming a third angle between the third fractal plate and the heat transfer sheet. One end of the fourth fractal plate and the fifth fractal plate are fixed side by side to the other end of the third fractal plate, forming a fourth angle between the fourth fractal plate and the third fractal plate, and forming a fifth angle between the fifth fractal plate and the third fractal plate. The third, fourth, and fifth angles are all between 0 and 180 degrees.

3. The magnetocaloric module for ultra-low temperature magnetic refrigeration according to claim 2, characterized in that, The fractal structure includes a sixth fractal piece and a seventh fractal piece. One end of the sixth fractal piece is fixed to one end of the flow hole, forming a sixth angle between the sixth fractal piece and the heat transfer sheet. The other end of the sixth fractal piece is provided with a concave groove. One end of the seventh fractal piece is fixed in the concave groove at the other end of the sixth fractal piece, forming a seventh angle between the seventh fractal piece and the sixth fractal piece. Both the sixth and seventh angles are between zero and 180 degrees.

4. The magnetocaloric module for ultra-low temperature magnetic refrigeration according to claim 1, characterized in that, The housing includes an outer shell and end caps. The opening is provided on the side wall of the outer shell, and the end caps are provided at each end of the outer shell to form the sealed cavity inside the outer shell. At least a portion of the heat-conducting element is located outside the end caps.

5. The magnetocaloric module for ultra-low temperature magnetic refrigeration according to claim 4, characterized in that, The end cap opposite to the sealed cavity is provided with the heat-conducting element, and the end facing the cavity is provided with multiple radially spaced positioning grooves. The ends of several heat transfer sheets are respectively fitted into the positioning grooves, so that the heat-conducting element is connected to the heat transfer sheets through the end cap for heat conduction.

6. The magnetocaloric module for ultra-low temperature magnetic refrigeration according to claim 4, characterized in that, The end cap has a central hole, and the ends of the plurality of heat transfer sheets are connected to each other to form the heat conductor. The heat conductor passes through the central hole so that at least a portion of the heat conductor is located on the outside of the end cap.

7. The magnetocaloric module for ultra-low temperature magnetic refrigeration according to claim 6, characterized in that, It also includes a support frame installed in the sealed cavity, a plurality of the heat transfer sheets passing through the support frame, the support frame being close to the heat conductor, and the heat conductor and the central hole being sealed by a low-temperature adhesive.

8. The magnetocaloric module for ultra-low temperature magnetic refrigeration according to claim 4, characterized in that, The end cap is snapped into the outer shell, and the cross-sectional shape of the outer contour of the end cap corresponds to the cross-sectional shape of the inner contour of the outer shell. The outer side of the end cap is provided with low-temperature adhesive.

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