Multilayer magnetic refrigeration device based on a single magnet and its working method

Abstract

This invention provides a multilayer magnetic refrigeration device based on a single magnet and its operating method. The device includes: a ring magnet, the interior of which forms a working space; a multilayer magnetic refrigeration kit, integrally disposed within the working space and coaxially arranged with the ring magnet; and a thermal switching system configured to switch between heat exchange and adiabatic states within the multilayer magnetic refrigeration device by temperature-controlled adsorption or release of exchange gas. The multilayer magnetic refrigeration kit includes at least two refrigeration units made of highly thermally conductive material and nested from the outside in. Each refrigeration unit has one or more cavities for accommodating a magnetic refrigerant. The magnetic refrigerants contained in different refrigeration units have different operating temperature zones, arranged in a progressively decreasing order from the outside to the inside. This invention reduces the number of components, makes the structure more compact, and provides excellent refrigeration performance.

Description

Technical Field

[0001] This invention belongs to the field of low-temperature magnetic refrigeration technology. Specifically, this invention relates to a multilayer magnetic refrigeration device based on a single magnet and its operating method. Background Technology

[0002] The magnetocaloric effect (MCE), as the physical basis of adiabatic demagnetization refrigeration technology, provides a unique and efficient technical path for achieving extremely low temperatures without relying on scarce helium resources. Adiabatic demagnetization refrigerators based on this principle have become key equipment for achieving sub-Kelvin temperatures, especially below 50 mK, in cutting-edge fields such as deep space exploration, physical property research, and quantum computing. Compared with dilution refrigeration and other technologies, it exhibits significant advantages in adaptability to the zero-gravity environment of space and its potential for high thermodynamic efficiency.

[0003] In traditional cryogenic magnetic refrigeration technology, a single magnetic refrigerant is limited by its inherent cooling temperature range and cooling capacity, typically requiring multi-stage series and parallel structures to achieve lower cooling temperatures and sufficient cooling capacity. In such multi-stage systems, thermal switches must be configured between each stage to achieve heat exchange and switching between adiabatic states. However, thermal switches capable of simultaneously achieving high on / off ratios and stability in cryogenic regions (such as superconducting thermal switches) lose their adiabatic properties and fail to function properly in strong magnetic fields due to the disruption of the superconducting state. This fundamental contradiction of "mutual exclusion between strong magnetic fields and superconducting thermal switches" severely restricts the evolution of technological approaches, forcing traditional designs to form a near-fixed path dependency: spatial isolation through "configuring independent magnets for each refrigeration stage" to avoid damage to the superconducting thermal switches by the magnetic field. While this approach solves the thermal switch compatibility problem, it inevitably leads to a significant increase in system size, weight, and control complexity.

[0004] In other words, most current adiabatic demagnetizing refrigeration systems developed to achieve ultra-low temperatures follow the traditional "multi-stage series-parallel" technical route. This route relies on the coordinated operation of multiple magnetic refrigerant modules operating in different temperature zones. To avoid the performance degradation of critical components in ultra-low temperature regions—especially superconducting thermal switches—by strong magnetic fields (i.e., the superconducting state is destroyed under strong magnetic fields, leading to thermal switch failure), existing designs have been forced into a near-fixed paradigm: configuring each stage of the refrigeration module with an independent dedicated magnet, allowing the thermal switch to operate in regions without or with weak magnetic fields through spatial isolation. While this solves the compatibility problem of the thermal switch, it inevitably leads to a complex architecture of "multiple magnets, multiple thermal switches, and multiple control circuits." This architecture not only introduces a large size, weight, and high cost, but also increases the system's thermal mass and heat leakage risk due to the numerous components and complex thermal links, ultimately posing serious challenges in terms of reliability, integration, and miniaturization.

[0005] Therefore, there is an urgent need in this field for an innovative solution that can fundamentally break through the path dependence of the above-mentioned "multi-magnet-multi-thermal switch" in order to significantly simplify the system structure, reduce manufacturing costs and achieve miniaturization of the device while maintaining or even improving the cooling performance, thereby broadening the application scenarios of magnetic refrigeration technology. Summary of the Invention

[0006] This invention completely breaks through traditional thinking by employing a "gas-type thermal switch" (implemented by a cryogenic adsorption pump) that can operate stably at relatively high temperatures (4-6 K). Before the demagnetization cooling begins, this thermal switch can establish a system-level global high-vacuum insulation environment outside the magnet. This design cleverly avoids the harsh condition that "the thermal switch must operate in a strong magnetic field and extremely low temperature environment," removing a core obstacle to achieving "single magnet drive."

[0007] Building upon the solution to the compatibility issues between thermal switches and magnetic fields, this invention further enhances system performance through a "multi-layer magnetic refrigeration kit." This structure is not simply a stacking of working fluids, but a systematic thermal management architecture. Magnetic working fluids at different temperature zones are simultaneously demagnetized within a single magnet and arranged spatially according to the principle of "temperature decreasing from the outside to the inside." While cooling, the outer working fluid actively absorbs and shields external heat leakage, creating a near-ideal highly insulating working environment for the inner core working fluid. This design not only significantly reduces the impact of external heat leakage on the core cryogenic working fluid but also replaces the complex active control components used for inter-stage thermal management in traditional multi-stage systems with a passive, highly reliable integrated mechanical structure.

[0008] Therefore, the purpose of this invention is to construct a novel magnetic refrigeration technology route that is completely parallel to the traditional "multi-magnet-multi-thermal switch" approach. The technical solution of this invention achieves refrigeration functionality within a single magnet, a function previously requiring complex multi-body systems. It not only significantly simplifies system complexity, size, weight, and control, but also achieves remarkable improvements in refrigeration efficiency and ultimate performance.

[0009] The above-mentioned objective of the present invention is achieved through the following technical solution.

[0010] In a first aspect, the present invention provides a multilayer magnetic refrigeration device based on a single magnet, comprising:

[0011] A ring-shaped magnet, the interior of which forms the working space;

[0012] A multi-layer magnetic refrigeration kit is set entirely within the working space of the annular magnet and is coaxially arranged with the annular magnet.

[0013] A thermal switching system is configured to switch between the heat exchange state and the insulation state inside the multilayer magnetic refrigeration device by adsorbing or releasing exchange gases through temperature control.

[0014] in,

[0015] The multilayer magnetic refrigeration kit includes at least two refrigeration units made of highly thermally conductive materials and nested from the outside to the inside;

[0016] Each of the refrigeration units is provided with one or more accommodating cavities for accommodating the magnetic refrigerant;

[0017] The magnetic refrigerants contained in different refrigeration units have different operating temperature zones, and they are arranged in a progressively decreasing order from the outside to the inside of the operating temperature zone; and all the magnetic refrigerants are configured to perform magnetocaloric effect operation synchronously under the time-varying magnetic field generated by the annular magnet.

[0018] This invention provides a compact, high-performance ultra-low temperature magnetic refrigeration device. This invention achieves an ultra-low temperature environment with practical cooling capacity using only a single magnet and a cryogenic adsorption pump (cold trap). The device employs a multi-layered integrated structure: magnetic refrigerants with different operating temperatures are assembled in layers from the outside in and from high to low temperature, forming a composite nested structure. The layers are connected by an insulating support structure to minimize heat leakage caused by heat conduction.

[0019] The workflow is as follows: First, in the initial cooling stage of the system, overall pre-cooling is achieved using exchange gas. The heat generated by the refrigerant during the excitation process is dissipated to the outside of the refrigeration module through the exchange gas. Subsequently, the exchange gas is removed by activating the cryogenic adsorption pump, forming a high-vacuum adiabatic environment. In the final adiabatic demagnetization stage, the refrigerants at each stage cool down simultaneously. The heat leakage from the external environment is absorbed step by step by each layer of magnetic refrigerant from the outermost layer to the innermost layer, significantly reducing the impact of heat leakage on the innermost cryogenic refrigerant, thus allowing almost all of its cooling capacity to be used for the target refrigeration function.

[0020] The refrigeration unit of this invention can be made of a high thermal conductivity material. This invention does not impose any particular limitation on the high thermal conductivity material; typically, its thermal conductivity is 10-100 W / (cmK) below 10K. For example, the high thermal conductivity material can be oxygen-free copper, silver, gold, etc.

[0021] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, the refrigeration units are coaxially nested in a manner that decreases in size from the outside to the inside, and adjacent refrigeration units are connected by thermally insulating support members to form gaps.

[0022] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, the refrigeration unit includes an outer shell and an inner shell coaxially disposed inside it;

[0023] Between the outer surface of the inner shell and the inner surface of the outer shell, a three-dimensional surrounding cavity is defined radially, at the top and bottom, and the three-dimensional surrounding cavity constitutes the accommodating cavity of the refrigeration unit.

[0024] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, both the outer shell and the inner shell are cylindrical structures with sealed ends.

[0025] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, the bottom of the outer shell is provided with a vent hole that communicates with the three-dimensional surrounding cavity.

[0026] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, the refrigeration unit includes a main body shell, and the interior of the main body shell is separated into two independent cavities that are not connected to each other in the axial direction by two radially arranged partitions, namely an upper cavity and a lower cavity, which constitute the accommodating cavity of the refrigeration unit.

[0027] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, the upper cavity is formed by the top wall, side wall and upper partition of the main body shell; the lower cavity is formed by the bottom wall, side wall and lower partition of the main body shell.

[0028] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, the bottom of the main body shell is provided with a vent hole that communicates with the lower cavity.

[0029] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, the outer and inner surfaces of the refrigeration unit are coated with a highly reflective metal film. The present invention does not impose any particular limitation on the highly reflective (R) metal film; typically, its emissivity (ε = 1 - R) is 0.05 to 0.1. For example, the highly reflective metal film can be a gold film, a copper film, a silver film, etc.

[0030] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, the thermal switching system includes:

[0031] An adsorption unit, which is filled with adsorbent;

[0032] A temperature control unit, which is thermally connected to the adsorption unit;

[0033] A weak thermal connection mechanism is used to thermally connect the adsorption unit to the external cold end.

[0034] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, the temperature control unit includes a heater and a temperature sensor that are thermally connected to the adsorption unit.

[0035] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, the heater is a columnar heater and the temperature sensor is a sheet thermometer.

[0036] In one specific embodiment of the present invention, the thermal switching system of the present invention may include the following: an adsorption unit filled with activated carbon adsorbent; a temperature control unit including a columnar heater and a plate thermometer thermally connected to the adsorption unit; a weak thermal connection mechanism for thermally connecting the adsorption unit to an external cold end; when the adsorption unit is cooled to a working temperature range below 6 K by the weak thermal connection mechanism, the adsorption exchange gas causes the system to enter an adiabatic state; when the adsorption unit is heated to a non-working temperature range of approximately 25 K by the columnar heater, the gas is released to restore the system to a heat exchange state.

[0037] Preferably, in the multilayer magnetic refrigeration device based on a single magnet according to the present invention, the adsorbent is activated carbon.

[0038] In one specific embodiment of the present invention, based on the inner diameter of the magnet, a design is made including at least two hollow frames made of highly thermally conductive metal; the frames are nested in a composite manner with radial dimensions increasing from small to large and from the inside to the outside, with a radial gap of not less than 1 mm; thermal insulation support members are provided between adjacent frames; the frame surface has a reflective layer and a vent hole at the bottom; and multiple magnetic refrigerants with different operating temperature zones are respectively arranged in the corresponding frames from the inside to the outside in order of their cooling temperature increasing from low to high.

[0039] Secondly, the present invention provides a method for operating the multilayer magnetic refrigeration device based on a single magnet, which includes the following steps:

[0040] (1) Pre-cooling and magnetization steps:

[0041] The multi-layer magnetic refrigeration device is pre-cooled; during or after pre-cooling, the annular magnet is energized to magnetize all the magnetic refrigerants and stabilize the system at the initial temperature; during this process, the thermal switch system is controlled to be in a high-temperature state that does not adsorb gas, so that the exchange gas flows through the gaps between all the refrigeration units and in each of the accommodating cavities to achieve uniform heat exchange.

[0042] (2) Insulation steps:

[0043] The thermal switch system is controlled to switch to its adsorption working state, adsorbing the exchange gas inside the device, thereby establishing a high vacuum thermal insulation environment inside the device.

[0044] (3) Refrigeration steps:

[0045] Under the aforementioned adiabatic environment, the annular magnet is demagnetized, and all magnetic refrigerants are simultaneously demagnetized in an adiabatic manner, causing their temperature to decrease, and the innermost refrigerant reaches the target cooling temperature.

[0046] (4) Reset steps:

[0047] The thermal switch system is controlled to switch back to the high-temperature state where the gas is not adsorbed, releasing the adsorbed gas and restoring the heat exchange state inside the device; at the same time, the annular magnet is re-energized, causing the magnetic refrigerant to be magnetized and heated, and the system returns to the initial temperature.

[0048] In one specific embodiment of the present invention, the operation method of the magnetic refrigeration device of the present invention includes the following steps:

[0049] (i) Pre-cooling and magnetization steps: Cool the device to 20K, apply the target initial magnetic field to the magnetic refrigerant, and then further cool it to the initial temperature (below 6K). During this process, maintain the cryogenic adsorption pump at about 20K to unify the temperature of the system through the exchange gas with that of the cold end.

[0050] (ii) Insulation steps: Turn off the low-temperature adsorption pump heater to cool it down and adsorb the gas, thereby establishing an adiabatic environment inside the system;

[0051] (iii) Cooling step: Under the insulated environment, the magnetic refrigerant is demagnetized to cool it to the target temperature for application;

[0052] (iv) Reset step: When the cooling capacity is insufficient, the system and adsorption pump are reheated to about 20 K to release the gas and restore heat exchange. At the same time, a magnetic field is applied to the magnetic refrigerant to return the system temperature and magnetic field to the initial state in preparation for the next refrigeration cycle.

[0053] Compared with the prior art, the multilayer magnetic refrigeration device and method based on a single magnet provided by the present invention have achieved the following significant beneficial effects:

[0054] (1) The system structure is greatly simplified and compacted: By adopting the design of "single magnet drive" and "integrated multi-layer magnetic refrigeration kit", the multiple independent magnets and complex interstage active thermal switching system required in traditional adiabatic demagnetization refrigeration systems are completely eliminated. The number of parts is greatly reduced, making the entire device more compact, smaller in size and lighter in weight, laying a solid foundation for the miniaturization and integration of magnetic refrigeration devices.

[0055] (2) Simplified control logic and improved reliability: The control system is fundamentally simplified because there is no need for complex time-series coordinated control of the excitation / demagnetization process of multiple magnets and multiple thermal switches. This not only reduces the difficulty and cost of system development, but also significantly improves the long-term stability and reliability of the entire refrigeration system due to the reduction of active control links and the increase of passive mechanical structures.

[0056] (3) Thermal management efficiency and refrigeration performance optimization: The innovative "multi-layer magnetic refrigeration kit" combined with the design concept of "step-by-step insulation" enables the outer magnetic working fluid to actively absorb and shield heat leakage from the external environment during the refrigeration process, thereby creating a highly insulated working environment for the core inner low-temperature working fluid. This effectively reduces the direct impact of heat leakage on the lowest temperature level, allowing almost all of the cooling capacity of the inner working fluid to be used for target refrigeration, significantly improving the system's refrigeration efficiency, minimum achievable temperature, and the duration of constant temperature maintenance in the extremely low temperature range.

[0057] (4) Reduced manufacturing and operating costs: As the core high-value component of the system, the reduction in the number of magnets directly leads to a significant decrease in material costs. At the same time, the simplification of the number of parts and the control system also effectively reduces processing, assembly, and debugging costs. In addition, this technology does not rely on scarce resources such as helium-3, resulting in lower operating costs.

[0058] (5) Wide range of applications: The device’s outstanding advantages in compactness, weight and reliability make it a promising candidate for application and market value in cutting-edge fields such as deep space exploration, satellite payloads, mobile experimental platforms and quantum computing, which are extremely sensitive to space and weight. Attached Figure Description

[0059] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0060] Figure 1 A schematic diagram of a three-stage conventional series magnetic refrigeration system is shown.

[0061] Figure 2 A schematic diagram of a multilayer magnetic refrigeration device based on a single magnet, according to a specific embodiment of the present invention;

[0062] Figure 3 A schematic diagram of a multilayer magnetic refrigeration device based on a single magnet, illustrating another specific embodiment of the present invention;

[0063] Figure 4a This is a schematic diagram of the magnetic refrigeration device used in Embodiment 1 of the present invention;

[0064] Figure 4b This is a schematic diagram of the magnetic refrigeration device used in Comparative Example 1 of the present invention;

[0065] Figure 5 A comparative diagram showing experimental data of adiabatic demagnetization refrigeration in Embodiment 1 and Comparative Example 1 of the present invention is provided.

[0066] Figure 6 The refrigeration curves of a conventional two-stage series magnetic refrigeration device of the prior art and the magnetic refrigeration device of the present invention are shown; wherein, the left figure shows the refrigeration curve of the conventional series magnetic refrigeration device (GGG+CPA[40 g]) of the prior art; the right figure shows the refrigeration curve of the multi-layer magnetic refrigeration device (GGG+CPA[2.8 g]) of the present invention;

[0067] Figure label:

[0068] 1-Magnet;

[0069] 2-Refrigerant A;

[0070] 3-Refrigerant B;

[0071] 4-Refrigerant C;

[0072] 5-Thermal switch;

[0073] 6-Cold end;

[0074] 7-Thermal switch system;

[0075] 8-Insulation support component. Detailed Implementation

[0076] A schematic representation of the multilayer magnetic refrigeration device based on a single magnet disclosed in this invention will now be described in detail with reference to the accompanying drawings. Although the drawings are provided to illustrate some embodiments of the invention, they are not necessarily drawn to the dimensions of the specific embodiments, and certain features may be enlarged, removed, or partially cut to better illustrate and explain the disclosure of the invention. Some components in the drawings may be repositioned according to actual needs without affecting the technical effect. The phrase "in the drawings" or similar expressions appearing in the specification do not necessarily refer to all drawings or examples.

[0077] It should be noted that when a component is referred to as being "connected" to another component, it can be directly on the other component or it can be located in between. Certain directional terms used in the description of the accompanying drawings below, such as "horizontal," "vertical," "front," "back," "inner," "outer," "above," "below," and other directional terms, will be understood to have their usual meaning and refer to those directions typically considered when viewing the drawings. Unless otherwise specified, the directional terms used in this specification generally follow the conventional directions understood by those skilled in the art.

[0078] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0079] Figure 1 The diagram illustrates a conventional series magnetic refrigeration system. This system equips each stage of the refrigeration module with an independent, dedicated magnet, allowing the thermal switch to operate in areas with no or weak magnetic fields through spatial isolation. While this solves the compatibility issue of the thermal switch, it inevitably leads to a complex architecture with multiple magnets, multiple thermal switches, and multiple control circuits. This architecture not only introduces a large size, weight, and high cost, but also increases the system's thermal mass and leakage risk due to the numerous components and complex thermal paths, ultimately posing significant challenges in terms of reliability, integration, and miniaturization.

[0080] Reference Figure 2 and Figure 3 This invention provides a multilayer magnetic refrigeration device based on a single magnet, comprising: a ring magnet 1, the interior of which forms a working space; a multilayer magnetic refrigeration kit, which is integrally disposed within the working space of the ring magnet 1 and coaxially arranged with the ring magnet 1; and a thermal switching system 7, configured to switch between heat exchange and adiabatic states within the multilayer magnetic refrigeration device by adsorbing or releasing exchange gases through temperature control; wherein the multilayer magnetic refrigeration kit includes at least two refrigeration units made of highly thermally conductive materials and nested from the outside in. Figure 2 and Figure 3 The device shown includes a multilayer magnetic refrigeration kit comprising three refrigeration units made of a highly thermally conductive material, namely oxygen-free copper.

[0081] Each refrigeration unit has one or more cavities for accommodating the magnetic refrigerant. The magnetic refrigerants contained in different refrigeration units have different operating temperature zones, and are arranged in a progressively decreasing order from the outside to the inside. Furthermore, all the magnetic refrigerants are configured to synchronously operate under the magnetocaloric effect under the time-varying magnetic field generated by the annular magnet. The refrigeration units are coaxially nested in a decreasing-size manner from the outside to the inside, with adjacent refrigeration units connected by insulating supports 8 and forming gaps. Figure 2 and Figure 3 In the device shown, the operating temperatures of refrigerant C4, refrigerant B3, and refrigerant A2 decrease sequentially.

[0082] exist Figure 2 In the illustrated device, the refrigeration unit includes an outer shell and an inner shell coaxially disposed within it. A three-dimensional surrounding cavity is defined radially, at the top, and at the bottom between the outer surface of the inner shell and the inner surface of the outer shell, forming the accommodating cavity of the refrigeration unit. Both the outer shell and the inner shell are end-sealed cylindrical structures. A vent hole communicating with the three-dimensional surrounding cavity is provided at the bottom of the outer shell.

[0083] exist Figure 3 In the illustrated device, the refrigeration unit includes a main housing. The interior of the main housing is divided into two axially separate cavities by two radially arranged partitions: an upper cavity and a lower cavity. These two cavities constitute the accommodating cavity of the refrigeration unit. The upper cavity is enclosed by the top wall, side walls, and upper partition of the main housing; the lower cavity is enclosed by the bottom wall, side walls, and lower partition of the main housing. A vent hole communicating with the lower cavity is provided at the bottom of the main housing.

[0084] exist Figure 2 and Figure 3 In the device shown, a highly reflective metal film, such as a gold film, is coated on the outer and inner surfaces of the cooling unit.

[0085] In a specific embodiment of the present invention, the thermal switch system 7 includes: an adsorption unit filled with an adsorbent; a temperature control unit thermally connected to the adsorption unit; and a weak thermal connection mechanism for thermally connecting the adsorption unit to an external cold end. The temperature control unit includes a heater and a temperature sensor thermally connected to the adsorption unit; the heater is a columnar heater, and the temperature sensor is a sheet thermometer; the adsorbent is activated carbon.

[0086] Example 1

[0087] A schematic diagram of the multilayer magnetic refrigeration device based on a single magnet used in this embodiment is shown below. Figure 4a The device consists of two cooling units made of highly thermally conductive materials.

[0088] Two cylindrical refrigeration units of different sizes were fabricated using high thermal conductivity oxygen-free copper. The outer refrigeration unit has an outer diameter of 19mm, an inner diameter of 18mm, and a height of 80mm, meaning its wall thickness is 1mm. The upper cavity of the outer refrigeration unit has a height of 20mm, and the lower cavity has a height of 20mm. Both the upper and lower cavities are filled with refrigerant B, namely gadolinium gallium garnet (Gd3Ga5O). 12 ) Block (total weight 50 g).

[0089] The internal refrigeration unit has an outer diameter of 14mm, an inner diameter of 13mm, and a height of 40mm, meaning its wall thickness is 1mm. The upper cavity of the internal refrigeration unit has a height of 10mm, and the lower cavity has a height of 10mm. Both the upper and lower cavities are filled with refrigerant A, namely barium ytterbium boric acid (Ba3Yb(BO3)3) blocks (effective refrigerant mass 10g).

[0090] The inner and outer surfaces of both the external and internal cooling units are polished and coated with a high-reflectivity gold film. A support structure is fabricated using polyimide material with low thermal conductivity. First, the internal cooling unit is suspended and fixed at the center of the external cooling unit. Then, the assembled nested structure is connected to the cavity via polyimide supports, thereby achieving mechanical connection and thermal isolation between layers and between the system and the external environment.

[0091] A ruthenium oxide (RuO2) thin-film thermometer is used to monitor the temperature of key components in the system. All electrical signal transmissions utilize fine-diameter enameled manganese copper wire to minimize heat transfer through the measuring leads. A cryogenic adsorption pump (cold trap) is mounted at the top of the chamber to maintain and switch the vacuum insulation state within the system.

[0092] Comparative Example 1

[0093] The schematic diagram of the magnetic refrigeration device based on a single magnet used in this comparative example is shown below. Figure 4b The device consists of a refrigeration unit made of a highly thermally conductive material.

[0094] A cylindrical refrigeration unit was fabricated using high thermal conductivity oxygen-free copper. The structure and dimensional parameters of this refrigeration unit are the same as those of the internal refrigeration unit in Example 1, and the working fluid it is filled with is also the same as that of the internal refrigeration unit in Example 1.

[0095] The inner and outer surfaces of the cooling unit are polished and coated with a high-reflectivity gold film. The support structure is made of polyimide material with low thermal conductivity. Ruthenium oxide (RuO2) thin-film thermometers are used to monitor the temperature of key components in the system. All electrical signal transmissions use fine-diameter enameled manganese copper wire to minimize heat flow introduced through the measuring wires. A cryogenic adsorption pump (cold trap) is mounted on top of the chamber to maintain and switch the vacuum insulation state inside the system.

[0096] Refrigeration performance characterization

[0097] The magnetic refrigeration device with two refrigeration units described in Example 1 was installed at the center of the magnetic field of a commercial physical property measurement (PPMS) cryogenic cavity. First, the system was pre-cooled to 25 K, then a 6T magnetic field was applied to fully magnetize both the internal and external refrigerants. Subsequently, the system was further cooled to a target initial temperature of 1.8 K. After the overall temperature stabilized, the cryogenic adsorption pump (cold trap) was activated to reduce the helium used as the exchange gas, establishing an adiabatic environment inside the system. Under adiabatic conditions, the magnetic field was slowly reduced to zero at a constant rate (50 O e / s). During demagnetization, the temperature of the gadolinium gallium garnet refrigerant in the external refrigeration unit dropped to 280 mK, and the ytterbium phosphate refrigerant in the internal refrigeration unit could be reduced to a minimum of 16.5 mK, remaining stably maintained in the extremely low temperature range below 30 mK for more than 5 hours.

[0098] In comparison, the magnetic refrigeration device with one refrigeration unit described in Comparative Example 1 was tested under exactly the same initial conditions and operating procedures. Please refer to... Figure 5 The results showed that the lowest temperature that a single-layer device could reach was only 47.3 mK, and due to heat leakage, the device exhausted its cooling capacity and returned to its initial temperature in just about 1 hour.

[0099] Furthermore, existing literature [Development of adiabatic demagnetizationrefrigerator for the HUBS, Mission Science Bulletin 68 (2023) 2709] reports the measured results of a two-stage conventional series magnetic refrigeration device. The high-temperature layer in this prior art uses gadolinium gallium garnet (Gd3Ga5O4). 12 (GGG), using 40 grams of hydrated paramagnetic salt CrK(SO4)2·12H2O (CPA) in the cryogenic layer. The prior art reports cooling effects based on... Figure 6 The left image.

[0100] This invention utilizes the same multilayer magnetic refrigeration device as in Example 1, and measures were taken using the same refrigerant as the prior art [Development of adiabatic demagnetization refrigerator for the HUBS, missionScienceBulletin 68 (2023) 2709]. Due to the reduced space, the amount of CPA used was 2.8g, which is much lower than reported in the literature.

[0101] Reference Figure 6 The results show that the minimum temperature of the refrigerant in the device of the present invention reaches 20 mK, which is much lower than the 44 mK reported in the literature. This indicates that the magnetic refrigeration device of the present invention has significant advantages over conventional magnetic refrigeration systems in controlling heat leakage of the inner refrigeration unit and improving refrigeration performance. Furthermore, the magnetic refrigeration device of the present invention reaches the minimum temperature in only 20 minutes, while conventional magnetic refrigeration devices require nearly 90 minutes to reach the minimum temperature due to the need to wait for thermal switching, greatly reducing cycle efficiency.

Claims

1. A single-magnet based multi-layer magnetic refrigeration device, comprising: a ring-shaped magnet, the inside of which constitutes a working space; a multi-layer magnetic refrigeration assembly, which is arranged in the working space of the ring-shaped magnet as a whole and is coaxial with the ring-shaped magnet; a thermal switch system, which is configured to switch the heat exchange state and the adiabatic state inside the multi-layer magnetic refrigeration device by controlling the adsorption or release of exchange gas according to temperature; wherein, the multi-layer magnetic refrigeration assembly comprises at least two refrigeration units made of high thermal conductivity material and nested from outside to inside; each refrigeration unit is provided with one or more accommodation cavities for accommodating magnetic refrigeration working medium; wherein the magnetic refrigeration working medium accommodated in different refrigeration units has different working temperature zones, and is arranged in order of gradually decreasing working temperature zone from outside to inside; and all the magnetic refrigeration working medium is configured to perform magnetic heat effect operation synchronously under the time-varying magnetic field generated by the ring-shaped magnet.

2. The single magnet based multilayer magnetic refrigeration apparatus of claim 1, wherein, The refrigeration units are coaxially nested in a size-decreasing manner from outside to inside, and are connected by adiabatic supports and form gaps between adjacent refrigeration units.

3. The single magnet based multilayer magnetic refrigeration apparatus of claim 1, wherein, The refrigeration unit comprises an outer shell and an inner shell coaxially arranged in the inner shell; the outer surface of the inner shell and the inner surface of the outer shell jointly define a three-dimensional surrounding cavity in the radial direction, top and bottom, which constitutes the accommodation cavity of the refrigeration unit.

4. The single magnet based multilayer magnetic refrigeration apparatus of claim 3, wherein, The outer shell and the inner shell are both cylindrical structures with sealed ends.

5. The single magnet based multilayer magnetic refrigeration apparatus of claim 3, wherein, The bottom of the outer shell is provided with a ventilation hole communicating with the three-dimensional surrounding cavity.

6. The single magnet based multilayer magnetic refrigeration apparatus of claim 1, wherein, The refrigeration unit comprises a main shell, the inside of which is separated into two independent cavities in the axial direction by two radially arranged partitions, i.e. an upper cavity and a lower cavity, which constitute the accommodation cavities of the refrigeration unit.

7. The single magnet based multilayer magnetic refrigeration apparatus of claim 6, wherein, The upper cavity is enclosed by the top wall, side wall and upper partition of the main shell; and the lower cavity is enclosed by the bottom wall, side wall and lower partition of the main shell.

8. The single magnet based multilayer magnetic refrigeration apparatus of claim 6, wherein, The bottom of the main shell is provided with a ventilation hole communicating with the lower cavity.

9. The single magnet based multilayer magnetic refrigeration apparatus of claim 1, wherein, The outer surface and the inner surface of the refrigeration unit are coated with a high-reflectivity metal film. 10.A working method of the single-magnet based multi-layer magnetic refrigeration device according to any one of claims 1-9, comprising the following steps: (1) precooling and magnetization step: precooling the multi-layer magnetic refrigeration device; during or after precooling, exciting the ring-shaped magnet to magnetize all the magnetic refrigeration working medium and stabilize the system at an initial temperature; during this process, controlling the thermal switch system to be in a high-temperature state of not adsorbing gas, so that the exchange gas flows in the gaps between all the refrigeration units and in each accommodation cavity, realizing uniform heat exchange; (2) adiabatic step: controlling the thermal switch system to switch to its adsorption working state to adsorb the exchange gas inside the adsorption device, thereby establishing a high-vacuum adiabatic environment inside the device; (3) refrigeration step: In the adiabatic environment, the annular magnet is demagnetized, all magnetic refrigeration working substances are simultaneously adiabatically demagnetized, and the temperature thereof is reduced, and the innermost working substance reaches the target refrigeration temperature; (4) resetting step: The heat switch system is controlled to switch back to the high-temperature state of not adsorbing gas, release the adsorbed gas, and restore the heat exchange state in the device; meanwhile, the annular magnet is re-excited, the magnetic refrigeration working substance is magnetized and heated, and the system returns to the initial temperature.

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