Bed for AMR refrigerator and magnetic refrigerator using same

Abstract

[Problem] To provide a bed for an active magnetic regenerator (AMR) refrigerator and an AMR refrigerator having fewer stages of magnetocaloric members and also having excellent cooling capacity. [Solution] In the present invention, a heat storage body 3 is arranged in the center of a plastic tube 2, and a circular hole 3a is formed in the center of the heat storage body 3. Magnetocaloric members 4a, 4b that are porous and allow permeation of a fluid are loaded on both sides of the heat storage body 3 which serves as the boundary therebetween. A magnetic transition temperature T1 of the magnetocaloric member 4a and a magnetic transition temperature T2 of the magnetocaloric member 4b satisfy T1>T2.

Description

AMR type refrigerator bed and magnetic refrigerator using same

[0001] The present invention relates to a bed for an AMR refrigerator and a magnetic refrigerator using the same.

[0002] In recent years, magnetic refrigerators have been attracting attention as a new type of refrigerator that does not require a gas liquefaction device. Magnetic refrigerators use a magnetocaloric substance as a refrigerant, which undergoes a reversible temperature change when a magnetic field is applied or removed, and perform cooling via the magnetocaloric effect. Magnetic refrigerators do not use gas refrigerants such as chlorofluorocarbons, which has the advantage of having less adverse effects on the environment.

[0003] In the field of magnetic refrigerators, Active Magnetic Regenerator (AMR) refrigerators have also been developed (see, for example, Patent Documents 1 and 2). AMR refrigerators utilize magnetocaloric materials that not only exhibit magnetic refrigeration but also cold storage functions, thereby enabling large temperature differences. In other words, AMR refrigerators actively utilize lattice entropy, which has traditionally been considered an obstacle to achieving large temperature changes through the magnetocaloric effect. In an AMR refrigerator, multiple magnetocaloric components made of magnetocaloric materials are arranged in series, with the magnetic transition temperatures of the components arranged in ascending order from one end to the other. This structural unit is called a "bed." Applying and removing a magnetic field to this bed activates the magnetocaloric effect, transferring heat from the low-temperature side to the high-temperature side.

[0004] U.S. Patent No. 4,332,135 JP 2023-9607 A

[0005] However, in the conventional AMR refrigerators described above, if the difference in magnetic transition temperatures between adjacent magnetocaloric components becomes too large, the magnetocaloric effect of either component will no longer be significant in the intermediate temperature range, resulting in incomplete heat transfer from the low-temperature material to the high-temperature material, and insufficient heat dissipation from the magnetocaloric components. For this reason, assuming a typical refrigerator operating with a temperature difference between the interior temperature (0°C to 5°C) and the heat sink temperature of 40°C, the difference in magnetic transition temperatures between adjacent magnetocaloric components must be approximately 2°C, resulting in the problem of requiring as many as 20 layers of magnetocaloric components. This necessitates the preparation of many different magnetocaloric materials, each with slightly different magnetic transition temperatures, resulting in complex arrangement of magnetocaloric components within the refrigerator and cumbersome and time-consuming preparation of the magnetocaloric materials.

[0006] The present invention has been made in consideration of the above-mentioned conventional situation, and aims to provide an AMR-type refrigerator bed and an AMR-type refrigerator that have a small number of stages of magnetocaloric components and excellent cooling capacity.

[0007] The inventors of the present invention have dared to question the conventional technical common sense that "nothing should be inserted between adjacent magnetocaloric components" in AMR refrigerators. As a result of extensive research, they have discovered the surprising effect that the above-mentioned problem can be solved by inserting a heat storage material between adjacent magnetocaloric components, and have completed the present invention.

[0008] In other words, the bed for an AMR refrigerator of the present invention has a plurality of magnetocaloric elements made of magnetocaloric material arranged in succession, the magnetic transition temperatures of the magnetocaloric elements being arranged in order of increasing temperature from one end to the other, and a heat storage body being inserted between adjacent magnetocaloric elements.

[0009] In the AMR refrigerator bed of the present invention, by inserting a heat storage material between adjacent magnetocaloric components, thermal cascade operation is established even if the difference in transition temperature between adjacent magnetocaloric components is large. Therefore, a large temperature difference can be achieved even with a small number of stages of magnetocaloric components.

[0010] While ceramics and metals can be used as heat storage materials, ceramics are particularly preferred. Ceramics have a high specific heat capacity, allowing for a large amount of sensible heat storage. Furthermore, their low thermal conductivity prevents heat transferred from the low-temperature side to the high-temperature side during the refrigeration cycle from flowing back through the heat storage material itself. Furthermore, ceramics are often low-density, and lower densities tend to result in lower thermal conductivity. Furthermore, near room temperature, specific heat is proportional to the number of molecules of the constituent elements according to the Duron-Petit law. In ceramics, due to the balance between the molecular weight determined by the atomic number of the constituent elements and the change in molecular bonding strength, many light molecules aggregate in the same volume. This means that low-density ceramics have a high specific heat capacity. This is because lower density ceramics have a higher number of molecules per unit weight. Therefore, low-density ceramics tend to exhibit both low thermal conductivity and high specific heat capacity. In this specification, ceramic refers to solid materials consisting of non-metallic elements (e.g., silicon and diamond), and inorganic compound materials that are a combination of metallic and non-metallic elements (e.g., metal oxides, metal carbides, metal nitrides, metal borides, etc.).

[0011] The specific heat of the heat storage body in the operating temperature range is preferably 350 J / kgK or more. This is because a specific heat of 350 J / kgK or more makes it possible to store enough heat to be transferred in the refrigeration cycle formed by the adjacent magnetocaloric materials. A specific heat of 500 J / kgK or more is more preferable, and 700 J / kgK or more is most preferable. Note that metals with a small atomic number have a high specific heat, but lack chemical stability in fluids. For this reason, a specific heat of 1000 J / kgK or less is preferable.

[0012] The thermal diffusivity of the heat storage material is 0.3 cm 2 It is preferable that the thermal diffusivity is 0.3 cm / s or less. 2 / s or less is sufficient to prevent backflow of heat. 2 / s or less, and most preferably 0.06 cm 2 / s or less. However, heat storage materials with low thermal diffusivity tend to have low chemical stability in the fluid, so the thermal diffusivity is 0.01 cm 2 It is preferable to set the value to / s or more.

[0013] The thermal conductivity of the heat storage body is preferably 100 W / Km or less. This is to prevent the heat transferred from the low-temperature side to the high-temperature side by the refrigeration cycle from flowing back through the heat storage body itself. 20 W / Km or less is more preferable, and 5 W / Km or less is most preferable. However, since heat storage bodies with low thermal conductivity tend to have reduced chemical stability and mechanical strength in fluids, a thermal conductivity of 2 W / Km or more is preferable.

[0014] Furthermore, the density of the heat storage body is preferably 8.5 g / cc or less. This is because a heat storage body with a density of 8.5 g / cc or less can achieve both a decrease in thermal conductivity and an increase in specific heat, and is expected to store heat while preventing heat backflow. A density of 6.5 g / cc or less is more preferable, and 5 g / cc or less is most preferable. However, because heat storage bodies with low density tend to have lower mechanical strength, a density of 1 g / cc or more is preferable.

[0015] The magnetic refrigerator of the present invention includes the AMR refrigerator bed of the present invention and a magnetic field changing means for repeatedly applying and removing a magnetic field to the AMR refrigerator bed. In the magnetic refrigerator of the present invention, the magnetic field changing means repeatedly applies and removes a magnetic field to the AMR refrigerator bed, thereby enabling cooling by the magnetocaloric effect.

[0016] FIG. 1 is a schematic cross-sectional view of an AMR refrigerator bed of embodiment 1. FIG. 2 is a schematic cross-sectional view of a magnetic refrigerator using the AMR refrigerator bed of embodiment 1. FIG. 3 is a process diagram when driving the AMR refrigerator of embodiment 1. FIG. 4 is a schematic cross-sectional view of each process when driving the AMR refrigerator of embodiment 1. FIG. 5 is a schematic diagram showing the refrigeration cycle of a GM refrigerator. FIG. 6 is a schematic cross-sectional view of an AMR refrigerator bed of embodiment 2. FIG. 7 is a schematic cross-sectional view of an AMR refrigerator bed of Example 1. FIG. 8 is a schematic view of an evaluation device for an AMR refrigerator bed.

[0017] <Embodiments> Hereinafter, embodiments of an AMR refrigerator bed and a magnetic refrigerator using the same of the present invention will be described.

[0018] (Embodiment 1) - Bed for AMR-type Refrigerator Fig. 1 shows a cross-sectional view of a bed 1 for an AMR-type refrigerator according to embodiment 1. In this bed 1 for an AMR-type refrigerator, a heat storage body 3 is disposed in the center of a plastic tube 2. The heat storage body 3 is disk-shaped with a circular hole 3a in the center. Magnetocaloric members 4a, 4b are loaded on both sides of the heat storage body 3. The magnetocaloric members 4a, 4b are made of powder of a magnetocaloric material and are permeable to fluids.

[0019] The magnetic transition temperature T of the magnetocaloric member 4a １ and the magnetic transition temperature T of the magnetocaloric member 4b ２ is T １ >T ２ Magnetocaloric materials include Gd5(Ge,Si)4, Mn(As,Sb), and MnFe(P,As) magnetocaloric materials, which undergo large entropy changes due to the simultaneous occurrence of magnetic and structural phase transitions, and La(Fe,Si) which exhibits an itinerant electron metamagnetic transition originating from spin fluctuations. 13 The magnetic transition temperature can be selected depending on the temperature at which the AMR refrigerator is used.

[0020] The heat storage body 3 can be made of ceramics such as alumina, zirconia, and ferrite, or metals such as stainless steel. When using a metal, a material with a high specific heat is preferable. This is because the specific heat of the heat storage body 3 in its operating temperature range can store enough heat to be transferred in the refrigeration cycle formed by the adjacent magnetocaloric material. Specifically, a specific heat of 350 J / kgK or more is preferable, 500 J / kgK or more is even more preferable, and 700 J / kgK or more is the most preferable. Metals with a low atomic number tend to have a high specific heat, but their chemical stability in the fluid tends to be reduced. For this reason, a specific heat of 1000 J / kgK or less is preferable.

[0021] The thermal diffusivity of the heat storage material is 0.3 cm2 It is preferable that the thermal diffusivity is 0.3 cm / s or less. 2 This is because a heat backflow can be sufficiently prevented if the flow rate is less than 0.1 cm / s. 2 / s or less, and most preferably 0.06 cm 2 / s or less. In titanium alloys containing large amounts of vanadium or aluminum, the thermal diffusivity is 0.01 cm 2 It is possible to adjust the thermal diffusivity to less than 0.01 cm / s, but this reduces the chemical stability. 2 / s or more is preferable

[0022] Furthermore, the thermal conductivity of the heat storage body is preferably 100 W / Km or less. This is to prevent the heat transferred from the low-temperature side to the high-temperature side by the refrigeration cycle from flowing back through the heat storage body itself. 20 W / Km or less is more preferable, and 5 W / Km or less is most preferable. However, since heat storage bodies with low thermal conductivity generally tend to have reduced chemical stability and mechanical strength in fluids, a thermal conductivity of 2 W / Km or more is preferable.

[0023] Furthermore, the density of the heat storage material is preferably 6.5 g / cc or less. This is because a heat storage material with a density of 6.5 g / cc or less can achieve both a decrease in thermal conductivity and an increase in specific heat, which is expected to prevent heat backflow and store heat. A density of 6.5 g / cc or less is even more preferable, and 5 g / cc or less is most preferable. It is possible to select a material with a density of around 1 g / cc by using a ceramic mixture made of oxides of light elements, including SiO2. However, if the density is too low, the mechanical strength decreases, making it difficult to use as a bed, so a density of 1 g / cc or more is preferable.

[0024] Magnetic Refrigerator Figure 2 shows a cross-sectional schematic diagram of a magnetic refrigerator using the AMR refrigerator bed of embodiment 1. This magnetic refrigerator includes covers 5a and 5b fitted to both ends of the AMR refrigerator bed 1. One end of water pipes 6a and 6b is connected to each of the covers 5a and 5b. The other ends of the water pipes 6a and 6b are connected to a reciprocating pump 7. Driven by the reciprocating pump 7, water serving as a heat exchange fluid reciprocates within the AMR refrigerator bed 1. Internal heat exchangers 8a and 8b are provided at both ends of the AMR refrigerator bed 1. The internal heat exchangers 8a and 8b are connected to water pipes 11a and 11b, which circulate water via external pumps 9a and 9b and external heat exchangers 10a and 10b. Neodymium magnets 12a and 12b are provided axially adjacent and facing each other on the outside of the AMR refrigerator bed 1. Furthermore, the neodymium magnets 12a and 12b can be moved to a position away from the AMR refrigerator bed 1 or inserted into a position close to the AMR refrigerator bed 1 by a magnet moving mechanism not shown.

[0025] The AMR refrigerator configured as described above is operated by repeating a cycle consisting of the following four steps (see Figures 3 and 4). 1) Magnetic Field Application Step (S1): The moving mechanism is driven to insert the neodymium magnets 12a, 12b into a position close to the AMR refrigerator bed 1. This magnetizes the magnetocaloric members 4a, 4b, generating heat and raising their temperature. 2) Heat Transfer Step (S2): Next, the reciprocating pump 7 is driven to flow water as a heat exchange fluid from the magnetocaloric member 4b side to the magnetocaloric member 4a side. This causes the water to move leftward in Figure 4, accompanied by heat transfer from the heated magnetocaloric members 4a, 4b to the water at its original temperature. 3) Magnetic Field Removal Step (S3): The reciprocating pump 7 is then stopped, and the moving mechanism is driven to move the neodymium magnets 12a, 12b to a position away from the AMR refrigerator bed 1, thereby removing the magnetic field applied to the magnetocaloric members 4a, 4b. As a result, the temperature of the magnetocaloric members 4a, 4b is lowered by the magnetocaloric effect. 4) Heat transfer step (S4) Then, the reciprocating pump 7 is driven to flow the water heat exchange fluid from the magnetocaloric member 4a side to the magnetocaloric member 4b side, and the water heat exchange fluid cooled by the temperature-lowering magnetocaloric members 4a, 4b moves to the right in FIG.

[0026] Through the above cycle, the left end of the AMR refrigerator bed 1 in Figure 2 becomes the high-temperature side, and the right end becomes the low-temperature side. Because the outside of the external heat exchanger 10a remains at room temperature, when valve 9a is opened, heat from the high-temperature end of the AMR bed is transferred from the internal heat exchanger 8a through the water pipe 11a and then dissipated to the outside by heat radiation from the external heat exchanger. Meanwhile, because the low-temperature end of the AMR external bed is lower than room temperature, when valve 9b is opened, the external heat exchanger 10b is cooled through the internal heat exchanger 8b and the water pipe 11b. Therefore, as long as the external temperature around the external heat exchanger 10b is close to room temperature, the external heat exchanger 10b absorbs heat from the surroundings, cooling the surroundings. In other words, the cold heat generated by the magnetic calorific element 4a in the cycle steps S1 to S4 is received and transferred by the liquid medium, and then passed on to the magnetic calorific element 4b, which has a large heat capacity, and this is then stored in the heat storage body 3 itself, creating a large heat pool and generating a large temperature difference between the high-temperature side and the low-temperature side.

[0027] In the bed for the AMR type refrigerator of embodiment 1, the heat storage body 3 is inserted between the magnetocaloric member 4a and the magnetocaloric member 4b, so that the heat storage body 3 plays the role of the passive operation of the GM (Gifford-McMahon) type refrigerator.

[0028] As shown in Figure 5, a GM-type refrigerator consists of a displacer, cylinder, regenerator, high- and low-pressure valves, and compressor. It repeats the following refrigeration cycles (a) to (d). (a) With the displacer at the bottom of the cylinder, the low-pressure valve is closed and the high-pressure valve is opened. This allows high-pressure gas from the compressor to enter the cylinder, increasing its pressure. (b) The displacer is moved to the top of the cylinder. This sends the high-pressure gas in the room-temperature space of the cylinder to the regenerator, where it is cooled and enters the expansion chamber. At this time, more high-pressure gas flows in through the high-pressure valve. (c) The high-pressure valve is closed and the low-pressure valve is opened. This reduces the pressure in the cylinder, and the high-pressure gas flows to the compressor, expanding and cooling the expansion chamber. (d) The displacer is moved to the bottom of the cylinder. This warms the low-pressure gas in the expansion chamber by the regenerator and moves it to room-temperature space. At this time, the low-pressure gas flows through the low-pressure valve to the compressor. In other words, a GM type refrigerator is a refrigerator that generates cold by applying pressure changes to a refrigerant / heat exchange gas in a compressor, and then passes the gas through a heat storage medium using a pump to exchange heat and store it.

[0029] In the refrigerator of the first embodiment, the heat storage body 3 plays the role of the heat storage body in a GM refrigerator, and the refrigerator is a combination of an AMR refrigerator and a GM refrigerator. Therefore, the magnetic transition temperature T １ and the magnetic transition temperature T of the magnetocaloric member 4b. ２ It is possible to transfer heat even if the temperature difference between the gas and the heat source is large. It is possible to transfer large amounts of heat. However, the temperature change of the heat storage body is a passive form brought about by gas flow, which is different from the role of magnetocaloric materials, which become a heat storage body that actively changes temperature with changes in the magnetic field.

[0030] (Embodiment 2) In an AMR refrigerator bed of embodiment 2, as shown in Fig. 6, three or more magnetocaloric members 21 are arranged in succession, and a heat storage body 22 is inserted between adjacent magnetocaloric members 21. The magnetocaloric members are arranged in descending order of magnetic transition temperature from one end to the other. The AMR refrigerator bed of embodiment 2 can generate a larger temperature difference between both ends compared to the AMR refrigerator bed of embodiment 1, which has two magnetocaloric members.

[0031] Example 1 In Example 1, the following magnetocaloric substances were used as magnetocaloric member A and magnetocaloric member B. Magnetocaloric member A: NaZn13-type rare earth-Fe-based hydrogenated material manufactured by Shin-Etsu Chemical Co., Ltd. (product name: PRT17P, ferromagnetic-paramagnetic transition temperature 17°C, average particle size 0.18 mm) Magnetocaloric member B: NaZn13-type rare earth-Fe-based hydrogenated material manufactured by Shin-Etsu Chemical Co., Ltd. (product name: PRT27, ferromagnetic-paramagnetic transition temperature 27°C, average particle size 0.23 mm) A nylon tube (manufactured by PISCO Co., Ltd.) with an outer diameter of 8 mm, an inner diameter of 6 mm, and a length of 120 mm was prepared, and a nonwoven fabric (approximately 0.2 mm thick) was packed in the center of the tube in the longitudinal direction. The tube was then stood upright, and dried powdered magnetocaloric member A (1 g) was poured in from the top end to be layered on the nonwoven fabric. Next, a nylon tube with an outer diameter of 6 mm, an inner diameter of 4 mm, and a length of approximately 15 mm was prepared. One end of the tube was sealed with a single sheet of nonwoven fabric. The nonwoven fabric side was inserted into the nylon tube on which the magnetocaloric component A was laminated, securing the magnetocaloric component A in place. Next, a doughnut-shaped plate made of alumina (Al2O3) ceramic (a washer-shaped member made by Hirosugi Seisakusho, with an outer diameter of 6 mm, an inner diameter of 3.3 mm, and a weight of 0.3 g) was inserted from the opposite side of the magnetocaloric component A. The magnetocaloric component B was then similarly secured to the doughnut-shaped plate, completing the construction of the AMR-type refrigerator bed of Example 1. Figure 7 shows a schematic cross-sectional view of the AMR-type refrigerator bed of Example 1.

[0032] Example 2 In Example 2, two doughnut-shaped alumina plates used in Example 1 were stacked as the heat storage body. The rest of the structure was the same as in Example 1, and a description thereof will be omitted.

[0033] (Example 3) In Example 3, a donut-shaped plate (TDK EPCOS ferrite ring core, outer diameter 6.3 mm, inner diameter 3.8 mm, weight 1 g) made of MnZn ferrite (Fe2(MnZn)O3) high magnetic permeability ceramic was used as the heat storage material. The following materials were used as magnetocaloric members A and B: Magnetocaloric member A: NaZn13-type rare earth-Fe-based hydride material manufactured by Shin-Etsu Chemical Co., Ltd. (product name: PRT21P, ferromagnetic-paramagnetic transition temperature 21°C); Magnetocaloric member B: NaZn13-type rare earth-Fe-based hydride material manufactured by Shin-Etsu Chemical Co., Ltd. (product name: PRT29, ferromagnetic-paramagnetic transition temperature 29°C). Other aspects were the same as in Example 1, and therefore will not be described again.

[0034] Example 4 In the AMR-type refrigerator bed of Example 4, zirconia (YTZ yttria-stabilized ZrO2, manufactured by Nikkato / Tosoh) was used as the heat storage material. Specifically, four fluororesin microcontainers (41579-6-1 manufactured by RD Support, outer diameter 2.5 mm, inner diameter 2 mm, length 10 mm) filled with 0.06 g of stabilized zirconia (YTZ yttria-stabilized ZrO2, manufactured by Nikkato / Tosoh) were prepared, and these four were bundled together to form the heat storage material, which was inserted axially between magnetocaloric member A and magnetocaloric member B. Other aspects were the same as in Example 1, and a description thereof will be omitted.

[0035] In Example 5, two stacked donut-shaped members (total weight 0.3 g) made of SUS304 (Nafco, stainless steel M3 nut-shaped member) were used as the heat storage body. The rest of the structure was the same as in Example 1, and the description will be omitted.

[0036] Example 6 In Example 6, a doughnut-shaped member made of SUS304 and weighing 1 g (Nafco, stainless steel M3 nut-shaped material) was used as the heat storage body. The rest was the same as in Example 1, and a description thereof will be omitted.

[0037] Example 7 In Example 7, a donut-shaped member (outer diameter: approximately 6 mm, inner diameter: approximately 4.5 mm, weight: 0.3 g) made of a Cu(Be) alloy (NGK CuBe #25 alloy) was used as the heat storage body. The rest of the structure was the same as in Example 1, and a description thereof will be omitted.

[0038] Comparative Example 1 In Comparative Example 1, no heat storage body was used, and magnetocaloric members were arranged on either side of a nonwoven fabric. The rest was the same as in Example 1, and a description thereof will be omitted.

[0039] Table 1 shows a summary of the magnetocaloric member A, the heat storage body, and the magnetocaloric member B in Examples 1 to 7 and Comparative Example 1. Table 2 also shows the types of heat storage bodies and their various physical properties in Examples 1 to 7 and Comparative Example 1.

[0040]

[0041] (Evaluation) An evaluation device was fabricated for the AMR-type refrigerator beds of Examples 1 to 7 and Comparative Example 1 fabricated as described above, and their characteristics were evaluated. Evaluation Device: As shown in FIG. 8 , T-shaped pipes 31 (T-shaped quick couplings manufactured by PISCO) were connected to both ends of an AMR-type refrigerator bed 30, and a thermocouple 32 was inserted into one end of the T-shaped pipe 31. The thermocouple 32 was inserted through one end of the T-shaped pipe 31 and positioned so that its tip was approximately 1 to 2 mm from the magnetocaloric members A and B. One end of a water supply tube 33 was connected to the remaining connection port of the T-shaped pipe 31, and the other end of the water supply tube 33 was connected to a displacer 34 (Koganei reciprocating rodless cylinder MRCH25) for generating a reciprocating water flow. The AMR-type refrigerator bed 30 was attached to the tip drive unit of a slider (Wittenstein Turnery TCC 102-046-020) (not shown). The slider is an actuator type slider with a built-in electric motor, and drives a member gripping the AMR refrigerator bed 30 in proportion to the analog input voltage. The AMR refrigerator bed 30 was adjusted so that the lower end of the slider's range of motion was located at the center of the magnetic field of the magnetic circuit 35 (manufactured by Hitachi Metals NEOMAX Ltd.: NdFeB magnet used, gap 20 mm, magnetic field center magnetic flux 0.8 T), and the upper end of the slider's range of motion was located at a position where the magnetic flux was nearly zero.

[0042] In this characteristic evaluation device, a magnetic field equivalent to a maximum magnetic flux density of 0.8 T was simultaneously applied to magnetocaloric components A and B in the AMR refrigerator bed 30, generating heat through adiabatic temperature change. Then, as magnetocaloric components A and B moved away from the magnetic circuit 35, the magnetic field was rapidly removed, causing them to cool through adiabatic temperature change. The time required for magnetic field application and removal was determined by changes in the analog input voltage, which determines the slider movement speed. Specifically, a 1 Hz square wave was input to the slider using a signal generator (NF Corporation WF1974). Magneto-caloric components A and B were controlled so that they moved approximately 60 mm from their closest position to their furthest position from the magnetic circuit 35 within 0.15 s, stopped at a predetermined position in the square wave system, and no magnetic field change occurred. This series of operations constituted one thermal cycle.

[0043] Meanwhile, the space from the inside of the displacer 34 to the inside of the AMR refrigerator bed 30 was filled with water before the heat cycle was started, and the water flow direction was switched depending on the direction of movement of the gate valve 34a of the displacer 34. That is, the gate valve 34a was moved in a predetermined direction to allow water to flow from magnetocaloric member B to magnetocaloric member A, and then the gate valve 34a was moved in the opposite direction to allow water to flow from magnetocaloric member A to magnetocaloric member B. In this state, the outer end of the gate valve 34a was connected to a separately prepared electric slider (TCC 102-046-020), and this slider was connected to another signal output terminal of the signal transmitter (WF1974 manufactured by NF Circuit Design Block Co., Ltd.). By doing so, the reciprocating movement of the water flow and the magnetic field application / removal operation of the bed were set to be synchronized within the output adjustment range of the signal transmitter. A 1 Hz triangular wave was input from the signal transmitter to the slider connected to the displacer 34, and the input voltage was adjusted so that a volume of water equivalent to approximately 0.6 cc was moved in each of the forward and return paths.

[0044] The AMR refrigerator bed 30 attached to the slider was placed in a thermostatic chamber (Espec Corporation LU-114), and the specified temperature was maintained until the temperatures measured by the two thermocouples both stabilized at 24°C ± 0.5°C. After the temperatures measured by the two thermocouples both reached 24°C ± 0.5°C, an analog voltage signal was applied from the signal transmitter to the slider, and the thermal cycle operation was repeated.

[0045] <Evaluation Results> The results for Examples 1 to 7 and Comparative Example 1 are summarized in Table 3. Here, T1-T2 (°C) represents the difference in magnetic transition temperature between magnetocaloric members A and B, and ΔT span (°C) indicates the maximum temperature difference between both ends of the bed that allows stable operation.

[0046] (Example 1) In the AMR refrigerator bed of Example 1, the temperature difference between both ends of the bed could be stably maintained up to a maximum of approximately 10°C. This shows that by inserting an alumina heat storage material between magnetocaloric member A and magnetocaloric member B, magnetocaloric member A and magnetocaloric member B work together to establish a thermal cascade operation and function as a heat pump.

[0047] (Example 2) In the AMR refrigerator bed of Example 2, by doubling the amount of alumina heat storage material compared to Example 1, it was found that the stable temperature difference between both ends of the bed expanded to 13°C. The difference in magnetic transition temperature between magnetocaloric member A and magnetocaloric member B was 10°C, and the temperature difference between both ends of the bed exceeded this, reaching 13°C, which was a unique effect not known in conventional AMR refrigerators. From these results, it was found that magnetocaloric member A and magnetocaloric member B worked together to establish a thermal cascade operation and function as a heat pump.

[0048] (Example 3) In the AMR refrigerator bed of Example 3, the temperature difference between both ends of the bed could be stably maintained up to a maximum of approximately 8°C. This shows that even when the material of the heat storage body is MnZn ferrite, the magnetocaloric member A and the magnetocaloric member B work together to establish a thermal cascade operation, and the bed functions as a heat pump.

[0049] (Example 4) In the AMR-type refrigerator bed of Example 4, the temperature difference between both ends of the bed could be stably maintained up to a maximum of approximately 8°C. This shows that even when the material of the heat storage body is stabilized zirconia, the magnetocaloric member A and the magnetocaloric member B work together to establish a thermal cascade operation, and the bed functions as a heat pump.

[0050] (Examples 5 and 6) In the AMR-type refrigerator beds of Examples 5 and 6, the temperature difference between both ends of the bed could be stably maintained up to a maximum of approximately 5°C. This shows that even if the material of the heat storage body is SUS304, the magnetocaloric member A and the magnetocaloric member B work together to establish a thermal cascade operation and function as a heat pump.

[0051] (Example 7) In the AMR refrigerator bed of Example 7, the maximum temperature difference between both ends of the bed that could be stably operated was about 5°C. This shows that even if the material of the heat storage body is Cu(Be), the magnetocaloric member A and the magnetocaloric member B work together to establish a thermal cascade operation and function as a heat pump.

[0052] (Comparative Example 1) In the AMR-type refrigerator bed of Comparative Example 1, the temperature difference between the low-temperature end of magnetocaloric component A (i.e., PRT17P) and the high-temperature end of magnetocaloric component B (i.e., high-temperature PRT27) reached about 7°C for about 2 minutes immediately after the start of the test, but it was always unstable and not sustained, making it difficult to perform thermal cascade operation.

[0053] <Discussion on Evaluation Results> From the evaluation results of the Examples and Comparative Examples, it was found that by inserting a heat storage material between magnetocaloric member A and magnetocaloric member B, even if there is a large difference in the magnetic transition temperatures of magnetocaloric member A and magnetocaloric member B, a thermal cascade operation is established in cooperation with magnetocaloric member A and magnetocaloric member B, and they function as a heat pump. In addition, the following were found to be preferable conditions for increasing the temperature difference between both ends of the AMR refrigerator bed and stabilizing that temperature difference throughout the test: 1) The specific heat of the heat storage material must be large. For this reason, ceramics are more preferable than metals. A specific heat of 350 J / kgK or more is particularly preferable, 500 J / kgK or more is even more preferable, and 700 J / kgK or more is most preferable. 2) The thermal diffusivity of the heat storage material is 0.3 cm 2 / s or less, and more preferably 0.1 cm 2 / s or less, and most preferably 0.06 cm 2 / s or less. 3) The density of the heat storage material is preferably 8.5 g / cc or less. 6.5 g / cc or less is particularly preferable, and 5 g / cc or less is most preferable. 4) When stainless steel, which has a particularly low thermal diffusivity among metals, is used as the heat storage material, better thermal cascade operation is achieved than with other metals.

[0054] The present invention is not limited to the above-described embodiments and examples, and various modifications within the scope of the claims and within the scope that can be easily conceived by a person skilled in the art are also included in the present invention.

[0055] The AMR refrigerator bed of the present invention can be suitably used in magnetic refrigerators, which are a new type of refrigerator. In addition, since it does not use a gas liquefaction device, it has the advantage of having little impact on the environment.

[0056] 30... AMR type refrigerator bed, 2... plastic tube, 3, 22... heat storage body, 4a, 4b, 21... magnetocaloric member, 5a, 5b... lid, 6a, 6b... water pipe, 7... reciprocating pump, 8a, 8b... internal heat exchanger, 9a, 9b... pump, 10a, 10b... external heat exchanger, 11a, 11b... water pipe, 12a, 12b... neodymium magnet, 34... displacer, 35... magnetic circuit

Claims

1. A bed for an AMR-type refrigerator in which a plurality of magnetocaloric components made of magnetocaloric material are arranged in series, the magnetic transition temperatures of the magnetocaloric components are arranged in order of increasing temperature from one end to the other, and a heat storage medium is inserted between adjacent magnetocaloric components.

2. A bed for an AMR type refrigerator according to claim 1, wherein the heat storage body is made of ceramic.

3. A bed for an AMR type refrigerator according to claim 1 or 2, wherein the specific heat of the heat storage body in the operating temperature range is 350 J / kgK or more.

4. The thermal diffusivity of the heat storage material is 0.3 cm 2 3. The bed for an AMR type refrigerator according to claim 1 or 2, wherein the cooling capacity is set to be equal to or less than 1 / s.

5. A bed for an AMR type refrigerator according to claim 1 or 2, wherein the thermal conductivity of the heat storage body is 100 W / Km or less.

6. A bed for an AMR type refrigerator according to claim 1 or 2, wherein the density of the heat storage body is 8.5 g / cc or less.

7. A magnetic refrigerator comprising the AMR refrigerator bed according to claim 1 or 2, and a magnetic field changing means for repeatedly applying and removing a magnetic field to the AMR refrigerator bed.

Images