EP0947785B1 - Materiau accumulateur de froid et refrigerateur a accumulation de froid - Google Patents

Materiau accumulateur de froid et refrigerateur a accumulation de froid Download PDF

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Publication number
EP0947785B1
EP0947785B1 EP98947963A EP98947963A EP0947785B1 EP 0947785 B1 EP0947785 B1 EP 0947785B1 EP 98947963 A EP98947963 A EP 98947963A EP 98947963 A EP98947963 A EP 98947963A EP 0947785 B1 EP0947785 B1 EP 0947785B1
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EP
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Prior art keywords
cold accumulating
cold
refrigerator
accumulating material
magnetic
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German (de)
English (en)
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EP0947785A1 (fr
EP0947785A4 (fr
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Masami Okamura
Tomohisa Arai
Keisuke Hashimoto
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Toshiba Corp
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Toshiba Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/012—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials adapted for magnetic entropy change by magnetocaloric effect, e.g. used as magnetic refrigerating material
    • H01F1/015—Metals or alloys
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
    • F25B9/14—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the cycle used, e.g. Stirling cycle
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/0009—Antiferromagnetic materials, i.e. materials exhibiting a Néel transition temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2309/00—Gas cycle refrigeration machines
    • F25B2309/003—Gas cycle refrigeration machines characterised by construction or composition of the regenerator

Definitions

  • the present invention relates to a cold accumulating material and a cold accumulating type refrigerator using the same, and more particularly to a cold accumulating material which exhibits significant refrigerating performance at an extremely low temperature region of 10K or less, and a cold accumulation refrigerator using the cold accumulating material.
  • a refrigerator based on such refrigerating cycle as Gifford MacMahon type (GM refrigerator), Starling method has been used.
  • GM refrigerator Gifford MacMahon type
  • Starling method has been used.
  • a magnetic floating train absolutely needs a high performance refrigerator.
  • a superconductive power storage apparatus (SMES) or a in-magnetic field single crystal pull-up apparatus has been provided with a high performance refrigerator as a main component thereof.
  • the operating medium such as compressed He gas flows in a single direction in a cold accumulating unit filled with cold accumulating materials so that the heat energy thereof is supplied to the cold accumulating material. Then, the operating medium expanded here flows in an opposite direction and receives heat energy from the cold accumulating material. As the recuperation effect is improved in this process, the heat efficiency in the operating medium cycle is improved so that a further lower temperature is realized.
  • a temperature gradient is formed such that a temperature of a high-temperature side end portion into which the operating medium flows is about 30K while a temperature of a low-temperature side (downstream side) end portion is about 4K.
  • cold accumulating material of which volumetric specific heat is large at entire region of the broad temperature range there exists no cold accumulating material of which volumetric specific heat is large at entire region of the broad temperature range. Therefore, in actual, various cold accumulating materials each having a suitable specific heat for the respective temperature regions corresponding to the temperature distribution in the cold accumulating unit are filled in the unit. Namely, a lower temperature side of the cold accumulating unit is filled with cold accumulating materials such as, for example, HoCu 2 having a large volumetric specific heat at a broad temperature range of low temperature side, while a higher temperature side of the cold accumulating unit is filled with cold accumulating materials such as, for example, Er 3 Ni having a large volumetric specific heat at a broad temperature range of high temperature side.
  • cold accumulating materials such as, for example, HoCu 2 having a large volumetric specific heat at a broad temperature range of low temperature side
  • cold accumulating materials such as, for example, Er 3 Ni having a large volumetric specific heat at a broad temperature range of high
  • a main factor having a great influence on a capacity (performance) of a cold accumulating type refrigerator operated at an extremely low temperature of about 4K is a kind of cold accumulating material to be filled in the lower temperature side of the cold accumulating unit.
  • the cold accumulating materials having various compositions such as ErNi 2 , ErNi 0.9 Co 0.1 , ErNi 0.8 Co 0.2 , ErRh and HoCu 2 are investigated and tried to be applied to the actual refrigerator.
  • HoCu 2 results in a particularly high refrigerating performance at a temperature of 4K.
  • the volumetric specific heat of HoCu 2 is still insufficient, so that a remarkable improvement in the refrigerating performance cannot be attained.
  • the cold accumulating materials composed of ErRh is antiferromagnetic substance, so that the cold accumulating material has an advantage of being hardly affected by the leakage magnetic field.
  • rhodium (Rh) as a constituent is extremely expensive, so that there may be posed a problem that it is extremely difficult to industrially utilize rhodium as a cold accumulating material for a refrigerator in which rhodium is used at an amount of several hundreds grams order.
  • the present invention has been achieved to solve the above described problems and an object of the invention is to provide a cold accumulating material capable of exhibiting a significant refrigerating performance at an extremely low temperature for a long period of time in a stable condition, and a cold accumulation refrigerator using the same.
  • another object of the present invention is to provide an MRI apparatus, a superconducting magnet for magnetic floating train, a cryopump and an in-magnetic field single crystal pull-up apparatus capable of exerting an excellent performance for a long period of time by using the aforementioned cold accumulation refrigerator.
  • the inventors of this invention had prepared a lot of cold accumulating materials having various compositions and specific heat characteristics, and filled the cold accumulating material into cold accumulating unit of a refrigerator. Then influences of the compositions and specific heat characteristics of the materials on a refrigerating performance of the refrigerator, life and durability of the material are comparatively investigated through experiments.
  • the cold accumulating material having a high specific heat at temperature of 4K and a low specific heat at temperature of 10K when the above cold accumulating material was filled in only the low temperature side of the cold accumulating unit by taking the temperature distribution in the cold accumulating unit into consideration, the high specific heat characteristic of the cold accumulating material at temperature of 4K was effectively utilized, so that performance (capacity) of the refrigerator was remarkably improved.
  • the cold accumulating material according to the present invention comprises magnetic substance expressed by the following general formula: RCu 1 - x M 1 + x wherein R denotes at least one of rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Er, Tm, Ho and Yb, M denotes at least one element selected from the group consisting of Ag, Au, Al, Ga, In, Ge, Sn, Sb, Si, Bi, Ni, Pd, Pt, Zn, Co, Rh, Ir, Mn, Fe, Ru, Cr, Mo, W, V, Nb, Ta, Ti, Zr and Hf, and wherein Ni and Ge are not simultaneously selected, and x in atomic ratio satisfies a relation: -0.95 ⁇ x ⁇ 0.90.
  • the cold accumulating material comprises magnetic substance expressed by the following general formula: Ho 1 - x R x (Cu 1 - y M y ) 2 wherein R denotes at least one of rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Er, Tm and Yb, M denotes at least one element selected from the group consisting of Ag, Au, Al, Ga, In, Ge, Sn, Sb, Si, Bi, Ni, Pd, Pt, Zn, Co, Rh, Ir, Mn, Fe, Ru, Cr, Mo, W, V, Nb, Ta, Ti, Zr and Hf, and wherein x and y in atomic ratio satisfy the following relations: 0 ⁇ x ⁇ 0.5, 0 ⁇ y ⁇ 0.5, x + y ⁇ o.
  • the magnetic substance expressed by the general formula of (1) or (2) has a crystal structure composed of hexagonal crystal or orthorhombic crystal at a ratio of 50 vol% or more.
  • the magnetic substance is antiferromagnetic body.
  • the cold accumulation refrigerator comprises a plurality of cooling stages each composed of a cold accumulating unit filled with a cold accumulating material through which an operating medium flows from a high temperature-upstream side of the cold accumulating unit of each cooling stage, so that heat is exchanged between the operating medium and the cold accumulating material thereby to obtain a lower temperature at a downstream side of the cold accumulating unit, wherein at least part of the cold accumulating material to be filled in the cold accumulating unit is composed of the cold accumulating material expressed by the general formula of (1) or (2).
  • this cold accumulating material is preferably filled in a low-temperature-downstream side (final cooling stage) of the cold accumulating unit.
  • each of the MRI (magnetic resonance imaging) apparatus, superconducting magnet for magnetic floating train, cryopump and in-magnetic field single crystal pull-up apparatus according to the present invention is characterized by comprising the cold accumulation refrigerator described above.
  • the cold accumulating material of this invention comprises magnetic substance prepared by properly controlling the amounts of Cu component and M component with respect to R component, or by substituting a part of Ho component of magnetic substance having a basic composition of HoCu 2 by R component, or by substituting a part of Cu component by M component.
  • R component is at least one of rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Er, Ho (excluded in general formula (2)), Tm and Yb, while M component is at least one element selected from the group consisting of Ag, Au, Al, Ga, In, Ge, Sn, Sb, Si, Bi, Ni, Pd, Pt, Zn, Co, Rh, Ir, Mn, Fe, Ru, Cr, Mo, W, V, Nb, Ta, Ti, Zr and Hf.
  • R components and M components are added for the purpose of shifting a temperature position of the volumetric specific heat peak of the magnetic substance toward lower temperature side and for broadening a mesial magnitude width of the peak so as to realize a specific heat which is effective as the cold accumulating material.
  • an adjusting amount x in atomic ratio of Cu component and M component with respect to R component is set to a range of -0.95 to 0.90.
  • the adjusting amount x is less than -0.95, RCu 1 - x M 1 + x substantially come close to a binary system of RCu 2 . or when the adjusting amount x exceeds 0.90, RCu 1 - x M 1 + x substantially come close to a binary system of RM 2 so that the mesial magnitude width of the specific heat peak of the magnetic substance will be narrowed. Therefore, the magnetic substance cannot maintain a high specific heat in a broad temperature range, and it becomes impossible to control the temperature position of the specific heat peak.
  • each of substituting amounts x, y of R component and M component with respect to Ho and Cu is set to a range of 0 to 0.5 in atomic ratio.
  • the temperature position of the volumetric specific heat peak is greatly shifted, so that aiming volumetric specific heat at temperature range of about 4K is lowered, or the mesial magnitude width of specific heat peak is excessively broadened thereby to lower the height of the peak.
  • the volumetric specific heat of the magnetic substance in extremely low temperature range is insufficient, so that the function as a cold accumulating material is lowered.
  • the temperature position of the volumetric specific heat peak can be shifted to a low temperature side, and the mesial magnitude width of specific heat peak can be effectively broadened. Accordingly, the lower limits of the addition amount (substituting amount) x, y of R component and M component are specified to include zero. However, there is no case where x value and Y value are simultaneously zero to each other. Namely, x and y satisfy a relation: x + y ⁇ 0.
  • At least one of various rare earth elements described hereinbefore can be used as R component.
  • these rare earth elements Ce, Pr, Nd, Er, Dy, Ho (excluded in general formula (2)), Tb and Gd are suitable for improving the specific heat characteristics of the cold accumulating material.
  • Pr, Nd, Er, Dy, Ho (excluded in general formula (2)) are more preferable.
  • M component among the above metal elements, Ag, Al, Ni, Ga, In, Ge, Sn, Si are particularly preferable. Al, Ga, Ge, Sn are more preferable. Further, regarding to M component as the same as R component, when a plurality of elements are selected, the mesial magnitude width of the specific heat peak of the magnetic substance and the temperature position of the specific heat peak can be controlled.
  • the magnetic substance having a crystal structure composed of hexagonal crystal or orthorhombic crystal with a ratio of at least 50 vol.% (50 - 99.99 vol.%) is particularly preferable.
  • the hexagonal crystal or orthorhombic crystal is a crystal structure having a lower symmetric property in comparison with cubic crystal system.
  • the inventors of this invention have confirmed that the symmetric property of the crystal structure has a great influence on the specific heat characteristic of the cold accumulating material through an effect of crystal field.
  • the crystal structure such as cubic crystal system having a high symmetric property which is tend to exhibit a sharp specific heat peak and a narrow mesial magnitude width is preferable as the cold accumulating material.
  • the inventors of this invention had paid attention to a specific heat peak having a broad mesial magnitude width rather than a sharp peak. Namely, the inventors of this invention had paid attention to a point that the magnetic substance mainly composed of hexagonal crystal or orthorhombic crystal having a low symmetry can rather realize a high specific heat in a broad temperature range.
  • the hexagonal crystal has a slightly higher crystal symmetry than the orthorhombic crystal, and exhibits an intermediate crystal symmetry between the cubic crystal system and the orthorhombic crystal, so that the hexagonal crystal has a relatively high peak value of specific heat and a relatively broad mesial magnitude width. That is, the hexagonal crystal is particularly preferable because of its well-balanced specific heat characteristic in a broad temperature range.
  • the magnetic substance expressed by the general formula (1) or (2) as is easily analogized from a phase diagram of a substance containing rare earth element, it is difficult to form a single phase structure, so that the magnetic substance generally comprises a plurality of intermetallic compound phases each having a different composition ratio and impurity phases such as oxide and carbide. Even if the aiming compositions are the same, the structural form (metal structure) varies in accordance with a slight difference in a material blending composition, small amount of impurities such as oxygen and carbon, melting temperature, melting atmosphere and solidifying rate. In particular, a cooling process ranging from a melting point to a solidus line has a sensitive influence on the metal structure, and it is extremely difficult to control the cooling process.
  • rare earth metal or solid solution thereof is contained in the metal structure of the magnetic substance constituting the cold accumulating material of this invention.
  • the rare earth metal or solid solution thereof has a low specific heat characteristic in comparison with the intermetallic compound containing rare earth element, so that it is preferable that the rare earth metal or solid solution thereof is not precipitated in the metal structure.
  • the metal structure in which rare earth metal or solid solution thereof is not precipitated can be realized by controlling the material blending composition at material preparation stage so that R component is slightly reduced from the aiming composition.
  • a ratio of the magnetic substance having a crystal structure composed of hexagonal crystal or orthorhombic crystal is set to 50 vol.% or more.
  • a ratio of the magnetic substance having a crystal structure composed of hexagonal crystal or orthorhombic crystal is set to 70 vol.% or more.
  • the ratio of 80 vol.% or more is furthermore preferable.
  • the form of the metal structure is liable to be complicatedly affected by a slight difference in a material blending composition, small amount of impurities such as oxygen and carbon, melting temperature, melting atmosphere and solidifying rate or the like. Therefore, it is difficult to definitely specify a method for realizing the above metal structure.
  • the phase diagrams become more complicated, so that it is furthermore difficult to realize the desired metal structure.
  • the operating medium such as helium gas smoothly flow in a cold accumulating unit packed with cold accumulating material, and in order to increase a heat exchange efficiency between the operating medium and the cold accumulating material, and to maintain the function of heat exchange in stable condition
  • the cold accumulating material from spherical-shaped-magnetic particles having uniform diameters.
  • a proportion of magnetic particles having a ratio of a major diameter to a minor diameter (aspect ratio) of not greater than 5 and having a size of 0.01 to 3 mm to the whole of the magnetic particles is controlled to be 70% or more by weight.
  • the size of the magnetic particles is a factor having a large influence upon the strength of the particles, the cooling functions and the heat transfer characteristics of the refrigerator. If the particle size is smaller than 0.01 mm, the density at which the cold accumulating material is packed in the cold accumulating unit is so high that the resistance to the passage of He gas provided as a refrigerant (operating medium) is abruptly increased and that the cold accumulating material enters the compressor with the flowing He gas and produces wear on the parts thereof to reduce the life of the same.
  • the average particle size is set to a range of 0.01 to 3 mm, more preferably, to a range of 0.05 to 1.0 mm, furthermore preferably, to a range of 0.1 to 0.5 mm.
  • the proportion of particles having this size must be set to at least 70 % by weight. Preferably, it is set to 80 wt.% or greater, more preferably, 90wt.% or greater.
  • the ratio of the major diameter to the minor diameter (aspect ratio) of the magnetic particle in accordance with the present invention is not greater than 5, preferably, not greater than 2 or, more preferably, not greater than 1.3.
  • the setting of the aspect ratio of the magnetic particles greatly influences the strength of the particles and the density at which the particles are packed in the cold accumulating unit. If the aspect ratio is greater than 5, the particles tends to be deformed and broken by mechanical actions and cannot be packed at a high density and with an uniform void. When a proportion of such particles to the whole particles exceeds 30 wt%, there may be a fear of reducing the cold accumulating efficiency.
  • the dispersion of the particle size and the dispersion of the ratio of the major diameter to the minor diameter are remarkably reduced in comparison with those formed by the conventional plasma spray method.
  • the proportion of magnetic particles out of the above range is thereby reduced.
  • the proportion of particles having sizes within the above range to the whole of the magnetic particles packed in the cold accumulating unit is set to 70 % or greater, preferably, 80 % or greater or, more preferably, 90 % or greater to obtain a cold accumulating material having a durability sufficient for practical use.
  • the surface roughness of the magnetic particles is a factor having a large influence upon the mechanical strength, cooling characteristics, the resistance to passage of the refrigerant, the cold accumulating efficiency and so on. This factor is determined by setting the maximum height R max of irregularities in accordance with JIS (Japanese Industrial Standard) B 0601 to 10 ⁇ m or less, preferably, 5 ⁇ m or less or, more preferably, 2 ⁇ m or less. These surface roughness are measured, for example, by a scanning tunnel microscope (STM roughness meter).
  • STM roughness meter scanning tunnel microscope
  • the surface roughness exceeds 10 ⁇ m R max , the possibility of formation of microcracks from which breaking of the particles is started is increased and the resistance to passage of the refrigerant becomes larger to increase the compressor load.
  • the area of contact between the packed magnetic particles is increased and the rate of transfer of cold heat between the magnetic particles is thereby increased, resulting in a reduction in the cold accumulating efficiency.
  • the proportion of magnetic particles to the whole which particles have small defects having a length longer than 10 ⁇ m and which influence the mechanical strength of the magnetic particles is set to 30 % or smaller, preferably, 20 % or smaller or, more preferably, 10 % or smaller.
  • the composition of the molten alloy is controlled to be slightly Cu-rich, or the solidifying rate is appropriately controlled, it is possible to convert the metal structure in the magnetic cold accumulating material particle into an antiferromagnetic body expressed by the general formula (1) or (2) and a multi-phased metal structure.
  • the magnetic cold accumulating material particle having a metal structure in which Cu metal phase is formed has a high mechanical strength. Therefore, even if shocks due to vibrations of the refrigerator are applied to the cold accumulating material during the operation of the refrigerator, or even if an excessively large stress is applied to the cold accumulating material at the time of packing the material into the cold accumulating unit, the cold accumulating material is free from being broken and finely pulverized.
  • the cold accumulation refrigerator of the present invention is constructed so as to comprise a plurality of cooling stages and magnetic cold accumulating material particles filled in at least part of a cold accumulating unit disposed at a final cooling stage of the refrigerator.
  • the cold accumulating material of this invention is filled in a low-temperature end side of a cold accumulating unit disposed at second stage.
  • the cold accumulating material of this invention is filled in a low-temperature end side of a cold accumulating unit disposed at third stage.
  • other filling spaces are filled with other cold accumulating material having a specific heat characteristic corresponding to the temperature distribution of the cold accumulating unit.
  • the volumetric specific heat in temperature range other than a temperature at which the volumetric specific heat has its peak, particularly the volumetric specific heat in temperature range of high temperature side becomes relatively small.
  • This small volumetric specific heat has a bad effect on entire cold accumulating unit.
  • the cold accumulating efficiency is lowered.
  • the filling amount of the magnetic cold accumulating material particles of this invention with respect to whole particles weight to be filled in the cold accumulating unit of the final cooling stage described above is set to 1 - 80 wt%.
  • the filling amount is preferably set to 2 - 70 wt%, more preferably to 3 - 50 wt%.
  • the amounts of Cu and M component are appropriately controlled with respect to R component, or a part of constituent of HoCu 2 magnetic material having a sharp peak of volumetric specific heat at extremely low temperature range is substituted by other rare earth element or transition metal or the like, so that the temperature position of the specific heat peak is shifted to a low temperature side and the mesial magnitude width of the specific heat peak is broadened thereby to obtain a cold accumulating material having a good specific heat characteristic.
  • a refrigerator having a high refrigerating performance at temperature range of about 4K, and capable of maintaining a stable refrigerating performance for a long time.
  • an MRI apparatus a cryopump, a superconducting magnet for magnetic floating train, and a in-magnetic field single crystal pull-up apparatus
  • performance of the refrigerator dominates the performance of each apparatus
  • an MRI apparatus, a cryopump, a superconducting magnet for magnetic floating train, and an in-magnetic field single crystal pull-up apparatus in which the above described refrigerators are assembled therein can exhibit excellent performances for a long term.
  • Each of the prepared magnetic particles was classified according to shape classification so as to obtain particles having an aspect ratio of 1.2 or less, then sieved to select 200g of cold accumulating materials of Examples 1 to 12 each composed of spherical magnetic particles having diameter of 0.2 - 0.3 mm, respectively.
  • Each of the prepared magnetic particles was classified according to shape classification so as to obtain particles having an aspect ratio of 1.2 or less, then sieved to select 200g of cold accumulating materials of Examples 13 to 23 each composed of spherical magnetic particles having diameter of 0.2 - 0.3 mm, respectively.
  • Crystal structures of thus prepared respective cold accumulating materials of Examples 1 - 23 were identified by X-ray diffraction method. Note, an existing ratio of the respective crystal structures was calculated from an integrated intensity of X-ray diffraction peak. The calculated results are shown in Table 1.
  • the two-staged expansion type GM refrigerator 10 shown in FIG. 1 is one embodiment of a refrigerator of this invention.
  • the two-staged expansion type GM refrigerator 10 shown in FIG. 1 has a vacuum container 13 containing a first cylinder 11 having a large diameter and a second cylinder 12 having a small diameter, which is connected coaxially to the first cylinder 11.
  • the first cylinder 11 contains a first cold accumulating unit 14 which is freely reciprocatable and the second cylinder 12 also contains a second cold accumulating unit 15 which is freely reciprocatable.
  • Seal rings 16, 17 are disposed between the first cylinder 11 and first cold accumulating unit 14, and between the second cylinder 12 and second cold accumulating unit 15, respectively.
  • the first cold accumulating unit 14 accommodates a first cold accumulating material 18 made of Cu mesh or the like.
  • the low temperature side of the second cold accumulating unit 15 contains a second cold accumulating material 19 made of a cold accumulating material of this invention for extremely low temperature cold.
  • the first cold accumulating unit 14 and second cold accumulating unit 15 have operating medium (refrigerant) paths for He gas or the like which are provided in gaps of the first cold accumulating material 18 and cold accumulating material 19 for extremely low temperature.
  • a first expansion chamber 20 is provided between the first cold accumulating unit 14 and second cold accumulating unit 15.
  • a second expansion chamber 21 is provided between the second cold accumulating unit 15 and an end wall of the second cylinder 12.
  • a first cooling stage 22 is provided on a bottom of the first expansion chamber 20 and further a second cooling stage 23 which is colder than the first cooling stage 22 is provided on a bottom of the second expansion chamber 21.
  • a high pressure operating medium (e.g., He gas) is supplied from a compressor 24 to the aforementioned two-staged GM refrigerator 10.
  • the supplied operating medium passes through the first cold accumulating material 18 accommodated in the first cold accumulating unit 14 and reaches the first expansion chamber 20, and further passes through the second cold accumulating material (second cold accumulating material) 19 accommodated in the second cold accumulating unit 15 and reaches the second expansion chamber 21.
  • the operating medium supplies heat energy to the respective first cold accumulating materials 18, 19 so that they are cooled.
  • the operating medium passing through the respective cold accumulating materials 18, 19 is expanded in the respective expansion chambers 20, 21 so as to produce cool atmosphere thereby cooling the respective cooling stages 22, 23.
  • the expanded operating medium flows in the respective cold accumulating materials 18, 19 in opposite direction.
  • the operating medium receives heat energy from the respective cold accumulating materials 18, 19 and is discharged.
  • the refrigerator is constructed so that the heat efficiency of the operating medium cycle is improved whereby a further lower temperature is realized.
  • the refrigerating capacity in the respective Examples is defined as a heat load at a time when a heat load supplied from a heater is applied to the second cooling stage during the operation of the refrigerator and a temperature rise in the second cooling stage is stopped at 4.2K.
  • Each of the prepared magnetic particles was classified according to shape classification so as to obtain particles having an aspect ratio of 1.2 or less, then sieved to select 200g of cold accumulating materials of Comparative Examples 1 to 3 each composed of spherical magnetic particles having diameter of 0.2 - 0.3. mm, respectively.
  • Crystal structures of thus prepared respective cold accumulating materials of Comparative Examples were identified by X-ray diffraction method, and an existing ratio of the respective crystal structures was calculated from an X-ray diffraction peak. The calculated results are shown in Table 1. In this regard, it was confirmed that 42 vol.% of crystal structure of the cold accumulating material formed of ErNi 2 according to Comparative Example 2 was composed of orthorhombic crystal, and remaining 58 vol.% of the crystal structure was composed of cubic crystal.
  • a mother alloy having the same composition (HoCuAl) as in Example 1 was prepared by high frequency melting method.
  • mother alloy was pulverized by means of a hammer mill to prepare pulverized powder having a grain size of 0.2 - 0.3 mm.
  • obtained pulverized powder was melted and dispersed by plasma spray method in an Ar atmosphere thereby to work the powder to be spherical particles.
  • a finally attainable Ar pressure in the plasma spray treatment was 180 KPa.
  • crystal structure was identified and an existing ratio thereof was measured in the same manner as in Example. The results shown in Table 1 were obtained.
  • the spherical particles having a composition ratio of Ho 42 Cu 29 Al 29 in at.% was prepared under the same conditions as in Example 1.
  • a crystal structure of thus obtained spherical particles was identified by means of X-ray diffraction method whereby results shown in Table 1 were obtained.
  • the obtained particles were observed by EPMA method, it was confirmed that Ho layer existed on surfaces of the particles.
  • Example 1 means Comparative Example. Sample No. Composition of Cold Accumulating Material (atomic ratio) Ratio of Hexagonal Crystal or Orthorhombic Crystal Refrigerating Capacity at 4.2K (w) Example. 1 H o C u A l 94 (h) 1. 26 Example. 2 H o C u 1.2 A l 0.8 88 (h) 1. 29 Example. 3 H o C u 0.7 A l 1.3 76 (h) 1. 21 Example. 4 D y C u S n 93 (h) 1. 07 Example. 5 H o C u S n 94 (h) 1. 25 Example.
  • FIG. 2 is a graph comparatively showing specific heat characteristics of the cold accumulating material of Example 2 having a composition of HoCu 1.2 Al 0.8 and the cold accumulating material of Comparative Example 2 having a composition of HoCu 2.0 .
  • the specific heat in low temperature range becomes large in comparison with the cold accumulating material of Comparative Example 3. Therefore, when the cold accumulating material of Example 2 is packed in the cold accumulating unit of the refrigerator, it can be confirmed that the refrigerating capacity is increased and a rising-up property of refrigerating operation can be improved.
  • the cold accumulating material of Comparative Example 4 since the cold accumulating material is prepared by conventional plasma spray method, the crystal structure per se is substantially different from that of the cold accumulating material of this invention using rapidly quenching method. Further, the ratio of the hexagonal crystal in the whole crystal structure is small, so that a sufficient refrigerating capacity is not achieved.
  • the cold accumulating material of respective Examples In contrast, in the cold accumulating material of respective Examples, the amount of rare earth element is relatively reduced, rare earth metal is not precipitated, and constituents other than impurities are all formed to be intermetallic compound. Therefore, the material exhibits an excellent specific heat characteristics, and a high refrigerating capacity is realized.
  • Fig.3 is a cross sectional view outlining a structure of a superconductive MRI apparatus to which the present invention is applied.
  • the superconductive MRI apparatus 30 shown in FIG. 3 is constituted of a superconductive magnetostatic field coil 31 for biasing a spatially homogeneous and a temporally stable magnetostatic field to a human body, a not shown compensating coil for compensating inhomogeneity of generating magnetic field, a gradient magnetic field coil 32 for providing a magnetic field gradient in a measuring region, and a probe for radio wave transducer 33.
  • the above described cold accumulation refrigerator 34 of the present invention is employed.
  • numeral 35 denotes a cryostat
  • numeral 36 denotes a radiation shield.
  • Fig. 4 is a perspective view outlining a structure of an essential portion of a superconducting magnet for magnetic floating train to which a cold accumulation refrigerator of the present invention is applied, a portion of a superconductive magnet 40 for a magnetic floating train being shown.
  • the superconductive magnet 40 for a magnetic floating train shown in FIG. 4 is constituted of a superconductive coil 41, a liquid helium tank 42 for cooling the superconductive coil 41, a liquid nitrogen tank 43 for preventing evaporation of the liquid helium and a cold accumulating type refrigerator 44 of the present invention.
  • numeral 45 denotes a laminated adiathermic material
  • numeral 46 denotes a power lead
  • numeral 47 denotes a persistent current switch.
  • a magnetic floating train in which such a superconductive magnet 40 is employed can exhibit its reliability over a long term.
  • FIG. 5 is a cross sectional view outlining a structure of a cryopump to which a cold accumulation refrigerator of the present invention is applied.
  • a cryopump 50 shown in FIG. 5 is constituted of a cryopanel 51 for condensing or absorbing gas molecules, a cold accumulation refrigerator 52 of the present invention for cooling the cryopanel 51 to a predetermined extremely low temperature, a shield 53 disposed therebetween, a baffle 54 disposed at an intake nozzle, and a ring 55 for varying exhaust speed of Argon, nitrogen, hydrogen gas or the like.
  • cryopump 50 involving the cold accumulation refrigerator 52 of the present invention
  • the operating temperature of the cryopanel 51 can be guaranteed to be stable over a long term. Therefore, the performance of the cryopump 50 can be exhibited over a long term with stability.
  • Fig. 6 is a perspective view outlining a structure of an in-magnetic field type single crystal pull-up apparatus involving the cold accumulation refrigerator of the present invention.
  • the in-magnetic field type single crystal pull-up apparatus 60 shown in FIG. 6 is constituted of a crucible for melting raw material, a heater, a single crystal pull-up portion 61 possessing a mechanism of pulling up a single crystal, a superconductive coil 62 for applying a magnetostatic field to a raw material melt, and an elevation mechanism 63 of the single crystal pulling up portion 61.
  • the above described cold accumulation type refrigerator 64 of the present invention is employed as a cooling means of the superconductive coil 62.
  • numeral 65 denotes a current lead
  • numeral 66 denotes a heat shielding plate
  • numeral 67 denotes a helium container.
  • the in-magnetic field type single crystal pull-up apparatus 60 involving a cold accumulation refrigerator 64 of the present invention, since the operating temperature of the superconductive coil 62 can be guaranteed to be stable over a long term, a good magnetic field for suppressing convection of the raw material melt of the single crystal can be obtained over a long term. Therefore, the performance of the in-magnetic field application type single crystal pull-up apparatus 60 can be exhibited with stability over a long term.
  • the amounts of copper and other metals are appropriately controlled with respect to rare earth component, or a part of constituent of HoCu 2 magnetic material having a sharp peak of volumetric specific heat at extremely low temperature range is substituted by the other rare earth element or transition metal or the like, so that the temperature position of the specific heat peak is shifted to a low-temperature side and the mesial magnitude width of the specific heat peak is broadened thereby to obtain a cold accumulating material having a good specific heat characteristic.
  • a refrigerator having a high refrigerating capacity at temperature range of about 4K, and capable of maintaining a stable refrigerating performance for a long time.
  • the refrigerator using the cold accumulating material for extremely low temperature enables the refrigerator to maintain an excellent refrigerating performance with good repeatability for a long time.
  • an MRI apparatus, a cryopump, a superconducting magnet for magnetic floating train, and an in-magnetic field type single crystal pull-up apparatus into which aforementioned refrigerators are assembled can exhibit excellent performances for a long term.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Hard Magnetic Materials (AREA)

Claims (9)

  1. Matériau d'accumulation de froid, comprenant une substance magnétique exprimée par la formule générale : RCu1-x M1+x dans laquelle R désigne au moins un élément de terres rares choisi parmi le groupe comprenant Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Er, Ho, Tm et Yb, M désigne au moins un élément choisi parmi le groupe comprenant Ag, Au, Al, Ga, In, Ge, Sn, Sb, Si, Bi, Ni, Pd, Pt, Zn, Co, Rh, Ir, Mn, Fe, Ru, Cr, Mo, W, V, Nb, Ta, Ti, Zr et Hf, et dans laquelle Ni et Ge ne sont pas simultanément choisis, et x dans le rapport atomique satisfait la relation
    - 0,95 ≤ x ≤ 0,90.
  2. Matériau d'accumulation de froid, comprenant une substance magnétique exprimée par la formule générale : Ho1-xRx(Cu1-yMy)z dans laquelle R désigne au moins un élément de terres rares choisi parmi le groupe comprenant Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Er, Tm et Yb, M désigne au moins un élément choisi parmi le groupe comprenant Ag, Au, Al, Ga, In, Ge, Sn, Sb, Si, Bi, Ni, Pd, Pt, Zn, Co, Rh, Ir, Mn, Fe, Ru, Cr, Mo, W, V, Nb, Ta, Ti, Zr et Hf, et dans laquelle x et y dans le rapport atomique satisfont les relations
    0 ≤ x ≤ 0,5, 0 ≤ x ≤ 0,5, x + y ≠ 0.
  3. Matériau d'accumulation de froid selon l'une ou l'autre des revendications 1 et 2, dans lequel ladite substance magnétique a une structure cristalline composée de cristaux hexagonaux ou de cristaux orthorhombiques sous un rapport volumétrique de 50 % ou plus.
  4. Matériau d'accumulation de froid selon l'une ou l'autre des revendications 1 et 2, dans lequel ladite substance magnétique est un corps anti-ferromagnétique.
  5. Réfrigérateur à accumulation de froid comprenant une pluralité d'étages de refroidissement composés chacun d'une unité d'accumulation de froid remplie d'un matériau d'accumulation de froid à travers lequel s'écoule un fluide de fonctionnement depuis un côté amont à haute température de l'unité d'accumulation de froid de chaque étage de refroidissement, de sorte que de la chaleur est échangée entre le fluide de fonctionnement et le matériau d'accumulation de froid afin d'obtenir grâce à cela une température plus basse sur un côté aval de l'unité d'accumulation de froid, dans lequel une partie au moins du matériau d'accumulation de froid à remplir dans l'unité d'accumulation de froid est composée du matériau d'accumulation de froid énoncé dans l'une ou l'autre des revendications 1 et 2.
  6. Aimant supraconducteur comprenant un réfrigérateur à accumulation de froid selon la revendication 5.
  7. Appareil d'imagerie par résonance magnétique (MRI) comprenant un réfrigérateur à accumulation de froid selon la revendication 5.
  8. Pompe cryogénique comprenant un réfrigérateur à accumulation de froid selon la revendication 5.
  9. Appareil d'extraction de monocristaux en champ magnétique comprenant un réfrigérateur à accumulation de froid selon la revendication 5.
EP98947963A 1997-10-20 1998-10-20 Materiau accumulateur de froid et refrigerateur a accumulation de froid Expired - Lifetime EP0947785B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP28720097 1997-10-20
JP28720097 1997-10-20
PCT/JP1998/004749 WO1999020956A1 (fr) 1997-10-20 1998-10-20 Materiau accumulateur de froid et refrigerateur a accumulation de froid

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EP0947785A1 EP0947785A1 (fr) 1999-10-06
EP0947785A4 EP0947785A4 (fr) 2000-06-07
EP0947785B1 true EP0947785B1 (fr) 2003-04-23

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Families Citing this family (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4551509B2 (ja) * 1998-12-28 2010-09-29 株式会社東芝 蓄冷材および蓄冷式冷凍機
JP5010071B2 (ja) * 2000-07-18 2012-08-29 株式会社東芝 蓄冷材，その製造方法およびその蓄冷材を用いた冷凍機
CN1300521C (zh) * 2002-03-22 2007-02-14 住友重机械工业株式会社 极低温蓄冷器以及冷冻机
WO2006022297A1 (fr) * 2004-08-25 2006-03-02 Ulvac Cryogenics Incorporated Unité d’entreposage au froid et cryopompe
JP2006242484A (ja) * 2005-03-03 2006-09-14 Sumitomo Heavy Ind Ltd 蓄冷材、蓄冷器及び極低温蓄冷式冷凍機
GB0519843D0 (en) 2005-09-29 2005-11-09 Univ Cambridge Tech Magnetocaloric refrigerant
CN103773995B (zh) * 2014-02-13 2017-09-15 北京科技大学 一种磁性蓄冷材料
EP3916068B1 (fr) * 2014-09-25 2024-04-24 Kabushiki Kaisha Toshiba Réfrigérateur comprenant des particules de matériau de stockage du froid à base de terres rares
US11370949B2 (en) 2017-04-28 2022-06-28 Santoku Corporation HoCu-based cold-storage material, and cold-storage device and refrigerating machine each equipped therewith
CN108981217A (zh) * 2018-06-04 2018-12-11 中船重工鹏力（南京）超低温技术有限公司 蓄冷材料及采用该蓄冷材料的蓄冷式低温制冷机
EP3858944A4 (fr) * 2018-09-28 2022-06-22 Kabushiki Kaisha Toshiba Matériau de stockage à froid, réfrigérateur, dispositif incorporant une bobine supraconductrice, et procédé de fabrication de matériau de stockage à froid
CN110440475A (zh) * 2019-07-23 2019-11-12 中船重工鹏力（南京）超低温技术有限公司 抗氧化蓄冷材料及采用该蓄冷材料的蓄冷式低温制冷机

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Publication number Priority date Publication date Assignee Title
JPH07101134B2 (ja) * 1988-02-02 1995-11-01 株式会社東芝 蓄熱材料および低温蓄熱器
JPH0796974B2 (ja) * 1988-11-09 1995-10-18 三菱電機株式会社 多段式蓄冷型冷凍機及びそれを組み込んだ冷却装置
JPH0784957B2 (ja) * 1989-05-30 1995-09-13 株式会社東芝 低温蓄熱器
JP2790549B2 (ja) * 1991-06-10 1998-08-27 三菱電機株式会社 結晶引上げ装置用超電導マグネット装置
JP2837795B2 (ja) * 1992-11-11 1998-12-16 住友重機械工業株式会社 極低温蓄冷器
US5593517A (en) * 1993-09-17 1997-01-14 Kabushiki Kaisha Toshiba Regenerating material and refrigerator using the same
DE69633793T2 (de) * 1996-02-22 2005-10-27 Kabushiki Kaisha Toshiba, Kawasaki Regeneratormaterial zur verwendung bei sehr niedrigen temperaturen

Also Published As

Publication number Publication date
EP0947785A1 (fr) 1999-10-06
DE69813767T2 (de) 2004-02-12
WO1999020956A1 (fr) 1999-04-29
CN1248319A (zh) 2000-03-22
EP0947785A4 (fr) 2000-06-07
CN1174200C (zh) 2004-11-03
DE69813767D1 (de) 2003-05-28

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