Metal treatment – Stock – Magnetic
Reexamination Certificate
1998-08-21
2001-03-06
Sheehan, John (Department: 1742)
Metal treatment
Stock
Magnetic
C148S101000, C148S303000, C062S003100, C062S006000
Reexamination Certificate
active
06197127
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a heat regenerating material which can be used at a very low temperature and for a refrigerator and the like, and a refrigerator using thereof.
BACKGROUND ART
Recent years, progress of the superconductive technology is remarkable, and, as its applicable field is expanded, development of a refrigerator of small size and high performance becomes inevitable issue. For such a refrigerator, light weight/small size and high thermal efficiency are required.
For example, in a superconductive MRI device and a cryopump, a refrigerator operating based on a refrigeration cycle such as a Gifford MacMahon system (GM system) or a Stirling system is used. Further, a high performance refrigerator is indispensable for a magnetic levitation train too, still further, for some single crystal growth devices, a refrigerator of high performance is being used. In such a refrigerator, inside a heat regenerator filled with a heat regenerating material, an operating medium such as a compressed He gas and the like flows in one direction to supply its heat energy to the heat regenerating material, and there expanded operating medium flows in the reverse direction to receive a heat energy from the heat regenerating material. As an recuperating effect becomes good through such a process, the thermal efficiency of the operating medium cycle can be improved, thereby, a further lower temperature can be realized.
As a heat regenerating material to be used for the above described refrigerator, conventionally, there has been mainly used Cu or Pb. However, since these heat regenerating materials become remarkably small in their specific heat at very low temperature of 20 K or less, the above described recuperating effect does not work sufficiently, resulting in difficulty in realization of a very low temperature.
Then, recently, in order to realize a temperature more close to the absolute zero degree, application of magnetic heat regenerating materials such as an Er—Ni based intermetallic compounds such as Er
3
Ni, ErNi, ErNi
2
(ref. Japanese Patent Laid Open No. HEI-1-310269) and RRh based intermetallic compounds (R: Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb) such as ErRh (ref. Japanese Patent Laid Open No. Sho-51-52378), all of which display a large specific heat at very low temperature, are under investigation.
Now, in an operating state of a refrigerator such as described above, an operating medium such as a He gas and the like passes through space between the heat regenerating material filled in the heat regenerator in such a manner that changes frequently its flowing direction under high pressure and with high speed. Therefore, a various kinds of forces including mechanical vibration are added on the heat regenerating material. Further, when a magnetic levitation train or an artificial satellite is equipped with a refrigerator, there operates a large acceleration on the heat regenerating material.
Thus, though various forces act on the heat regenerating material, since the above described magnetic heat regenerating materials consisting of the intermetallic compounds such as Er
3
Ni and ErRh are brittle materials in general, due to the cause such as the above described mechanical vibration or acceleration during operation, there was a problem that they were prone to be pulverized. The pulverized fine particles hinder the gas sealing to adversely affect on the performance of the heat regenerator, thus, resulting in deterioration of the capacity of the refrigerator.
An object of the present invention is to provide a heat regenerating material which can be used at a very low temperature and is excellent in their mechanical performance against the mechanical vibration or the acceleration, and a refrigerator which enabled to exhibit an excellent refrigeration performance over a long term by using such a heat regenerating material. Further, the other object is to provide an MRI device, a cryopump, a magnetic levitation train, and a magnetic field application type single crystal growth device all of which are made possible to exhibit excellent performance over a long term by using such a refrigerator.
DISCLOSURE OF INVENTION
A heat regenerating material for very low temperature use of the present invention is a heat regenerating material for very low temperature use comprising a magnetic heat regenerating material particle aggregate, wherein, among the magnetic heat regenerating material particles which constitute the magnetic heat regenerating material particle aggregate, the ratio of the magnetic heat regenerating material particles which are destroyed when a simple harmonic oscillation of the maximum acceleration of 300 m/s
2
is added on the magnetic heat regenerating material particle aggregate 1×10
6
times is 1% by weight or less.
A refrigerator of the present invention comprises a heat regenerator container and a heat regenerator having the above described heat regenerating material for very low temperature use of the present invention which is filled in the heat regenerator container.
Further, all of an MRI (magnetic Resonance Imaging) device, a cryopump, a magnetic levitation train, and a magnetic field application type single crystal growth device of the present invention comprises the above described refrigerator of the present invention.
The heat regenerating material for very low temperature use of the present invention is consisting of a magnetic heat regenerating material particle aggregate, that is, an aggregate (group) of the magnetic heat regenerating material particles. As a heat regenerating material to be used in the present invention, for instance, an intermetallic compound including a rare earth element and expressed by the following general formula,
General formula: RM
z
(1)
(in the formula, R denotes at least one kind of rare earth element selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, M denotes at least one kind of metallic element selected form Ni, Co, Cu, Ag, Al and Ru, z denotes a number of in the range of 0.001 to 9.0. Same in the following) or an intermetallic compound including a rare earth element and expressed by the following general formula
general formula: RRh (2)
can be cited.
The above described heat regenerating material particles make more smooth the gas flow when their particle diameters are more uniform and their shape are more spheroidal. Thus, 70% by weight or more of the magnetic heat regenerating material particle aggregate (total particles) is preferable to be constituted of the magnetic heat regenerating material particles of particle diameter in the range of 0.01 to 3.0 mm. When the particle diameter of the magnetic heat regenerating material particles is less than 0.01 mm, their packing density becomes too high, thus the pressure loss of the operating medium such as He is likely to be increased. On the contrary, the particle diameter exceeds 3.0 mm, heat transmitting surface area between the magnetic heat regenerating material particles and the operating medium becomes small, resulting in degradation of heat transmission efficiency. Therefore, when such particles occupy more than 30% by weight of the magnetic heat regenerating material particle aggregate, deterioration of heat regenerating performance or the like is likely to be invited. The more preferable particle diameter is in the range of 0.05 to 2.0 mm, still more preferable to be in the range of 0.1 to 0.5 mm. The ratio of the particles of which particle diameter are in the range of 0.01 to 3.0 mm in the magnetic heat regenerating particle aggregate is more preferable to be 80% by weight or more, still more preferable to be 90% by weight or more.
The heat regenerating material for very low temperature use of the present invention is composed of a magnetic heat regenerating material particle aggregate in which the ratio of the magnetic heat regenerating material particles destroyed when a simple harmonic oscillation of the maximum acceleration of 300 m/s
2
is added 1×10
6
times on the above described group
Okamura Masami
Sori Naoyuki
Foley & Lardner
Kabushiki Kaisha Toshiba
Sheehan John
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