Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
1999-12-22
2002-04-02
Doerrler, William (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
Reexamination Certificate
active
06363727
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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 is free from the risk of being pulverized into fine particles, and is excellent in durability, and exhibits significant refrigerating performance at a low temperature region, and relates to a cold accumulation refrigerator using the cold accumulating material.
2. Description of the Related Art
Recently, superconductivity technology has been progressed remarkably and with an expanding application field thereof, development of a small, high performance refrigerator has become indispensable. For such a refrigerator, light weight, small size and high heat efficiency are demanded, and a small-sized refrigerator has been practically applied to various industrial fields.
For example in a superconductive MRI apparatus, cryopump and the like, a refrigerator based on such refrigerating cycle as Gifford MacMahon type (GM refrigerator), Starling method has been used. Further, a magnetic floating (levitating) train absolutely needs a high performance refrigerator for generating magnetic force by using a superconductive magnet. Further, in recent years, a superconductive power storage apparatus (SMES) or an in-magnetic field single crystal pull-up apparatus has been provided with a high performance refrigerator as a main component thereof.
In the above described refrigerator, 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 can be realized.
As a cold accumulating material for use in the above-described refrigerator, conventionally Cu, Pb and the like have been used. However, these cold accumulating materials have a very small specific heat in extremely low temperatures below 20K. Therefore, the aforementioned recuperation effect is not exerted sufficiently, so that even if the refrigerator is cyclically operated under an extremely low temperature, the cold accumulating material cannot accumulate sufficient heat energy, and it becomes impossible for the operating medium to receive the sufficient heat energy. As a result, there is posed a problem of that the refrigerator in which the cold accumulating unit filled with aforementioned cold accumulating material is assembled cannot realize the extremely low temperatures.
For the reason, recently to improve the recuperation effect of the cold accumulating unit at extremely low temperature and to realize temperatures nearer absolute zero, use of magnetic cold accumulating material made of intermetallic compound formed from a rare earth element and transition metal element such as Er
3
Ni, ErNi, ErNi
2
, HoCu
2
having a local maximum value of volumetric specific heat and indicating a large volumetric specific heat in an extremely low temperature range of 20K or less has been considered. By applying the magnetic cold accumulating material to the GM refrigerator, a refrigerating operation to produce an arrival lowest temperature of 4K is realized.
The magnetic cold accumulating material described above is normally worked and used in a form of spherical-shape having a diameter of about 0.1-0.4 mm for the purpose of effectively performing the heat exchange with He gas as cooling medium in the refrigerator. In particular, in a case where the magnetic cold accumulating material (particulate cold accumulating substance) is intermetallic compound containing rare earth element, the particulate cold accumulating substance is worked so as to have a spherical-shape in accordance with working methods such as centrifugal atomizing method. However, according to the working methods such as centrifugal atomizing method, there is caused a disadvantage of that a production yield of the cold accumulating substance having an aimed particle diameter is low, and manufacturing cost of the substance is increased such that the substance cannot be industrially used.
For the reason, there has been tried a method in which magnetic particles prepared by being mechanically pulverized are used. However, there had been raised a problem of that the mechanically pulverized magnetic particles were liable to be further finely pulverized due to vibrations and shocks to be applied to the magnetic particles during the operation of the refrigerator, so that a flow resistance of the cooling gas is increased thereby to abruptly lower the heat exchange efficiency. Therefore, the mechanically pulverized magnetic particles have not been practically used still now.
On the other hand, for the purpose of preventing the mechanically pulverized magnetic particles from being further finely pulverized, the inventors of this invention had investigated an integrating method in which the magnetic particles are bound to each other by utilizing binders such as resin or the like. The method using the binder described above is recognized to be effective in a point of reinforcing the cold accumulating particles having a low mechanical strength, and in a point of preventing the fine cold accumulating particles from spilling out from a cold accumulating unit of the refrigerator.
However, in the cold accumulating material prepared by mutually binding the cold accumulating particles by using the binder, a diameter of the cold accumulating particle is small to be 0.1-0.4 mm and fine pores formed between the cold accumulating particles is liable to be choked or clogged with the binders such as resin, so that there is posed a problem that a percentage of void (porosity) of the cold accumulating unit filled with the cold accumulating material is remarkably lowered to be about 10%. When the percentage of void of the cold accumulating unit is lowered, it becomes difficult for the operating gas (He gas) of the refrigerator to pass through the cold accumulating unit, and to perform the heat-exchange with the cold accumulating material. As a result, there is also posed a problem that function of the refrigerator is lost and the refrigerating effect is abruptly lowered.
In addition, when the cold accumulating materials composed of ferromagnetic substances such as ErNi
2
, ErNi
0.9
Co
0.1
, ErNi
0.8
Co
0.2
are applied to refrigerators for superconduction systems, such cold accumulating materials were liable to be affected by leakage magnetic field from the superconducting magnet, so that there may be posed a problem of causing a fear, for example, that magnetic force is applied to component parts of the refrigerator thereby to cause a biased wear and deformations to the component parts.
On the other hand, 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. However, 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.
SUMMARY OF THE INVENTION
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 which is free from the fear of being finely pulverized, and has a high mechanical strength, and capable of exhibiting a significant refrigerating performance at an extremely low temperature range for a long period of time in a stable condition, and which can be mass-produced with a high production yield and low cost, and provide a cold accumulation refrigerator using the same.
In addition, anoth
Arai Tomohisa
Hashimoto Keisuke
Okamura Masami
Doerrler William
Drake Malik N.
Kabushiki Kaisha Toshiba
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