Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
2001-07-18
2002-10-22
Doerrler, William C. (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
C165S004000, C252S067000
Reexamination Certificate
active
06467277
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cold accumulating material, a method of manufacturing the material and a cold accumulating type refrigerator using the cold accumulating material, and more particularly to a cold accumulating material which is free from the risk of being pulverized into fine particles, and is excellent in mechanical strength and durability, and capable of exhibiting a significant refrigerating performance at a low temperature region, and relates to a method of manufacturing the cold accumulating material, refrigerator using the cold accumulating material and various application devices using the regenerator.
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, basic requirements such as 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 super-conductive MRI apparatus, cryopump and the like, a refrigerator based on such refrigerating cycle as Gifford MacMahon type (GM refrigerator), Starling method, pulse-tube type refrigerator has been used. Further, a magnetic floating (levitating) train absolutely needs a high performance refrigerator for generating magnetic force by using a super-conductive magnet. Further, in recent years, a super-conductive power storage apparatus (SMES) or an in-magnetic-field single crystal pull-up apparatus (magnetic field applied Czochralski) has been provided with a high performance refrigerator as a main component thereof. Further, a development and practical use of the pulse tube type refrigerator has been aggressively advanced, because the pulse tube type refrigerator is expected to attain a high reliability.
In the above described refrigerator, the operating medium such as compressed He gas or the like flows in a specified direction in a regenerator (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 20 K. 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 regenerator (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 regenerator 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 20 K 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 4 K is realized.
With the advance of reviews for practically applying the above refrigerator into various refrigerating systems, a technical demand for cooling and refrigerating a large-scaled object under a stable state for a long time has been increased, so that it is required to further improve the refrigerating performance (refrigerating capacity) of the refrigerator.
In order to cope with the above technical demand, there has been tried a countermeasure in which a part of the cold accumulating material composed of conventional metal-type magnetic particles generally used is substituted with an oxide-type magnetic cold accumulating material such as GdAlO
3
or the like containing rare earth element, so that a specific heat characteristic of the whole cold accumulating material are suitably controlled thereby to improve the refrigerating capacity.
The magnetic cold accumulating material described above is normally worked and used in a form of spherical-shape having a diameter of about 0.1-0.5 mm for the purpose of smoothly flowing He gas, and for effectively performing the heat exchange with He gas as cooling medium in the refrigerator thereby to stably maintain the heat exchange efficiency. 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 provide a spherical-shape in accordance with working methods such as centrifugal atomizing method.
However, in the above oxide-type magnetic cold accumulating material, since the oxide substance has a high melting point, it is impossible to work the oxide substance so as to provide spherical shape in accordance with a centrifugal spraying method through which the conventional metal-type magnetic cold accumulating material has been worked. Therefore, the conventional oxide-type magnetic cold accumulating material has been worked and manufactured so as to provide a shape close to sphere in accordance with a method comprising the steps of granulating a fine raw material powder to form granulated particles each having an appropriate size; and sintering the granulated particles.
Further, in a Starling-type refrigerator and a pulse-tube type refrigerator or the like to be operated with a high speed, there has been posed a problem that a pressure loss at the regenerator packed with spherical magnetic cold accumulating particles is disadvantageously increased, so that a sufficient refrigerating capacity cannot be realized. Further, in the GM refrigerator or the like, there has been liable to cause the following disadvantages. Namely, pressure vibrations caused by a highly pressurized He gas, various stresses and impact forces are applied to the magnetic body particles (magnetic cold accumulating particles) during the operation of the refrigerator and the magnetic particles were liable to be further finely pulverized, so that a flow resistance of the cooling medium gas is increased thereby to abruptly lower the heat exchange efficiency.
In particular, in case of the GM refrigerator, a stress caused by reciprocal movement of a displacer (i.e. a piston for compressing the cooling medium) is applied to the cold accumulating material, thus exerting a great influence on the characteristic of the cold accumulating material. Further, at a time of starting the refrigerator, the temperature of the regenerators of the refrigerator rapidly lowered in a short time from a room temperature (RT) to an extremely low temperature close to about 4 K, so that a large thermal shock (heat impact) is applied to the cold accumulating material.
However, in general, the oxide substances exhibit an extreme brittleness, insufficient mechanical strength and a small heat impact resistance, so that the following disadvantageous phenomena are liable to cause. That is, the oxide type cold accumulating material is broken during the operation of the refrigerator, a part of surfaces of the cold accumulating material peels off thereby to generate fine powders.
Arai Tomohisa
Okamura Masami
Doerrler William C.
Kabushiki Kaisha Toshiba
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