Refrigeration – Low pressure cold trap process and apparatus
Reexamination Certificate
2000-10-19
2002-07-02
Doerrler, William C. (Department: 3744)
Refrigeration
Low pressure cold trap process and apparatus
C062S006000
Reexamination Certificate
active
06412290
ABSTRACT:
BACKGROUND OF THE INVENTION
The entire disclosure of Japanese Patent Applications No. Hei 11-296636 filed on Oct. 19, 1999 and No. 2000-309235 filed on Oct. 10, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a cryogenic refrigerating device, and more particularly to a cryogenic refrigerating device having an adiabatic vacuum tank and a refrigerator accommodated in the adiabatic vacuum tank.
2. Description of Related Art
It is necessary for an electronic device to be refrigerated to a temperature level of liquefied nitrogen (about 80K) in order to maintain or to generate a particular characteristic thereof. This type of cryogenic refrigeration is often achieved by a refrigerator such as GM (Gifford-McMahon) type refrigerator or pulse tube refrigerator for cooling the electronic device. In order to minimize the effect of external heat, such refrigeration is carried out in an adiabatic vacuum tank. Therefore, such a refrigerating device generally includes an adiabatic vacuum tank and a refrigerator disposed in the tank.
The conventional refrigerating device, however, has a drawback in that the pressure in the adiabatic vacuum tank increases due to molecules released from the metal inner surface of the tank or molecules adhered on the inner wall of the tank and released therefrom. This pressure increase in the tank has been prevented by various means hitherto proposed. One such proposal is to provide a vacuum pump within the adiabatic vacuum tank. According to this proposal, the molecules generated and released in the tank are discharged by the vacuum pump.
Another proposal is to provide a panel (adsorption panel) to which is attached a porous material, such as activated carbon, in the cold head portion (low temperature generating portion) of the refrigerator accommodated in the adiabatic vacuum tank. According to this proposal, molecules floating in the cold head portion of the refrigerator are adsorbed and trapped in the panel. This will prevent an increase of the pressure in the tank.
A further proposal is to provide a hydrogen storage alloy (for example, vanadium alloy) in the adiabatic vacuum tank. According to this proposal, the hydrogen molecules are stored in the hydrogen storage alloy, and other molecules having a relatively high freezing point (for example oxygen molecules) are chemically reacted with the hydrogen storage alloy to generate a chemical compound such as oxide (vanadium oxide), and so are kept in the alloy.
These proposals, however, have certain drawbacks. According to the first proposal of providing a vacuum pump in the adiabatic vacuum tank, the vacuum level in the tank is limited to the capacity of the vacuum pump. In order to obtain a desired high vacuum level in the tank, the vacuum pump has to be large and expensive. This leads to high cost and a larger size refrigerating device as a whole. Further, it is necessary to provide an additional driving source and device for driving the vacuum pump in addition to the driving of the refrigerator itself. The consumption of energy becomes large and the refrigeration system cannot maintain the vacuum within the system independent of the vacuum pump.
According to the second proposal of providing an adsorption panel, while it needs no vacuum pump, the adsorption panel cannot trap molecules such as hydrogen molecules having a freezing point below the ambient temperature of liquefied nitrogen level (about 80K). The vacuum level may therefore increase over time due to the release of hydrogen molecules from the tank inner wall. This problem may be addressed by improving the performance capacity of the refrigerator to lower the temperature at the cold head to about 20K so that even the hydrogen molecules may be trapped in the panel. It is, however, not realistic to improve the capacity of refrigerator just for the purpose of trapping the molecules, because the basic role of the refrigerator is to cool the electronic devices to be refrigerated and not to trap gas molecules. Also, excess cooling or refrigeration may reduce the performance of the electronic devices to be cooled.
According to the third proposal of providing the hydrogen storage alloy, it can store the hydrogen molecules in the alloy and at the same time keep the other molecules of higher freezing point in the alloy as chemical components by chemical reaction with the alloy. However, the amount of other molecules of higher freezing point to be kept in the alloy is very small compared to the hydrogen molecules and accordingly the hydrogen storage alloy has to be re-activated by being heated to 500 to 800° C. This heating requires a heating device, which leads to an increase in consumption of electric power. Further, during the operation of the refrigerating device, such reactivation has to be done frequently.
As stated, the conventional proposals are unable to provide an inexpensive cryogenic refrigerating device having an adiabatic vacuum tank, or such a tank capable of long time stable operation to keep the vacuum at a constant level.
SUMMARY OF THE INVENTION
It is therefore, an object of the present invention to provide an improved cryogenic refrigerating device which can obviate the above conventional drawbacks.
It is another object of the present invention to provide an improved cryogenic refrigerating device having an adiabatic vacuum tank and a refrigerator, a part thereof formed integrally with the adiabatic vacuum tank, without increasing the cost, and yet capable of keeping the vacuum level in the adiabatic vacuum tank to a desired and stable level for a relatively longer time or for a lifetime of operation.
According to the present invention, a cryogenic refrigerating device includes an adiabatic vacuum tank, a refrigerator having at least a low temperature generating portion (a cold head portion) thereof being disposed in the adiabatic vacuum tank, an adsorption panel attached to the low temperature generating portion of the refrigerator, and a hydrogen sorbing device provided in the adiabatic vacuum tank for sorbing the hydrogen molecules therein.
According to the present invention, the adsorption panel attached to the low temperature generating portion of the refrigerator adsorbs molecules other than the hydrogen in the adiabatic vacuum tank, and a hydrogen sorbing device provided in the adiabatic vacuum tank sorbs the hydrogen molecules selectively. The adsorption panel adsorbs molecules of relatively high freezing point in the adiabatic vacuum tank and the hydrogen sorbing device sorbs hydrogen molecules of lower freezing point in the adiabatic vacuum tank selectively, so that most of the molecules in the adiabatic vacuum tank may be trapped either in the adsorption panel or in the hydrogen sorbing device.
The adsorption panel may include an activated carbon layer or molecular sieve for adsorbing the relatively high freezing point molecules in the adiabatic vacuum tank. The hydrogen sorbing device is formed for sorbing molecules of lower freezing point such as hydrogen and may include hydrogen storage alloys such as vanadium alloy or zirconium alloy.
During the operation of the cryogenic refrigerating device, relatively high freezing point molecules such as oxygen or nitrogen are adsorbed by the adsorption panel provided on the low temperature generating portion of the refrigerator and relatively low freezing molecules such as hydrogen are adsorbed by the hydrogen sorbing device provided in the adiabatic vacuum tank. Accordingly, the hydrogen molecules in the adiabatic vacuum tank are sorbed by the hydrogen sorbing device and the molecules other than hydrogen are adsorbed by the adsorption panel, to thereby sorb most of the molecules generated or present in the adiabatic vacuum tank during operation, thereby to keep the vacuum level in the tank to a desired level for a long time.
This structure does not include a vacuum pump and yet keeps the vacuum level in the tank constant by use of the cryogenic re
Hamajima Takanori
Okumura Nobuo
Aisin Seiki Kabushiki Kaisha
Doerrler William C.
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