Refrigeration – Refrigeration producer – Compressor-condenser-evaporator circuit
Reexamination Certificate
2002-05-02
2003-09-23
Jones, Melvin (Department: 3744)
Refrigeration
Refrigeration producer
Compressor-condenser-evaporator circuit
C062S335000, C062S498000, C062S612000
Reexamination Certificate
active
06622518
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a multi-stage expansion/suction type of cryogenic refrigerating system, wherein the Bernoulli's principle that as the flow velocity of a fluid in a tube increases, pressure exerted by the fluid in the tube decreases is applied to a refrigerating cycle system so that low temperature can be achieved in a refrigerating chamber of a refrigerator by lowering temperature and pressure of a refrigerant in multiple stages when the refrigerant flows from a high temperature side to a low temperature side.
More specifically, the present invention relates to a cryogenic refrigerating system, wherein a specific refrigeration effect thereof is increased only by one compressor in such a manner that a process of lowering pressure of a low-temperature side refrigerant by means of strong suction force in an evaporated refrigerant carrying tube generated when a liquid refrigerant is expanded and injected at a high velocity toward an inlet of a double tube is repeatedly performed in multiple stages, and thus, evaporation pressure of the refrigerant can be maintained below suction pressure of the compressor and its stability can be ensured even in case of continuous operation thereof.
BACKGROUND ART
Generally, ultra low temperature is needed for long-term preservation of tissue, cells or genes, a semiconductor fabricating process, an apparatus for inducing a superconductivity phenomenon, etc. Particularly, in case of biological materials such as cells, if they are kept at temperature of −130° C. or less that corresponds to recrystallization temperature of ice, water contained therein is not crystallized but is in amorphous state. Thus, since it is not likely that a cell membrane is destructed, the term of preservation therefore can be greatly prolonged over 10 years. Although there are various technologies for achieving such ultra low temperature, a method using a vapor compression refrigeration cycle or liquid nitrogen is widely used. In order to achieve ultra low temperature of about −135° C. to −150° C., it is necessary to employ a multi-stage cascade refrigerating cycle having three stages or more, or to use the liquid nitrogen having liquefaction temperature of −196° C. However, since the liquid nitrogen is used up only once, it is necessary to refill the liquid nitrogen for another use. Thus, its use is inconvenient and its operating cost is increased. On the other hand, in case of the multi-stage cascade refrigerating cycle, there is a problem in efficiently achieving the desired ultra low temperature. In addition, there is another problem in that an apparatus employing the multi-stage cascade refrigerating cycle is complex in its structure, and thus, failures of the apparatus frequently occur and its operating cost is also increased.
In consideration of these problems, there has been proposed a cryogenic refrigerator, which is disclosed in an article, entitled “Temperature in Refrigerating Chamber of Compressor-type Refrigerator” in
Nikkei Mechanical,
No. 496 (Dec. 23, 1996), pp. 44-45, Japan. The cryogenic refrigerator employs a two-stage cascade mixed-refrigerant refrigeration circuit (i.e., a combination of a two-stage cascade refrigeration circuit and a mixed-refrigerant circuit) for achieving lower temperature in a low-temperature side refrigeration circuit by using a high-temperature side refrigeration circuit
In the two-stage cascade mixed-refrigerant refrigeration circuit, achievable temperature in a final evaporator is −155° C., and temperature obtained in the refrigerating chamber is −152° C. As schematically shown in
FIG. 2
, there are the two separate high- and low-temperature side refrigeration circuits which in turn are connected with each other through a cascade condenser. The cascade condenser serves as an evaporator for the high-temperature side refrigeration circuit and as a condenser for the low-temperature side refrigeration circuit. The high-temperature side refrigeration circuit is used for achievement of further lower temperature in the low-temperature side refrigeration circuit.
In particular, in order to achieve temperature of −100° C. or less, the mixed-refrigerant refrigeration circuit was employed in the low temperature side. A typical refrigerant is a mixed-refrigerant comprised of seven kinds of refrigerants such as R412A having evaporation temperature of −40° C. for the high temperature side, and R508 (mixture of R23 and R116) having evaporation temperature of −86° C., R22 having evaporation temperature of −41° C., and R14 having evaporation temperature of −128° C. for the low temperature side. The mixed-refrigerant goes through the respective stages to achieve the low temperature.
However, in the two-stage cascade mixed-refrigerant refrigeration circuit, since two compressors are separately installed in the respective high- and low-temperature side refrigeration circuits, consumption of electric power is increased and the structure of the refrigeration cycle thereof is complicated. In addition, in order to maintain the temperature in the refrigerating chamber at −152° C., it is necessary to continuously operate the refrigerator. However, it is difficult to operate continuously and stably the refrigerator since there is a problem in that residual oil which has been moved along with the refrigerant from the compressor to a low pressure side is not completely collected into the compressor to cause the lubricating oil to lack on sliding surfaces in the compressor and consequently a cylinder of the compressor to get scorched and stuck. Moreover, there are also problems in that suction pressure at low temperature is reduced and refrigeration performance is reduced.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a refrigerating system which ensures reliability of the equipment thereof by maintaining stable performance even in case of continuous operation of the cryogenic refrigerating system.
Another object of the present invention is to provide a refrigerating system which improves life or reliability of the equipment thereof by ensuring the smooth operation of a compressor.
A further object of the present invention is to provide a refrigerating system which ensures external competitiveness of a product by enhancing the refrigeration efficiency thereof over 20% and stabilizing the operation thereof at ultra low temperature.
The above objects of the present invention can be achieved by a multi-stage expansion type of cryogenic refrigerating system, wherein a liquid refrigerant is expanded at an upper portion of an evaporated refrigerant carrying tube and is injected toward a downstream side with respect to a flow direction of evaporated refrigerant vapor in multiple stages so as to strongly draw refrigerant vapor in the evaporated refrigerant carrying tube and thus to lower evaporation pressure of the refrigerant below suction pressure of a compressor. Since the evaporated refrigerant vapor is strongly drawn and urged at a high velocity, flow velocity and pressure of the refrigerant vapor are increased and the suction pressure of the compressor is maintained over predetermined pressure. Accordingly, volumetric efficiency of the compressor can be improved and residual oil in a refrigeration circuit can be completely returned to the compressor. According to the present invention, it is possible to achieve final evaporation temperature of −160° C. and temperature of a refrigerating chamber of −156° C.
Further, the above objects of the present invention can be achieved by a multi-stage mixed-refrigerant system comprising a compressor for compressing a mixed-refrigerant; an oil separator for separating oil from the refrigerant compressed by the compressor, collecting the separated oil into the compressor, and then discharging the refrigerant; a condenser for cooling the high-temperature and high-pressure gaseous refrigerant discharged from the oil separator to liquefy the gaseous refrigerant; a heat exchan
Bacon & Thomas
Jones Melvin
Operon Co., Ltd.
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