Compositions – Vaporization – or expansion – refrigeration or heat or energy...
Reexamination Certificate
2000-12-05
2002-12-17
Hardee, John (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
Reexamination Certificate
active
06495061
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a working fluid used as a refrigerant in refrigerators and for other purposes. More particularly, the present invention relates to a refrigerant for providing an ultra-low temperature which does not possess any ozone destruction capability, thereby enabling to notably inhibit the influence thereof on the atmosphere of the earth (facilitating the reduction of the ‘green-house’ effect), and which can be easily used at the same capacity as that of a compressor used in conventional refrigeration rooms or chambers.
BACKGROUND ART
Recently, refrigeration rooms at a ultra-low cooling temperature of less than −50° C. to −60° C., which is lower than conventional refrigeration rooms, have been used with development of the biotechnology and food transportation systems, and demand of such refrigeration rooms are increasing.
In the field of biotechnology, cells, biological tissues and other biological substances have to be stably stored for an extended time of period at the above-mentioned ultra-low temperature to ensure their good survival activity rate after thawing. To satisfy this requirement, the refrigeration rooms used for cells and other biological substances need to have highly increased refrigerating power, along with a high reliability and a low maintenance cost. Further, in order to enable biotechnology to be applied in hospitals and other institutions in addition to application in laboratories, the refrigeration rooms have to be constructed simply, at low cost; and also need to be easy to operate.
Similar problems also occur in food transportation systems etc. To maintain freshness of the food for a long period, the refrigeration rooms used in the transportation system must have high refrigerating power without any problems such as system failure, along with easy maintenance and low operation cost.
Under these circumstances, it is preferable to provide refrigeration rooms in which a refrigerant is repeatedly used in refrigeration cycles. However, refrigerants capable of providing an ultra-low cooling temperature of less than −50° C. can not be easily liquefied at room temperature, because the critical pressure thereof is generally increased with the reduction of the standard boiling point, and have a low critical temperature.
Hitherto, a refrigerator unit, based on a multistage cooling cycle, using two or more refrigerants having different boiling points has been used as a refrigerator for ultra-low temperature. Namely, by using a refrigerant having a high boiling point capable of being liquefied at room temperature for a refrigeration process that liquefies a refrigerant having a lower boiling point, an ultra-low temperature can be obtained.
A multistage cooling cycle-based refrigerator unit is illustrated in, for example,
FIG. 1
in which two types of refrigerants are used and two sets of refrigerator units are operated with two compressors at two stages, respectively.
In the illustrated refrigerator room, a first refrigerant is compressed in a high temperature side-positioned compressor
1
and the gaseous compressed refrigerant is subjected to heat radiation and cooling in a high temperature side-positioned condenser
3
provided with a fan
2
, thereby producing a liquefied first refrigerant. The liquefied first refrigerant is guided through a capillary tube
5
to an outer tube
11
of the double tubed heat exchanger
10
. After the vaporized first refrigerant in the outer tube
11
is used to cool a second refrigerant in an inner tube
12
of the heat exchanger
10
, the first refrigerant is returned to the high temperature side-positioned compressor
1
. In the above process, the reference numerals
6
and
7
represent a drier and a liquid separator (accumulator), respectively.
A second refrigerant, after being compressed in a low temperature side-positioned compressor
20
, is led into an inner tube
12
of the heat exchanger
10
, and is cooled and liquefied with the first refrigerant. The liquefied second refrigerant is guided through a capillary tube
15
to a low temperature side-positioned evaporator
30
. In the evaporator
30
, the second refrigerant is vaporized under a reduced pressure to thereby cool the interior of the refrigerator room. The used second refrigerant is returned again to the compressor
20
. In the above process, the reference numerals
26
and
27
represent a drier and an oil separator for removing mist-like oil, respectively.
In the above illustrated refrigeration system, it becomes possible to provide an ultra-low temperature which has a system power and capacity comparable to conventional refrigeration rooms. However, because it is constructed from two sets of refrigerators, the total size of the refrigeration system is increased and has a complicated structure, thereby causing difficulty in maintenance, substantially increasing the cost of the refrigeration room.
Alternatively, as illustrated in
FIG. 2
, a single compressor multicycle refrigeration system in which a mixture of two or more refrigerants having different properties such as different boiling points is used in combination with a single compressor has been researched.
In the illustrated refrigeration system, three types of refrigerants are previously mixed to obtain a mixed refrigerant. The mixed refrigerant is compressed in a compressor
40
provided with a fan
2
, followed by being subjected to heat radiation in a condenser
41
to thereby liquefy a first refrigerant having the highest critical temperature.
The liquefied first refrigerant is then separated in a liquid separator
45
to remove and recover therefrom an mist-like oil contaminated by the compressor
40
and return the oil to the compressor
40
. The separated first refrigerant is vaporized in a heat exchanger
50
to simultaneously cool and liquefy a gaseous second refrigerant having a lower critical temperature than that of the first refrigerant. The second refrigerant liquefied in the heat exchanger
50
is separated in a liquid separator
46
and then vaporized in a heat exchanger
51
in which a third refrigerant having the lowest critical temperature is cooled and liquefied with the vaporized second refrigerant. The third refrigerant liquefied in the heat exchanger
51
is vaporized in an evaporator
55
. The thus the produced vapor of the third refrigerant is used to cool the interior of the refrigeration room to a predetermined ultra-low temperature.
In the above refrigeration system, the first to third refrigerants vaporized in the heat exchangers
50
and
51
and the evaporator
55
are returned through a common return pipe
61
to the compressor
40
.
Using the illustrated refrigeration system, it becomes possible to reduce the amount of machinery utilized in the refrigeration room because only one compressor is included therein. However, contrary to this advantage, the flow circuit for circulating the three refrigerants is complicated and thus the total size of the refrigeration room is unavoidably increased along increased difficulty of the maintenance.
In addition to the improvement of the refrigeration system, an improvement of the refrigerant used as the working liquid therein has been also made. Hitherto, fluorohydrocarbons which are generally referred to as “flons” have been used as refrigerants. However, due to recent evidence proving that flon gas can cause destruction of the ozone layer adding to global warming, such flons are prohibited from being used as refrigerants. Namely, use of “specified flons” capable of causing notable ozone destruction and flons capable of adding substantially to general global warming can not be used under established regulations. Therefore, it is highly desirable to develop a novel refrigerant which has zero ozone destruction properties and a negligible effect on global warming.
At present, many types of the refrigerants which can be used without causing any adverse effect on the environment and which can show excellent properties comparable to those of the conventional flons have been prop
Hiruta Isamu
Kurita Susumu
Morita Makoto
Seino Toshio
Greenblum & Bernstein P.L.C.
Hardee John
Nihon Freezer Co., Ltd.
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