Refrigeration – Automatic control – Refrigeration producer
Reexamination Certificate
2002-01-10
2003-05-27
Esquivel, Denise L. (Department: 3744)
Refrigeration
Automatic control
Refrigeration producer
C062S510000
Reexamination Certificate
active
06568198
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a multi-stage compression refrigeration apparatus having a multiplicity of compression means for compressing a refrigerant in multi-stages.
BACKGROUND OF THE INVENTION
A typical multi-stage compression refrigeration apparatus for use in a refrigerator and an air conditioner includes a rotary compressor consisting of a first and a second stage compression means which are housed in an enclosed container and each have a roller for compressing a refrigerant in the respective cylinder. The compressor performs compression of the refrigerant in two stages, first by the first stage compression means serving as a low-pressure compressor and then by the second stage compression means serving as a high-pressure compressor adapted to further compress the refrigerant gas compressed by the first stage low-pressure compressor.
Such a multi-stage compression refrigeration apparatus can attain a high compression ratio while suppressing variations of torque per one compression.
However, such multi-stage compressor has a drawback in that when a refrigerant has a high specific heat ratio, the second stage compression means has a low suction efficiency because it receives hot refrigerant heated by the first stage compression means. The multi-stage compressor also suffers from a further disadvantage that the temperature of the refrigerant is heated in the second stage high-pressure compression means to a great extent that the lubricant used therein will be thermally hydrolyzed into acids and alcohol, particularly when ester oil (for example, polyol ester, POE) is used. These acids disadvantageously develop sludges which tend to clog capillary tubes of the compressor, degrade the lubricant, and hence lower the performance of the apparatus.
In order to circumvent these problems, some compressors are provided with a cooling unit for cooling the refrigerant gas discharged from the first stage compression means before it is supplied to the second stage high-pressure compression means, thereby sufficiently lowering the temperature of the refrigerant gas discharged from the second stage compressor. For example, one type of such multi-stage compression refrigeration apparatus as shown in
FIG. 5
has: a multi-stage compressor
511
which consists of a first stage low-pressure compression means and a second stage high-pressure compression means; a condenser
512
; a first decompression means
513
, an intercooler
514
, a second decompression means
515
, and an evaporator
516
. The refrigerant exiting the condenser
512
is diverted into two parts, with one part passed to the intercooler
514
via the first decompression means
513
, but the other part passed directly to the intercooler
514
, and then passed to the second decompression means
515
and the evaporator
516
. The two parts undergo heat exchange in the intercooler
514
. The refrigerant exiting the evaporator
516
is fed to the first stage compression means of the multi-stage compressor
511
. On the other hand, the part of the refrigerant that has passed through the intercooler
514
is mixed with the refrigerant discharged from the first stage low-pressure compression means before entering the second stage compression means.
Thus, this multi-stage compression refrigeration apparatus has a refrigeration cycle as depicted in the P-h diagram (solid line) shown in FIG.
6
. In this conventional apparatus, the enthalpy of the refrigerant is reduced by &dgr;Ho, as shown in
FIG. 6
, by the heat exchange between the two parts of the refrigerant in the intercooler
514
, i.e. heat exchange between the refrigerant passed through the first decompression means
513
and the refrigerant passed directly to the intercooler
514
. This arrangement may increase an enthalpy difference across the evaporator
516
.
However, such conventional apparatus fails to cool the refrigerant in the intercooler
514
sufficiently prior to decompression by the second decompression means
515
due to the sensible heat in the tubes of the intercooler
514
for example, so that, at an early stage of a start-up operation, the evaporator
516
cannot create intended enthalpy difference &dgr;Ho required for a normal operation (as indicated in FIG.
6
).
Another drawback pertinent to the prior art apparatus is that, following stopping of the refrigeration operation, hot refrigerant in the condenser
512
flows into the evaporator
516
via the second decompression means
515
, resulting in a large amount of liquefied refrigerant staying in the evaporator
516
. Hence, it takes a fairly long time to have the entire liquefied refrigerant in the evaporator
516
to be evaporated during a restart of the compressor
511
, thereby requiring a time for the apparatus to recover its normal operating condition. This lowers the efficiency of the apparatus.
As a measure to circumvent this problem, an integral valve system might be provided which has cooperative first and second valves mounted upstream and downstream ends, respectively, of the evaporator
516
, such that the first valve is closed in response to a backflow from the compressor
511
following the stopping of the compressor and the second valve is then closed in response to the first valve, thereby stopping the backflow from the second decompression means
515
to the evaporator
516
.
In this arrangement, the backflow of the liquid refrigerant into the evaporator
516
can be prevented. However, in an apparatus as mentioned above where the refrigerant discharged from the first stage compression means is mixed with the refrigerant from the condenser
512
before it is fed to the second refrigeration means, hot liquid refrigerant remaining in the condenser
512
will flow into the intercooler
514
after the compressor
511
is stopped. As a result, when the apparatus is restarted, sensible heat that remains in the intercooler
514
will prevent sufficient cooling of the refrigerant in the intercooler
514
before passing it to the second decompression means
515
. Consequently, super-cooling of the refrigerant for the intended enthalpy difference &dgr;Ho is not obtained by the evaporator
516
.
It is therefore an object of the invention to overcome the problems as mentioned above by providing an improved multi-stage compression refrigeration apparatus having a first and a second stage compression means and equipped with an intercooler which is adapted to cool the compressed refrigerant gas discharged from the first (low-pressure) compression means. Thus, the apparatus is capable of lowering the temperature of the gas discharged from the second (high-pressure) compression means to create a large enthalpy difference in an evaporator during an early stage of startup.
It is another object of the invention to provide an improved multi-stage compression refrigeration apparatus adapted to stop the backflow of refrigerant into the evaporator and the intercooler when the apparatus is stopped, thereby allowing the apparatus to resume creation of a large enthalpy and attain an improved refrigeration efficiency during an early stage of startup.
DISCLOSURE OF THE INVENTION
In accordance with one embodiment of the invention, there is provided a multi-stage compression refrigeration apparatus including a compressor having a first stage low-pressure compression means and a second stage high-pressure compression means, a condenser, a first decompression means, a first intercooler, a second decompression means, and an evaporator, wherein the refrigerant discharged from the second stage compression means is passed through the condenser, and is diverted into first and second parts, with the first part passed to the first intercooler via the first decompression means, while the second part is passed to the first intercooler to undergo heat exchange therein with the first part, and then passed to the second decompression means, the evaporator, and-further to the first stage low-pressure compression means; and wherein the first part of the refrigerant exiting the first intercooler is mixed with the s
Ebara Toshiyuki
Oda Atsushi
Tadano Masaya
Yamakawa Takashi
Armstrong Westerman & Hattori, LLP
Esquivel Denise L.
Norman Marc
Sanyo Electric Co,. Ltd.
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