Refrigeration – Refrigeration producer – Heat exchange between diverse function elements
Reexamination Certificate
2002-08-27
2003-11-11
Esquivel, Denise L. (Department: 3744)
Refrigeration
Refrigeration producer
Heat exchange between diverse function elements
Reexamination Certificate
active
06644068
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to refrigeration systems. More particularly, the invention is directed to an evaporatively-cooled, direct-expansion refrigeration system that can be constructed at a reduced cost in relation to conventional refrigeration systems of similar capability. The invention is also directed to a method of operating such a system.
BACKGROUND OF THE INVENTION
FIG. 1
depicts an evaporatively-cooled, direct-expansion refrigeration system
10
of conventional design. The refrigeration system
10
comprises a compressor
12
, a condenser
14
, an evaporative subcooler
16
, an expansion device
18
, and an evaporator
20
. The compressor
12
, condenser
14
, evaporative subcooler
16
, expansion device
18
, and evaporator
20
are interconnected by piping
22
.
A refrigerant, e.g., halocarbon, enters the compressor
12
as superheated vapor (see arrow
26
in FIG.
1
). The compressor
12
raises the pressure and temperature of the superheated refrigerant. The high-pressure, superheated refrigerant is circulated to the condenser
14
by way of the piping
22
(arrow
28
). The refrigerant is cooled and condensed to saturated liquid in the condenser
14
. In particular, thermal energy is transferred from the refrigerant to the ambient environment in the condenser
14
.
The refrigerant is drawn out of the condenser
14
by gravity, and is subsequently routed through the evaporative subcooler
16
(arrow
30
). The refrigerant is subcooled in the evaporative subcooler
16
, i.e., the temperature of the refrigerant is reduced below the refrigerant's saturation temperature (as in the condenser
12
, thermal energy is transferred from the refrigerant to the ambient environment in the evaporative subcooler
16
). Subcooling is necessary to prevent vaporization of the refrigerant due to pipe friction after the refrigerant leaves the evaporative subcooler
16
. Subcooling also increases the effectiveness of the evaporator
20
, thereby improving the overall efficiency of the refrigeration system
10
.
The subcooled refrigerant subsequently flows to the expansion device
18
(arrow
32
). The pressure and the temperature of the refrigerant are reduced as the refrigerant passes through the expansion device
18
. The lower-pressure, lower-temperature refrigerant then flows to the evaporator
20
via the piping
22
(arrow
34
). The heat-transfer medium that is to be chilled or cooled, e.g., water, is circulated into and out of the evaporator
20
via piping
25
(arrows
36
and
38
). The subcooled refrigerant absorbs thermal energy from the heat-transfer medium, thereby chilling or cooling the medium and providing the desired refrigerating effect. The refrigerant is typically superheated to approximately ten degrees Fahrenheit in the evaporator
20
. Superheating is necessary to ensure that potentially damaging liquid droplets are not present in the refrigerant when the refrigerant reenters the compressor
12
upon leaving the evaporator
20
. The above-noted cycle is started once again upon the return of the superheated refrigerant to the compressor
12
.
The use of the evaporative subcooler
16
in the conventional refrigeration system
10
presents substantial disadvantages. For example, the coils of a typical evaporative subcooler such as the subcooler
16
are relatively large, thereby increasing the refrigerant-charge requirements for the system
10
. Also, the cost of an evaporative subcooler typically represents a substantial portion of the initial overall cost of a refrigeration system such as the system
10
. Furthermore, evaporative subcoolers are usually heavy, and occupy a relatively large volume of equipment space. These characteristics are particularly disadvantageous in rooftop installations, where constraints are commonly imposed on the allowable dimensions and weight of the evaporative subcooler.
In light of the above discussion, it is evident that an unfilled need exists for an evaporatively-cooled, direct-expansion refrigeration system that operates without the use of an evaporative subcooler.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an evaporatively-cooled, direct-expansion refrigeration system that operates without the use of an evaporative subcooler. In accordance with this objective, a presently-preferred refrigeration system comprises a compressor for increasing a temperature and a pressure of a refrigerant, and a condenser fluidly coupled to an outlet of the compressor for condensing the refrigerant. The presently-preferred system also comprises an expansion device for decreasing the temperature and pressure of the refrigerant, and an evaporator fluidly coupled to an outlet of the expansion device for evaporating the refrigerant by transferring thermal energy between the refrigerant and a second fluid. The presently-preferred system further comprises a heat exchanger having a first flow path fluidly coupled to an inlet of the compressor and an outlet of the evaporator, and a second flow path fluidly coupled to an outlet of the condenser and an inlet of the expansion valve. The heat exchanger is adapted to superheat the refrigerant in the first flow path and subcool the refrigerant in the second flow path by transferring thermal energy between the refrigerant in the first and second flow paths.
A further object of the present invention is to provide a method for lowering a temperature of a heat-transfer medium. In accordance with this object, a presently-preferred method of lowering a temperature of a heat-transfer medium comprises compressing a superheated refrigerant to increase a temperature and a pressure thereof, condensing the compressed refrigerant, and subcooling the condensed refrigerant. The presently-preferred method further comprises expanding the subcooled refrigerant to decrease the temperature and pressure thereof, and evaporating the expanded refrigerant by transferring thermal energy to the expanded refrigerant from the heat-transfer medium. The presently-preferred method also comprises superheating the evaporated refrigerant by transferring thermal energy to the evaporated refrigerant from the condensed refrigerant.
A further object of the present invention is to provide a method for operating an evaporatively-cooled, direct-expansion refrigeration system without the use of an evaporative subcooler. In accordance with this object, a presently-preferred method of operating a refrigeration system comprises flowing a superheated refrigerant through a compressor to raise a temperature and a pressure of the superheated refrigerant, flowing the compressed refrigerant through a condenser to condense the compressed refrigerant, and flowing the condensed refrigerant through a first flow path of a heat exchanger to subcool the condensed refrigerant. The presently-preferred method also comprises flowing the subcooled refrigerant through an expansion device to lower the temperature and pressure of the refrigerant, and flowing the expanded refrigerant through an evaporator to evaporate the expanded refrigerant and transfer thermal energy to the expanded refrigerant from a second fluid. The presently-preferred method further comprises flowing the evaporated refrigerant through a second flow path of the heat exchanger to superheat the evaporated refrigerant by transferring thermal energy from the condensed refrigerant to the evaporated refrigerant.
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Drake Malik N.
E-Pak Technology, Inc.
Esquivel Denise L.
Woodcock & Washburn LLP
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