Refrigeration – Refrigeration producer – Distinct vapor liquid separator and separated liquid recycle
Reexamination Certificate
2000-11-30
2001-11-20
Bennett, Henry (Department: 3744)
Refrigeration
Refrigeration producer
Distinct vapor liquid separator and separated liquid recycle
C062S515000, C165S173000
Reexamination Certificate
active
06318118
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to cooling systems, such as air conditioning and refrigeration systems, and in particular to an improved evaporator with enhanced refrigerant distribution.
BACKGROUND ART
In space conditioning systems, such as air conditioners, heat pumps and refrigeration systems, wherein a phase change refrigerant is used as the heat transfer medium, two heat exchangers are typically used, one to substantially evaporate liquid refrigerant to cool an external fluid such as air passing through the evaporator, and the other as a condenser to substantially condense vapor refrigerant by transferring heat to an external fluid passing through the condenser.
Heat exchangers having refrigerant conduits of relatively flat cross-section are known in the art. Such heat exchangers are often referred to as “parallel flow” heat exchangers. In such parallel flow heat exchangers, the interior of each conduit is divided into a plurality of hydraulically parallel flow paths of relatively small hydraulic diameter (e.g., 0.070 inch or less), which are often referred to as “microchannels”, to accommodate the flow of heat transfer fluid (e.g., a phase change refrigerant) therethrough. Parallel flow heat exchangers may be of the “tube and fin” type in which tubular conduits are laced through a plurality of heat transfer enhancing fins or of the “serpentine” type in which serpentine fins are coupled between the conduits. The relatively small hydraulic diameter flow paths enhance heat transfer between a fluid such as a phase change refrigerant flowing inside the heat exchanger conduits and an external fluid such as air flowing through the heat exchanger on the outside of the conduits, particularly when the heat exchanger is used as a condenser.
However, when parallel flow heat exchangers are used as evaporators, performance is degraded by the uneven distribution of liquid refrigerant in the various flow paths. This uneven distribution results in some flow paths having too much liquid refrigerant and some having not enough. One approach to solving the aforementioned problem of uneven refrigerant distribution in an evaporator is described in U.S. Pat. No. Re. 35,502. This patent shows an evaporator having an inlet header with two inlets at respective opposed ends thereof to generate streams of incoming liquid refrigerant, which impinge upon one another to dissipate the kinetic energy and/or momentum of the streams, and an outlet header with two outlets at respective opposed ends thereof to generate two streams of outgoing vapor refrigerant, which reduces outlet resistance. The configuration of the inlet and outlet headers results in a more uniform flow of the refrigerant through the evaporator flow paths. Although some improvement in refrigerant distribution is achieved using this approach, uneven distribution of refrigerant still results because of the mixed phase (ie., liquid and vapor) refrigerant entering the evaporator.
There is, therefore, a need for improved refrigerant distribution among the flow paths of an evaporator and in particular among the flow paths of a “parallel flow” evaporator.
SUMMARY OF THE INVENTION
In accordance with the present invention, an improved evaporator for evaporating a phase change refrigerant by transferring heat to the refrigerant from an external fluid is provided. The evaporator is comprised of inlet means for introducing the refrigerant into the evaporator, outlet means for discharging the refrigerant from the evaporator; plural conduits defining a plurality of hydraulic flow paths between the inlet means and outlet means; and a separator operable to substantially separate liquid refrigerant from vapor refrigerant before the refrigerant is introduced into the evaporator, such that substantially only the liquid refrigerant is introduced into a selected one or more of the conduits.
In accordance with a feature of the invention, the separator has an inlet port through which the refrigerant is able to enter the separator, a first outlet port through which the liquid refrigerant is able to exit the separator and a second outlet port through which the vapor refrigerant is able to exit the separator.
In accordance with another feature of the invention, the inlet means includes an inlet header and the outlet means includes an outlet header. The conduits extend between the inlet header and the outlet header. The inlet header has at least one inlet through which refrigerant is able to enter the evaporator and the outlet header has at least one outlet through which refrigerant is able to exit the evaporator.
In accordance with yet another feature of the invention, a refrigerant expansion device is operably associated with the separator.
In accordance with one embodiment of the invention, bypass means is provided for bypassing the evaporator with the vapor refrigerant. In accordance with another embodiment, the bypass means includes a refrigerant line communicating between the second outlet port of the separator and a suction line of a refrigerant compressor. The bypass line is in heat exchange relationship with a liquid refrigerant line, whereby heat is transferred from the liquid refrigerant to the vapor refrigerant to superheat the vapor refrigerant.
In the preferred embodiment, the evaporator is not bypassed, but rather a baffle is located in the inlet header to divide the inlet header into first and second portions. The first portion is in fluid communication with the first outlet port of the separator for introducing substantially only the liquid refrigerant into the first portion. The second portion is in fluid communication with the second outlet port of the separator, such that substantially only the vapor refrigerant is introduced into the second portion. A first one or more of the conduits communicates with the first portion, such that only liquid refrigerant is introduced into the first one or more of the conduits. A second one or more of the conduits communicates with the second portion, such that substantially only the vapor refrigerant is introduced into the second one or more of the conduits. Also, in the preferred embodiment, the inlet header has only one inlet for introducing refrigerant into the evaporator and the outlet header has two outlets for discharging the refrigerant from the evaporator.
Empirical testing has shown that the evaporator according to the present invention provides substantially increased cooling capacity as compared to prior art evaporators. The pressure drop across the evaporator is also substantially reduced compared to the pressure drop across prior art evaporators. This improvement in performance is believed to be due to better distribution of the refrigerant among the hydraulically parallel flow paths of the evaporator, which is achieved by substantially separating the liquid refrigerant from the vapor refrigerant before the refrigerant enters the evaporator The present invention is particularly advantageous in improving refrigerant distribution among the flow paths in “parallel flow” evaporators.
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Hanson Oved W.
Van Essen Leonard J.
Bennett Henry
Jiang Chen-Wen
Lennox Manufacturing Inc.
McCord W. Kirk
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