Refrigeration – Automatic control – Refrigeration producer
Reexamination Certificate
2000-11-13
2002-10-08
Tapolcai, William E. (Department: 3744)
Refrigeration
Automatic control
Refrigeration producer
C062S513000
Reexamination Certificate
active
06460358
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a refrigerant suction side to liquid refrigerant heat exchanger located in such a way that the sensing bulb of a thermostatic expansion valve (TXV) whether mechanical or electronic, is located downstream of the heat exchanger, which is in turn downstream of the evaporator, in the direction of flow of the suction gas towards the compressor, so that the preset superheat setting of the thermostatic expansion device/valve is not exceeded by the action of the heat exchanger.
This invention more particularly pertains to the heat exchanger reducing or eliminating both the flash gas loss and superheat regions of an evaporator, thereby increasing the effective surface area of an evaporator and providing for a colder average temperature of the evaporator and providing for an increased mass flow of refrigerant through the evaporator and thereby an increased heat absorbing capacity of the evaporator.
Where the primary function of the refrigerant is to provide heat such as in a heat pump, pool heater or dedicated heat pump water heater, the overall coefficient of performance of the heat pump is dramatically increased in the evaporator efficiency improvement as well as by the heat reclaiming action of the heat exchanger of the heat contained in the liquid refrigerant.
2. Description of the Background Art
Presently there exist many types of devices designed to operate in the thermal transfer cycle. The vapor-compression refrigeration cycle is the pattern cycle for the great majority of commercially available refrigeration systems. This thermal transfer cycle is customarily accomplished by a compressor, condenser, throttling device and evaporator connected in serial fluid communication with one another. The system is charged with refrigerant, which circulates through each of the components. More particularly, the refrigerant of the system circulates through each of the components to remove heat from the evaporator and transfer heat to the condenser. The compressor compresses the refrigerant from a low-pressure superheated vapor state to a high-pressure superheated vapor state thereby increasing the temperature, enthalpy and pressure of the refrigerant. A superheated vapor is a vapor that has been heated above its boiling point temperature. It then leaves the compressor and enters the condenser as a vapor at some elevated pressure where the refrigerant is condensed as a result of the heat transfer to cooling water and/or to ambient air. The refrigerant then flows through the condenser condensing the refrigerant at a substantially constant pressure to a saturated-liquid state. The refrigerant then leaves the condenser as a high pressure liquid. The pressure of the liquid is decreased as it flows through the expansion valve causing the refrigerant to change to a mixed liquid-vapor state. The remaining liquid, now at low pressure, is vaporized in the evaporator as a result of heat transfer from the refrigerated space. This vapor then enters the compressor to complete the cycle.
The ideal cycle and hardware schematic for vapor compression refrigeration is shown in
FIG. 1
as cycle
1
-
2
-
3
-
4
-
1
. More particularly, the process representation in
FIG. 1
is represented by a pressure-enthalpy diagram, which illustrates the particular thermodynamic characteristics of a typical refrigerant. The P-h plane is particularly useful in showing the amounts of energy transfer as heat. Referring to
FIG. 1
, saturated vapor at low pressure enters the compressor and undergoes a reversible adiabatic compression,
1
-
2
. Adiabatic refers to any change in which there is no gain or loss of heat. Heat is then rejected at constant pressure in process
2
-
3
, an adiabatic pressure change occurs through the expansion device in process
3
-
4
, and the working fluid is then evaporated at constant pressure, process
4
-
1
, to complete the cycle.
However, the actual refrigeration cycle may deviate from the ideal cycle primarily because of pressure drops associated with the fluid flow and heat transfer to or from the surroundings.
It is readily apparent that the evaporator plays an important role in removing heat from the thermal cycle. Evaporators convert a liquid to a vapor by the addition of heat extracted from the air or other material in contact with the evaporator. The evaporator surface area has three distinct zones; the flash gas loss area, where the liquid refrigerant is cooling adiabatically (no heat transfer theoretically) to the phase change temperature; the phase change area where the liquid refrigerant is evaporating because of heat being absorbed from the material the evaporator is in contact with and; the superheat region where all of the liquid has been evaporated and now the gas phase refrigerant is absorbing heat.
Both the flash gas loss region and the superheat region of the evaporator are less effective at removing heat than the phase change area. By reducing or eliminating both of these areas and increasing the area of phase change, the entire surface area of the evaporator becomes more effective in removing heat. In fact, the colder the refrigeration application the greater the effect of this elimination of the flash gas loss and superheat regions. The low pressure, suction side to liquid refrigerant heat exchanger, with the sensing bulb or sensor of a mechanical or electronic thermostatic expansion valve located downstream of the heat exchanger in the direction towards the compressor, accomplishes maximum subcooling by allowing sufficient excess refrigerant through the TXV to fully subcool the liquid refrigerant while maintaining the superheat setting of the TXV, thereby reducing or eliminating both the flash gas loss region and superheat regions of the evaporator.
There currently are known low pressure, suction side to liquid refrigerant heat exchangers where superheat above the TXV superheat set point is utilized to subcool the liquid refrigerant. The problem with these known heat exchangers are that this increased superheat temperature reduces the volumetric efficiency of the compressor, increases the hot gas discharge temperature, increases the operating temperature of the compressor thereby decreasing the operational life expectancy of the compressor and only minimally affects the liquid refrigerant temperature because of the limited effectiveness of using superheat only to cool the liquid refrigerant.
None of the known embodiments of the suction side to liquid refrigerant heat exchanger art deals with these known deficiencies that exist within the scope of this type of heat exchanger art.
In response to these realized inadequacies of earlier configurations of low pressure, suction side to liquid refrigerant heat exchangers used within the thermal transfer cycle of air conditioners, refrigeration equipment and heat pumps, it became clear that there is a need for a suction side to liquid refrigerant heat exchanger that would overcome these realized inadequacies. The result of the use of this new low pressure, suction side to liquid refrigerant heat exchanger system design being greater refrigeration capacity and improved dehumidification (for air cooling systems), both gained at relatively little additional power consumption for the total refrigeration thermal cycle. The greater capacity being realized from the higher mass flow of refrigerant through the evaporator due to improved evaporator heat exchange brought about by the reduction or elimination of the flash gas loss and superheat regions in the evaporator through the use of the new and improved low pressure, suction side to liquid refrigerant heat exchanger system. Further, in heating applications, in addition to the improved heat absorption effect on the evaporator, the low pressure, suction side to liquid refrigerant heat exchanger acts as a reclaimer for heat normally wasted in the flash gas region thereby providing even more heating capacity. Inasmuch as the art comprises various types of evaporator low pressure, suction side to liquid refr
Holland & Knight LLP
Tapolcai William E.
LandOfFree
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