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Refrigeration Superheat and Subcooling

written by: Lamar Stonecypher • edited by: Lamar Stonecypher • updated: 12/24/2009

If you are interested in learning about how large refrigeration systems work, it is important to know about subcooling and superheating. This article will highlight the important features of these terms.

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    What is Subcooling?

    Before we discuss subcooling and super heating, it is essential to understand what refrigeration is. Refrigeration is the extraction of heat, or the transmission of heat by mechanical methods, from one location to another. Subcooling in refrigeration implies cooling the refrigerant in liquid state, at uniform pressure, to a temperature that is less than the saturation temperature, which corresponds to condenser pressure.

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    Advantages Of Subcooling

    • Refrigeration is improved when a liquid refrigerant is subcooled by a circulation of cold water in the heat exchanger or by some other methods. As a general rule, a 1% increase in refrigeration can be achieved for every 2 degrees of liquid subcooling obtained. Due to this characteristic, designs of condensers have been changed to achieve obtain liquid subcooling.
    • Production of flash gas is reduced during the process of expansion.
    • Greater latitude is achieved in management of piping and location of evaporator.
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    Methods Of Subcooling

    Refrigerant can be subcooled by following methods:

    • By improving and carrying out modifications in condensers so that subcooling arrangement is included.
    • By Installing internal and external heat exchangers to provide subcooling.
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    What Is Superheating?

    After liquid refrigerant enters an evaporator, it is normally entirely vaporized before it arrives at the outlet of evaporator. The liquid is vaporized at low temperature, while the vapor is cold after the liquid has been totally evaporated. As the cold vapor flows though the evaporator, it continues to absorb heat, and becomes superheated. As the vapor becomes superheated, it absorbs sensible heat in the evaporator. Thus, the effect of refrigeration for every pound of refrigerant is enhanced. Refrigerant absorbs not only the heat required to vaporize it, but also an extra quantity of sensible heat, due to which it is superheated

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    Effect Of Superheating

    Superheating is the sensible heating of refrigerant vapor at invariable pressure in the evaporator to a temperature more than the temperature of saturation corresponding to the evaporator pressure. Though the effect of refrigeration is increased by superheating, the density of vapor which quits the evaporator and enters the compressor is reduced. Consequently, the quantity of vapor which enters the compressor is decreased by superheating. Thus we see that the capacity of the system of refrigeration increases with superheating of the vapor, and simultaneously the refrigeration capacity is decreased with the decrease in density during superheating. The result of these two opposite trends must be observed to establish whether or not the refrigerating capacity of a system is increased by superheating. However, superheating ensures total evaporation of the liquid refrigerant before it goes into the compressor.