02-03-2013, 03:02 PM
Energy Efficient Refrigeration
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THE BASIC REFRIGERATION CYCLE
Mechanical refrigeration is achieved by constantly circulating, evaporating, and
condensing a fixed suppy of refrigerant inside a closcd systen.
Mechanical refrigeration is made possible thrcugh the proper use of tcmperature, Prcssure,
latent hcat of vaporization, and latent heat of condensation.
Evaporation occrus at a low pressure and 1ow temperature. Condensation occurs
at a high temperature and high pressure. Thus, it is possible to transfer lteat ftom
an area of 1ow temperatrre to an area of high temperature
If we begin the rcfrigeration cycle at the evaporator inlet the 1ow-pressure liquid expands
absorbs heat, and evaporates, changing to a low prcssurc vapor at the ortlet of the
evaporator. During the cxpansion process approrimately 20 petcent of the refrigerant
tums to flash gas. Flash gas cools the remaining refrigeranlt down to evaporator
temperature.
The compressor draws this vapor from the evaporator and increases its pressure. The
high prcssure vapor is then dischargcd to the condenser . In the condenser, the heat is
removed from the vapor, causing it to condense and become warm, high-pressure liquid.
The next component encountered by the refrigerant as it travels through the system is the
liquid line strainer/drier, which prevents plugging of the flow-control device by trapping
scale, dirt, and moisture. The flow of refrigerant into the evaporator is controlled by a
pressure differential across the flow control device.
As the warm, high-Pressurc liquid refrigerant cnters the evaporator, it is subjected to a
much lower pressure owing to the combined suction of the comprcssor and the pressrre
drop across the flow control device. Thus, thc refrigerant tends to expand and evaporate.
In order to evaporate, the liquid mrst absorb heat from the air passing over the evaporator.
Eventually, the dcsired temperature is reached inside thc conditioned space and a
tcmperature control (thermostat) will stop the compressor. As the tempenttre of the
conditioned space rises, the temperatue control starts the compressor again. After the
compressor starts, the cycle is continued.