Consider the Vapor compression refrigeration system from Table 1.1, ‘Selected Areas of Application of Engineering Thermodynamics’ in the text book.
The refrigerator is a commonly used household appliance to preserve and store perishable foods and other things by producing a low temperature where the food spoiling agents like bacteria and fungus cannot grow. Refrigerator achieves the low temperature by having a thermally insulated compartment, and an arrangement of a compressor, condenser, expansion device and an evaporator.
Working of a Vapor Compression refrigeration system:
Most of the refrigerators operate on a vapor compression cycle. Initially, the refrigerant enters the compressor as a low-pressure vapor, which is at or above the temperature inside the refrigerator. The vapor is then compressed to a high-pressure, high-temperature vapor. This vapor now travels through the condenser, a series of winding tubes which are exposed to the air (usually on the backs of refrigerators). The refrigerant losses its heat to the surrounding air and gets converted into liquid refrigerant at high pressure.
This high pressure liquid refrigerant the flows through the expansion device, usually a thin tube of copper. Throttling process occurs inside the expansion device; as a result it loses its pressure and temperature. This low temperature refrigerant is sent through the evaporator where the cooling effect is to be produced. The low temperature refrigerant absorbs the heat from the refrigeration space and maintains low temperature.
After absorbing the heat, the refrigerant again enters the compressor and the cycle continues. The refrigerant used normally used is R-134a or R-22, to help absorb and dispel heat. The thermodynamic processes that occur during the refrigeration are compression, condensation, expansion and evaporation. The efficiency of the refrigerator is measured in terms of COP (Coefficient of Performance) and its value is always greater than 1.
