Refrigeration may be defined as the process by which the temperature of a given space or a space or a substance is lowered below that of the atmosphere or surroundings. the system maintained at the lower temperature is knows as refrigerated system which the equipment used to maintain this lower temperature is knows as the refrigerating system. In order to maintain the temperature below the refrigerated space, must be extracted out to maintain the desired temperature differential.
The cooling effect may be obtained by any of the following principles:
i) By chemical means on which case a chemical reaction is carried out which absorbs heat for its completion. The heat required for this purpose is taken from the substance or space to be cooled.
ii) By brining the substance to be cooled directly or indirectly in contact with some cooling medium such as chilled water or ice from which heat has already been removed either naturally or other wise.
iii) By using mechanical or heat energy to operate a " heat pump" by which heat may b abstracted from a low temperature region and rejected together with the energy required to sustain the process to a region of high temperature