Refrigeration may be defined as the process by which the temperature of a given space or a substance is lowered below that of the atmosphere or surroundings. The system maintained at the lower temperature is known as refrigerated system which the equipment used to maintain this lower temperature is known as the refrigerating system. In order to maintain a temperature below the surrounding atmosphere, it is essential that whatever amount of heat gets into refrigerated space, must be extracted out to maintain the desired temperature differential.
The cooling effect may be obtained by any of the following principles:
· By chemical means in 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.
· By bringing 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.
· By using mechanical or heat energy to operate a "heat pump" by which heat may be abstracted from a low temperature region and rejected, together with the energy required to sustain the process, to a region of high temperature.