Refrigeration
The word 'refrigerate' means to chill or freeze a substance, specifically, to lower its temperature by removing some of its heat. Thus, refrigeration is the process of removing heat from a substance and rejecting the heat so removed to the atmosphere which is at a higher temperature level.
Basic Refrigeration Cycle
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Heat flows from a body at a higher temperature to another body at a lower temperature. But it requires external energy to make the heat flow from a lower temperature to another higher temperature level. To make heat flow from lower temperature (i.e. a refrigerator), level to a higher temperature level, (i.e. atmosphere or natural water), external energy has to be used and we also need a substance as a carrier of heat. The carrier substance which carries the heat is called a refrigerant.
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The mechanical refrigeration is made possible by the practical application of the physical law that the boiling point of a liquid or condensing temperature of a gas can be changed at will by varying the pressure of the vapor in an enclosed space above the liquid level. In the evaporator of a refrigeration system where the heat from the substance to be cooled is removed, the pressure of the refrigerant is lowered whereby the refrigerant boils at a lower temperature enabling the heat to flow from the substance to the refrigerant inside the evaporator. The latent heat of vaporization required for the change of state of the boiling refrigerant liquid to vapor is taken from the substance to be cooled, thereby reducing its temperature. The vapor thus formed is pumped, and its pressure increased and sent to the condenser where the vapor is cooled by atmospheric air or water, and consequently condenses into liquid (being at a higher pressure) for reuse in the evaporator. Refrigeration is accomplished by various methods such as the vapor compression system, absorption system, steam jet refrigeration cycle, etc.
The mechanical vapor compression system of refrigeration is the most widely used method for air-conditioning of buildings and automobiles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and industrial services. Oil refineries, petrochemical and chemical processing plants, and natural gas processing plants are among the many types of industrial plants that often utilize large vapor-compression refrigeration systems. In the context of energy shortages, the vapor-absorption refrigeration system also is gaining in importance, as it works on low pressure steam, hot water or waste heat, and needs only very little of electrical energy for its operation.
The mechanical vapor compression system of refrigeration is the most widely used method for air-conditioning of buildings and automobiles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and industrial services. Oil refineries, petrochemical and chemical processing plants, and natural gas processing plants are among the many types of industrial plants that often utilize large vapor-compression refrigeration systems. In the context of energy shortages, the vapor-absorption refrigeration system also is gaining in importance, as it works on low pressure steam, hot water or waste heat, and needs only very little of electrical energy for its operation.