The refrigerator is a domestic as well as commercial electronic device. It is popularly known as freeze. It is an apparatus or chamber that keeps food items and other substances cool and fresh. It is very useful in storing food in good condition for several days without decay and stale. And particularly in summer and hot weather its importance is barely felt for cold water and other cold products. Again certain food items can be stored for longer duration in the freezing compartments of the refrigerator. Hence for keeping both cooked as well as raw food items, fruits and vegetables, milk and its products, fruit juice and aerated drinks, medicines etc refrigerator is most essential.
The refrigerator was invented by J. Harrison and A. Catlin of Britain in 1851. There are various types of refrigerators. The domestic refrigerators are used in households and the commercial refrigerators are used in shops. Again there are large refrigerators called as freezers and deep freezers which are used for storing things cool and fresh for longer periods. The working principle of all the refrigerators are almost same with a very little difference.
The domestic refrigerator which is commonly used is a compression and absorption refrigerator. Compression and absorption systems cool by altering a refrigerant from a liquid state to a gaseous state and back into the liquid form again. The substance is liquid ammonia sulphur dioxide. It has a storage tank filled with Freon gas, the refrigerant control device, the evaporator, the compressor and the condenser. When the refrigerator is switched on, Freon gas goes out of the storage tank under high pressure. It moves through the pipes of the refrigerant control device, which act as evaporator. The liquid Freon soaks heat from the pipes and are evaporated. As the heat is drawn out, the temperature inside the cabinet of the refrigerator is dropped. The condenser and compressor again transfer Freon gas into liquid. As this cycle goes on, the temperature inside the refrigerator continues to fall to zero degree and also much less. When the inside temperature reduces to an optimum value, a thermostat control cuts of the electric power and the machine halts. Again the temperature starts rising and when it reaches at a certain point, thermostat control again starts the machine. In this way a constant temperature is maintained and the food items are kept cool and fresh. Food items remain fresh inside it as germs can not grow under zero degree temperature.