Ur intro

Introduction A refrigerator (colloquially fridge) is a popular household appliance

that consists of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room.

Refrigeration is an essential food storage technique in developed countries.

The lower temperature lowers the reproduction rate of bacteria, so the refrigerator reduces the rate of spoilage.

Cont.… A refrigerator maintains a temperature a

few degrees above the freezing point of water. Optimum temperature range for perishable food storage is 3 to 5 °C (37 to 41 °F).

A similar device that maintains a temperature below the freezing point of water is called a freezer.

The refrigerator replaced the icebox, which had been a common household appliance for almost a century and a half. For this reason, a refrigerator is sometimes referred to as an icebox in American usage.

History In 1834, the first working vapor-compression refrigeration system was built. The first commercial ice-making machine was invented in 1854. In 1913, refrigerators for home use were invented. In 1923 Frigidaire introduced the first self-contained unit.

Components

It has 4 main components: Compressor – Pressure producer by compressing gas Condenser Evaporator – Heat exchanger Throttling device – obstructs the flow of liquid

Basic principal of refrigeration The basic principle of refrigeration is simple.

You simply pass a colder liquid continuously around the object that is to be cooled. This will take heat from the object. In the example shown, a cold liquid is passed over an apple, which is to be cooled. Due to the temperature difference, the apple loses heat to the refrigerant liquid. The refrigerant in turn is heated due to heat absorption from the apple. t is clear that, if we can produce cold liquid refrigerant continuously, we can achieve continuous refrigeration. This simple fact forms the core of the refrigeration technology

Refrigeration cycle

The refrigerant comes into the compressor as a low-pressure gas, it is compressed and then moves out of the compressor as a high-pressure gas.

The gas then flows to the condenser. Here the gas condenses to a liquid, and gives off its heat to the outside air.

The liquid then moves to the expansion valve under high pressure. This valve restricts the flow of the fluid, and lowers its pressure as it leaves the expansion valve.

The low-pressure liquid then moves to the evaporator, where heat from the inside air is absorbed and changes it from a liquid to a gas.

As a hot low-pressure gas, the refrigerant moves to the compressor where the entire cycle is repeated.

Refrigerant Modern refrigerators usually use a refrigerant called HFC-134a

(1,1,1,2-Tetrafluoroethane), which does not deplete the ozone layer, instead of Freon. A R-134a is now becoming very uncommon in Europe. Newer refrigerants are being used instead. The main refrigerant now used is R-600a, or isobutane.

Leakage hazard A gas leak in a refrigerator, although not likely to occur, can

decrease the ability of your refrigerator to do its job correctly. Although it's not generally believed that such a leak can be

hazardous to your health, the short-term discomfort caused by breathing Freon -- the gas used in older refrigerators -- can be problematic.

Uses of refrigeration Separation of air into its constituents by fractional distillation. Air

is liquefied at -1910C. Liquefaction temperature of Nitrogen is -1860C and that of oxygen is -1960C.

Separation of gases in the petroleum industry (Refinery). Lowest temperature needed is -1600C and the cooling capacity needed are 10000 tons of refrigeration.

Synthetic ammonia plants condense ammonia gas with temperatures between -200C to +100C before storage or before shipment.

Preservation of food items Ice manufacturing

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