Why Air Conditioning Placed At The Top Of The Room And Why Does a Single Compartment Refrigerator Have the Freezer Always At The Top In The  Refrigerator

Why Air Conditioning Placed At The Top Of The Room And Why Does a Single Compartment Refrigerator Have the Freezer Always At The Top In The Refrigerator


Domestic Refrigerator

The basic components of the Domestic refrigerator are Evaporator, Compressor, Condenser, and Expansion Valve or device. The Evaporator where the refrigerants or working fluid evaporates absorbing the latent heat o vaporization in the coldest part of the freezer cabinet, where it is located. In the modern frost-free refrigerators,, the evaporator is located outside the cabinet. A fan circulates the air from the evaporator to the freezer. Just below the Freezer, there is a chiller tray. Further below are compartments with progressively higher temperatures.

The bottom-most compartments meant for vegetables are the least cold one. The cold air being heavier flows down from the freezer to the bottom of the refrigerator. The warm air being Lighter flow upward from the vegetable box to the freezer gets cooled and flows down again. Thus, a natural convection current is set up which maintains a temperature gradient between the top and bottom of the refrigerator. The temperature maintained in the freezer is about -15 degrees centigrade. The condenser is usually a wire-and-tube type mounted at the back of the refrigerator, having no fan. 

The refrigerant vapor is condensed with the help of surrounding air which rises above by natural convection as it gets heated after absorbing the latent heat of condensation from the refrigerant. After condensation, the high-pressure liquid refrigerant is reduced to the low pressure of the evaporator bypassing through an expansion device (throttle value of the capillary tube) and the cycle is complete.

Earlier the refrigerant used was R-12(Dichlorodifluoromethane is a colorless gas usually known as Freon-12) and because of the ozone layer depletion, it is now isobutene (C4 H10), propane (C3 H8) or Tetrafluoroethane (C2H2F4 or R134a).

Room Air Conditioner

A window-type air conditioner is given in. Let us consider a room to be maintained at a constant temperature of 25 Degree Centigrade. The air from the room is drawn by a fan and is made to pass over a cooling coil of the evaporator, the surface of which is maintained at a temperature of 10c. After passing over the coil, the air is cooled to around 10c before being supplied to the room at 25 Degree Centigrade by the fan. In the cooling coil, the refrigerant, R-22 (Difluoromonochloromethane is a colorless gas is also known as HCFC-22 is Refrigerant) or R-134a (Hydrofluorocarbon that is non-flammable and non-explosive, has toxicity within limits and good chemical stability) enters at, say 5c and evaporates absorbing the latent heat of vaporization from the room air.

The refrigerant vapor from the evaporator is compressed to high pressure before entering the condenser where the atmospheric air at about say 45 Degree Centigrade, is summer is circulated by a fan. After picking up the latent heat of condensation from the refrigerant, the air is thrown back to the atmosphere say at 55 Degree Centigrade. The high-pressure liquid refrigerant from the condenser is reduced to the low evaporator pressure by passing through the expansion device(capillary tube) before entering the evaporator. The cycle repeats itself.

6 Responses to "Why Air Conditioning Placed At The Top Of The Room And Why Does a Single Compartment Refrigerator Have the Freezer Always At The Top In The Refrigerator"

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