LAYOUT OF TYPICAL DOMESTIC REFRIGERATOR
Refrigerators, once considered a luxury, are now a necessity of daily life. They have usage in homes, hotels, office, laboratories, hospitals, shops restaurants, etc. They are manufactured in several sizes and many brands are available. The different models are rated on the basis of gross volume such as 100 litres, 165 litres, 200 litres, 250 litres and so on.
The construction of household refrigerator, with location of main components.
1. Evaporator: The evaporator is located in a coil form on the freezer box. The liquid refrigerant is evaporated in the evaporator by absorbing heat from the contents of the domestic refrigerator in the cabinet. The evaporator consists of copper metal rubbing surrounding the freezing and cooling compartments.
2. Condenser: The condenser is located as zigzag tubes behind the refrigerator on a mesh. In the condenser, the heat from the refrigerant at a higher temperature is rejected to the atmospheric air.
3. Compressor: The compressor is located at the base at the rear end. It compresses the refrigerant vapour to a high pressure. Reciprocating compressor is used for low capacity domestic refrigerator.
4. Expansion Valve or Throttling Valve: An expansion valve is used to reduce the temperature and pressure of the liquid refrigerant, before it passes to the evaporator. The expansion capillary is located inside the refrigerator body hear the wall. The capillary tube is small diameter tube used as an expansion device.
5. Refrigerator cabinet: The refrigerator cabinet is thermally insulated to minimize heat flow from the atmosphere into the refrigerator. The insulation is glass fiber and the external body is of stainless steel.
The refrigerator works on the vapour compression refrigeration cycle. The refrigerant vapour is first compressed in the compressor. The compressor is a special one known as the hermetic compressor. In this unit, the compressor is sealed casing along with an electrical motor to run. This sealing prevents leakage of refrigerant and lubrication oil. The pressure and temperature of the refrigerant increases after compression and is subsequently condensed in a condenser. In the condenser, the refrigerant rejects heat to a coolant and cools down and finally gets condensed. The condensate is then allowed to pass through capillary to reduce temperature and pressure by expansion of refrigerant. The refrigerant is filtered before entering the capillary tube. The pressure of the refrigerant, when it leaves the capillary, is maintained above atmospheric and temperature corresponds to saturation temperature so that the refrigerant can absorb heat in the evaporator. The refrigerant enters the evaporator and is heated by the heat absorbed from the body or space thereby producing the refrigeration effect. The vapour refrigerant enters the compressor again and the cycle is completed.
When power to the compressor is switched on, a humming sound is heard and the refrigerator is functional. The refrigerant flows through its circuit and ice is produced in the freezer. Frost, i.e., moisture from ambient air, gets deposited on the evaporator coil. Defrosting removes this frost. The water from defrosting is collected in a tray to be removed manually. Articles to be refrigerated are placed on shelves. Fruits and vegetables, which contain moisture, are stored at the base. The temperature here is around 8°C. Thus there are temperature gradients in the refrigerator, negative temperature in the freezer and positive temperature at the base.