In a refrigerator what produces the cooling?
(1) The ice which deposits on the freezer
(2) The sudden expansion of a compressed gas
(3) The evaporation of a volatile liquid
(4) None of these
Answer: (4) Basically, a refrigeration system consists of devices that compress and expand refrigerant gas. When refrigerant gas is compressed it expels heat and when it is suddenly expanded, absorbs heat. A refrigerator (colloquially fridge) is a common 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. A vapour compression cycle is used in most household refrigerators, refrigerator-freezers and freezers. In this cycle, a circulating refrigerant such as R134a enters a compressor as a low-pressure vapour at or slightly above the temperature of the refrigerator interior. The vapour is compressed and exits the compressor as high-pressure superheated vapour. The superheated vapour travels under pressure through coils or tubes comprising the condenser, which are passively cooled by exposure to air in the room. The condenser cools the vapour, which liquefies. As the refrigerant leaves the condenser, it is still under pressure but is now only slightly above room temperature. This liquid refrigerant is forced through a metering or throttling device, also known as an expansion valve (essentially a pin-hole sized constriction in the tubing) to an area of much lower pressure.
