A special gas called the refrigerant is used in the vapour compression cycle of a refrigerator. It used to be CFC (chlorofluorocarbon). But due to environmental concerns with CFC, namely, the depletion of ozone layer, the gas used nowadays is HFC-134a, also called tetrafluoroethane. The refrigerant passes through the various components of the refrigeration cycle listed in the figures 1 and 2.
Fig. 2 Vapour compression cycle or refrigeration cycle
Here is how the components of the refrigeration cycle interact to cool your food:
1. The compressor constricts the refrigerant vapour, raising its pressure and temperature, and pushes it into the coils of the condenser on the outside of the refrigerator.
2. When the hot gas in the coils of the condenser meets the cooler air temperature of the kitchen, it becomes a liquid.
3. Now in liquid form at high pressure, the refrigerant cools down as it flows through the expansion valve into the evaporator coils inside the freezer and the fridge.
4. The refrigerant absorbs the heat inside the fridge when it flows through the evaporator coils, cooling down the air in the fridge.
5. Last, the refrigerant evaporates to a gas due to raised temperature and then flows back to the compressor, where the cycle starts all over again.
The main component of a refrigerator that needs power is the compressor. It is essentially a pump which is driven by a motor. The hum you hear when the fridge is on is that of the compressor working. The thermostat controls the temperature of the fridge by switching on-and-off the compressor.