Domestic refrigerators can either be worked by gas or, as in the vast majority of cases, electricity. In the electric model a compressor is driven by an electric motor to circulate a fluid refrigerant (a liquid cooling agent). This fluid boils at an extremely low temperature. This fluid is usually Freon, which is a substance which contains both carbon and fluorine. As the refrigerant transforms into a vapour, it absorbs the heat from the evaporator or freezing compartment. This vapour becomes compressed and is then driven at high pressure to the condenser. At this stage the refrigerant condenses back to its liquid form, losing its heat to the outside air. After expansion to low pressure at a valve, the liquid then returns to the evaporator.
Inside the gas refrigerator, a generator is filled with ammonia gas which has been dissolved in water. With the use of a gas flame, the liquid is heated up and the resulting ammonia vapour is driven off. The vapour becomes liquefied within a condenser, thereby losing its heat. It then proceeds on to an evaporator, where it absorbs the heat from the refrigerator and changes back to its gaseous state. The gas sinks down to the base of the evaporator and is drained to the absorber. From this point it can return to the generator.
