Absorption refrigeration is refrigeration based on the absorption system in which one part of the system has to be heated. However, because no compressor is used and there are no other moving parts that need to be driven, this type of refrigeration does not have to be electrical. All gas refrigerators are absorption refrigerators. One great advantage is that there are no moving parts to wear out.

 

Ammonia is used as the refrigerant. It has the advantage of a high latent heat but the disadvantage that it is poisonous, gives off a unpleasant smell if the refrigerator springs a leak, and is corrosive so that materials have to be carefully chosen.

 

The absorption system works on the principle that a liquid such as water will absorb the gas ammonia to form a highly concentrated solution. When this is heated, ammonia gas comes off at high pressure and can then be liquefied by cooling. The absorption device does away with the need for a compressor.

 

When the concentrated ammonia solution in the generator (see diagram) is heated, ammonia vapor at high pressure comes off. The vapor is air-cooled and liquefied by the condenser. The liquid passes on to the evaporator which in this case is a chamber filled with hydrogen gas under pressure. The liquid ammonia rapidly expands, becomes a gas and cools as it does so. This cooling can be used to cool food. Heat passes from the food into the colder vapor. This is able to expand. Because the pressure of the ammonia gas is very low (although the total pressure of hydrogen and ammonia is quite high), the whole system is kept at the same pressure.

 

In the next stage, the absorber, the ammonia dissolves in water forming a concentrated solution. A certain quantity of weak solution that has lost most of its ammonia siphons over from the generator to level up the pressures. In doing so the weak solution is able to absorb more ammonia. The newly formed concentrated ammonia solution flows over into the generator to be heated by the gas flame and release its ammonia. The whole cycle continually repeats itself.