The domestic absorption type refrigerator was invented by two Swedish engineers, Carl Munters and Baltzer Von Platan, in 1925.
This type of refrigerator is called three fluids absorption system. Three fluids are, namely ammonia, hydrogen and water. Ammonia acts as a refrigerant, water as an absorbent and hydrogen gas promotes evaporation of refrigerant in the evaporator.
The main purpose of this system is to eliminate the pump so that in the absence of moving parts the machine becomes noiseless. Moreover, there is no machinery to give mechanical trouble. The following points must be noted for the fluids used in this system:
The ammonia is toxic, but due to the absence of moving parts, there is very little chance of leakage, and the total amount of refrigerant used is also small.
Hydrogen is a light gas and is used to increase the rate of evaporation of liquid ammonia passing through the evaporator. Hydrogen was used in the evaporator to lower the partial pressure of the ammonia, in a similar way to the expansion valve in traditional refrigerators. The hydrogen is also non-corrosive and insoluble in water. It is used in the low-pressure side of the system.
Water is used as a solvent because it has the ability to absorb ammonia readily.
Principle of operation of a domestic Electrolux type refrigerator
The principle of operation of a domestic Electrolux type refrigerator, as shown is discussed below
The strong ammonia solution from the absorber through the heat exchanger is heated in the generator by applying heat from an external source, usually a gas burner.
During this heating process, ammonia vapors are removed from the solution and passed to the condenser.
A rectifier or a water separator is fitted before the condenser removes water vapor carried with the ammonia vapors, so that dry ammonia vapors are supplied to the condenser.
These water vapors, if not removed, will enter into the evaporator causing freezing and choking of the machine.
The ammonia vapors in the condenser are condensed by using an external cooling source.
The liquid refrigerant leaving the condenser flows under gravity to the evaporator where it meets the hydrogen gas.
The hydrogen gas which is being fed to the evaporator permits the liquid ammonia to evaporate at low pressure and temperature according to Dalton's principle.
The mixture of ammonia vapor and hydrogen is passed to the absorber where ammonia is absorbed in the water while the hydrogen rises to the top and flows back to the evaporator.