Refrigeration & Equipment Engineering

Unit 2 - Refrigeration Systems

2.8.The function of an absorption refrigeration system

In a simple absorption refrigeration, the low pressure refrigerant vapour (ammonia) coming from the evaporator is absorbed in the absorber by the weak solution of refrigerant in water. Absorption of ammonia lowers the pressure in the absorber, which in turn draws more ammonia vapour from the evaporator; water cooling system is engaged in the absorber to remove the heat of solution. The solution in the absorber is called a strong solution because it is rich in refrigerant. The strong solution from the absorber is pumped to the generator, which is at a higher pressure. Heat is added to the generator from the heating source, which may be a gas burner or steam.
 
As a result of heating, ammonia gas gets expelled from the strong solution in the generator and passes onto the condenser, where it is again condensed to liquid and passed on to receiver. The weak solution in the generator after ammonia is expelled pass through the reducing valve to the absorber.
 
Ammonia and water combination is commonly used in (domestic refrigeration) absorption due to the following reasons.

• Water has the ability to absorb ammonia in large quantity.
• Ammonia and water have different boiling points.
• Ammonia has high latent heat value.
• Ammonia and water are easily available.

 Some times absorption refrigeration machine does nit give proper cooling effect because of the following causes.

• Generator is not being heated properly
• Condenser is not being cooled properly
• Absorber is not being cooled properly
• Cabinet is overloaded
• Door leakage of the cabinet

 

Heat absorbed in evaporator

C.O.P of absorption refrigeration system=-----------------------------------------------

Work done by pump +Heat supplied in generator