In the earlier twentieth century, the vapor absorption cycle using water-ammonia systems was very popular and widely used, but after the development of the vapor compression cycle it lost much of its importance because of its low coefficient of performance (0.3 to 0.5). the vapor absorption cycle is used only where waste heat is available or where heat is derived from solar collectors. Absorption refrigerators are a popular alternative to regular compressor refrigerators where electricity is unreliable, costly, or unavailable, where noise from the compressor is problematic, or where surplus heat is available (e.g., from turbine exhausts or industrial processes, or from solar plants).
Let us understand NH3H2O vapour absorption refrigeration system working in simple way
Absorbent :H2O
Refrigerant :NH3
Ammonia vapour leaves the evaporator and enters the absorber where it is dissolved in water forming ammonium hydroxide which is an exothermic reaction. and also the amount of ammonia that can be dissolved in water is inversely proportional to the temperature of the solution therefore to dissolve maximum amount of ammonia in water , cooling water is circulated continously in absorber.
The solution rich in ammonia is pumped to generator while passing from regenerative heat exchanger, while passing from regenerative heat exchanger it absorb some heat before entering the generator.
In generator heat is added in solution and ammonia is separated by forming high pressure ammonia vapours.
These high pressure ammonia vapours may contain some water vapour hence it is passed through analyser where some water vapour is condensed and falls back in generator.
Sometimes, Rectifier is also installed to ensure complete removal of water vapour before ammonia vapour enter the condensor.
(if water vapour is present with ammonia vapour then it may freeze in refrigeration system if temperature goes below 0*c , thus can choke the system. Hence we remove water vapour enter the condenser )
In condenser ammonia vapour loses heat to surrounding and get cooled because if pressure has increased therefore temperature is also increased therefore it has to brought down to get cool liquid so condenser is used, send to throttling device.
The throttling device restricts the flow, which causes a tremendous pressure drop. Due to the drop in pressure, the boiling point of the refrigerant is lowered, and it starts to evaporate. The heat required for evaporation comes from the refrigerant itself, so it loses heat, and its temperature drops
Evaporator is the compartment where the material to be cooled is kept, the cold ammonia liquid is flown in a heat exchanger as a result it absorbs heat thus it evaporates and convert into pure vapour.
And the cycle continues ...
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