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Describe a practical vapour absorption cycle with a neat sketch for ammonia water system.

Subject:- Refrigeration and Air Conditioning

Topic:- Design of air conditioning systems

Difficulty:- Low

1 Answer
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The simple absorption system is not very economical. So it is fitted with an analyser, a rectifier and two heat exchangers as shown in figure, to make it more practical.

Analyser: In the simple system some water also vaporizes along with ammonia in the generator. If these unwanted water particles are not removed before entering condenser, they will enter into expansion valve and will freeze and choke the pipeline.

Therefore, an analyser is used above the generator. It consists of series of trays such that strong solution from absorber and aqua from rectifier are introduced on the top tray and flow downwards The vapor rising from generator is cooled due to exposure to considerable liquid surface area and most of water vapour condenses. Since aqua is heated by vapour, less external heat is required in generator.

Rectifier:Its function is to cool further the ammonia vapours leaving analyser so that the vapours condense. This condensate is returned to top of analyser by a drip return pipe. It is also known as dehydrator.

Heat Exchangers: The heat exchanger provided between pump and generator is used to cool the weak hot solution returning from generator to absorber and to heat the strong solution leaving the pump and going to generator. This reduces heat supplied to generator and amount of cooling required for absorber, thus increasing plant economy.

The heat exchanger between condenser and evaporator is called liquid sub-cooler since it sub-cools the liquid refrigerant leaving condenser by low temperature ammonia vapour from evaporator.

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