25-08-2017, 09:32 PM
Vapor Absorption Refrigeration System
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ABSTRACT
Some liquids like water have great affinity for absorbing large quantities of certain
vapors (NH3) and reduce the total volume greatly. The absorption refrigeration system
differs fundamentally from vapor compression system only in the method of
compressing the refrigerant. An absorber, generator and pump in the absorption
refrigerating system replace the compressor of a vapor compression system.
Figure 6.7 shows the schematic diagram of a vapor absorption system. Ammonia vapor
is produced in the generator at high pressure from the strong solution of NH3 by an
external heating source. The water vapor carried with ammonia is removed in the
rectifier and only the dehydrated ammonia gas enters into the condenser. High pressure
NH3 vapor is condensed in the condenser. The cooled NH3 solution is passed through a
throttle valve and the pressure and temperature of the refrigerant are reduced below the temperature to be maintained in the evaporator. The low temperature refrigerant enters
the evaporator and absorbs the required heat from the evaporator and leaves the
evaporator as saturated vapor. Slightly superheated, low pressure NH3 vapor is
absorbed by the weak solution of NH3 which is sprayed in the absorber as shown in
Fig.6.7.
Weak NH3 solution (aqua–ammonia) entering the absorber becomes strong solution
after absorbing NH3 vapor and then it is pumped to the generator through the heat
exchanger. The pump increases the pressure of the strong solution to generator
pressure. The strong NH3 solution coming from the absorber absorbs heat form high
temperature weak NH3 solution in the heat exchanger. The solution in the generator
becomes weak as NH3 vapor comes out of it. The weak high temperature ammonia
solution from the generator is passed to the heat exchanger through the throttle valve.
The pressure of the liquid is reduced to the absorber pressure by the throttle valve.