TITLE.PM5

742 ENGINEERING THERMODYNAMICS

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before being returned to the evaporator. The separation is accomplished by the application of direct
heat in a ‘generator’. The solubility of the refrigerant and absorbent must be suitable and the plant
which uses ammonia as the refrigerant and water as absorbent will be described.

14.4.2. Simple vapour absorption system

Refer Fig. 14.21 for a simple absorption system. The solubility of ammonia in water at low
temperatures and pressures is higher than it is at higher temperatures and pressures. The ammo-
nia vapour leaving the evaporator at point 2 is readily absorbed in the low temperature hot solution
in the absorber. This process is accompanied by the rejection of heat. The ammonia in water
solution is pumped to the higher pressure and is heated in the generator. Due to reduced solubility
of ammonia in water at the higher pressure and temperature, the vapour is removed from the
solution. The vapour then passes to the condenser and the weakened ammonia in water solution is
returned to the absorber.

Absorber

2

Evaporator

1

Expansion

valve

Receiver

4

Condenser

GeneratorGenerator^3

Pump

Strong

solution

Fig. 14.21. (a) Simple vapour absorption system.

Fig. 14.21. (b) Simple vapour absorption system—T-s diagram.