VAPOUR ABSORPTION SYSTEM
In this system, absorber, pump and generator combindely replaces compressor of vapour compression system. The refrigerant flows as
absorber ® Pump® Generator® Condenser® Expander® Evaporator
- Absorber: Here lies a weak solution which after absorbing the refrigerant becomes rich solution.
- Pump:it pumps rich solution raising its pressure to condenser pressure.
- Generator: It distills vapour refrigerant from rich solution making it weak solution for recycling in absorber.
the cycle of rich solution flows as absorber ® pump ® generator ® valve ® absorber
- Vapour absorption system may be considered as a combination of heat engine & refrigerating machine.
- So for maximum COP
- Th should be as high as possible
- Tk should be as low as possible
- T0 should be as high as possible
- COP of vapour absorption system first increases with generator temperature
(Th). reaches an optimum then it decreases
REQUIREMENT OF REFRIGERANT ABSORBENT PAIR
- Low viscosity to minimize pump work
- Low freezing point
- Chemical & thermal stability
- Refrigerant should be highly soluble in absorbent
- Their boiling point difference should be large.
Ex. Refrigerant NH3 + Absorbent H2O
Refrigerant H2O + Absorbent LiBr2
- It works on 3 fluid System e.g.,
NH3 + H2O + H2
- There is no solution circulation pump
- Third fluid remains in the evaporator.
- H2 is chosen as it is non corrosive & insoluble in water.
- Two U bends are provided to prevent H2 from going to solution
- The cycle runs on the basis of partial pressure variation.