vapour absorption refrigeration

1. Vapour absorption refrigeration
system
2022/2023
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2. Introduction
o Vapour Absorption Refrigeration system: Is the type of
refrigeration system which utilizes absorption and desorption
mechanisms to achieve cooling effect. It includes all processes
in vapour compression refrigeration system, such as
compression, condensation, expansion and evaporation.
o The system utilizes absorbent – refrigerant pair such as:
 Water – lithium Bromide (LiBr-H2O)
 Ammonia – water (H2O-NH3)
o The absorption refrigeration machine was introduced in
1928 targeting users in rural areas where electricity was
scarce 2

3. Components of Vapour Absorption System
o Absorber
o Pump(s)
o Generator (or desorber)
o Condenser
o Throttle valves
o Evaporator
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4. Working Principle of Vapour Absorption System
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5. o In the absorber, the absorbent fluid absorbs within it the
refrigerant in the vapour phase, with the consequence of heat
release.
o The refrigerant absorbent mixture is then transferred to the
generator via a pump.
o In this unit (generator), heat is transferred to the mixture in order
to drive off the refrigerant from the mixture, leaving behind a
weak mixture (low percentage of refrigerant) which is transferred
back to the absorber via a throttle valve.
o As the refrigerant-absorbent mixture is pumped to the generator
some heat may be gained from the weak mixture leaving the
generator through a solution heat exchanger.
o This greatly enhances the Coefficient of Performance (COP) of
the system 5

6. Difference between Vapour Absorption and Vapour
Compression Refrigeration System
Vapour Absorption Vapour Compression
1. Requires absorber, pump and generator for
inputting heat energy
Require a compressor to do work
2. Low COP (Currently maximum ~1.4) High COP
3. Performance Not very sensitive to evaporator
temperatures
Performance (COP and Capacity)very
sensitive to evaporator temperatures
4. Very few moving part Many moving parts
5. Economical when low- cost fuels or waste heat
is available
Economical when electricity is available
6. Less noise and vibrations Higher noise and vibrations
7. Presence of liquid at the exit of evaporator is
not a serious problem
Liquid at the exit of evaporator may
damage a compressor

7. Advantages of VAR over Vapour compression
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 High reliability due to absence of moving parts
 Very little maintenance
 Systems require only low grade thermal energy, hence no need
for any grid power
 Silent operation