Explain Vapor Absorption System

Vapor Absorption System 

In this system refrigerant is absorbed by an absorbent on low pressure side of the system and rich
solution is pumped up on higher pressure side. Heat is released in absorption and condensation,
which is taken away by cooling water. Refrigerant is separated from absorbent in generator
where heat is supplied by steam or hot water or other heat source. Rich (or strong) solution from
absorber is pumped to generator via a heat exchanger, which serves the purpose of cooling the
weak solution on its return to absorber and heating the strong solution on way to generator. This
saves heat supplied to generator and heat removed in absorber.
Significant features and advantages

1. It is similar to standard vapor compression cycle, but it is heat operated system. Energy
source, other than electricity can be used to operate the system. Compressor is replaced
by an absorber and generator loop.

2. A secondary fluid or crystal called absorbent is used to absorb refrigerant in a vessel
called absorber. A liquid rather than a gaseous substance is pumped from low pressure
side to high pressure side which requires less work. Strong solution from absorber is
pumped to generator, where refrigerant is evaporated from absorbent by supply of
external heat to the system. Refrigerant vapor from generator is passed on to condenser
where it is condensed to liquid by removal of heat by cooling medium (air or water).
Liquid refrigerant is throttled to evaporator pressure and passed to the evaporator, where
it removes the heat from the cooled substance (called load).

3. “Performance factor” (ηp) or “COPabs” (Coefficient of Performance Absorption cycle) is
defined as:

where, qg = heat rate supplied to generator,
and qe = heat rate taken in to evaporator.

In this definition smaller quantity of mechanical work input to pumps is ignored as compared to
large quantity of heat rate sin generator and evaporator. In general, if we take into consideration
the pump work also, then the definition will be as:

[Note: In industrial practice, sometimes it may be expressed in terms of rate of steam supplied to
the system per ton of refrigeration, e.g., 20 kg / hr. ton]
Application:
1. Domestic refrigerator “Electrolux” of “Servel” company.
2. Commercial refrigeration for air conditioning in chiller plant.