Absorption Refrigeration

Absorption refrigeration is a form that is economically attractive when there is a source of
thermal energy at a temperature between 100 to 200°C. An example of inexpensive thermal
energy sources are, solar energy, waste heat from co generation or process steam plants,
geothermal energy, and natural gas when available at a low price.
The absorption refrigeration involve the absorption process of a refrigerant by a transport
medium called absorbent to form a liquid solution. The liquid solution the pumped to the
higher pressure. Due to the average specific volume of the liquid solution is much less than
of the refrigerant vapor , significantly less work is needed. Accordingly, absorption
refrigeration system have the advantage of relatively small work input compared to vapor-
compression system.
Absorption refrigeration systems differ from compressor refrigerating systems at least in
two major aspects :
1. The refrigerant drawn out of the evaporator is compressed not by a mechanical
process, but by a thermal heat-exchange which consists of an absorber, a generator,
and a pump.
2. Operation of thermal compressors requires a solvent (for a second working fluid) as
well as refrigerant.
Two most generous industrial absorption-type refrigeration systems are :
1. Aqua ammonia system.
2. Lithium bromide-water system.
Both of the system respectively used ammonia and water as the refrigerant. Ammonia –
water is used for evaporating temperature on the range -60 until 10°C, while water-lithium
bromide is used for evaporating temperatures more than 0°C. No other any pair
components had been suggested that widely used except the two of them. Figure 5
represents the basic absorption refrigeration system.