Vapour absorption refrigeration system is one of the oldest methods of producing refrigerating effect. John Leslie in 1810 kept H2SO4 and water in two separate jars connected together. H2SO4 has very high affinity for water. It absorbs water vapour and this becomes the principle of removing the evaporated water vapour requiring no compressor or pump. H2SO4 is an absorbent in this system that has to be recycled by heating to get rid of the absorbed water vapour, for continuous operation. Windhausen in 1878 used this principle for absorption refrigeration system, which worked on H2SO4.
Ferdinand Carre invented aqua-ammonia absorption system in 1860. Water is a strong absorbent of NH3. If NH3 is kept in a vessel that is exposed to another vessel containing water, the strong absorption potential of water will cause evaporation of NH3 requiring no compressor to drive the vapours. A liquid pump is used to increase the pressure of strong solution. The strong solution is then heated in a generator and passed through a rectification column to separate the water from ammonia. The ammonia vapour is then condensed and recycled. The pump power is negligible hence; the system runs virtually on low- grade energy used for heating the strong solution to separate the water from ammonia. These systems were initially run on steam. Later on oil and natural gas based systems were introduce. In 1922, Balzar von Platen and Carl Munters, two students at Royal Institute of Technology, Stockholm invented a three fluid system that did not require a pump. A heating based bubble pump was used for circulation of strong and weak solutions and hydrogen was used as a non-condensable gas to reduce the partial pressure of NH3 in the evaporator. Geppert in 1899 gave this original idea but he was not successful since he was using air as non-condensable gas. Commercial production began in 1923 by the newly formed company AB Arctic, which was bought by Electrolux in 1925. In 1926 Albert Einstein and his former student Leó Szilárd proposed an alternative design known as Einstein refrigerator. In 2008, Adam Grosser demonstrated his research of a new, very small, refrigeration system for use in third world countries at the TED conference The absorption refrigeration cycle is similar to the vapour compression cycle in that employs a volatile refrigerant ,usually ammonia or water , which alternatively vaporizes under low pressure in the evaporator by absorbing the latent heat from material being cooled and condenses under high pressure in the condenser by surrendering the latent heat to surrounding .The vapour absorption system uses heat energy instead of mechanical energy as in vapour compression systems in order to change the condition of the refrigerant required for the operation of the refrigeration cycle. The function of the compressor in vapour compression system is to be withdrawn from the vapour refrigerant from the evaporator. It then raises its temperature and pressure higher than the cooling agent in the condenser so that the higher pressure vapour can reject the heat in the condenser. The liquid refrigerant is ready to expand to evaporator condition again.
Much of an internal combustion engine’s heat from combustion is discarded out of the exhaust or carried away via the engine cooling water. all this wasted energy could be useful. The common automobile, truck or bus air conditioner uses shaft work of the engine to turn a mechanical compressor. Operating the mechanical compressor increases the load on the engine and therefore increases fuel consumption, emissions and engine operating temperature. With an adsorption compression system, we can utilize the exhaust heat and the heat absorbed by the engine’s cooling water. This heat, which could be considered as free energy, would be enough to drive an adsorption refrigeration system.
2.1 Simple vapor compression cycle: