Most of industrial process uses a lot of thermal energy by burning fossil fuel to produce steam or heat for the purpose. After the processes, heat is rejected to the surrounding as waste. This waste heat can be converted to useful refrigeration by using a heat operated refrigeration system, such as an absorption refrigeration cycle. Electricity purchased from utility companies for conventional vapor compression refrigerators can be reduced. The use of heat operated refrigeration systems help reduce problems related to global environmental, such as the so called greenhouse effect from CO2 emission from the combustion of fossil fuels in utility power plants.
Another difference between absorption systems and conventional vapor compression systems is the working fluid used. Most vapor compression systems commonly use chlorofluorocarbon refrigerants (CFCs), because of their thermo physical properties. It is through the restricted use of CFCs, due to depletion of the ozone layer that will make absorption systems more prominent.
However, although absorption systems seem to provide many advantages, vapor compression systems still dominate all market sectors. In order to promote the use of absorption systems, further development is required to improve their performance and reduce cost.
The absorption system differs fundamentally from VCR system in the method employed for compressing the refrigeration. In the absorption system, the compressor is replaced by the combination of an absorber, a generator, and a pump.
The combination called aqua ammonia was used in absorption systems years before LiBr-water combination become popular. The absorption systems have experienced many ups and downs. The absorption was the predecessor of the vapour compression system in 19th century and aqua- ammonia system enjoyed wide applications In domestic refrigerators and large industrial installations in the chemical and process industries. The LiBr-water system was commercialized in the middle of the 20th century as water chillers for large buildings air-conditioning.
In the LiBr-water system water is the refrigerant. This imposes restriction on its use for applications requiring temperatures below 0
°c
.And the LiBr being a salt has a re-crystallization zone when it becomes solid and hence imposes flow restrictions .The vapour absorption system practically LiBr-water system has bounced back with the use of solar energy and the recent emphasis on co-generation which makes available, the otherwise waste heat , for external direct heating source in vapour absorption system.The analysis of this system is relatively easy as the vapour generated in the generator is almost pure refrigerant (water), unlike ammonia-water systems where both ammonia and water vapour are generated in the generator.
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