Entropy generated and exergy destroyed in lithium bromide thermal compressors driven by the exhaust gases of an engine
✍ Scribed by M. Izquierdo; M. de Vega; A. Lecuona; P. Rodríguez
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 151 KB
- Volume
- 24
- Category
- Article
- ISSN
- 0363-907X
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✦ Synopsis
This work is devoted to the study of the entropy generated and the exergy destroyed in the lithium bromide absorption thermal compressors of single and multiple e!ects, driven by the heat of the exhaust gases of an engine, when the absorption heat is directly transferred either to water or to air. Air-cooled systems work with temperature and pressure gradients higher than those cooled by water. The absorption temperature in air-cooled systems can reach and even exceed 503C. Under these conditions, boiling temperature within the high desorber of the double and triple e!ect systems can exceed 200 and 3003C, respectively. Maximum pressures reach values of 1.7 and 15 bar, respectively. The thermal compressor cooled by air generates more entropy and destroys more exergy than the one cooled by water. The triple-e!ect thermal compressor destroys less exergy than the one of double e!ect and the latter destroys less exergy than the one of single e!ect.
The lithium bromide thermal compressor of single e!ect cooled by air is not feasible when working with absorption temperatures around 503C. The one of double e!ect is feasible since the high-pressure desorber can work at higher temperatures. Under these conditions, the solution cycle described within the highpressure desorber remains out of the zone of crystals formation, and o!ers the possibility of producing more refrigerant than the one of single e!ect. Also, in the double-e!ect compressor less entropy is generated, and therefore less exergy is destroyed than in the single e!ect. The triple-e!ect compressor cooled by air o!ers the possibility of producing more refrigerant than the one of double e!ect, but at higher expenses of temperatures and boiling pressures of the solution. This creates corrosion and control problems, which do not have an easy solution yet. Less exergy destruction does not compensate for the increase of these problems. In any case, the compression process of the cooling steam occurs with entropy reduction.