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Finite time thermodynamics study and exergetic analysis of ammonia-water absorption systems.

Author(s) : LE LOSTEC B., MILLETTE J., GALANIS N.

Type of article: Article

Summary

This paper presents an optimization study of a single stage absorption machine operating with an ammonia-water mixture under steady state conditions. The power in the evaporator, the temperatures of the external fluids entering the four external heat exchangers as well as the effectiveness of these heat exchangers and the efficiency of the pump are assumed fixed. The results include the minimum value of the total thermal conductance as well as the corresponding mean internal temperatures, overall irreversibility and exergetic efficiency for a range of values of the coefficient of performance (COP). They show the existence of three optimum values of the COP: the first minimises the total thermal conductance , the second minimises the overall irreversibility and the third maximises the exergetic efficiency. They also show that these three COP values are lower than the maximum COP which corresponds to the convergence of the internal and external temperatures towards a common value. The influence of various parameters on the minimum thermal conductance of the heat exchangers and on the corresponding exergy efficiency has also been evaluated. From an exergetic viewpoint it is interesting to reduce the temperature at the desorber and at the evaporator and to raise the values of that parameter at the condenser and the absorber. However these changes must be accompanied by an important increase in the total thermal conductance if it is desired to conserve a constant COP. The internal heat exchangers between the working fluid and the solution improve both the overall exergy efficiency and the coefficient of performance of the absorption apparatus. [Reprinted with permission from Elsevier. Copyright, 2010].

Details

  • Original title: Finite time thermodynamics study and exergetic analysis of ammonia-water absorption systems.
  • Record ID : 2011-0130
  • Languages: English
  • Source: International Journal of thermal Sciences - vol. 49 - n. 7
  • Publication date: 2010/07
  • DOI: http://dx.doi.org/10.1016/j.ijthermalsci.2010.02.005

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