Key issues on the exergetic analysis of H2O/LiBr absorption cooling systems

Abstract

This paper deals with the key aspects of the exergy analysis of H2O/LiBr absorption refrigeration cycles where, instead of agreement, disparity of opinion exists among researchers. As a result, comparisons with the literature are often difficult or meaningless. Based on an in-depth literature review, the key issues highlighted were: a) the identification of the dead state, b) the calculation of the exergy of the currents, and c) the definition of the exergy efficiency of the devices and of the overall system. This study clarifies controversial and divergent assumptions and proposes a coherent approach. In addition, a comparison with the literature is performed. As a case study, a single effect absorption cycle, refrigerated with water, has been considered here. Related to the dead state, consideration of different subsystems results in practical interest. The results highlight the importance of the correct calculation of the chemical exergy for the exergy analysis of the absorption refrigeration system. It is also described here how to define the rational exergetic efficiency, or fuel-product exergy, according to physical and chemical exergies of the streams. The comparison with the literature shows discrepancy specially in the exergy analysis of the desorber and the absorber, where the chemical exergy plays an important role.

Keywords

• Exergy analysis
• Dead state
• Chemical exergy
• Exergetic efficiency
• H2O/LiBr
• Absorption machine