Exergy analysis of single and double effect water-LiBr absorption refrigeration systems

Abstract

Exergy analyses are a powerful tool in order to assess and define possible energy efficiency improvements in energy systems. Through this kind of analysis, the origin, cause, and magnitude of the inefficiencies and irreversibilities of an energy system are identified and quantified. This work presents a new perspective on exergy analysis of a single and a double effect absorption refrigeration system. The working fluid is the mixture water-LiBr. The systems have been modeled using commercial software. A new approach has been considered for the definition of the dead state in the exergy analysis. The role of the chemical exergy has also been evaluated, taking into account the mixing and separation processes that the mixture water-LiBr goes through. The main parameters involved in the energetic and exergetic analyses have been evaluated. The exergy analysis has been performed at the component level. The exergy destruction and the exergetic efficiency of each component are reported. This way, the true inefficiencies are located. In the single and double-effect absorption refrigeration cycle, the device with the lowest exergetic efficiency is the absorber with a value of 2.2% and 1.8%, respectively. The absorber is also the device with the highest exergy destruction rate with 74.5% in the single effect, and 83.5% in the double effect. The evaporator is the second device where the greatest irreversibility is produced, followed by the generators, even though the latter present exergetic efficiencies of more than 90%.