Energetic and Exergetic Performance Comparison of a Compression-Absorption System Working with NH3-H2O, NH3-LiNO3 and NH3-NaSCN

Abstract

The inclusion of a compressor in absorption refrigeration systems is one of the practices that are becoming more common in the refrigeration field, since a lower generation temperature is required. Among the mixtures most used and studied in refrigeration-compression cycles (CARC) are NH3-LiNO3 and NH3-NaSCN. This is mainly due to the assumption that these two mixtures have a better energy efficiency than the conventional absorption refrigeration cycle working with NH3-H2O (BARC). Therefore, this work shows an energy and exergy study of a CARC cycle, in which its analysis extends to the use of the NH3-H2O mixture, to show the potential that presents the mixture for refrigeration and air conditions applications, as well as the advantages and disadvantages to operating in this type of configurations. The results obtained are compared with the mixtures NH3-LiNO3 and NH3-NaSCN at different evaporation, condensation, generation temperatures and different compressor pressure ratio. The results show that the generation temperature, as well as the energetic and exergetic efficiency are strongly dependent on the compressor pressure ratio. For compression ratio values lesser than 1.6, NH3-NaSCN mixture is energetically higher than NH3-H2O and NH3-LiNO3 at generation temperatures higher than 70°C. The results show the three mixtures have very similar exergetic behavior for almost all wide range of operating conditions. When the system works with rp=2.0, the COP of NH3-H2O mixture is 3.26% higher than the other two mixtures, while under the same operations conditions, the energetic behavior is very similar for the three mixtures for different generation and evaporation temperatures.