First and Second Law Analysis of a LiBr-Water Absorption Cycle with Recovering Condensation Heat for Generation

In conventional absorption refrigeration systems (ARS), the heat from the condenser is usually rejected by the environment in place to be used in the system, so recuperating this is a good alternative to enhance the system’s performance. For instance, in this paper, an alternative ARS in which LiBr/Water is used as a refrigerant mixture, where part of condensing heat is recovered via the solution heat recovery generator absorption cycle (HR-ARS) was energy and exergy evaluated. The influence of generator, condenser and evaporator temperatures, as well as the efficiency of the solution heat exchanger on the coefficient of performance, exergy performance and exergy destroyed of the HR-ARS system, were analyzed and compared with the traditional ARS system at the same working conditions. The results showed an increase between 5.8%–6.3% on the COP and 3.7%–9.5% in the exergy efficiency when condenser/absorber temperature was reduced from 40°C to 30°C. However, when the evaporation temperature rose from 5°C to 15°C, the COP (coefficient of performance) increased by around 8%, although this could be increased by 2.3%–6.3% if the generator temperature decreases from 100°C to 80°C. Moreover, the COP and exergetic performance for the HR-ARS is more significant at the lowest generator, condenser and evaporator temperatures, as well as at high efficiency in the solution heat exchanger, in comparison to ARS system. Furthermore, the COP and exergy performance for the HR-ARS system was improved by 2.57% to 3.11% and 0.22% to 0.7%, respectively, while the recovering condensation heat for generation is around 1.51%–3.76% lower than with the ARS. It also was found that for all ranges of evaporator and condenser temperatures, the COP for the HR-ARS system is around 3% higher than that obtained with the ARS at the three different generator temperatures here analyzed, while when the solution heat exchanger effectiveness was increased from 0.7–1.0, the total exergy destruction for the HR-ARS resulted be 3.24%–5.01% smaller than the ARS system. Finally, it can be concluded that the components with the most exergy destroyed in the systems (80% to 94%) are the generator and absorber.