Energy and Exergy Analyses for Optimization of the Operating Temperatures in Double Effect Absorption Cycle

Energy and exergy analyses of double effect lithium bromide-water vapour absorption cycle has been carried out to optimize the operating temperatures in the main generator and the secondary condenser/ generator for maximum coefficient of performance (COP) and exergetic efficiency. There exists maximum COP and also maximum exergetic efficiency as the temperature in the secondary generator and the main generator are varied, thus leading to the optimum temperatures. Because of two generators in the double effect cycle, the optimization has been done in two steps. Since the secondary generator operates by using the heat of condensation release in the secondary condenser, the temperature in the secondary condenser will be nearly same as in the secondary generator. The analysis has been done for fixed temperatures in the evaporator, main condenser and the absorber. Results show that the COP increases while the exergetic efficiency decreases with increases in the evaporator temperature. The optimum parameters such as temperatures in the main generator, secondary generator and condenser, including the LiBr-Salt concentrations in the two generators, are presented for different values of the evaporator, main condenser and the absorber temperatures. A computer program has been developed for simulating the cycle.