Simulation Optimization Of Absorption Refrigeration System With Lithium-Bromide Driven By Low Grade Heat Source

Energy crisis and environmental problems have been highlighted in recent years, which lead to the wide concern on absorption chiller driven by low grade heat. But the low thermal coefficient and large unit volume limit its large-scale application, so it is essential for the optimization study of absorption chiller. In this paper, putting the single effect LiBr absorption chiller as the research object, the working fluid, refrigeration system, and operating parameters has been studied,in which optimization and exergy analysis method was used.Through the theory analysis of heat and mass transfer, the mathematical and physical model for single effect lithium bromide absorption chiller are established. We select ELECNRTL method and the convergence method of limited wegstein as the basic operation method;The physical properties of lithium bromide-water working fluid with nitrate lithium as additives are studied. It was found that the viscosity of is reduced,and the crystallization has been significantly solved after the additive is added,while the system performance parameters (thermal coefficient, circular ratio) get greatly raise. After analysis and comparison, the optimum molar ratio of bromide lithium nitrate is 4:1, the driving heat source temperature is lower, which demonstrate it is better suited to the absorption chiller driven by low grade heat source;The optimization of refrigeration system was carried out by using Aspen Plus, which analysed the influence on the performance of the system by solution heat exchanger, series form of cooling water and dilute solution parameters. The optimum range of hot-outlet and cold-inlet temperature approach is 7-15℃; The optimum form of cooling water is series form 1 (absorber to condenser),if the cooling water temperature is lower than the 26.5 ℃. The series form 2 should be used while the cooling water temperature is higer than the 26.5 ℃ At the same time, we should try to reduce cooling water inlet temperature.Making the maximum of circular ratio and the inlet concentration of dilute solution of liquid as the goal would optimize the system performance of single effect absorption refrigeration.On the basis of previous research, we analyse the effects of evaporation temperature, condensation temperature, driving of heat source temperature and other external parameters on the of energy loss of system and its components,using exergy method. The results show that,while the capacity was fixed, improvement of single effect lithium bromide absorption refrigeration cycle should focus on the solution circulation.lt is the basic principles for the optimization on system that low condensation temperature, reduce the evaporation temperature and driving heat source temperature.