Study On Thermo-economic Performance Optimization Of Ejector Refrigeration System

Ejector refrigeration system powered by low-grade energy has been a helpful approach to ease the current situation of energy crisis.At present,the study of ejector refrigeration is mainly focused on the COP,so the research is not complete referring to exergy destruction,economic performance and multi-objective optimization including all performances above.On account of that,this thesis presents an optimized study on ejector refrigeration system by advanced exergy analysis,thermo-economic theory and multi-objective optimization.The suitable operating conditions for various refrigerants are determined and performances are compared with various refrigerants in optimal operating conditions.The main conclusions are as follows:The model and working principle of ejector refrigeration system are expounded.The entrainment ratio's difference in real operating condition,empirical correlation and the experimental value is compared.Although Dorantes' s empirical correlation has some error,the changing trend with operating condition still can be reflected correctly.Considering the characteristics of simple and quick calculation,it can be utilized in optimization and analysis on ejector refrigeration system.Establishing advanced exergy analysis model,exergy destruction of ejector refrigeration system is split into several parts in different rules.The exergy destruction can be reduced and its performance be improved by comparison of a realistic potential for improvement and optimization focus with different refrigerant and operating conditions.It indicates that ejector has the largest in all components and most of its exergy destruction is endogenous.Exergy destruction in generator's potential is taking second place to ejector and condenser is third.Most parts of them are exogenous exergy destruction.In most working conditions,R717 is the most suitable refrigerant.When using it,the avoidable exergy destruction in total system is approximate 40%,which is the highest and nearly 50% for ejector.Higher generation and evaporation temperature and lower condensation temperature are helpful to reduce the system exergy destruction.The cost of refrigeration I calculation model is determined by establishing the thermo-economic model.Calculation results show that the lowest cost of refrigeration was obtained for R717 followed by R134 a,R600a and R236 fa,and the highest one was obtained for R123 in given standard conditions.Studying the suitable operating condition with various refrigerants,the optimal evaporation temperature is 8~10 ? and optimal condensation temperature is 33~34 ?.A lower generation temperature brings a better performance.Establishing the exergoeconomic model,two exergoeconomic variables,product unit cost and exergoeconomic factor,are optimized and analyzed.Research results indicate that the lowest product unit cost was obtained for R717 and the highest one was obtained for R123,which is as same as cost of refrigeration.Product unit cost is monotonic with the increasing temperature and there is no optimal point.Exergoeconomic factor is between 70% and 90% with various refrigerants and operating condition temperatures,which is generally high.The maximum COP and minimum exergy destruction and cost of ejector refrigeration system are used as objective function for multi-objective optimization.The optimization results of single parameter are studied with other fixed parameters.Genetic algorithm is utilized to complete optimization of multiple parameters which are changing at the same time and the optimal operating conditions for various refrigerants are obtained.Analytic hierarchy process is utilized for a comprehensive evaluation with multiple factors consists of refrigerants and three thermo-economic performances.It indicates that the best comprehensive performance is obtained for R717,the worst one is obtained for R123,which is as same as the results above.Compared with the results for single objective optimization,the optimal refrigerant obtained from multi-objective optimization is same.However,the optimal operating condition for various refrigerants is different.