Research And Optimization Of Organic Rankine Cycle Performance Based On Mixed Working Fluid

At present,with the development of the global economy,the problem of energy shortage is becoming increasingly serious,and it is particularly important to improve energy efficiency and develop renewable energy.Among them,waste heat recovery technology can effectively improve energy utilization efficiency,and China is rich in waste heat resources,which exist in a large number of all walks of life,and the reasonable and efficient use of these waste heat resources has become a research hotspot.The Organic Rankine Cycle(ORC)technology has the advantages of simple structure,wide range of waste heat sources and good environmental performance,and has been recognized and has good development prospects in the field of energy recovery.In this thesis,the organic Rankine cycle system of medium and low temperature waste heat power generation is taken as the research object,and the application of hybrid working fluid is carried out.Firstly,through the optimization of working quality,five pure working fluids(R245fa,R245 ca,R123,etc.)were identified from the aspects of heat,safety and environmental protection.R245 fa working fluid as the mixed object,R245 ca,R123,R141 b,R113 four working fluids mixed with R245 fa mixed working fluids for the study of binary mixed working fluids.Secondly,the thermodynamic model and economic model of the hybrid working fluid ORC system are established,and R245ca/R245 fa,R123/R245 fa,R141b/R245 fa and R113/R245 fa are selected as research objects to study the effects of different types of binary mixed working fluid on the overall thermal and economic properties of the circulating system under different components,and compare with the pure working fluid ORC system.In addition,the influence of evaporation temperature and condensation temperature on system performance was studied.The results show that the influence trend and degree of the first working fluid mass fraction on the system performance of different working fluid pairs are different,and the slip temperature,the physical properties and thermal properties of the working fluid itself need to be comprehensively considered.The thermal and economic properties of mixed working fluids are not necessarily better than pure working fluids;The existence of optimal evaporation temperature respectively maximizes the thermal efficiency of the system and the lowest average power cost.An increase in condensation temperature leads to reduced thermal efficiency of the system and poor economic performance.Finally,the thermodynamic model,economic model and environmental model of the hybrid working fluid double-pressure ORC system are also established,and the influence of mixed working fluid components on the double-pressure ORC system is studied with the hybrid R141b/R245 fa as the research object,and compared with the pure working fluid.In addition,the effects of key parameters such as high-pressure evaporation temperature,low-pressure evaporation temperature and narrow point temperature difference on the thermal performance,economic performance and environmental performance of the system were studied.The multiobjective sparrow search algorithm is introduced to optimize the three-objective thermal environment of the system.The results show that the thermal performance,economic performance and environmental performance of mixed working fluid are not necessarily better than those of pure working fluid.There are different optimal high-pressure evaporation temperatures and optimal low-pressure evaporation temperatures to make the system thermal,economic and environmental performance the best.Increasing the narrow point temperature difference will lead to the overall decline of the thermal performance,economic performance and environmental performance of the system.Improving the thermal performance and environmental performance of the system will inevitably reduce the economic performance;The operating parameters of the hybrid working fluid double-pressure organic Rankine cycle system with the best comprehensive performance were R245 fa mass fraction of 0.1,the highpressure circulating evaporation temperature was 387.65 K,the low-pressure circulating evaporation temperature was 357.83 K,and the narrow point temperature difference was 5.02 K.