Influence Of Pinch Point Temperature Difference Of Evaporator For The Performance Of ORC System

Nowadays,energy shortage has become one of the greatest problems on human development all over the world.Modern industrialization leads to a large amount of low-temperature waste heat not only wastes energy,but also causes thermal pollution to the environment,therefore,recycling this heat has a great significance.The main method to recover this low-temperature waste heat is organic Rankine cycle(ORC)technology.Evaporator as imperative part of ORC system,its performance has a significant impact on overall system,therefore,the pinch point temperature difference,an essential parameter in evaporator,needs to be encountered seriously.In this paper,an optimization analysis for the pinch point temperature difference in evaporator with simulation analysis and experimental research being taken into consideration will be proposed for ORC system.The main research contents and results are as follows:(1)Under the conditions of heat source temperature and different working fluids at120?and R245fa,R1234ze,R1234yf,R134a,R600a,R227ea respectively,simulate analysis was conducted for the ORC system using Aspen Plus software.The effects of the pinch point temperature difference on the net output power,the thermal efficiency,exergy efficiency and comprehensive evaluation index F(X)were investigated.The simulation results show that as the pinch point temperature difference of the evaporator increases,the net output power,exergy efficiency and thermal efficiency of the system all decrease,while the value of F(X)decreases first and then increases.Taking F(X)as the evaluation index,the six working fluids all have the optimal evaporator pinch temperature difference?T,which makes the system performance the best.The working fluids R134a,R1234yf,R1234ze,R600a,R245fa and R227ea correspond to the optimal pinch point temperature difference of 15,12,9,15,15,9?.The F(X)value of R245fa is the smallest and the performance is the best among the six working fluids.(2)Using R245fa as the working fluid,Both from the perspective of working fluid mass flow and evaporation temperature,the effect of the pinch point temperature difference of evaporator on ORC system performance under different heat source temperature(105?165?).The pinch point temperature difference is in the range of3?30?under the given waste heat condition in this paper.The results showed that the net output power,exergy efficiency and thermal efficiency all decreased with the increase of the pinch point temperature difference.There are differences between that the pinch point temperature difference optimized from the viewpoint of evaporator temperature and the viewpoint of working fluid flow rate.From the perspective of evaporator temperature,when the heat source temperature is 165?,the value of F(X)is the minimum,and the optimal pinch point temperature difference is 15?.There is no optimal pinch point temperature difference in this range when analyzed from the perspective of working fluid flow rate.(3)Select the best working fluid R245fa,and adjust the flow rate of working fluid,heat source and cooling water of the system to experimentally study the effect of the pinch point temperature difference on the performance of the ORC system at heat source temperature of 120?.The experimental results show that:The larger working fluid flow rate,the smaller heat source flow rate,the larger cooling water flow rate,and the smaller pinch point temperature difference.With the increase of working fluid flow rate,the net output power,thermal efficiency and exergy efficiency all increase.Under the same working fluid flow rate,the net output power,thermal efficiency and exergy efficiency will decrease with the increase of pinch point temperature difference.With the increase of heat source flow rate,the net output power,thermal efficiency and exergy efficiency first increase and then decrease,reaching the maximum value when the heat source flow rate is 4 m~3/h.Under the same heat source flow rate,the net output power,thermal efficiency and exergy efficiency all decreased with the increase of pinch point temperature difference.With the increase of cooling water flow rate,the net output power,thermal efficiency and exergy efficiency all increase.Under the same cooling water flow rate,as the pinch point temperature difference increase,the net output power,thermal efficiency and exergy efficiency first increase and then decrease.