Adjusting Pinch Point Of Heat Transfer To Improve The Thermal Performance Of Organic Rankine Cycle And Reconfiguration Of Cycle

Organic Rankine cycle（ORC）has become an effective means to recovery low-grade heat resources and a hotspot of research.Thermal performance of organic Rankine cycle（ORC）exists optimum condition with the maximum or monotonic increase according to the temperature relation between low grade heat source（LGHS）and the critical temperature of working fluids.Performance with monotonic increase is better than that with optimum condition.The main reason for this difference of the situation is that due to the different location of heat transfer pinch point in heating process,the heat addition changes differently with evaporation temperature.However,the performance of basic organic Rankine cycle（ORC）using working fluids with higher critical temperature（e.g.R245fa）with LGHS generally falls into the optimum conditions,and the heat transfer process is mismatching.In order to achieve preferable cycle performance with monotonic increase and better heat transfer matching,higher heat source temperature is needed,which brings limitations to the improvement of cycle performance.Based on this consideration,the theoretical model of adjustable heat transfer pinch point and the prototype of organic Rankine cycle with adjustable heat transfer pinch point（APPORC）are proposed.And the relationship between APPORC and ORC and the relationship between the upper and lower boundary of the cycle performances of APPORC are deduced theoretically.On the basis of APPORC,a variety of new methods and configurations are proposed to adjust heat transfer pinch point and improve the cycle performance of ORC,including organic Rankine cycle with ejector（EORC）,organic Rankine cycle with flasher（ORFC）and its improved cycles:organic Rankine cycle with regenerator and flasher（RORFC）and organic Rankine cycle with ejector and flasher（EORFC）.By adjusting the mass flow ratio of the auxiliary loop and the main loop,new configurations of cycle can adjust the position of heat transfer pinch point to increase the heat addition and improve the performances.Furthermore,Compared to ORC,the heat transfer matching of new configurations of cycle is enhanced,which reduce the irreversibility of heat transfer in the process of heat addition and cooling.finally,the calculation modeling of each cycle is simulated on MATLAB.And the first law and the second law of thermodynamics are used to compared and analyzed the performances of the cycles.The results show that:theoretically,with same condition,the power output and thermal efficiency of APPORC meet the relationships of W_TLC>W_APPORC≥W_ORCandη_ORC≥η_APPORC>η_TLC.Neglecting the influence of heat source,the thermal efficiency of APPORC decreases monotonically with the increase of mass flow rate of the auxiliary loop,while its net output power increases monotonically;From the simulation results,compared to the ORC,the optimum conditions are extended by EORC,RORFC and EORFC,and the performances of cycles are improved greatly.The maximum net output power of each cycle is lower than that of TLC and meets the relationship of Wmax,RORFC<Wmax,EORC<Wmax,EORFC,and the corresponding thermal efficiency is lower than that of ORC and meets the relationship ofη_opt,EORFC<η_opt,EORC<η_opt,RORFC.In EORC,the performances of azeotropic mixture are better than that of pure.An additional benefit for zeotropic mixtures in EORC with this adjustment can be obtained,where the condensation temperature glide of zeotropic mixtures can be adjusted to match the cold source to reduce the irreversibility of the heat transfer in the cooling process.