Simultaneous Optimization Of Mixture And System Of Organic Rankine Cycle Based On PC-SAFT

Organic Rankine Cycle(ORC)is a low-grade thermal power generation technology.Because of its simple structure,convenient operation and suitable pressure,it is widely used in industrial waste heat recovery and renewable energy utilization,such as solar energy and geothermal energy.Working fluid is the carrier of energy transmission and conversion in ORC system.It plays an important role in ORC and has a crucial impact on the performance of ORC system.It is of great theoretical and practical significance to carry out the research of working fluid screening or design and synchronous optimization with ORC system parameters for improving ORC system performance.Aiming at the shortcomings of traditional screening methods,such as discontinuous variables,time-consuming and laborious exhaustive method,and step-by-step screening and system optimization of working fluid properties,the idea and method of synchronous optimization of zeotropic mixtures screening or design and ORC system parameters based on Perturbed-Chain Statistical Associating Fluid Theory(PC-SAFT)was proposed.The main contents of this thesis are as follows:Firstly,a physical property calculation model based on PC-SAFT was proposed to calculate the thermodynamic properties and vapor-liquid equilibrium of mixtures.Because of the complexity and difficulty of solving vapor-liquid equilibrium,a prediction model of initial value of vapor-liquid equilibrium based on the Extreme Gradient Boosting(xgboost)was proposed.The prediction model was coupled with PC-SAFT,and the molecular parameters of PC-SAFT were used as variables to identify different working fluids.The results of four kinds of vapor-liquid equilibrium calculation were pre measured,and the results were used as initial value to assist the solution of gas-liquid equilibrium based on PC-SAFT.The results showed that the accuracy of PC-SAFT was higher than that of PR equation of state,and the maximum error of net work was 3.01% compared with REFPROP.Secondly,a heuristic rule selection method was proposed to optimize mixtures and parameters of ORC system simultaneously.325 mixtures,which were composed of 26 pure working fluids,were screened by heuristic rules based on temperature slip and condensation pressure.Finaly,44 mixtures were left.Heuristic rule selection method effectively reduced the search space.By coding the selected mixtures,the parameters of mixtures and ORC system could be optimized synchronously with the net work and exergy efficiency as the objectives,and the optimal mixed mixtures and working conditions of ORC system could be obtained.Then,the influence of heat source inlet temperature and cold source temperature rise on the performance of mixtures and ORC were analyzed.R12/perfluoropentane(0.924/0.076)and R40/R160(0.423/0.577)were obtained to maximize the net work and efficiency,respectively.Finally,44 mixtures selected by heuristic rules were used to compare simple ORC and dual-pressure evaporation ORC.Based on Computer-Aided Molecular Design(CAMD),a simultaneous optimization model for mixtures design and ORC system of dual-pressure evaporation ORC was proposed.The mixtures were designed according to the type of working fluid and the total number of carbon atoms,and the net work and exergy efficiency were taken as the optimization objectives respectively to realize the simultaneous optimization of mixtures design and dual-pressure evaporation ORC system parameters.Then,the effects of heat source inlet temperature and cold source temperature difference on the performance of dual-pressure evaporation ORC were studied.