基于吉布斯自由能变的非共沸混合工质有机朗肯循环热力性能分析

Analysis of Thermal Performance of Organic Rankine Cycle With Zeotropic Mixture Working Fluids Based on Gibbs Free Energy Change

吉布斯自由能变(ΔG)可以度量系统对外界所做的最大非膨胀功,为研究非共沸有机朗肯循环热力性能与确定最佳混合工质组分比提供判据。文中将ΔG引入有机朗肯循环一般性热力学模型,推导出功、热量与ΔG的关系式。采用R245fa/R227ea非共沸混合工质,利用Aspen Plus软件模拟计算每个热力过程的ΔG,度量非共沸混合工质的做功能力,确定最佳混合工质组分比,并可算出循环过程中吸热量、净输出功等值。模拟结果对比分析得出:利用推导的ΔG公式计算出的功、热效率等变化规律与参考文献一致,计算误差在允许范围内。吸热过程的ΔG最大值可作为确定最大热效率的非共沸混合工质组分比的依据;膨胀过程的ΔG最大值可作为筛选出最大输出功的非共沸混合工质组分比的依据。ΔG在R245fa质量分数为0.589时最大,此时获得最大热效率为7.514%;ΔG在R245fa质量分数为0.493时最大,此时获得最大净输出功为4.176 kW。

Gibbs free energy change(ΔG) can measure the maximum non-volume work done by the system to the outside,and provide a criterion for the study of the thermodynamic performance of organic Rankine cycle(ORC) with zeotropic mixture working fluids and the determination of the optimal component ratio of mixture working fluids.In this paper,ΔG was introduced into the general thermodynamic model of the ORC,and the relationships between power,heat and ΔG were derived.The zeotropic mixture working fluids of R245fa/R227ea were used for simulation calculation.Aspen Plus software was used to simulate and calculate the ΔG of each process.The functional capacity of the zeotropic mixture working fluids could be measured,the best component ratio of zeotropic mixture working fluids could be determined,and the heat absorption and net output power could be calculated.The comparison and analysis of the simulation results and the references show that the change trends of net output power and thermal efficiency calculated by the deduced ΔG equations are consistent with the reference,and calculation errors are within the allowable range.The maximum value of ΔGin the endothermic process can be used as the basis for determining the component ratio of zeotropic mixture working fluids with the maximum thermal efficiency;the maximum value of ΔGin the expansion process can be used as the basis for selecting the component ratio of zeotropic mixture working fluids with the maximum output power.When the mass fraction of R245fa is 0.589,ΔGachieves the maximum,the maximum thermal efficiency is 7.514%;when the mass fraction of R245fa is 0.493,ΔGachieves the maximum,and the maximum net output power is 4.176 kW.