Abstract: A multi-objective optimization model is built, which incorporates the net power output W_net, exergy drop of exhaust fluid from inlet to outlet ΔE_g, total exergy destruction rate I, and total cost C₂₀₁₃ of system into one function, and solved with the method of linear weighted evaluation function. Taking single working fluids R600a, R245fa, R601a and Pentane, and non-azeotropic mixed working fluids R600a/R601a, R245fa/R601a, R245fa/Pentane, and R600a/R245fa as examples, the evaporation temperature T_e and condensation temperature T_c of subcritical organic Rankie cycle (ORC) are optimized. The results reveal that sometimes the optimal point can not be obtained using single-objective function, while it always can with multi-objective function. Moreover, the multi-objective optimization of ORC seems superior to single-objective optimization, because the multi-objective optimization coordinates the relationships among various performance indicators, which makes each indicator reach the optimal point as possible. Additionally, there exists optimal evaporation temperature T_e,opt and condensation temperature T_c,opt minimizing the multi-objectivefunction F(X) values, but they vary with working fluids. For multi-objective optimization at T_e,opt and T_c,opt, the comparisons of different single-objective function values and F(X) between non-zeotropic mixed working fluids and single working fluids show that the ORC performance of mixed working fluids is not always better than that of single working fluids.

Key words: organic Rankine cycle, single working fluid, mixed working fluid, multi-objective optimization, exergy, economics, thermodynamics

摘要： 以系统净输出功率W_net、热源流体进出口(火用)降DE_g、系统总不可逆损失I和系统总投资成本C₂₀₁₃构建多目标优化模型，采用线性加权评价函数法对该模型进行求解，以R600a、R245fa、R601a、Pentane 4种纯工质以及R600a/R601a、R245fa/R601a、R245fa/Pentane和R600a/R245fa 4种非共沸混合工质为例，对亚临界有机朗肯循环（ORC）的蒸发温度T_e和冷凝温度T_c进行优化。研究结果表明：采用单目标有时得不到最优值，而采用多目标均能得到最优值，且多目标优化可以较好地协调各性能指标间的关系，使所要求的各项指标均能达到较优，因此多目标优化比单目标优化更加合理；存在最优蒸发温度T_e，opt和最优冷凝温度T_c，opt使多目标函数F（X）最小，同时，T_e，opt、T_c，opt随工质不同而不同；在T_e，opt或T_c，opt下，对比纯工质和混合工质的不同单目标函数值和F（X）值时，混合工质并不总是优于纯工质。

关键词: 有机朗肯循环, 纯工质, 混合工质, 多目标优化, (火用), 经济, 热力学