Parametric optimization and performance analysis of subcritical organic Rankine cycle based on multi-objective function
WU Shuangying, YI Tiantian, XIAO Lan
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A multi-objective optimization model is built, which incorporates the net power output Wnet, exergy drop of exhaust fluid from inlet to outlet ΔEg, 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 Te and condensation temperature Tc 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 Te,opt and condensation temperature Tc,opt minimizing the multi-objectivefunction F(X) values, but they vary with working fluids. For multi-objective optimization at Te,opt and Tc,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.