Multi-objective optimization of evaporation and condensation temperatures for subcritical organic Rankine cycle

A multi-objective function F(X) by the incorporation of single-objective functions, i.e., net power output Wnet, exergy drop of the exhaust gas from inlet to outlet ΔEg, total exergy destruction rate I and system total cost C2013, has been put forward as the subcritical organic Rankine cycle (ORC) performance indicator and solved with the method of linear weighted evaluation function. The optimization of the evaporation temperature Te and condensation temperature Tc of subcritical ORC has been carried out by the use of pure working fluids R600a, R245fa, R601a, R601, R123, and non-azeotropic mixed working fluids R600a/R601a, R245fa/R601a, R245fa/R601, R600a/R245fa. The results reveal that there exist optimal evaporation temperature Te,opt and condensation temperature Tc,opt minimizing the multi-objective function F(X); while Te,opt and Tc,opt can not exactly exist when choosing single-objective functions, i.e., Wnet, I, C2013 and ΔEg as the performance indicators. Although Te,opt and Tc,opt vary with different working fluids, the ORC performance of mixed working fluids is not always better than that of pure working fluids. The multi-objective optimization of ORC shows superiority to the single-objective optimization, owning to its pursuit of the best comprehensive performance.