Multi-objective optimization of organic Rankine cycle using hydrofluorolefins (HFOs) based on different target preferences

Thermodynamic and economic performance are common conflicting indicators to evaluate the organic Rankine cycle (ORC). Different preferences between thermodynamic and economic criteria lead to different results. In this study, a numerical target preference based ORC model using multi-objective optimization and multi-criteria decision-making (MCDM) method is proposed, which provides corresponding optimal system parameters and working fluid according to decision-makers’ different preferences. Four MCDM methods are used to select optimal solutions in 51 preference cases with the weight of economic performance (W₁) increasing from 0 to 1. As an example, a subcritical ORC using seven eco-friendly hydrofluorolefin fluids is analyzed. Results reveal the great influence of target preference on optimal solutions. In terms of system parameters, evaporation temperature is the most relevant decision variable, which should be reduced as W₁ increases. While the superheat degree should be kept minimum value, regardless of target preference. For working fluid, when thermodynamic performance is dominating (W₁<0.2), R1234ze(E) is optimal with the largest power output of 50.8 kW, 14% higher than R245fa. Otherwise (W₁≥0.3), R1234ze(Z) is optimal. Besides, four MCDM methods are compared, and LINMAP is recommended. The method proposed in this study provides decision-makers with more flexible options and more reliable results.