Thermo-economic selection criteria of working fluid used in dual-loop ORC for engine waste heat recovery by multi-objective optimization

Abstract

The dual-loop organic Rankine cycle(DORC) is considered as an important way for engine waste heat recovery (WHR). Currently, researchers mainly focus on thermodynamic analysis and the performance comparison of multiple existing working fluid pairs without optimizing the working fluid pairs. Therefore, a novel analysis method of selection criteria based on thermodynamic and economic is provided to select a suitable working fluid using the multi-objective optimization. Firstly, a multi-objective optimization was performed using the Non-dominated sorting genetic algorithm-Ⅱ(NSGA-Ⅱ) to maximize exergy efficiency and minimize payback period under 24 candidate working fluid pairs from the references. And the Technical for Order Preference by Similarity to an Ideal Solution (TOPSIS) method was applied to select the Pareto optimal solutions using different kinds of working fluid pairs. Finally, the optimization results were analyzed by the grey relational analysis(GRA). The results show that the critical temperature can be used as the thermo-economic critical for working fluids selection in DORC system, such as the ideal working fluid pairs with the critical temperature in the range of 580–600 K of the HT cycle and the critical temperature in the range of 380–415 K of the LT cycle. And the optimal candidate is toluene/R124.