Multi-objective optimization and off-design evaluation of organic rankine cycle (ORC) for low-grade waste heat recovery

Organic Rankine Cycle (ORC) is a technically feasible way for low temperature waste heat recovery. Multi-objective optimization of the ORC using R245fa is conducted considering both thermodynamic performance and economic factors simultaneously, by means of Non-dominated sorting genetic algorithm-II. The optimum operating parameters were achieved by sorting the Pareto-optimal solutions using the technique for order preference by similarity to ideal situation. A comprehensive analysis on the off-design performance of the optimized ORC system is examined. R-ls is defined as the ratio of latent heat to sensible heat of the input heat to investigate the relation between the distribution of the input heat and the system performance. The effects of hot water temperature and mass flow rate, cooling water temperature and mass flow rate, superheated degree, subcooling degree and working pump rotational speed, on thermal efficiency, exergy efficiency, net power output, investment cost per unit power and R-ls were investigated. The fitted correlations between R-ls and the system performance indexes were derived. The novelties of the present paper are the multi-objective optimization for the further off-design behavior analysis and the quantitative relation investigation between R-ls and system performance indexes. It is indicated that the direction of system optimization is to reduce R-ls. (C) 2020 Elsevier Ltd. All rights reserved.