Thermodynamic analysis of compound cycle system for automotive waste heat recovery and air conditioning refrigeration

A compound cycle system, which integrates an automotive waste heat recovery (WHR) and air conditioning (A/C) refrigeration functions, is proposed in this paper. The models of this compound cycle system, independent organic Rankine cycle (ORC) system and independent A/C system are built by Aspen Plus software. R134a and R1234yf are selected as working fluids because of their common use in air conditioning system. R245fa is employed as working fluid for independent ORC system as a comparison. The targets of this analysis are more power output and smaller heat transfer area. Linear weighted method is applied to optimize this multi-objective problem using the working fluid flow rate and WHR evaporating pressure as variables. The simulation results indicate that the compound system behaves better than independent system both in the power output and heat transfer area with the same working fluid. The independent system with R245fa-R134a generates the most power output of 13.01 kW. The compound system with R1234yf shows the smallest total heat transfer area and total heat transfer area decreasing ratios (THTADRs) are 6.2-14.8% comparing with independent systems.