Thermal analysis and optimal fluid selection for the novel integrated vapor compression cycle and ORC system for ultra-low grade waste heat recovery using the desuperheating method

Abstract

This research investigates the thermal performance and working fluid selection from ultra-low-grade waste heat recovery. The study examines the desuperheating method of a novel integrated Vapor Compression Cycle (VCC) and the organic Rankine Cycle (ORC) system for electricity generation. Two cooling methods are analysed and compared, water-cooled VCC-water-cooled ORC and air-cooled VCC -air-cooled ORC. The study was conducted on a vapor compression system with 35-kW refrigeration capacity and evaluated various performance indices. The results indicate that for the water-water cooled system, R407c-R141b is the potential working fluid, achieving an overall coefficient of performance (COP_sys) of 3.20, ORC thermal efficiency of 7.56 %, and net electricity output of 0.28 kW. R410a-R141b is recommended in the air-air-cooled system due to its higher ORC thermal efficiency (7.67 %) than the water-water-cooled system (7.56 %), resulting in a power output of 0.44 kW. Sensitivity analysis reveals that desuperheating is preferable for obtaining higher ORC thermal efficiency. Increasing the condensing water temperature improves net electricity and ORC thermal efficiency. Furthermore, a higher mass flow rate of condensing water enhances system COP and system exergy efficiency but decreases ORC thermal efficiency.