Multi-stage liquid separation condensation high-temperature heat pump system using zeotropic working fluid: System construction and comparison with traditional solutions

Aiming to solve the problem of energy efficiency degradation and large heat transfer irreversible loss caused by the temperature mismatching for traditional high temperature heat pump system. Zeotropic multi-stage liquid-vapor separation condensation (MLSC) high-temperature heat pump system is proposed. The double-stage (DLSC) and triple-stage (TLSC) liquid-vapor separation condensation heat pump systems are further studied. The energy, exergy, economic and environmental analysis models are established, and the system performance are compared with single-stage condensation (SC) heat pump system that utilizes pure and zeotropic working fluid. The results show, maximum coefficient of performance (COP) can be obtained under optimal vapor quality for MLSC system. The temperature matching between the working fluid and the heat transfer fluid for the MLSC system is alleviated with thermal match indicator of the TLSC and DLSC system decreases by 8.9–23.83 % compared with the SC system using zeotropic working fluid. The TLSC system is capable of remarkably decreasing the exergy destruction, with a reduction rate of 23.78 %. The TLSC system demonstrates better heat transfer performance with the total heat transfer coefficient being 9.83 % higher. The heat transfer area and cost of the condenser for TLSC system is reduced by 13.25–17.09 % and 9.91–12.85 % in comparison to the SC system using zeotropic working fluid, respectively. The MLSC system shows a reduction of 14.85–16.76 % in life cycle carbon emissions when compared with SC system that uses pure working fluid. This study is able to offer a theoretical reference for the progress of advanced high-temperature heat pump system with higher energy efficiency.