Abstract
A two-phase ejector recovers the energy in the refrigerant cycles’ throttling process, improving the coefficient of performance (COP) of high-temperature heat pumps (HTHPs). This study investigated the effects of the mixing pressure on the performance of two-phase ejectors and ejector-assisted HTHPs. A 1D theoretical model of a two-phase ejector was built to predict the internal fluid dynamics and evaluate ejector performance. A thermodynamic model of an ejector-assisted HTHP was built to evaluate the COP of HTHPs and the volumetric heating capacity of low-global warming potential refrigerants. The results demonstrate that an optimum mixing pressure in a two-phase ejector provides the best performance of a two-phase ejector and ejector-assisted HTHP. The optimum mixing pressure was slightly lower than the evaporation pressure. At this pressure, the two-phase flow in the ejector was subsonic. For ejector-assisted HTHPs using low–global warming potential refrigerants at a sink temperature of 120°C, temperature lift of 40°C, and subcooling of 10°C, a two-phase ejector has an average ejector efficiency of 0.334, and the COP and volumetric heating capacity were improved by 7.2% and 7.3%, respectively.
