Exploration of dual-phase change coupled heat transfer in solar regenerative evaporator

Abstract

To improve the efficiency of the system, a solar assisted heat pump (SAHP) evaporator could be used in conjunction with phase change slurry (PCS) as a working fluid for heat storage, transfer, and release. However, more research needs to be carried out on the state-of-the-art of dual-phase change coupled heat transfer between PCS and refrigerant. In order to explore coupled heat transfer and the influences on the upper and lower coupling interfaces of the horizontal evaporator pipe, a numerical heat transfer model that integrates phase change material capsule (PCMC) flow is applied. The ideal mixture of 15 vol% PCS with the particle size of 10 μm was shown to increase heat transfer by 0.60 %–1.17 % and 1.14 %–1.69 % at the upper and lower coupling interfaces, respectively. As a consequence, an increase in PCS inflow rate and inlet vapor leads to an increase in the equilibrium concentration of PCMC near the lower coupling interface. Additionally, a decrease in heat transfer around 3.64 %–4.87 % was experienced when the inflow rate of PCS was increased from 0.2 m∙s−1 to 0.4 m∙s−1. When the initial volume fraction of vapor at the upper coupling interface increased from 0 vol% to 5 vol%, the heat transfer coefficient decreased from 329.44 W∙m−2 K−1 to 299.36 W∙m−2 K−1. Although the heat transfer reduction ratios at the lower coupling interface varied from 4.16 % to 4.51 %, they were still higher than those at the upper coupling interface. The study provides first findings and insights into the coupled heat transfer under consideration.