Numerical study on heat transfer and evaporation vaporization performance of solar assisted heat pump regenerative evaporator based on dual-phase change coupled heat transfer

Using phase-change slurry (PCS) as the working medium for solar energy systems, for example, in solar-assisted heat pump (SAHP), offers numerous advantages such as photovoltaic (PV) and photothermal (PT) energy generation and heat supply. The PCS experiences a dual-phase change coupled heat transfer during the heat release and refrigerant vaporization, as investigated through simulation. This study confirmed a coupled heat transfer with dual-phase change. It was found that there is more vapor at the upper coupling interface than at the lower coupling interface, and the difference is obviously enhanced when the flow rate decreases from 0.4 m s−1 to 0.1 m s−1 or the temperature increases from 12 °C to 16 °C. The increased rate of flow or decrease in refrigerant temperature is associated with a reduced equilibrium concentration at the lower coupling interface. Nevertheless, an increase in the flow rate at the lower coupling interface causes a decrease in the equilibrium concentration, while raising the temperature increases the concentration. When the flow rate increases from 0.1 m s−1 to 0.4 m s−1, the heat transfer coefficient at the upper/lower coupling interface increases from 159.77 W m−2 K−1/292.58 W m−2 K−1 to 593.54 W m−2 K−1/654.36 W m−2 K−1, and the heat transfer enhancement ratio reaches 45.39% and 9.29%, respectively. When the refrigerant temperature increases from 12 °C to 16 °C, the heat transfer coefficient at the upper/lower coupling interface decreases from 579.16 W m−2 K−1/572.91 W m−2 K−1 to 329.44 W m−2 K−1/365.67 W m−2 K−1, respectively. Increasing tilt angle of the pipe within a moderate range is a potential solution to enhance heat transfer and improve heat transfer uniformity.