Thermal energy release analyses of direct absorption/storage solar collector based on the photo-thermal conversion composite PCM for heat pump evaporator heat source

Compared with traditional solar thermal systems, the direct absorption/storage solar collector (DASSC) based on photothermal conversion composite phase change materials (CPCM) demonstrate significant advantages, including reduced heat loss, fewer heat transfer stages, and enhanced solar energy utilization efficiency. Nevertheless, the heat release performance of its use as a heat source for a heat pump evaporator under the constraint of a specific discharging power has not been fully explored in previous studies. In this study, photothermal conversion CPCM are prepared to construct a DASSC. A non-steady-state heat release model to investigate the heat release characteristics and performance factors of DASSC as a heat source for the evaporator in a heat pump unit under discharge rate constraints. The effects of individual parameters and their interactions are evaluated using sensitivity analysis and the response surface methodology. Experimental results indicate that the absorbance of the photothermal conversion CPCM is 3.03 times higher than that of pure PCM. Both the effective discharged heat and the average discharging rate are most sensitive to the specific surface area and least sensitive to the branch length. The interaction between the EG mass fraction and the specific surface area, as well as the specific surface area and the Reynolds number, have the most significant influence respectively. This study establishes a theoretical foundation for enhancing the heat release performance of the DASSC and broadening its application potential within solar heat pump systems.