Thermal performance of a novel composite phase change material for solar-assisted air source heat pump packed bed thermal energy storage application

• A novel melting point modified CPCM for heat storage in SAASHP systems. • Al 2 O 3 nanoparticles provides dual benefits in improving thermal properties. • The addition of KNO 3 effectively reduces the melting point of SAT. • KNO 3 weakens the interaction between CH 3 COONa molecules and water molecules. • A cyclic heat storage mathematical model of the PBTES system was developed. The thermal properties of the heat storage medium in the solar-assisted air source heat pump (SAASHP) systems must be aligned with the system’s heat generation temperature while satisfying the heat demand. In this study, a novel composite phase change material (CPCM) for efficient heat storage in SAASHP systems was developed. Our investigation revealed that the incorporation of 8 wt% KNO 3 , 1.5 wt% thickener, and 1.0 wt% Al 2 O 3 nanoparticles into sodium acetate trihydrate resulted in the manifestation of desirable properties suitable for SAASHP systems. The compound exhibited a suitable melting point of 48.66 °C, high latent heat of 235.97 kJ/kg, low supercooling degree of 2.25 °C, and good thermal conductivity of 0.905 W/(m·K). Furthermore, the novel CPCM demonstrated exceptional thermal stability, with only an 8.64 % loss of latent heat after undergoing 200 cycles, while maintaining a supercooling degree within a range of 6 °C for each cycle. Moreover, molecular dynamics simulation results further indicated that the presence of KNO 3 weakened the interaction between CH 3 COONa molecules and water molecules, leading to a reduction of the melting point. Additionally, numerical analysis revealed that the total heat storage capacity and exergy storage capacity of the packed bed thermal energy storage (PBTES) system filled with the novel CPCM are 358.8 MJ and 25.1 MJ, respectively. With an increase in the heating power of the SAASHP system from 10 kW to 30 kW, the cycle heat storage time of the PBTES system can decrease by 38.8 %, while an increase in the flow rate from 2 m 3 /h to 6 m 3 /h can reduce the time by 26.3 %. These findings have significant implications for the selection and composition design of thermal storage materials in SAASHP systems.