Research on Thermal Performance and Structural Optimization of Finned Shell-and-Tube Storage Units for Air-Source Heat Pump Systems

Thermal storage tanks offer significant potential for addressing the performance degradation and supply–demand mismatch of air-source heat pump (ASHP) systems in cold regions. This study employs a combined numerical and experimental approach to systematically investigate the impacts of fin structure, composite phase change material (CPCM) composition, and inlet temperature on the performance of shell-and-tube storage units. Results indicate that natural convection is the dominant heat transfer mechanism, and the incorporation of expanded graphite (EG) substantially enhances the thermal conductivity of the PCM. A critical finding is the identification of an optimal finning coefficient range (4.16 to 5.68) that maximizes enhancement performance. A validated numerical model (error < 5%) and a predictive formula for melting time were developed. Experimental data show that the optimized finned structure reduces PCM melting time by 47% to 59%. This research provides theoretical and practical tools for designing high-efficiency thermal storage, supporting the development of flexible and integrated building energy systems.