Numerical calculation and experimental study on the influence of multiple factors on heat transfer characteristics of spherical bed heat storage reactor filled

This study proposes a solar thermal-phase change heat storage packed bed system to address heating demand and centralized heating limitations in extremely cold and arid regions. A spherical-bed experimental setup and a validated 3D numerical model were used to test heat storage and simulate phase change material (PCM) melting. Parametric analyses were conducted on airflow direction, inlet velocity, PCM sphere diameter, central occlusion area ratio, tank height-to-diameter ratio (H/D) and conical taper angle. Results indicate that upward airflow reduces complete PCM melting time by 17.0% and increases the average heat storage rate by 4.7% relative to downward airflow. Increasing inlet velocity from 0.05 m/s to 0.15 m/s shortens melting time by 60.0% and enhances the average heat storage rate by 108.5%. Reducing PCM sphere diameter from 60 mm to 40 mm decreases full-melting duration by 50.4% and improves the average heat storage rate by 86.1%. When the central occlusion area ratio decreased from 28.8% to 13.6%, the total melting time was shortened by 52.7% and the average heat storage rate increased by 40.1%. Elevating the H/D ratio from 0.75 to 1.25 reduces melting time by 13.7% and raises the average heat storage rate by 8.2%, albeit with a 37.9% increase in pressure drop. Finally, compared with a divergent top, a conically tapered top mitigates thermal stratification, reducing the melting time by 62.2% and increasing the average heat storage rate by 111.1%. Collectively, these results provide a quantitative basis for the performance-oriented design and optimization of solar-integrated packed-bed thermal energy storage systems.