Double-pass solar air heater with staggered vertical phase change material cylinders: Thermal performance evaluation

Low thermal efficiency and inconsistent temperature distribution remain key obstacles in current solar air heater designs. To address this problem, this study proposes a novel double-pass solar air heater featuring a sandwich structure with vertical phase change material cylinders arranged in a staggered layout within the second channel. A combined numerical and indoor experimental approach was employed to study the thermal performance under varying mass flow rates of 0.01–––0.05 kg/s and solar irradiances of 400–1000 W/m². The numerical simulations provided detailed insights into temperature distribution and velocity contours, highlighting the impact of cylinder configuration on flow dynamics and heat transfer behaviour within the system. For experimental results, the system achieved a maximum thermal efficiency of 90.97 %, with a temperature rise of 25.9 °C at a mass flow rate of 0.05 kg/s and 0.01 kg/s, respectively, under a solar irradiance of 1000 W/m². For optimum performance, a mass flow rate of 0.01–0.03 kg/s is suitable for practical applications like solar drying and space heating. Relative errors varied in the range of 1.60 % and 3.26 % for thermal efficiency between numerical and experimental results, which portrays a good agreement. The findings suggest that this storage design is a promising solution for enhancing energy efficiency and thermal stability in solar air heater applications.