Thermal performance enhancement and assessment of a double-pass solar air heater using perforated vertical V-baffles and semi-circular ducts

The thermal efficiency of the double-pass solar air heater is generally low, as reported by researchers. This limits the full utilization of the double-pass solar air heater's potential. To address this issue, surface roughness is introduced, which improves convective heat transfer by disrupting the thermal boundary layer between the absorber plate and the airflow. This study investigates the impact of a novel design featuring perforated PCM-filled vertical V-baffles, used as surface-roughness elements, combined with integrated PCM semi-circular tubes, on the thermal performance of double-pass solar air heaters. The combined approach employs computational fluid dynamics and experimental validation to assess flow characteristics, friction factors, and Nusselt numbers over a range of Reynolds numbers of 3,000 - 19,000 and solar irradiances (400 - 1000 W/m 2 ). By modifying the baffle-to-perforation height ratio and varying the semi-circular duct radius, the observed outcomes include increased heat absorption, enhanced convective effects, and improved overall efficiency. Higher Reynolds numbers correlate with stronger turbulence and heat transfer, yet moderate pressure drops ensure balanced performance. Furthermore, the phase change material provides effective thermal energy storage by partially or fully melting under high irradiance and then releasing latent heat during periods of reduced solar input. Final configurations yield thermal efficiencies up to 62.6% at higher airflow rates and a TEF of 2.48 at a Reynolds number of 3,000.