impact of angle of attack and relative width of v-shaped ribs on the thermo-hydraulic performance of a solar air heater

Solar air heaters offer a low-cost way to convert solar energy into usable heat, but their efficiency is limited by the inherently low heat transfer coefficient of air. to address this limitation, artificial roughness elements such as v-shaped ribs are commonly added to the absorber plate to boost turbulent mixing and improve thermal performance. this study numerically investigates the thermo-hydraulic characteristics of a solar air heater duct equipped with v-shaped ribs by analyzing the combined effects of angle of attack and relative rib width using computational fluid dynamics. the results demonstrate that both thermal performance and flow characteristics are influenced by rib geometry. the nusselt number reaches its maximum enhancement of 2.8 times that of a smooth duct when using a single v-rib with a relative width of 1 and a 30° angle of attack. however, reducing the relative width results in progressively diminished heat transfer effectiveness. the thermo-hydraulic performance parameter peaks at 1.63 for the optimal relative width of 1 at a 30° angle of attack, indicating the most favorable ratio of nusselt number enhancement to friction factor increase. these results offer essential guidance for optimizing roughened solar air heater designs, suggesting that a single, properly oriented v-rib offers the most favorable compromise between thermal enhancement and energy efficiency.