PERFORMANCE ENHANCEMENT OF SOLAR AIR HEATERS USING HYBRID ARTIFICIAL ROUGHNESS TECHNIQUES: AN EXPERIMENTAL INVESTIGATION

Abstract

Solar air heaters (SAHs) are among the most economical and environmentally friendly solar thermal devices used for space heating, crop drying, and industrial heating applications. However, their widespread utilization is limited by the inherently low convective heat transfer coefficient between the absorber plate and the flowing air, resulting in lower thermal efficiency. Artificial roughness techniques have been extensively investigated to enhance heat transfer by creating turbulence near the absorber surface. In recent years, hybrid roughness configurations have attracted considerable attention due to their ability to generate stronger turbulence and improve thermal performance compared to single roughness geometries. Experiments were conducted under varying airflow conditions corresponding to Reynolds numbers ranging from 3000 to 18000. The thermal performance of the hybrid roughened solar air heater was compared with that of a conventional smooth duct solar air heater under identical operating conditions. The experimental results demonstrate a significant improvement in thermal efficiency, Nusselt number, and overall heat transfer characteristics due to the combined effect of ribs and dimples. The hybrid roughness configuration achieved a maximum thermal efficiency of approximately 72%, compared to 54% for the smooth duct arrangement. Furthermore, a substantial enhancement in heat transfer was observed with only a moderate increase in friction losses. The findings indicate that the proposed hybrid roughness technique effectively improves the thermal performance of solar air heaters and offers a promising solution for high-efficiency solar thermal energy applications.