Thermo-hydraulic performance of solar air heater with built-in one-eighth sphere vortex generators

•A novel one-eighth sphere vortex generator is proposed and studied.•It can create strong longitudinal vortices and weak transverse ones.•The optimal performance is observed at a deflection angle of 180°.•New correlations of Nusselt number and friction factor were developed. The primary objective of optimizing solar air heaters is to enhance their thermal efficiency, and the incorporation of perturbing elements into the absorber plate has proven to be an effective approach. The present study employed an electric heating plate to simulate solar heating and proposed a novel one-eighth sphere vortex generator to create strong longitudinal vortices and weak transverse vortices, thereby achieving enhanced overall performance. The experimental investigation focused on examining the impact of parameters, including deflection angle (α), relative transverse pitch (S/H), relative longitudinal pitch (L/H), relative height (e/H), and Reynolds number (Re), on both heat transfer and flow characteristics. The results show that new vortex generator performs best at deflection angles of 180°. The maximum thermo-hydraulic performance parameter of 2.03 was observed in this study. Additionally, it was found that the maximum Nusselt number (Nu) and friction factor (f) were 2.45 and 1.96 times higher than those obtained for a smooth duct, respectively. New correlations of Nusselt number (Nu) and friction factor (f) were developed to predict the heat transfer and flow resistance characteristics of solar air heater with built-in one-eighth sphere vortex generators. This study proposes a new idea to enhance the performance of solar air heaters.