Heat Transfer and Friction Factor Study of a Solar Air Heater Having Multiple Arcs with Gap-Shaped Roughness Element on Absorber Plate

In this study, effect of roughness parameter on heat transfer and pressure characteristics has been studied. Multiple arc-shaped roughness with gaps was used as roughness element in this study. This roughness geometry was created on the underside of plate. The selected parameters were based upon operating conditions and practical feasibility in solar air heaters. The experiments were done for Reynolds number ( Re ) varies from 2100 to 21,000, relative gap width ( g / e ) ranges from 0.5 to 2, relative gap distance ( d / x ) in the range of 0.25–0.85, relative roughness width ( W / w ) in the range of 1–7. The fixed parameters were arc angle (α) of 60°, relative roughness height ( e / D ) of 0.044, and relative roughness pitch ( p / e ) of 8. The thermohydraulic performance parameter was found maximum for d / x , g / e and W / w values of 0.65, 1.0 and 5, respectively.