A review of artificial roughness geometries employed in solar air heaters

Enhancement of heat transfer in the solar air heater ducts can be achieved by breaking laminar sub-layer near the absorbing surface and can be efficiently done by employing ribs as roughness elements. However, this gain is accomplished at the expense of increase in pressure drop. This paper presents the detailed review of various investigations made on artificial roughness geometries summarizing their outcomes. Attempt have been made to study the effect of various influencing roughness and flow parameters on the thermal and hydraulic performance of solar air heater through the flow visualization.