Thermo-hydraulic performance analysis of solar air heaters having artificial roughness-A review

Enhancement of heat transfer in the solar air heater ducts can be achieved by several means like using baffles, fins, ribs and groves. Until now, various attempts have been made to investigate the effects of these geometries on the enhancement of the heat transfer rate; however it is achieved at the cost of the increase in the pressure drop across the surfaces on which these elements are mounted. This paper is an attempt to summarize and conclude the investigations involving the use of small height elements and surface protrusions on absorber plate and channel walls as artificial roughness elements of various geometries and its effect on heat transfer and friction factor through experiments. It also summarizes the various correlations which have been developed for Nusselt number (Nu) and Friction factor (f) and reported in the previous investigations. The comparative study has been done to understand the results of these investigations for solar air heaters with different roughness elements on its absorber surface.