Effect of roughness geometries on heat transfer enhancement in solar thermal systems - A review

The performance characteristics of a solar heater and heat exchangers can be effectively improved by using artificial roughness in different forms, shapes and sizes. Artificial roughness is provided in the form of different geometries such as ribs, dimple shape roughness, wire mesh, baffles, delta winglets etc. To determine the effect of these geometries on thermal performance of solar heaters and heat exchangers, several experimental and numerical studies have been carried out by various researchers. In this paper, an attempt has been made to review various roughness element geometries employed in solar air heaters and heat exchangers in terms of heat transfer, friction factor and flow simulation techniques. Correlations developed for heat transfer and friction factor for different roughness geometries by various investigators in solar air heaters are presente.