Effect of Roughness and Glass Cover on Solar Air Heater Performance-A Review

Flat plate solar air heaters are usually applied in space heating and drying processes of agricultural products, herbal medicines, clothing etc. This system occupies an important place among solar thermal systems because of minimal use of materials. A solar air heater has low heat transfer coefficient between absorber plate and the flowing air that results in higher heat losses to the environment which ultimately leads to low thermal efficiency of such thermal systems. In order to improve the heat transfer rate several methods for enhancement of thermal performance have been proposed and investigated by researchers. In the present paper the effect of artificial roughness of various geometries and glass cover on the performance of solar air heaters, investigated and analyzed by different investigators, has been mentioned. Also the results due these roughness and glass covers have been illustrated.