and without obstacles was experimentally studied by Akpinar and Kocyigit [103].They found that the efficiency of the solar air collectors depends significantly on the solar radiation, surface geometry of the collectors and the extension of the air flow line. They concluded also that, the largest irreversibility was occurring at the solar air heater without obstacles for which the collector efficiency was smallest. A computational analysis of heat transfer augmentation and flow characteristic due to rib roughness over the absorber plate of solar air heaters were presented by Chaube et al. [104]. Sahu and Bhagoria [105] investigated experimentally the heat transfer coefficient by using 90 broken transverse ribs on the absorber plate of a solar air heater. They concluded that the roughened absorber plates increase the heat transfer coefficient 1.25-1.4 times as compared to smooth rectangular duct under similar operating conditions at higher Reynolds number. The heat transfer and friction characteristics of rectangular solar air heater duct using rib-grooved artificial roughness was studied by Jaurker et al. [106]. They inferred that as comparison to the smooth duct, the presence ofrib-grooved artificial roughness yields Nusselt number up to 2.7 times while the friction factor rises up to 3.6 times in the range of the parameters investigated. The performance of solar air heaters having v-down discrete rib roughness on the absorber plate was investigated by Karwa and Chauhan [107] Analysis of fluid flow and heat transfer in a rib grit roughened surface solar air heater was presented