Solar air heater is used for agricultural grain products drier, curing of industrial products and for other systems requiring low grade thermal energy. Their usefulness and the quantitative energy collections has been limited because of low thermal efficiency primarily as a result of low convective heat transfer coefficient, between the absorber plate and air leading to higher plate temperature, and thus resulting in greater thermal energy losses. One of several methods that have been proposed and investigated for the enhancement of heat transfer coefficient is the use of artificial roughness. Since the use of expanded metal mesh wire rib roughness has shown to enhance the heat transfer rate considerably, it is worth exploring. Experimental investigation has been carried out to study heat transfer enhancement by using small diameter wire ribs on absorber plate of solar air heater duct, with the roughened wall exposed to the glazing side while the remaining three walls were insulated. The roughened wall has relative roughness height (e/Dh) 0.0135-0.0406, relative roughness pitch (p/e) 10-20, rib height 0.5-1.5 mm, expanded metal mesh (L/e) 25-75, Short way mesh (S/e) 15-45 ,angle of attack 450 for inclined configuration, duct aspect ratio of 12 and the air flow rate corresponds to Reynolds number between 2,000 to 18,000. Results of the experimental investigation revealed that provision of expanded metal mesh as artificial roughness resulted in a considerable enhancement in heat transfer and friction factor. It has been found that the heat transfer coefficient could be improved by a factor up to 2.2 and the friction factor had been found to increase by a factor of 1.2 times that of the smooth duct. The investigation emphasized that the secondary flow rolling along the inclined ribs is responsible for higher heat transfer rates. Thermal efficiency increased from 50.58 % - 65.75 %. Finally, correlation is developed for both Nusselt number and friction factor using sigma plot software, which can be selected by the designer for a given operating condition.