This paper presents a Computational Fluid Dynamics (CFD) analysis of solar air heater duct to estimate its thermo-hydraulic performance. On the inner side of absorber plate, inclined circular ribs are provided to create artificial roughness. The roughness parameters were studied in the present work are inclination angle (α) of ribs 45 and 60 and roughness height (e) 1mm and 2mm at a constant roughness pitch (p) of 20mm. Reynolds number (Re) in the range of 6000 to 15000 and constant heat flux (I) having a value of 1000W/m2 on absorber plate were used as operating parameter during the analysis. Renormalization group (RNG) k-ε turbulence model is selected for the analysis from the different turbulence model after comparing the results of these models with empirical correlation results for smooth duct, as RNG k-ε model results was found in good agreement. The effect of different roughness parameters has also been compared on the basis of overall enhancement ratio to obtain the optimum roughness parameters.