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Solar air heating devices have been employed in a wide range of industrial and home applications for solar energy conversion and recovery. It is a useful technique for increasing the rate of heat transfer by artificially creating repetitive roughness on the absorbing surface in the form of semicircular ribs. A thermo-hydraulic performance analysis for a fully developed turbulent flow through rib-roughened solar air heater (<i>SAH</i>) is presented in this article by employing computational fluid dynamics. Both 2-dimensional geometrical modeling and numerical solutions were performed in the finite volume package ANSYS FLUENT. The renormalization-group (<i>RNG</i>) <i>k-ε</i> turbulence model was used, as it is suitable for low Reynolds number (<i>Re</i>) turbulent flows. A thermo-hydraulic performance analysis of an <i>SAH</i> was carried out for a ranging <i>Re</i>, 3800–18,000 (6 sets); relative roughness pitch (<i>RRP</i>), 5–25 (12 sets); relative roughness height (<i>RRH</i>), 0.03–0.06 (3 sets); and heat flux, 1000 W/m². The numerical analysis revealed that with an <i>RRP</i> of 5 and an <i>RRH</i> of 0.06, the roughened duct produces the highest augmentation in average <i>Nu_r</i> in the order of 2.76 times that of a plain duct at an <i>Re</i> of 18,000. With an <i>RRP</i> = 10 and <i>RRH</i> = 0.06, the roughened duct was found to provide the most optimum thermo-hydraulic performance parameter (<i>THPP</i>). The <i>THPP</i> was determined to have a maximum value of 1.98 when the <i>Re</i> is equal to 15,000. It was found that semi-circular ribs which have a rib pitch = 20 mm and a rib height = 2 mm can be applied in an <i>SAH</i> to enhance heat transfer.