Thermo-hydraulic performance due to relative roughness pitch in V-down rib with gap in solar air heater duct—Comparison with similar rib roughness geometries

This paper presents thermo-hydraulic performance comparison of rib roughness under investigation, ‘V-down ribs with gap’ and similar reported rib roughness geometries used in solar air heater duct. The present rib roughness has flow-attack-angle and relative roughness height of 60° and 0.043, respectively. The duct has aspect ratio of 12 and the Reynolds number ranged from 3000 to 15,000. The roughened wall was uniformly heated while the remaining three walls were insulated. These boundary conditions correspond closely to those found in conventional solar air heaters. Five rib roughened plates having relative roughness pitch of 4, 6, 8, 10 and 12 have been tested. The Nusselt number and friction factor were found to be highest for relative roughness pitch of 8. Maximum enhancement in Nusselt number and friction factor has been found to be 2.70 and 2.86, respectively. Thermo-hydraulic performance parameter ranged from 1.27 to 1.93. Thermo-hydraulic comparison with similar rib geometries show that the present roughness geometry performs better for Reynolds number range of 3000–12,000.