CFD simulation of artificially roughened solar air heater using discrete W-shaped ribs

CFD simulation is performed for an artificially roughened solar air heater using discrete W-shaped ribs to study heat transfer and friction characteristics. For this analysis commercial CFD software ANSYS FLUENT (ver. 15.0.7) is used to investigate the effect of relative roughness height (0.0168 to 0.0338), Reynolds number (3000 to 15000) and angle of attack (30°, 45°, 60° and 75°) on duct thermal performance and results are compared with smooth duct. The roughened horizontal absorber plate is uniformly heated using constant heat source of 1000 W/m2 and remaining three sides are insulated. Maximum Nusselt number (Nu) and friction factor (f) found to be 96.83, 0.45 and 52.19, 0.024 for artificially roughened duct and smooth duct respectively. Nusselt number enhanced by 120 % in roughened SAH over the smooth duct. Optimum parameters in roughened duct found to be: angle of attack (α) = 60°, relative roughness height (e/Dh) = 0.0338, relative pitch ratio (p/e) = 10 and aspect ratio (W/H) = 8.