Heat transfer and friction correlations for artificially roughened solar air heater duct with discrete W-shaped ribs

An experimental investigation has been carried out to study the heat transfer and friction characteristics in solar air heater by using discrete W-shaped roughness on one broad wall of solar air heater with an aspect ratio of 8:1, the roughened wall being heated while the remaining three walls are insulated. The experiment encompassed Reynolds number (Re) range from 3000 to 15,000, relative roughness height (e/Dh) in the range of 0.0168–0.0338, relative roughness pitch (p/e) 10 and the angle of attack (α) in the range of 30–75°. The effect of parameters on the heat transfer and friction are compared with the result of smooth duct under similar flow conditions. Correlations for heat transfer and friction have been developed as a function of roughness and flow parameters.