Heat transfer and friction factor correlations development for solar air heater duct artificially roughened with 'S' shape ribs

This paper presents the experimental investigation for heat transfer and friction factor for an artificially roughened solar air heater duct having an aspect ratio of 12. Arc shape wire ribs arranged in 'S' shape having roughness parameters as relative roughness pitch (p/e) in the range of 4-16, relative roughness height (e/Dh) in the range of 0.022-0.054, arc angle (α) in the range of 30-75°, relative roughness width (W/w) in the range of 1-4 and Reynolds number (Re) ranges from 2400 to 20,000. It has been found that performance of roughened solar air heater duct is better than the performance of smooth duct for the range of roughness parameters investigated. Experimental results show that maximum enhancement in Nusselt number (Nu) and friction factor (f) have been found at relative roughness width (W/w) value of 3, relative roughness pitch (p/e) value of 8, arc angle (α) value of 60° and relative roughness height (e/Dh) value of 0.043. Based on the data collected from the test runs for roughened duct for various combinations of the roughness parameters correlations are also developed for heat transfer and friction factor in terms of roughness parameters and operating parameter (Reynolds number).