Experimental investigation of heat transfer augmentation using multiple arcs with gap on absorber plate of solar air heater

In this present article an experimental study has been carried out on heat transfer and friction factor in rectangular channel which is having multiple-arc shaped with gaps as roughness element. The investigation encompassed Reynolds number (Re) ranges from 2100 to 21,000 (7 values), relative roughness height (e/D) ranges from 0.016 to 0.044 (4 values), relative roughness pitch (p/e) ranges from 4 to 16 (4 values), arc angle (α) values are 30-75° (4 values), relative roughness width (W/w) ranges from 1 to 7 (5 values), relative gap distance (d/x) values are 0.25-0.85 (4 values) and relative gap width (g/e) ranges from 0.5 to 2.0 (4 values). The maximum increment in Nusselt number (Nu) and friction factor (f) is 5.85 and 4.96 times in comparison to the smooth duct. Utilizing these data, correlations were developed for Nu and f.