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The present paper explains the effects of roughness parameters on Nusselt number ( Nur ) and friction factor ( f r) for spherical ball roughened collectors. Flow and roughness geometrical parameters were varied as relative roughness pitch ( p/e ) 9–18, relative roughness height ( e/D h) 0.024–0.040, ball’s height-diameter ratio ( e/d b) 0.5–2, angle of attack ( α ) 35˚–75˚ and Reynolds no (Re) 2500–18500. Maximum augmentation in ‘Nu r ’ and ‘f r ’ for varying ‘p/e’, ‘e/D h ’, ‘e/d b ’ and ‘α’ was found as 2.1 to 3.54 times, 1.87 to 3.21 times, 2.89 to 3.27 times and 1.74 to 3.56 times for ‘Nu r ’ and 0.84 to 1.79 times, 1.46 to 1.91 times, 1.67 to 2.34 times and 1.21 to 2.67 times for ‘f r ’ compared to smooth duct, respectively. Correlations of Nu r  and f r  are derived. Values of  Nur  and  f rso obtained from experimentation and correlation matched with considerably good accuracy, with a mean deviation of ±3.5% for ‘Nu s ’ and ±4.4% for ‘f s ’.

Effects of roughness parameters on the heat transfer and friction of an inclined spherical ball roughened flat plate solar collector