Evaluation of thermal performance factor for solar air heaters with artificially roughened channels

Heat transfer augmentation has become the utmost industrial desire. Turbulence promoters seems to be a better option for better heat transfer but at the expense of enormous pressure drop. In the current study, experimental optimization of heat transfer and pressure drop in various configurations of ribbed and corrugated surfaces on the bottom wall of the Solar Air Heater channel, having aspect ratio of 26:5 was performed. The results were evaluated in terms of enhancement in heat transfer (Nu/Nu s ) , friction factor ratio ( f / f s ) and thermal performance factor ( η ) . Three different cases and nine configurations with a pitch to rib/corrugation height ratio of 4.0 were studied. Case A consists of a smooth, continuous square rib, inline and staggered broken ribs. Case B comprises 30 ◦ , 45 ◦ , 60 ◦ and 90 ◦ trapezoidal corrugated geometries while case C is the comparison of smooth, wavy corrugated and the best configurations of cases A and B. The results show that rectangular duct with staggered broken ribs and trapezoidal corrugation at 45 ◦ are the best configurations for case A and B, respectively. The 45 ◦ corrugated configuration is the best one amongst all, with values of 1.53, 1.5 and 1.33% for Nu/Nu s , f / f s and η respectively.