Effect of gap width on thermal performance of solar air heater having arc-shaped ribs with symmetrical gaps: an experimental investigation

In this paper, thermal performance of a solar air heater (SAH) having arc-shaped ribs with symmetrical gaps has been investigated experimentally and compared with that of smooth SAH. An experimental investigation has been carried out to observe the effect of various gap widths on heat transfer and friction characteristics. The investigation includes the roughness parameter; relative gap width (g/e) ranging from 2 to 5 and flow parameter; and Reynolds number ranging from 3000 to 18,000. The fixed parameters for this study were relative roughness height (e/D) of 0.047, arc angle (α) of 60° and relative roughness pitch (P/e) of 12. Results of the present work have also been compared with previously published work. Nusselt number and friction factor for roughened absorber surface is found to be 3.66 and 2.77 times higher than that obtained for smooth plate, respectively. Maximum value of thermo-hydraulic performance parameter is found to be 2.66 at g/e = 4. Heat transfer and friction factor correlations for proposed roughness have also been developed.