Performance enhancement of solar air heaters through ribbed absorbers with varied hole configurations

The performance of solar heaters for heating air could be significantly upgraded by adding obstructions on the absorber. Experiments were conducted to obtain both thermal performance and friction factor information inside an air heater channel containing convergent, divergent and uniform holes on ribs fixed on the absorber surface. This study covers a Reynolds number range of 3000-18000, rib heights, e, varying between 2 mm and 4 mm, hole diameters, D, spanning from 1- 3 mm, and ribs featuring various hole arrangements. Surface roughness effects on the Nusselt number and friction factor, f, were investigated, and the findings have been compared with that of a flat absorber. Nusselt number and friction factor increased through 3.54 and 2.7 times, respectively, over the flat absorber. At Re = 18000, the convergent hole rib (e = 4 mm, D = 2 mm) provided the greatest enhancements in Nusselt number and friction factor.