Effect of roughness elements on thermal and thermohydraulic performance of double pass solar air heater duct having discrete multi V-shaped and staggered rib roughness on both sides of the absorber plate

In this work, an experimental setup consisting of a double pass solar air heater duct provided with discrete multi V-shaped and staggered rib as artificial roughness on both sides of the absorber plate has been designed and fabricated. The parameters of interest investigated experimentally cover a wide range of Reynolds number (Re) from 2000 to 20000, relative staggered rib pitch (p'/p) from 0.2 to 0.8, relative staggered rib size (r/e) from 1 to 4, and relative roughness width (W/w) from 5 to 8. Experimental data related to heat transfer, pressure loss, and thermohydraulic performance has been determined. Substantial improvement has been obtained with some penalty of friction losses.