An Experimental Investigation of Heat Transfer and Friction Factor in Solar Air Heater Duct Using Double ARC Reverse Shaped RIB Roughness on Absorber Plate

A solar air heater is a thermal system that uses artificial roughness in the form of repeated ribs on the absorbent plate to improve the rate of heat transfer. An experimental study was conducted to investigate the thermo hydraulic performance using Double arc reverse shaped ribs in the air absorption plate that passes through the rectangular duct, the rough wall is heated while the other three walls are insulated. The roughness of the wall have a pitch (p) of 10 mm, the relative roughness pitch (p/e) = 8.33, the height of the rib (e) is 1.2 mm, the height of the relative roughness (e /Dh) of 0.027 and the flow of air corresponds to the Re between 3000 and 14000. The arc angle of the roughness geometry varies between 300 and 750. The results of the heat transfer were compared with those of the smooth ducts under similar flow conditions and thermal limits to determine the thermal efficiency of the solar air heater. The convection heat transfer coefficient and the Nu increase with increasing Re for a unique Double arc reverse shaped rib roughness. The increase in Nu is 1.26 to 2.478 & the f is 1.40 to 1.74 times compared to the smooth plate respectively. Roughness also increases the value of the friction factor, but the increase in its value is small compared to the increase in the heat transfer coefficient. The maximum improvement in the Nu is 2.478 for the pitch of 10 mm, the arc angle of 750 for the Re 14,000 in comparison with the smooth plate. Thermo hydraulic yields show a first increasing variation, and then decrease with respect to the increase in the Re. The maximum improvement in thermo hydraulic performance is observed with the Re 7000, pitch of 10 mm and the arc angle of 750 with respect to the smooth plate, after which it begins to decrease with the increase in the Re.