Heat transfer and friction factor correlations for rectangular double/two pass solar air heater with inclined and transverse ribs as roughness elements

Abstract

Experimentations were done to analyse the effect of using inclined and transverse ribs separately over the absorber plate as artificial roughness in a double/two pass solar air heater. The material of the absorber plate is Galvanized Iron (GI) with ribs of aluminium attached over it which enhances the rate of heat transfer. The shape of the duct used is rectangular having an aspect ratio of 10. The relative roughness pitch (p/e) ranges between 5 and 20, relative roughness height (e/Dh) ranges between 0.043 and 0.045, angle of attack (α) ranges between 30°- 90° and Reynolds number ranges from 4000 to 18000. The data obtained for heat transfer and friction factor from various roughness placed over the absorber plates are compared with the data obtained for the smooth plate operated in same conditions. It is seen that there is an increase in heat transfer and friction factor characteristics after placing ribs over the absorber plate. At the end the correlations of Nusselt number and friction factor were developed.