Investigations of the heat transfer and friction coefficient in a duct with surface injection: Experimental approach

Several engineering equipment's and installations often operates under severe conditions such as elevated temperatures and high pressures in turbines, combustion furnaces and chambers, engines, generators, etc. This results in lessening the life time of such facilities. Hence, many efforts have been made to study the effects of such conditions with few focusing on the effects of surface injection on heat transfer (HT) characteristics. In this work, a test rig was developed to investigate the influence of blowing ratio (M), from 0 to 4, as well as injection angle Φ (from 30° to 150°) on the flow and HT characteristics. The velocity distribution was measured using particle image velocimetry (PIV) technique. A significant increase in both friction coefficient and heat transfer were obtained by increasing the Re for the case of Φ > 90° at constant M and a decrease for angles Φ < 90°. Results indicated that, the average Nusselt number (Nu) ratio increases with increasing the M for all injection angles, with minimum and maximum values occurring at the angles of 60° and 150°, respectively. General correlations for the Nu and friction factor have been proposed as functions of the flow, Φ, and M based on the results of this work. The correlations, were found to represent the experimental data with reasonable accuracy. Also, the experimental results were well compared with the previous work with highest deviation of about 6.42% for the ratio of heat coefficient.