(The) effect of inclination on impinging jets at small nozzle-to-plate spacing

Abstract

In this study, the effect of inclination on impinging jets at small nozzle-to-plate spacing was experimentally investigated. Parameters varied in the experiments were the Reynolds number (Re = 5000 - 25000), the inclination angle of the flat plate (θ = 0° - 40°) and the dimensionless nozzle-to-plate spacing ($H/d_h$ = 0.125 - 1). The hydraulic diameter of the slot jet was fixed at 4 mm and air was used as the working fluid. Thermocouples were used to measure local temperatures so that the impingement point and average Nusselt numbers and their distributions on the inclined plate could be obtained. Experimental results show that the effect of inclination on impinging jets at the small nozzle-to-plate spacing is totally different from that at the large nozzle-to-pate spacing. First, pressure drop at the jet exit increased linearly as the inclination angle of the flat plate increased at small nozzle-to-plate spacing, while the inclination didn’t affect the pressure drop at large nozzle-to-plate spacing. Second, the impingement point and average Nusselt numbers increased with increasing inclination angle. Finally, it was shown that the increase in the Nusselt numbers with increasing inclination angle resulted from the increase in the pumping power of the impinging jet which was caused by the increase in pressure drop at the jet exit. Based on the experimental results, correlations for the impingement point and average Nusselt numbers of the impinging jet are suggested as functions of the pumping power alone.