A study of the heat transfer characteristics of turbulent round jet impinging on an inclined concave surface using liquid crystal transient method

Abstract

The effects of concave hemi-spherical surface with an inclined angle on the local heat transfer from a turbulent round impinging jet were investigated through experimentation. The liquid crystal transient method was used in this study. This method suddenly exposes a preheated wall to an impinging jet and then a video system records the response of the liquid crystals to measure the surface temperature. The Reynolds numbers 11,000, 23,000 and 50,000; were used nozzle-to-surface distance ratio was from 2 to 10 and the surface angles were α = 0°, 15°, 30° and 40°. The correlations of the stagnation point Nusselt number according to Reynolds number, jet-to-surface distance ratio and dimensionless surface angle were also presented. In the stagnation point, in terms of Re n , where n ranges from 0.43 in case of 2 ⩽ L/ d ⩽ 6 to 0.45 in case of 6 < L/ d ⩽ 10, there roughly appears to be a laminar boundary layer result. The maximum Nusselt number, in this experiment, occurred in the upstream direction. The displacement of the maximum Nusselt number from the stagnation point increases with increasing surface angle or decreasing nozzle-to-surface distance. Under this condition, with surface curvature at D/ d = 10, the maximum displacement is about 0.7 times of the jet nozzle diameter.