Effect of compressibility and nozzle configuration on heat transfer by impinging air jet over a smooth plate

Jet impingement experiments are conducted to study influence of nozzle profile on heat transfer for compressible subsonic jets. Three different circular profiles namely contoured nozzle, orifice and pipe are selected for the present experimental study. For each nozzle profile, Mach numbers covered are 0.3, 0.5 and 0.7 and the corresponding Reynolds numbers are around 48,000, 82,000 and 120,000. Appropriate diameters for these nozzles are chosen to maintain nearly same Reynolds number. Thin metal foil technique with infrared red camera is used to measure the heat transfer coefficient and adiabatic wall temperature. Pressure distribution in the stagnation regions is measured for all the cases. Correlations for local heat transfer distribution over the surface are presented in this study. Pipe nozzle provides higher heat transfer coefficient compared to contoured nozzle and orifice. The Mach number affects the heat transfer in the stagnation region. The recovery factor distribution is insensitive to change in Reynolds number.