An investigation of heat transfer characteristics in axisymmetric and two-dimensional impinging jets

This thesis investigates two distinct phenomena that have different applications in practice although both of them fall within the field of impingement heat transfer. The first investigation concerns the effect of surface roughness on the local and the average heat transfer between an axisymmetric air jet and a circular plate. The second investigation concerns the effect of inclination of a two-dimensional air jet impinging on a rectangular surface.; To determine the effect of surface roughness, two aluminum plates, one with a flat surface and a second with protrusions added to the surface (roughened surface) were used. The roughness took the shape of a circular array of protrusions of 0.5mm base and 0.5mm height. Temperatures were measured over a Reynolds number ranging from 9600 to 38500 based on flow rate through a 6.85mm diameter nozzle. The temperature measurements were repeated for nozzle exit-to-plate spacing, z/d, ranging from 1 to 10. The average Nusselt number for both cases was plotted versus the Reynolds number and their functional correlation was determined. The results indicate an increase of up to 6% of the average Nusselt number due to roughness.; The local heat transfer was also experimentally investigated for an axisymmetric air jet impinging on a uniformly heated surface with protrusions. Two stainless steel plates were used for comparison: a flat circular disk of 72mm in diameter and a disk of the same diameter with a circular array of protrusions. The array had a radius equal to twice the number in the range used in this study. For low values of inclination angle, the local Nusselt number on the uphill side was found to be insensitive to jet exit-to-plate spacing. Correlations are proposed to predict the local Nusselt number as a function of x/D, z/D, theta and Re.; In the third part of this study, the stagnation and the wall jet regions solutions for a two-dimensional jet impinging on a flat surface are developed using heat transfer relations available in the literature. These solutions were analyzed and compared to the present experimental results.