Impinging round jets are used in a wide variety of practical cooling and drying applications and thus have been the subject of numerous investigations. These investigation, recently reviewed by Jambunatham et al. [1] and others, have examined how many features of the impinging jet, including, the jet-to-plate spacing, nozzle configuration, and jet temperature, affect the heat transfer to the jet. Measurements by Colucci and Viskanta [2] and others have also shown that a confining wall mounted flush with the jet exit has a significant effect on heat transfer produced by the jet when the jet-to-plate distance is small. However, these investigations did not directly examine the effect of the confinement by measuring the heat transfer produced by the same nozzle with and without the wall, nor did they examine how the confining wall affects the development of the flow field. This investigation examines the effect of the confining wall by measuring the heat transfer produced by an impinging jet exiting a fully developed pipe with and without a confining wall. The fully developed pipe was used because the exit conditions of the jet are well known. The Nusselt number distributions in the confined and unconfined impinging jets were measured for jet-to-plate spacing ranging from 0.25 to 6 diameters. The effect of the confining wall on the flow field was investigated using flow visualization and measurements of the dynamic pressure on the impingement surface. The flow visualization experiments were inconclusive and are not discussed but the results of the pressure measurements are presented.
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