Slot jet impingement heat transfer in the presence of jet-axis switching

Jet-axis switching is an established phenomenon whereby a non-circular, three-dimensional free jet undergoes a major change in cross-sectional shape with increasing downstream distance from the jet origin. This phenomenon has been demonstrated here to also occur for impinging jets. The focus of the present work is to investigate the heat transfer and fluid flow characteristics of rectangular slot jets which experience jet-axis switching. The jets in question have initial cross-sectional aspect ratios of 5:1 and 10:1. The jet cross sections, although highly skewed at first, evolve through near circularity and subsequently become skewed in the direction perpendicular to that of the initial skewness. In addition to the two initial aspect ratios, parametric variations were made of the Reynolds number, the distance of the impingement plate from the jet origin, and the contraction experienced by the flow passing through the aperture of the jet-forming orifice (i.e., the blockage ratio). The investigation was implemented by means of numerical simulation from which local and average Nusselt numbers were determined as functions of the foregoing parameters. Higher Reynolds numbers, greater downstream distances of the impingement plate, and greater blockages served to enhance the Nusselt number values. It remains to be seen whether there is an initial jet aspect ratio that is large enough to preclude axis switching and thereby allow two-dimensional modeling. (C) 2014 Elsevier Ltd. All rights reserved.