The role of jet inlet geometry in impinging jet heat transfer, modeling and experiments

Abstract

Effects of jet inlet geometry and aspect ratio on local and average heat transfer characteristics of totally nine confined impinging jets have been investigated experimentally using thermochromic liquid crystals and numerically by using a 3-D low Reynolds number ke3 model. Experimental study by using liquid crystals for temperature measurement was conducted for three different jet exit geometries (circular, elliptic, rectangular). In addition, simulations were performed at the same mass flow rate for totally nine jet exit geometries including circular, elliptic and rectangular jets with different aspect ratios for dimensionless jet to plate distances 2, 6, and 12. As the aspect ratio of equal cross-sectional area elliptic and rectangular jets increases, heat transfer enhancement in the stagnation region was obtained. As a result higher aspect ratio jets can be used as a passive enhancement technique for localized heating or cooling especially at small jet to plate distances. Wall jet region comprises very large portion of the impinging plate under study and generally lower heat transfer rates were attained for higher aspect ratio jets in this region especially at small jet to plate distances. Therefore as the aspect ratio increases, lower average heat transfer rates were acquired. The effect of aspect ratio on local and average heat transfer decreases with increasing jet to plate distance. Even though the mass flow rate is the same, heat transfer rate of rectangular jets were reduced with increasing the cross-sectional area. With increasing jet to plate distance very similar heat transfer characteristics were observed along the major and minor axis directions. © 2010 Elsevier Masson SAS. Allrights reserved.