An Experimental Study of Multiple-jets Impingement Heat Transfer

Abstract

This study experimentally examined the detailed heat transfer distributions over a free surface of an array of orthogonal impinging air jets. Detailed heat transfer measurements were made at jet Reynolds numbers of 830, 1110, 1660, 2220 and 2770 for five different heating levels with separation distances keeping at 0.1, 0.25, 0.75, 1, 1.5. 2, 2.5, 3, 4 and 6 jet diameters. The graphic representations of the local Nusselt number contours evaluated from the infrared thermal images of the impinging surface under different flow conditions and the dependence of Nusselt number values on Reynolds number, heating level and separation distance were presented. It was found that four regions of impeded closed-loop heat transfer contours located between jets developed in the jet array assembly. A geostrophic heat transfer phenomenon among the central jet region was observed when the separation distance became very small (S/D(subscript j)≤1) which phenomenon could weaken the heat transfer identities of central jet and was ini.tiated at the lower value of heat flux if the jet Reynolds number reduced. Due to the complicate flow phenomena and the geostrophic flow behavior developed over the central jet region, the variations of heat transfer values did not correspond monotonically with the increase of separation distance.