Effects of Orifice Geometry on the Heat Transfer Distribution for Impinging Jet Array

Abstract

Abstract The recent technological advances in the areas of gas turbine blades, tempered metals and in particular electronic components, require a rapid rate of removal of heat. With an array of impinging jets a large surface involved in the cooling or heating process can be covered using relatively small flow work, or driving pressure. A properly spaced and configured impinging jet array produces a high heat transfer rate. The present study details the role of impinging jets in the heat transport phenomena. The average and local heat transfer coefficient distribution is mapped using thermochromic liquid crystals for three equal flow area jet orifice geometries in a 3-by-3 submerged impinging water jet square array. The hydrodynamic conditions are established for low Reynolds number values, from 800 to 1500, and impingement distances of 1, 2 and 4 jet hydraulic diameters. The constant temperature jets impinged normally on a constant heat flux surface and liquid crystal images were recorded under thermal and hydrodynamic steady state conditions. The results indicate that there is a Reynolds number dependence of the degree of heat transfer enhancement for different shaped jet orifices. The heat transfer within the central unit cell varies with impingement distance and jet geometry. Two types of heat transfer coefficient spatial variation have been identified: one deals with large scale jet flow characteristics and the other with smaller scale effects caused by flow turbulence. Details are presented illustrating the nonuniformity of the heat transfer for the various geometries.