Experimental investigation of local distribution of heat transfer and fluid flow characteristics of impinging slot air jet

Abstract

Jet impingement cooling has received considerable attention due to its inherent newlinecharacteristics of high heat transfer rate. Impinging flow devices allow for short flow newlinepaths and relatively high rate of cooling from comparatively small surface area. Few newlineindustrial processes that employ impinging jets are drying of food products, textiles, films newlineand papers, processing of some metals and glass, cooling of gas turbine blades and outer newlinewall of the combustion chamber, cooling of electronic equipments, etc. Air will continue newlineto be used as the working fluid due to its low cost, easy availability and reliability. newline The requirement for increased gas turbine engine performance has led to the use of much newlinehigher turbine entry temperature. The higher gas temperatures require active cooling of newlinethe turbine blade using compressor bleed air. Heat transfer enhancement by jet newlineimpingement has significant potential to increase the local heat transfer coefficient. newlineArrays of impinging jets are one of the methods currently used to reduce the blade newlinetemperature on the mid-chord and leading edge regions. The present study focuses on one newlineof the thermal issue of uniformity of distribution of heat transfer. The influence of newlinevarious geometric and flow parameters of the impingement system on the local newlinedistribution of heat transfer coefficients are investigated. The local heat transfer newlinecharacteristics are studied experimentally using a thin foil heater and an infrared thermal imaging technique.The local heat transfer and fluid flow distribution on smooth flat surface impinged by a newlinesingle slot air jet is studied for different jet-to-plate distances (0.5Dh-10 Dh) and Reynolds newlinenumbers (2500-20000). Semi-empirical correlations for local heat transfer coefficients in newlinethe stagnation region are obtained. Further, local heat transfer enhancements on rough flat newlinesurface (detached ribs) impinged by a single slot air jet is examined for different newlinegeometric parameters of ribs at various jet-to-plate distances. newline newline newline