Effects of Surface Roughness on Stagnation Heat Transfer of Impinging Liquid Jet on Metal Surface

Abstract

The liquid jet impingement with phase change heat transfer has long been an attractive method of cooling especially in steelmaking process and heat treatment in metals. The current study focuses on making detailed measurements of the stagnation-point heat transfer as a jet impinges on the rough metal surfaces at high temperature nominally up to 900°C. The local heat flux measurements are introduced by a novel experimental technique in which test block assemblies with cartridge heaters and thermocouples are used to measure the heat flux distribution on the surface of hot steel plate as a function of heat flux gauge. The effects of surface roughness on the stagnation-point heat transfer were investigated for well-characterized four rough surfaces with root-mean-square average roughness heights ranging from 40 to 80 µm. The results show that surface protrusions on rough surface can penetrate the thermal sublayer in the stagnation point and thus increase the heat transfer. The heat transfer enhancement mechanism on roughened surface can be investigated by the different boiling regimes.