Study on convective heat transfer characteristics of inclined jet impinging cylindrical target surface in the confined space

Abstract

• Heat transfer of cylinder surface with flow confinement is experimentally tested. • The effects of jet angle and Reynolds number on heat transfer have been studied. • The mechanism of heat transfer for different jet angles is analyzed in detail. In this study, the convective heat transfer characteristics of a cylinder with flow confinement under the impingement of a circumferentially arranged turbulent inclined circular air jet array are experimentally studied. This jet configuration can be effectively applied in the cooling/heating of rotating machinery, such as cooling of the steam turbine shaft, cement rotary kiln cooling, and textile drying. The purpose of the study is to elucidate the effect of the jet angle ( θ ) and the jet Reynolds number ( Re d ) on the heat transfer behaviors of the cylindrical target surface. The jet Reynolds number varies from 20,000 to 35,000, and three different jet angles ( θ =20°,30°,45°) are adopted. The local Nusselt number distribution of the region of interest on the cylindrical target surface is experimentally measured by applying the transient thermochromic liquid crystal technique. Numerical studies are conducted to obtain details of flow patterns in the confined space, so as to analyze the convective heat transfer mechanisms. The results show that for small jet angles ( θ =20°,30°), due to the intense circumferential cross-flow, the overall distribution of the Nusselt number is relatively uniform. As the jet angle increases to 45 °, the Nusselt number in the middle of the target surface increases significantly because of the formation of the stagnation region. As the jet angle increases from 30 ° to 45 °, the heat transfer uniformity on the cylindrical surface decreases significantly. The maximum difference of the variation coefficient of the Nusselt number is 26.6% at Re d = 35 , 000 . As the jet Reynolds number increases, the local Nusselt number on the cylindrical target surface increases as a whole. The average Nusselt number with Re d = 35 , 000 increases by 64.3%-74.9% compared with the cases of Re d = 20 , 000 .