Wall effect on heat transfer from a micro-cylinder in near-wall shear flow J.-M. Shi, M. Breuer, F. Durst * Lehrstuhl f€ ur Str€ omungsmechanik, Universit€ at Erlangen-N€ urnberg, Cauerstr. 4, D-91058 Erlangen, Germany Received 5 December 2000; received in revised form 12 April 2001 Abstract A two-dimensional numerical study on the heat transfer from small cylinders in near-wall shear flow was carried out taking the conjugated heat conduction in the solid wall into account. The finite volume flow solver (FASTEST-2D) enhanced with multigrid acceleration and the local grid refinement technique was used to achieve efficient computations and accurate numerical results. The effects of the wall thermal conductivity ð10 2 6 k  w 6 10 4 Þ on the heat transfer from a cylinder under different flow conditions (the shear parameter G  ¼ 0:0033, 0.01, 0.1 and the cylinder Reynolds number 10 3 6 Re D 6 1:0Þ were investigated in detail. The cylinder to wall distance was varied in the range 0:1 6 Y þ 6 10 to cover the influence range of the wall effect. It was found that the wall material even of low conductivity, such as mirror glass and Perspex, still has a dominant influence on the heat transfer rate from the cylinder in the vicinity of a wall. However, when Y þ is above 5.0, the wall effect becomes minor and the average heat loss rate of the cylinder depends only on the cylinder Reynolds number while the shear parameter influences the local Nusselt number distribution. Different heat exchange processes of the fluid and the solid wall were found between materials of high and low con- ductivities. Based on the numerical results and with the help of dimensional analysis, the physical mechanism of the hot- wire near-wall correction was further revealed. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Computational methods; Heat transfer; Measurement techniques 1. Introduction Heat transfer from a circular cylinder in cross-flow has been intensively investigated. The earlier exper- imental and analytical results on the effects of a variety of influencing factors have been reviewed by  Zukauskas and  Ziug zd [1]. Recently, numerical studies have been increasingly focused on this topic. However, most of the available studies are limited to the case where the cyl- inder is located in a uniform cross-flow. Despite its basic importance in both engineering and science, the problem of a cylinder in shear flows has received relatively little attention. Kwon et al. [2] studied the free shear effect on the flow characteristics over a cylinder for a range of Reynolds numbers from 600 to 1600. Sung et al. [3] in- vestigated the free shear effect on the mass transfer from a cylinder for higher Reynolds numbers of 24,000 and 48,000. They found that the overall mass transfer rate depends almost exclusively on the Reynolds number while the distribution of the local mass transfer rate on the cylinder surface is characterized by the shear rate without a strong dependence on the Reynolds number. Goldstein and Karni [4] examined the effect of a wall boundary layer on the local mass transfer from a cyl- inder. However, almost no study has dealt with the heat transfer from a cylinder in wall-bounded shear flow ex- cept for investigations on the hot-wire near-wall cor- rection. Most of them are experimental, as reviewed by Bruun [5]. The experimental data reflect only the total effect of all possible influencing factors and additionally show a high degree of scatter, which makes it difficult to understand the observed phenomena. Nowadays, nu- merical analysis is a powerful tool for overcoming this International Journal of Heat and Mass Transfer 45 (2002) 1309–1320 www.elsevier.com/locate/ijhmt * Corresponding author. Tel.: +49-9131-852-9500; fax: +49- 9131-852-9503. E-mail addresses: shi@lstm.uni-erlangen.de (J.-M. Shi), breuer@lstm.uni-erlangen.de (M. Breuer), durst@lstm.uni- erlangen.de (F. Durst). 0017-9310/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0017-9310(01)00225-3