Wall effect on heat transfer from a micro-cylinder in near-wall shear flow

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 (10−2⩽k∗w⩽104) on the heat transfer from a cylinder under different flow conditions (the shear parameter G∗=0.0033, 0.01, 0.1 and the cylinder Reynolds number 10−3⩽ReD⩽1.0) were investigated in detail. The cylinder to wall distance was varied in the range 0.1⩽Y+⩽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+ 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 conductivities. 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.