Cylinder moving in pressure- and buoyancy-induced channel flow: A numerical study of transport due to three aiding/opposing mechanisms

The flow and heat transfer associated with the convective cooling of a heated cylinder moving in a channel with buoyancy- and pressure-induced flow has been numerically investigated. Three distinct transport mechanisms arise in this case due to material motion, forced flow, and buoyancy. Considered in this study are uniform flows at the inlet of the cooling channel in the same, as well as in the opposite, direction as the movement of the cylindrical rod. This problem is of interest in several manufacturing processes such as hot rolling, continuous casting, extrusion, wire drawing, and glass fiber drawing. The transport processes are time dependent at the initial stages, following the onset of motion, and usually attain steady state conditions at large time. The temperature distribution in the solid is of particular interest in materials processing. A detailed numerical study is carried out, assuming an axisymmetric, transient circumstance with laminar flow. The governing full, elliptic equations are solved, employing the finite volume method. The conjugate problem, coupling the transport in the solid material with that in the fluid, is solved. The effect of thermal buoyancy on the heat transfer and on the flow for different orientations is studied in detail. Of particular interest is the numerical imposition of the boundary conditions. Not much work has been done in this regard with the combined effects of material motion, buoyancy, and forced flow present. When the flow opposes the movement of the rod, either due to pressure-induced flow or due to buoyancy, a recirculating region arises near the rod surface. This recirculation region plays a major rote in the heat transfer and thus affects the resulting temperature decay in the moving rod. Validation of the numerical results is carried out by comparisons with earlier experimental results, indicating fairly good agreement.