Effect of Microscopic Vortices Caused by Flow Interaction With Solid Obstacles on Heat Transfer in Turbulent Porous Media Flows

Turbulent flow in a homogeneous porous medium was investigated through the use of numerical methods by employing the Reynolds Averaged Navier-Stokes (RANS) modeling technique. The focus of our research was to study how microscopic vortices in porous media flow influence the heat transfer from the solid obstacles comprising the porous medium to the fluid. A Representative Elementary Volume (REV) with 4 × 4 cylindrical obstacles and periodic boundary conditions was used to represent the infinite porous medium structure.

Our hypothesis is that the rate of heat transfer between the obstacle surface and the fluid (q_avg) is strongly influenced by the size of the contact area between the vortices and the solid obstacles in the porous medium (A_vc). This is because vortices are regions with low velocity that form an insulating layer on the surface of the obstacles. Factors such as the porosity (φ), Pore Scale Reynolds number (Re_p), and obstacle shape of the porous medium were investigated. All three of these factors have different influences on the contact area A_vc, and, by extension, the overall heat transfer rate q_avg. Under the same Pore Scale Reynolds number (Re_p), our results suggest that a higher overall heat transfer rate is exhibited for smaller contact areas between the vortices and the obstacle surface. Although the size of the contact area, A_vc, is affected by Re_p, the direct influence of Re_p on the overall heat transfer rate q_avg is much stronger, and exceeds the effect of A_vc on q_avg. The Pore Scale Reynolds number, Re_p, and the mean Nusselt number, Nu_m, have a seemingly logarithmic relationship.