Numerical Analysis of Natural Convection Flow and Heat Transfer from an Enclosed Cylindrical Heat Source

A numerical study of the natural convection flow arising from a confined thermal source is presented. The physical system considered is a 2D cavity of square cross-section, containing a horizontal cylindrical source, the heat carrier fluid being air at Prandtl number Pr = .7. The heating body is placed in central position; the resulting flow is investigated with respect to the variation of the Rayleigh number and the ratio between the source diameter and the cavity side length. Either Dirichlet and Neumann thermal boundary conditions are imposed on the cylinder surface. The analyses make use of two Navier-Stokes, finite- volume codes: a general-purpose CFD package, and a Direct Numerical Simulation software. Main issues of the work are the rise of steady and transitional flows and the heat transfer performance of the system, as influenced by the different boundary conditions at the heat source wall. A correlating equation for the average Nusselt number on the cylinder, previously obtained for the isothermal case, is validated for the uniform heat flux condition.