A numerical study of natural convection in a vertical annulus with constant heat flux on the inner wall

A numerical study of natural convection of air in a vertical annulus has been conducted, where the inner wall is heated with constant heat flux at its inner side, the outer wall of the annulus being maintained at constant temperature, and the top and bottom plates are assumed to be insulated. The cases of radius ratio K = 3, aspect ratio A = 10∼30, and Ra* = 10³∼1.7 × 10⁷ have been simulated. Both axial conduction and surface radiation are taken into account to reveal their effects on the distributions of inner wall temperature and local Nusselt number. Emphasis is on the comparison between the numerical results and the relevant experimental data, and the comparison between numerical solutions with and without considering the surface radiation. The numerical results of heat transfer are found to be in good agreement with the corresponding experimental results in the literature. The dependence of average relative conductivity on aspect ratio and the effect of imperfection in top and bottom insulation on the inner wall temperature are also discussed.