Natural Convection in Eccentric Annuli packed with Spheres

A numerical investigation of two-dimensional natural convection about a horizontal circular heated cylinder embedded in cylindrical packed bed of spheres under the condition of local thermal non-equilibrium is reported. The present parametric investigation concentrates on the use of two-phase energy model (local thermal non-equilibrium LTNE), which does not consider the condition of thermal equilibrium between the flowing fluid and the solid spheres, to predict the thermal characteristics and the heat transfer rates within the annuli. The investigation is conducted for a constant cylinder-to-particle diameter ratio (Di/d) = 30, porosity (ɛ) = 0.5, and solid/fluid thermal conductivity ratio (kR) = 1.0. The effects of three annular eccentricities (e = 0, – 0.8, 0.8) on the rates of heat transfer throughout both the fluid Nuf and solid Nus phases are examined for various Rayleigh numbers (Ra = 104 – 5×107). The results show that the increase in Rayleigh number has a considerably positive impact on Nuf ; however, Nus is hardly affected by increasing it. In addition, a significant increase in Nuf can be obtained by moving the inner cylinder towards the bottom of the outer cylinder.