SIMULATION OF MIXED CONVECTION HEAT TRANSFER AT THE WALL OF A PACKED BED

Abstract

Numerical investigations of the effect of mixed convection on the fluid flow pattern and heat transfer at the boundary layer of a packed bed are reported. A volume-averaged Navier-Stolces equation incorporating the Boussinesq approximation is used to predict the fluid flow, and a volume-averaged heat balance equation, the heat transfer. An exponential variation in the porosity of the packing is assumed in the region near the wall. Simulations are performed using a modified penalty Galerkin finite-element method. The Nusselt number is found to depend on the Grashof to Reynolds number ratio, Graetz number, and ratio of thermal conductivity of the solid and fluid phases. The heat transfer rate is enhanced by a positive Grashof number and hindered by a negative value. The velocity and temperature profiles in the bed are also found to be strong functions of the Gr/Re² ratio. At higher values of this ratio the flow becomes unsteady