Thermal energy transport in packed bed of solid particles involves convection, heat conduction through fluid and solid particles, convective, and radiative heat transfer. Modeling this complex phenomenon is challenging especially when all heat transfer mechanisms play an important role.
At high temperatures, such as those found in fixed bed catalytic reactors, the radiative heat transfer mechanism may become dominant and has to be properly modeled. A possible modeling approach, efficiently applicable to CFD simulations, is to use an effective thermal conductivity able to account for both packed bed conduction and radiation phenomena.
In this work we present an analysis of the effects of different models of porous medium effective thermal conductivity on the CFD simulations of an Experimental Short Contact Time reactor suitable for Catalytic Partial Oxidation of a Methane-Oxygen mixture. The CFD simulations, performed with ANSYS-Fluent, were based on the porous media approach to model the reactor packed bed regions. Thermal conductivity in the porous regions was simulated with a standard approach based on the assumption of conduction through the solid and across the fluid occurring in parallel, and with an advanced approach, based on an effective thermal conductivity, taking into account radiation also. The advanced model of effective thermal conductivity was implemented via User Defined Functions (UDF).
The reference experimental data were gathered from tests of the above cited SCT reactor with a catalytic bed formed by alumina spheres impregnated with Rodhium and fed with a mixture of pure Oxygen and Methane with a volume ratio of 0.575. Simulation results and comparison with experiments are presented and discussed. |
