Numerical modelling of microwave heating of a porous catalyst bed

A Multiphysics numerical model was developed using COMSOL Multiphysics to study the effect of size, shape and position of catalyst bed within the microwave reactor (2450 MHz). The dielectric properties of HZSM-5 catalyst were measured at different frequencies and nine different temperatures ranging from 25 degrees C to 370 degrees C. The heat transfer in porous media was coupled with RF electromagnetics module and flow-through porous media by extracting the heat source term Q for the heat transfer problem from the electromagnetics. A solid-fluid thermal non-equilibrium condition was modelled as the heat is generated within the catalyst. It was observed that sample position, shape and size of the sample, all significantly affect the heating profile and temperature gradient inside the porous media. The experimental results and the predicted temperatures were in good agreement. Microwave heating had higher total internal energy but conventional heating had lower temperature gradient after reaching steady state. Brick-shaped sample heats more uniformly compared to cylindrical sample. If the radius of the sample is decreased, while maintaining the volume of the sample, microwaves penetrate deeper inside the sample, and more uniform temperature distribution is observed throughout the length of the sample.