Modelling of reactive gas transport

Abstract: A rather general microscopic model for reactive gastransport in porous media is developed and applied to twodifferent processes in powder metal technology: carburization,and reduction of surface oxides.The carburization model is developed from the kinetic modelproposed by Grabke and applied to a 2-D porous geometryobtained from images. The effect of pore geometry on convectiveand diffusive transport is discussed by model problems andaveraging. The exercise demonstrates the capacity of theFEMLABenvironment for strongly non-linear models.Homogenization requires estimates of effective parameters. Anumerical experiment is performed to assess the variance indiffusivity estimates from calculations on the microscopicmodel on unit cells of different sizes.The model of the reduction of surface oxides has beencompared to experiments on chromium oxides by parameter fittingin the kinetics and transport models. The measurements areconsistent with a simple first order reduction reaction andfast gas transport. The model reproduces the experimental datawell and allows extraction of meaningful parameters such as theactivation energies.