Numerical simulation of Knudsen diffusion in metallic foam

This paper addresses diffusion of air within a cellular metal. A Knudsen diffusion simulation is performed on both simplified model structures and, for the first time, computed tomography data of real materials. In the first part, the three deflection models (mirror reflection, random deflection and random cosine deflection) are compared. It is found that the Knudsen diffusivities of the model structures exhibit different values for each deflection model. The second part is a Knudsen diffusion simulation on computed tomography data of M-Pore® aluminium foam from which an estimate of its Knudsen diffusivity is obtained. Four sub-geometries of the same specimen are converted into voxel calculation models. All calculations show high Knudsen diffusivities with average values of 1.99 m2/s (random cosine deflection) and 2.09 m2/s (random deflection). Plots of the Knudsen diffusivity versus porosity show an increase of diffusivity with porosity.