Use the Molecular Diffusion command to model diffusion processes for intermediate Knudsen numbers, i.e., in situations where both molecule-molecule interactions and molecule-wall interactions take place and the diffusion process cannot be described by either one of these processes alone.

This command models the diffusion of particles by a random-walk algorithm. Both molecule-molecule and molecule-wall collisions are modeled. Einstein's formula is used to derive the diffusivity from the computed average particle displacement. The resulting homogenized effective diffusivity depends on gas species, ambient conditions and the pore structure of the material.