The Simulate Diffusion Experiment command allows to compute a stationary diffusive flux and concentration distribution if the structure contains porous constituent materials. As explained in the DiffuDict theoretical background, this is done by solving

together with the appropriate boundary conditions for the concentration at the boundaries of the domain. Here, the local diffusivity depends on the local material. When simulating e.g. the diffusion of oxygen, in the pore space is the diffusion coefficient of oxygen, in porous materials is the effective diffusivity of oxygen inside of the porous material, and in solid materials .

The computed diffusive flux is used to determine the homogenized diffusivity of the 3D structure. For this, Fick’s first law is used and the effective diffusivity is determined from the computed overall diffusive flux :