Kernel requires a diffusion coefficient for each component in each phase, as well as a tortuosity, .
These are provided as material properties in PorousFlow. Two formulations are available:
A simple model where the diffusion constants and tortuosity are constant.
A saturation dependent model proposed by Millington and Quirk (1961), where the diffusion coefficients are constant but the tortuosity is (1)
- R. J. Millington and J. P. Quirk.
Permeability of porous solids.
Trans. Faraday Soc., 57:1200–1207, 1961.[BibTeX]