The PorousFlowDispersiveFlux 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:

Constant diffusivity


A simple model where the diffusion constants and tortuosity are constant.

Millington-Quirk diffusivity


A saturation dependent model proposed by Millington and Quirk (1961), where the diffusion coefficients are constant but the tortuosity is (1)


  1. R. J. Millington and J. P. Quirk. Permeability of porous solids. Trans. Faraday Soc., 57:1200–1207, 1961.[BibTeX]