Hi all,

does anyone have some further insights into how OGS5 computats the effective Diffusion coefficient? In the keywords it says

```
Fick’s law in the porous media (effective diffusion coefficient):
\[ D^* = \omega \cdot D_d \]
where omega is a coefficient that is related to the tortuosity (Empirical coefficient, lab: 0.5~0.01)
```

Is omega simply the tortuosity given in $TORTUOSITY ?

And is there a possibility to account for unsaturated cases, i.e. to make tortuosity a function of water content as e.g. in the Millington-Quirk relation:

tortuosity = (water content)^n / (porosity)^m

or is saturation accounted for once the mass dispersion tensor is computed?

(It seems so from the code in rf_mmp_new.cpp under MassDispersionTensorNew, but saturation is only a linear factor there… )

Cheers, Erik