Local variations in the velocity as the fluid flows around solid particles lead to mechanical mixing, referred to as dispersion. Use this feature to account for dispersion in a Porous Medium or a Unsaturated Porous Medium

This subfeature is available when both the Mass transfer in porous media mass transfer check box and the Convection check box are selected in the Settings window for the physics interface.

Select the Specify dispersion for each species individually check box to specify the dispersion tensor DD (SI unit: m2/s) for each species separately. When not selected the same dispersion tensor DD is used for all species.

Select an option from the Dispersion tensor list — Dispersivity or User defined.

Select Dispersivity to specify the dispersion in terms of dispersivities (SI unit: m). Select an option from the Dispersivity model list: Isotropic (the default) or Transverse isotropic based on the properties of the porous media. For isotropic porous media, specify the longitudinal and transverse dispersivities. For transverse isotropic porous media, specify the longitudinal, horizontal transverse, and vertical transverse dispersivities.

For User defined, specify the dispersion components in terms of constants or expressions. Select Isotropic, Diagonal, Symmetric, or Full to enable the appropriate tensor components.