This subnode should be used to model the heat transfer due to hydrodynamic mixing in a fluid flowing through a porous medium. It adds an extra term ∇ ⋅ (kdisp∇T) to the right-hand side of the heat equation in porous media, through the modification of the effective thermal conductivity keff with the dispersive thermal conductivity kdisp:

This section defines the Longitudinal dispersivity λlo and Transverse dispersivity λtr used for the computation of the tensor of dispersive thermal conductivity:

where D is the dispersion tensor

and λijkl is the fourth-order dispersivity tensor

In 3D, the Define transverse dispersivity from list allows to choose between Horizontal and vertical transverse dispersivities, and Isotropic transverse dispersivity. With the first option, the Transverse horizontal dispersivity λtr, h and Transverse vertical dispersivity λtr, v can be defined separately. With the second option, the Transverse dispersivity λtr is defined instead, and used for both the horizontal and vertical dispersivities.

In 3D, it is assumed that z is the vertical direction and it defines the dispersion tensor as

In 2D, since w = 0, and in 2Daxi, since v = 0, the dispersion tensor is function of only one transverse dispersivity (the vertical one for 2D, and the horizontal one for 2Daxi respectively), therefore only one Transverse dispersivity λtr can be defined. The dispersion tensor is defined as:

In 1D and 1Daxi dimensions, since v = 0 and w = 0, the dispersion tensor is function of only the longitudinal dispersivity, therefore only the Longitudinal dispersivity λlo can be defined. The dispersion tensor is defined as

Physics tab with Porous Medium selected in the model tree: