Use the Dual Permeability Medium feature to model transport in a saturated dual permeability medium where Darcy’s Law describes the transport in each system.

The feature has three default subfeatures —the Fluid subfeature where the fluid density ρ (SI unit: kg/m3) and dynamic viscosity μ (SI unit: Pa·s) are defined, the Macropores subfeature where the hydraulic properties of the macroporous matrix are defined, and the Micropores where the hydraulic properties of the microporous matrix are defined.

Select a coordinate system from the Coordinate system list for the interpretation of directions in anisotropic material properties. The default is the Global coordinate system, and the list contains any additional orthonormal coordinate system (except boundary coordinate systems) added under the Definitions node.

The subnodes inherit these coordinate system settings. In particular, the Permeability or Hydraulic conductivity (in the Macropores and Micropores subnodes) should be set according to the coordinate system selected in this section.

With this option under the Porous Medium section, Equation 7-1 is formulated with respect to a storage term (analogous to Equation 4-4). Therefore, choose from a drop-down menu one of the following formulations:

with i=M for the macropores and i=m for the micropores.

Specify the Fluid Transfer Function αw which is used to calculate the interporosity flow, which is the mass exchange between macro- and microscale system:

with pM being the pressure in the macropores and pm the pressure in the micropores.