The Moisture Transport in Free and Porous Media (mt) interface () is used to model moisture transport in moist air and into the pores of a porous medium, through convection and diffusion of vapor in moist air, and convection and capillary flow of liquid water. Both a Moist Air (Moisture Transport Interface) model and a Hygroscopic Porous Medium model are added by default. The first one is active on all domains, while the second one has no selection. Also, the Equilibrium between liquid and gas phases option of the Hygroscopic Porous Medium feature is set to Nonequilibrium formulation.

When this physics interface is added, these default nodes are added to the Model Builder: Moist Air, Hygroscopic Porous Medium, Insulation (the default boundary condition), Nonequilibrium Boundary (showing all the boundaries adjacent to domains where both the relative humidity and liquid saturation are solved for the moist air and liquid phases), Porous Interface, and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions. You can also right-click Moisture Transport in Free and Porous Media to select physics features from the context menu.

Specific subnodes are present by default under the Liquid Water and Moist Air subnodes of the Hygroscopic Porous Medium node:

Other subnodes implementing boundary conditions specific to the liquid and moist air phases can be added to model flow conditions and fluxes. To do so, right-click a Liquid Water or Moist Air node to select physics features from the context menu.

Specific subnodes are also present under the Porous Interface node:

In the liquid water flux and vapor flux features available under the Liquid Water and Moist Air subnodes, the user input corresponds to the moisture flux per total unit surface. It is multiplied by the volume fraction of each phase and added into the corresponding water mass conservation equation. The surface fraction is approximated by the volume fraction.

By default, the shape functions used for the relative humidity and the liquid saturation in all domains are Linear.