The Nonequilibrium Moisture Transport in Porous Media Interface
The Nonequilibrium moisture Transport in Porous Media (mt) interface () is used to model moisture transport into the pores of a porous medium, through convection and diffusion of vapor in moist air, and convection and capillary flow of liquid water. A Hygroscopic Porous Medium model is active by default on all domains, with Equilibrium between liquid and gas phases set to Nonequilibrium formulation.
The water mass conservation equations in the liquid and in the moist air phases of the porous medium are solved and coupled through a transfer term proportional to the difference between the partial vapor pressure and the equilibrium vapor pressure. If this difference can be neglected, use The Equilibrium Moisture Transport in Porous Media Interface instead.
When this physics interface is added, these default nodes are added to the Model Builder: Hygroscopic Porous Medium, Insulation (the default boundary condition), overridden by 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), and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions. You can also right-click Nonequilibrium Moisture Transport in Porous Media to select physics features from the context menu.
Specific subnodes are also present by default under the Liquid Water and Moist Air subnodes of the Hygroscopic Porous Medium node:
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Initial Values, which allows to set a specific initial liquid water saturation and relative humidity.
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Insulation, which sets a no flux condition for each water phase.
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.
Liquid Water Flux and Vapor Flux
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 porous media are Linear.
See Settings for the Moisture Transport Interface and Feature Nodes for the Moisture Transport Interface for details.
Theory for Moisture Transport in Porous Media