The Moisture Transport in Solids (mts) interface (), found under the Chemical Species Transport branch (), is used to model moisture diffusion in a solid.

When this physics interface is added, these default nodes are also added to the Model Builder: Porous Medium, No Flux (prescribing no moisture flux across all external boundaries on which no other boundary condition has been specified), and Initial Values. Then, from the Physics toolbar, you can add other nodes that implement, for example, boundary conditions and source terms. You can also right-click Moisture Transport in Solids to select physics features from the context menu.

The Label is the default physics interface name.

The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.

The default Name (for the first physics interface in the model) is mts.

For 1D components, enter a cross-sectional area Ac (SI unit: m2) to define a parameter for the area of the geometry perpendicular to the 1D component. The default value is 1 m2.

Enter the Reference pressure level pm,ref (SI unit: Pa). The default value is 1[atm].

By default there are no gravity effects added. Select the check box Include gravity to account for the acceleration of gravity in the liquid velocity. When this check box is selected, a global Gravity feature node is shown in the interface model tree.

Enter a value for the acceleration of gravity. The default value g_const is the predefined standard acceleration of gravity on earth.

The default variable names use the pattern <name>.hr and <name>.pm for the relative humidity and moist air pressure variables.

In the Moisture Transport in Solids interface, you can choose the order of the discretization for the dependent variables. The default is to use Quadratic shape functions.

The Compute boundary fluxes check box is not activated by default. When this option is selected, the solver computes variables storing accurate boundary fluxes from each boundary into the adjacent domain.

Also, the Apply smoothing to boundary fluxes check box is available if the previous check box is checked. The smoothing can provide a better behaved flux value close to singularities.

For details about the boundary fluxes settings, see Computing Accurate Fluxes in the COMSOL Multiphysics Reference Manual.

The Value type when using splitting of complex variables setting should in most pure mass transport problems be set to Real which is the default. It makes sure that the dependent variable does not get affected by small imaginary contributions, which can occur, for example, when combining a Time Dependent or Stationary study with a frequency-domain study. For more information, see Splitting Complex-Valued Variables in the COMSOL Multiphysics Reference Manual.

To display other settings for this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box.