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

When this physics interface is added, these default nodes are also added to the Model Builder: Solid, No Flux (prescribing no flux in the diffused variable 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 Transport in Solids to select physics nodes 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 ts.

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.

From the Transported quantity list, select Concentration, Mass density, or Number density to assign the unit for the dependent variable.

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

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

The Compute boundary fluxes checkbox is activated by default so that COMSOL Multiphysics computes predefined accurate boundary flux variables. When this option is selected, the solver computes variables storing accurate boundary fluxes from each boundary into the adjacent domain.

The flux variable affected in the interface is ntflux_c, where c is the dependent variable. This is the normal total flux and corresponds to the boundary flux plus additional external flux.

Also the Apply smoothing to boundary fluxes checkbox is available if the previous checkbox is selected. The smoothing can provide a more well-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 be set to Real, which is the default.

Define the number of the dependent variables and the variable names. The default name for the transported quantity field is c by default.

Enter the Number of dependent variables. Use the Add transported quantity () and Remove transported quantity () buttons as needed.