The Transport of Diluted Species in Fractures Interface

The interface (

), found under the branch (

), is used to model the transport of a solute species along thin porous fractures, taking into account diffusion, dispersion, convection, and chemical reactions. The fractures are defined by boundaries and the solute species is assumed to be present in a solvent.

The interface supports simulation of species transport along boundaries in 2D and 3D, and axisymmetric components in 2D. The dependent variable is the molar concentration, c. Modeling multiple species transport is possible, whereby the physics interface solves for the molar concentration, ci, of each species i.

	This interface is only available in a limited set of add-on products. For a detailed overview of which interfaces are available in each product, visit http://www.comsol.com/products/specifications/

The is the default physics interface name.

The 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 field. The first character must be a letter.

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

If model geometry includes boundaries that should not be included in the mass transfer simulation, remove those from the selection list.

Mass transport due to diffusion is always included. Use the check box, available under , to control whether to also include convective transport.

To display this sections, click the button (

) and select . Use this section to control the application of the available consistent stabilization methods; and .

•

When the check box is selected, a weak term that reduces spurious oscillations is added to the transport equation. The resulting equation system is always nonlinear. There are two options for the :

— the default option. This type of crosswind diffusion reduces undershoots and overshoots to a minimum but can in rare cases give equation systems that are difficult to fully converge.

. This option is less diffusive compared to the Do Carmo and Galeão option but can result in more undershoots and overshoots. It is also less effective for anisotropic meshes. The Codina option activates a text field for the glim. It defaults to 0.1[mol/m^3)/tds.helem, where tds.helem is the local element size.

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For both consistent stabilization methods select an . is the default and means that derivatives of the diffusion tensor components are neglected. This setting is usually accurate enough and is computationally faster. If required, select instead.

To display this section, click the button (

) and select . By default, the check box is not selected, because this type of stabilization adds artificial diffusion and affects the accuracy of the original problem. However, this option can be used to get a good initial guess for underresolved problems.

To display all settings available in this section, click the button (

) and select .

The setting should in most pure mass transfer problems be set to , 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.

The dependent variable name is c by default. A dependent variable name must be unique with respect to all other dependent variables in the component.

Add or remove species variables in the model and also change the names of the dependent variables that represent the species concentrations.

Enter the . Use the (

) and (

) buttons as needed.