The Transport of Diluted Species in Fractures Interface
The Transport of Diluted Species in Fractures (dsf) interface (), found under the Chemical Species Transport 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 https://www.comsol.com/products/specifications/
Settings
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 dsf.
Boundary Selection
If the model geometry includes boundaries that should not be included in the mass transfer simulation, remove those from the selection list.
Out-of-Plane Thickness
For 2D components, the Thickness field (default value: 1 m) defines a parameter for the thickness of the geometry perpendicular to the two-dimensional cross-section. Both constant and varying thicknesses are supported. The value of this parameter is used, among other things, to automatically calculate molar flow rates from the total molar flux.
Transport Mechanisms
Use the Convection check box, available under Additional transport mechanisms, to control whether to also include convective transport.
Consistent Stabilization
To display this sections, click the Show button () and select Stabilization. Use this section to control the application of the available consistent stabilization methods; Streamline diffusion and Crosswind diffusion.
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When the Crosswind diffusion 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 Crosswind diffusion type:
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Do Carmo and Galeão — 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.
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Codina. 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 Lower gradient limit glim. Its default value is 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 Equation residual. Approximate residual 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 Full residual instead.
Inconsistent Stabilization
To display this section, click the Show button () and select Stabilization. By default, the Isotropic diffusion 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 under resolved problems.
Discretization
To display all settings available in this section, click the Show button () and select Advanced Physics Options.
The Value type when using splitting of complex variables setting should in most pure mass transfer 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.
Dependent Variables
The dependent variable name is Concentration 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 Number of species. Use the Add concentration () and Remove concentration () buttons as needed.
Further Reading
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Mass Transport in Fractures in the theory section.
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Numerical Stabilization in the COMSOL Multiphysics Reference Manual.
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Domain, Boundary, and Pair Nodes for the Transport of Diluted Species Interface
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In the COMSOL Multiphysics Reference Manual, see Table 2-4 for links to common sections and Table 2-5 for common feature nodes. You can also search for information: press F1 to open the Help window or Ctrl+F1 to open the Documentation window.