This feature is only available in a limited set of add-on products. See http://www.comsol.com/products/specifications/ for more details on availability.

Use this node to model the concentration of diluted species transported through interstices in porous media. A part form convection and diffusion, the node contains functionality to include species evolution through adsorption, dispersion, and reaction.

The temperature model input is always available. Select the source of the Temperature. For User defined, enter a value or expression for the temperature in the input field. This input option is always available.

You can also select the temperature solved for by a Heat Transfer interface added to the model component. These physics interfaces are available for selection in the Temperature list.

Select an option from the Porous material list. The default is Domain material.

By default the Porosity, εp (dimensionless) is taken From material. For User defined, enter a different value. The default is 0.3.

When the Mass transport in porous media check box is selected in the Settings window of the physics interface, a setting for the Density ρ of the porous media is available. By default it is set to be taken From material.

If transport by convection is active, the velocity field of the solvent needs to be specified. Select the source of the Velocity field. For User defined, enter values or expressions for the velocity components in the input fields. This input option is always available.

You can also select the velocity field solved for by a Fluid Flow interface added to the model component. These physics interfaces are available for selection in the Velocity field list.

Select a Fluid material (when available and applicable).

Specify the Fluid diffusion coefficient DF,i (SI unit: m2/s). Enter a value or expression for each of the species in the corresponding input field. The default is 1 x 10-9 m2/s.

Select the Effective diffusivity model: Millington and Quirk model (the default), Bruggeman model, Tortuosity model, or User defined. For Tortuosity model, enter a value for the tortuosity τF,i (dimensionless). The default is 1.

This section is available when the Migration in electric field check box is selected. From the Electric potential list, select the source of the electric field.

By default the Mobility is set to be calculated based on the species effective diffusivity and the temperature using the Nernst-Einstein relation. For User defined, and under Mobility, select the appropriate scalar or tensor type — Isotropic, Diagonal, Symmetric, or Anisotropic — and type in the value of expression of the effective mobility ume,c.

Enter the Charge number zc for each species.

This section is available when the Dispersion in porous media check box is selected on the Settings window for the physics interface.

Select the Specify dispersion for each species individually check box to specify the dispersion tensor DD (SI unit: m2/s) for each species separately. The default is to use the same dispersion tensor DD for all species.

Select an option from the Dispersion tensor list—User defined (the default) or Dispersivity. For User defined, use it to specify the dispersion components as user-defined constants or expressions. Select Isotropic, Diagonal, Symmetric, or Anisotropic based on the properties of the dispersion tensor.

Select Dispersivity when Convection has been added as the transport mechanism. Specify the dispersivities (SI unit: m) to define the dispersion tensor DD (SI unit: m2/s) together with the velocity field u. Select an option from the Dispersivity model list: Isotropic (the default) or Transverse isotropic based on the properties of the porous media. For isotropic porous media, specify the longitudinal and transverse dispersivities. For transverse isotropic porous media, specify the longitudinal, horizontal transverse, and vertical transverse dispersivities.