Porous Media Transport Properties

The node is used to model mass transfer in porous media using the Transport of Concentrated Species interface. The node adds the equations governing the mass fractions of all present species, and provides inputs for the transport mechanisms and for the material properties of the fluid mixture.

The settings in this node are dependent on the check boxes selected under Transport Mechanisms in the Settings window of the Transport of Concentrated Species interface.

	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.

Specify the temperature and pressure to be used in the physics interface. The temperature model input is used when calculating the density from the ideal gas law, but also when thermal diffusion is accounted for by supplying thermal diffusion coefficients. The pressure model input is used in the diffusional driving force in Equation 6-2 (that is, when a Maxwell-Stefan Diffusion Model is used) and when calculating the density from the ideal gas law.

Select the source of the field T:

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Select to enter a value or an expression for the temperature (SI unit: K). This input is always available.

Select the source of the p:

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Select to enter a value or an expression for the absolute pressure (SI unit: Pa). This input is always available.

Enter a value or expression for the εp (dimensionless), of the porous media.

In order use a porosity defined in a material; specify the material using the list, and select from the list.

Use this section to define the mixture density, and to specify the molar masses of the participating species.

Select a way to define the density from the list— or :

Here M is the mean molar mass of the mixture and Rg is the universal gas constant. The absolute pressure, p, and temperature, T, used corresponds to the ones defined in the Model Inputs section.

Enter a value or expression for the Mw for each species. The default value is 0.032 kg/mol, which is the molar mass of O2 gas.

This section is available when the check box is selected.

Select the source of the u:

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Select to enter values or expressions for the velocity components. This input is always available.

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Select a velocity field defined by a Fluid Flow interface present in the model (if any). For example, select to use the velocity field defined by the node fp1 in a Single-Phase Flow, Laminar Flow interface with spf as the Name.

Specify the species molecular and thermal diffusivities in nonporous media in the manner described for the Transport Properties node.

To account for the effect of porosity in the diffusivities, select an — , , , or Using one of the first four models, the effective transport factor, fe, is defined from the porosity and the fluid tortuosity factor in the manner of:

For , the effective transport factor is set to one.

The species diffusivities and mobilities are automatically adjusted for porous media transport using the effective transport factor.

This section is available when the check box is selected in the Transport Mechanisms section of the interface, select the source of the V:

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Select to enter a value or expression for the electric potential. This input is always available.

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If required, select an electric potential defined by an AC/DC interface that is present in the model (if any). For example, select to use the electric field defined by the Current Conservation node cucn1 in an Electric Currents interface ec.

Settings for the mobilities are needed for the and diffusion models. By default the mobility is set to be calculated based on the species diffusivities (adjusted by the in the section) using the . To manually specify the mobilities, select for the mobility um,w (SI unit: s·mol/kg) and enter one value for each species.

Enter the zc (dimensionless, but requires a plus or minus sign) for each species.