Convection, Diffusion, and Migration
The Convection, Diffusion, and Migration is the main physics interface node which adds the concentration and electric field variables and the Nernst-Planck equations governing them.
Model Inputs
The temperature model input is always available, and set to Common model input by default. Select the source of the Temperature field T:
•
Select User defined to enter a value or an expression for the temperature (SI unit: K). This input is always available.
•
If required, select a temperature defined by a Heat Transfer interface present in the component (if any). For example, select Temperature (ht) to use the temperature defined by the Heat Transfer in Fluids interface with the ht name.
convection
This section is available when the Convection check box is selected.
The velocity field for the convection of the solvent, which is used in the convective term, needs to be specified as feature input. Select the source of the Velocity field u:
•
Select User defined to enter values or expressions for the velocity components. This input is always available.
•
Select a velocity field defined by a Fluid Flow interface present in the model (if any). For example, select Velocity field (spf) to use the velocity field defined by the Fluid Properties node fp1 in a Single-Phase Flow, Laminar Flow interface with spf as the Name.
Diffusion
Select a Material from the list (when applicable and available). The default is None.
Specify the Diffusion coefficient Di for each species. This can be a scalar value for isotropic diffusion or a tensor describing anisotropic diffusion. Enter the values in the field (one for each species).
Migration in Electric Field
Specify the Mobility and the Charge number of the ionic species. These properties affect the migration of ionic species. By default the Mobility is set to be calculated based on the species diffusivities and the temperature using the Nernst-Einstein relation. To manually specify the mobility, select User defined for the mobility um,i and enter one value for each species.
Enter the Charge number zi (dimensionless, but requires a plus or minus sign) for each species.
Specify the temperature (if you are using mobilities based on the Nernst-Einstein relation) in the Model Inputs section.