Equation 5-1 in its form above includes the transport mechanisms diffusion and convection. If
Migration in Electric Field is activated (only available in some add-on products), the migration mechanism will be added to the equation as well. See more details in the section
Adding Transport Through Migration.
The flux vector N (SI unit: mol/(m
2·s)) is associated with the mass balance equation above and used in boundary conditions and flux computations. For the case where the diffusion and convection are the only transport mechanisms, the flux vector is defined as
If Migration in Electric Fields is activated, the flux vector is amended with the migration term as shown in the section
Adding Transport Through Migration.
The first term on the left side of Equation 5-1 corresponds to the accumulation (or indeed consumption) of the species.
The third term on the left side of Equation 5-1 describes the convective transport due to a velocity field
u. This field can be expressed analytically or obtained from coupling this physics interface to one that computes fluid flow, such as
Laminar Flow.
On the right-hand side of the mass balance equation (Equation 5-1),
Ri represents a source or sink term, typically due to a chemical reaction or desorption on a porous matrix. To specify
Ri, another node must be added to the Transport of Diluted Species interface—the
Reaction node, which has a field for specifying a reaction equation using the variable names of all participating species.