The convective flux variable, cflux, is defined as the concentration times the velocity field:

The convective flux magnitude, cfluxMag, is the magnitude of the convective flux, defined as the square root of the sum of the convective flux components squared:

The diffusive flux variable, dflux, is defined as the negative of the diffusion coefficient times the concentration gradient:

The diffusive flux magnitude, dfluxMag, is the magnitude of the diffusive flux, defined as the square root of the sum of the diffusive flux components squared:

The variable domflux is used to calculate fluxes if the Compute boundary fluxes check box is cleared, see Computing Accurate Fluxes. The flux variables ndflux and ntflux are then computed from the dependent variables using extrapolation. In a system with only diffusive flux, domflux is defined as the diffusive flux times the out-of-plane geometry extension, d (out-of-plane thickness for 2D systems, or cross-sectional area for a 1D or 1D axisymmetric system):

In a system with convection using the conservative form (see Convective Term Formulation) the domflux variable is defined as:

The predefined variable dpflux is available when both the Mass transfer in porous media check box, and the Convection check box are selected on the Settings window for the physics interface.

Dispersion, or dispersive flux, is defined as the negative of the dispersion tensor, DD times the gradient of concentration:

Transport of ionic species through migration, as described in section Adding Transport Through Migration, is described by the electrophoretic flux variable mflux:

The diffusive flux magnitude, dfluxMag, is the magnitude of the electrophoretic flux, defined as the square root of the sum of the electrophoretic flux components squared:

The variable for a species total rate expression, R, is defined as the sum of all the reaction rates for that species. As an example, for a species i reacting in a first order, irreversible reaction j the total rate expression is:

Total flux is the sum of all mass transport fluxes present. The definition of total flux, tflux, will depend on the transport mechanisms available in the system. As an example, the total flux in a system with diffusion and migration of ionic species is: