The variable bndFlux is defined using the Boundary Flux Operators: uflux and dflux. These operators are used when the Compute boundary fluxes check box is selected, see Computing Accurate Fluxes.

On exterior boundaries, bndFlux is defined as:

The up and downside is defined by the surface normal, which points from downside to the upside. On interior boundaries, bndFlux is the mean of the fluxes on both sides:

Also, d is the out-of-plane geometry extension (out-of-plane thickness for 2D systems, or cross-sectional area for a 1D or 1D axisymmetric system).

The variable cbf is used to account for convection when defining boundary conditions and is defined as:

The variable ncflux is defined as:

The variable ndflux is defined as:

The variable nmflux is defined as:

The variable ntflux is defined as: