The Heavy Species Flux boundary condition prescribes the mass flux of the specified species on selected boundaries as:

where n denotes the outward pointing normal of the boundary. By default, the flux due to diffusion and migration in an electric field is prescribed. This is the appropriate flux condition when the relative velocity at the boundary is zero. When the fluid velocity is not equal to that of the boundary, for example due to a fluid injection, it is often convenient to prescribe the total flux including convection. To do so select Include in the Convection section. In this case the prescribed flux is defined as:

Similar to the Inflow boundary condition, a table is used to define the normal flux on the selected boundaries for the specified species. Note that the species computed From mass constraint is also excluded and the names must correspond to the exact name in the Species name field in the Species feature.