The boundary condition parameters for the Species module apply to boundaries in the Flow Analysis Tree. The boundary conditions appear in the Properties panel when a boundary is selected in the Flow Analysis Tree under General Boundaries.

For a user-defined species or scalar, the Zero Flux boundary condition is used when its normal gradient to the boundary is zero or negligible. For a fluid zone or volume, Zero Flux is the default species boundary condition on a wall surface.

Symmetry means that the zero-flux or zero-gradient condition automatically applies for the species. The Symmetry boundary condition for Species usually corresponds to a physical symmetry in the model.

Use Specified Value for a boundary condition where the value of the species is a known quantity, either as a constant or function that you define in the Expression Editor. The Specified Value boundary condition usually corresponds to the physical inlet boundary in the model, when you set the Flow boundary condition to Specified Velocity, Specified Volumetric Flux, Specified Total Pressure, or Specified Pressure Inlet.

Use Outlet boundary condition at an opening where the species flow is expected to exit the domain. This boundary condition usually corresponds to the physical outlet boundary, when you set the Flow boundary condition to Specified Pressure Outlet or Resistor Capacitor. The default condition is zero flux. The specified value is applied if the species is enters the domain for the boundary.

Convective Flux applies for a boundary where the Exchange Coefficient and Ambient Value (Concentration) of the species are known.

Use Specified Flux boundary condition to specify the flux per unit area, when you know the flux per area, either as a constant or a function using the Expression Editor .The direction of flux is set by one of the options below:

The Specified Total Flux boundary condition allows you to set the total flux of the species across the boundary. The flux per area is determined by the solver, and it is then treated in the same way as the Specified Flux condition.

The interface attributes for the Species module are the same as for the boundary conditions, if and only if the volume on one side of the Interface has been Blanked for Species. If the Species module is Active on both sides of an interface, then no boundary conditions are required at the Interface.