The boundary conditions and related Multiphase parameters are specified as follows:

• Geometric Entities Panel > Boundaries > [Desired Boundary]
• Properties Panel > Model Tab > Multiphase

This condition means that there is no flux or gradient of components normal to the boundary. This boundary condition typically corresponds to a solid boundary in the model.

• When the mixture boundary condition is set to Zero Flux under Multiphase module, the boundary conditions are fixed to Zero Flux for the components (as indicated by the blue font).
• This is the default boundary condition for Multiphase module, when the boundary condition under Flow module is Wall and Rotating Wall.

Contact Model

The Contact Angle allows to set the wetting angle for a Component at a Wall. The Contact Model is activated to Yes for a component under the Flow module and the Angle is specified.

This condition allows to set the volume fractions of the components at an opening.

• When the mixture boundary condition is set to Specified Value under Multiphase module, the boundary conditions are fixed to Specified Value for the components (as indicated by the blue font). The volume fraction is specified for Value under each component.
• This is the default boundary condition for Multiphase module, when the boundary condition under Flow module is Specified Velocity, Specified Volumetric Flux, Specified Total Pressure or Specified Pressure Inlet. It would not typically make physical sense to prescribe a Specified Valuecondition for a boundary that was not an opening.

This condition allows to set the volume fractions of the components at an opening.

• When the mixture boundary condition is set to Outlet under Multiphase module, the boundary conditions are fixed to Outlet for the components (as indicated by the blue font). The volume fraction is specified for Value under each component.
• This is the default boundary condition for Multiphase module, when the boundary condition under Flow module is Specified Pressure Outlet or Resistor Capacitor. It would not typically make physical sense to specify an Outlet boundary condition for a boundary that was not an opening.

The volume fractions specified for the components at an Outlet boundary should be set to the volume fraction that would enter in the event of back flow. The volume fraction set at an outlet does not dictate the mass fraction that exits the boundary. The volume fraction of the component for any fluid exiting the domain is based on the internal (upwind) volume fraction.

This condition means that there is no shear, no normal component of velocity and no normal gradient of pressure at the boundary. This boundary condition usually corresponds to a physical symmetry in the model.

• When the mixture boundary condition is set to Symmetry under Multiphase module, the boundary conditions are fixed to Symmetry for the components (as indicated by the blue font).
• This is the default boundary condition for Multiphase module, when the boundary condition under Flow Module is Symmetry.

This allows to set the volumetric flux of each component at an opening. This corresponds to the Volumetric Flow boundary condition for the Flow module. For the Specified Volumetric Flux Boundary Condition, the Value of the volume fraction for each component needs to be set under Component > Specified Value.