Use Volume Fraction

For the momentum equation, the volume fraction of a given phase is multiplied by the total wall shear stress to determine the component of wall shear stress that is due to that phase. For energy and other scalar equations, an analogous procedure is applied.

Use Wall Boiling Fraction (only if wall boiling is active)

If wall boiling is active, an additional option for the wall contact model is available: Use Wall Boiling Fraction. In this case, the area fractions obtained during the wall heat partitioning process, which determines how the wall heat flux is distributed among the phases, are applied for all other wall fluxes in other equations (for example, wall shear stress in the momentum equations). If wall boiling is active, Use Wall Boiling Fraction is the recommended option because it treats all equations consistently.

Specify Area Fraction

For the momentum equation, the area fraction of a given phase is multiplied by the total wall shear stress to determine the component of wall shear stress that is due to that phase. For energy and other scalar equations, an analogous procedure is applied.

This option is suitable, for example, in the case of a thin liquid film whose thickness is smaller than the nearest node distance from the wall. In this case, the liquid volume fraction may be very small, but the area fraction of the liquid is one. You may set area fractions of one or zero to model films.

For a case where the wall is partially covered by liquid film, the liquid area fraction may be a complicated function of liquid volume fraction. In such a case, you can use CEL to implement a complex model for the wall contact area fraction.