The Mass Flux node can be used to specify the total mass flux of a phase across a boundary. Set the mass flux for all phases except the one computed from the volume constraint. This ensures that the sum of the volume fractions is equal to one.

For modeling mass flux from very thin objects add a Line Mass Source or a Point Mass Source node.

The Line Mass Source node adds mass flow originating from a tube of infinitely small radius. It is available for edges in 3D geometries or points in 2D and 2D axisymmetric geometries.

The Point Mass Source node models mass flow originating from an infinitely small sphere centered around a point. It is available for points in 3D geometries.

Specify the inward mass flux for each phase individually. Select the check box for the phase to prescribe a mass flux and enter a value or expression for the flux in the corresponding field. To use another boundary condition for a specific phase, click to clear the check box for the flux of that phase. Use a positive value for an inward flux. The units are based on the geometric entity: Boundaries: (SI unit: kg/(m2·s)), Lines (SI unit: kg/(m·s), and Points (SI unit: kg/s)).