Information on the mass flow rate inlet boundary condition for single phase flow is available in Mass Flow Rate.

For multiphase flow, mass flow inlets may be specified either for a particular phase or for the bulk flow. In both cases, the flow direction and the volume fraction profile at the inlet must be specified.

If the mass flow rate for a particular phase is specified, then the mass flux (defined as mass flow per unit area of the phase) is assumed to be uniform over the entire boundary.

Boundary conditions for other phases are also required. These may also be phasic mass flow conditions, or any other available velocity specifications. The phasic mass flow inlet condition is not available for homogeneous multiphase simulations.

If a bulk mass flow inlet condition is applied, then the bulk mass flux is assumed to be uniform over the entire boundary. The mass flux of each phase is calculated from the bulk mass flux according to the specified volume fraction profile.

The bulk mass flow inlet condition is available for both homogeneous and inhomogeneous simulations.