The theory described in this section only applies to inhomogeneous multiphase flow. When using the homogeneous model, momentum transfer between phases is assumed to be very large.

Interphase momentum transfer, , occurs due to interfacial forces acting on each phase , due to interaction with another phase . The total force on phase due to interaction with other phases is denoted , and is given by:

(5–32)

Note that interfacial forces between two phases are equal and opposite, so the net interfacial forces sum to zero:

(5–33)

The total interfacial force acting between two phases may arise from several independent physical effects:

(5–34)

The forces indicated above respectively represent the interphase drag force, lift force, wall lubrication force, virtual mass force, turbulence dispersion force and solids pressure force (for dense solid particle phases only).

CFX provides a wide range of physical models for these forces. These models are described in the following places:

For more information, see Multiphase Flow with Turbulence Dispersion Force in the CFX Reference Guide.