Constitutive equation for vapor drift velocity in two-phase annular flow

A constitutive equation for a vapor drift velocity which specifies the relative motion between phases in the drift flux model is developed for two-phase annular flows. The constitutive equation is derived by taking into account the interfacial geometry, the body force field, and the interfacial momentum transfer, since these macroscopic effects govern the two-phase diffusions. A comparison of the model with three sets of experimental data obtained over a wide range of flow parameters shows a satisfactory agreement.