THEORETICAL BASES OF THE DRIFT-FLUX FIELD EQUATIONS AND VAPOR DRIFT VELOCITY
The field equations forming the basis of the drift-flux (DF) model of transient two-phase flow are shown to be obtainable from a representative set of two-fluid (TF) or separated flow field equations. The simplifying assumptions required to yield the DF field equations are explicitly accounted for. A general expression for the transient velocity difference between phases is obtained from which the vapor drift velocity may be derived. A method of extending the usefulness of empirical steady-state vapor drift velocity correlations is suggested.