Applicability of the homogeneous flow model to two-phase flow

An improved criterion for the onset of the homogeneous flow pattern in co-current vapor-liquid flow was developed. This criterion was based on the visual flow observations obtained during this study and those available in the literature and is consistent with a general approach to the suspension of small bubbles and particles. One-dimensional momentum theory was used for the prediction of abrupt area change pressure losses in two-phase flow. Pressure change across expansions were well predicted if slip was assumed to occur at all the locations. Pressure drop across contractions were well correlated by assuming slip to occur at all locations except at the vena-contracta where the mixing action was postulated to cause a flow homogenizing effect. Pressure drop across expansion-contraction combinations was also in line with the separate contraction and expansion pressure changes. Two-phase frictional pressure drop in straight pipes and pressure changes across abrupt expansions and contractions are also found to be in accord with the criterion of the onset of the homogeneous flow pattern