Void Fraction in Bubbly, Slug and Churn Flow in Vertical Two-Phase Up-Flow

This paper presents a flow pattern approach to estimating void fraction during vertical upward recurrent two-phase flow recognizing the four major flow regimes—bubbly, slug, churn and annular. Expressions for void fraction in bubbly, slug and churn flow regimes are derived from the relationship between the phase velocities. Recirculation effect in large diameter pipes during bubbly flow and modifications to account for this effect are established. The differences in the predictive procedure for bubbly-slug flow transition between large and small diameter pipes are pointed out. The similarities between slug and churn flow and the modifications needed for void fraction prediction during churn flow are demonstrated. The predictions of the proposed model for flow pattern transition and void fraction are compared with experimental data gathered for this work as well as from independent sources. Good agreement between the data and the predictions of the model is noted.