In this paper

the prediction of void fraction and pressure drop for upward gas-liquid annular flow in a vertical annulus is studied.According to the idea of Kelessidis(1989)for the flow pattern transition from churn to annular flow and the integral analysis method of Wallis(1969)for the velocity profile of single-phase flow in an annulus

a new model for prediction of void fraction and pressure drop is proposed based on considering the structural feature of the concentric annulus and the flow pattern characteristics.The present model is compared with existing models and the experimental data from this paper and the literature.It is in better agreement with experimental data than existing models.