Modelling of annular dispersed two-phase flow in vertical pipes

An investigation is made into the reliability with which pressure loss, film thickness and liquid entrainment can be predicted by an annular flow model that is based on the well-known two-fluid (separated flow) concept. For this purpose a two-fluid model is presented which accounts for the interrelation between these variables. In this connection the existence of multiple liquid hold-up solutions is mentioned. New correlations for interfacial friction and liquid fraction entrained are proposed using data compiled previously at AERE Harwell. Our new model is compared with previous models. Differences between predictions are illustrated by reference to the Harwell data bank, recent large-diameter tests and hypothetical gas-well cases relevant to the oil industry. Application of the annular flow models, in particular their entrainment correlations, appears to give rise to widely varying results, restricting the predictive value of the models when extrapolated to large-diameter and/or high pressure systems.