A Mechanistic Model for the Initiation of Bubble Centering in Horizontal Gas-Liquid Slug Flow*

Slug flow is a commonly observed, complex flow pattern in two-phase horizontal pipe flow. It is characterized by alternating flow of aerated liquid slugs and elongated bubbles which form a stratified-type flow with a thin liquid film as the bottom layer. Accurate modeling and understanding of slug flow is paramount to the design of a flowing system which may encounter the flow pattern. Bubble centering in horizontal slug flow is infrequently discussed in the current state of literature. Typically, the elongated bubble is assumed to flow along the upper wall of the pipe due to gravity segregation. At some conditions, however, the bubble is seen to travel closer to the centerline of the pipe. Until now, there has not existed a model which can offer clear insight into what causes this mechanism.

A novel model which predicts the initiation of the bubble centering mechanism is presented. The model is mechanistic and thus focuses on characterizing and capturing all physical processes involved. Prediction of initial bubble detachment matches reasonably well with available air-water data. The presentation of this research includes an overview of slug flow, model development, and results.