Upward two-phase flow patterns in vertical circular pipe under rolling condition

Abstract

The experiments on the air-water two-phase flow patterns in a 24 mm diameter vertical circular pipe under both static and rolling conditions were conducted. The superficial velocities were in the range of 0.05–4.07 m/s and 0.02–20.55 m/s for water and air, respectively. Five typical flow pattern morphologies resulting from a rolling motion were observed: dispersed bubbles; bubbles; slug; churn; and annular flow. Flow pattern transitions were identified by analysis of visual images and a bubble chord-length probability distribution function (PDF). The static experimental data was used to validate existing flow pattern transition models that were then modified to fit rolling conditions by considering the additional forces caused by rolling motion. These models also agreed well with the experimental data. Investigation of the influence of the rolling motion on flow pattern transition showed that, as the rolling amplitude increases, the formation of dispersed bubble flow requires a higher superficial liquid velocity. It was also found that, the greater the rolling amplitude, the larger region of churn. The rolling period, however, has little impact on flow pattern transitions.