Slug Flow Analysis in Vertical Large Diameter Pipe

The existence of slug flow in vertical co-current two-phase flow is studied experimentally and theoretically. The existence of slug flow in vertical direction implies the presence of Taylor bubbles separated by hydraulically sealed liquid slugs.;Previous experimental studies such as Ombere-Ayari and Azzopardi (2007) showed the evidence of the non-existence of Taylor bubbles for extensive experimental conditions. Models developed to predict experimental behavior [Kocamustafaogullari et al. (1984), Jayanti and Hewitt. (1990) and Kjoolas et al. (2017)] suggest that Taylor bubbles may disappear at large diameters and high velocities.;A 73-ft tall and 101.6-mm internal diameter test facility was used to conduct the experiments allowing holdup and pressure drop measurements at large L/D. Superficial liquid and gas velocities varied from 0.05-m/s to 0.2 m/s and 0.07 m/s to 7.5 m/s, respectively. Test section pressure varied from 38 psia to 84 psia. Gas compressibility effect was greatly reduced at 84 psia. The experimental program allowed to observe the flow patterns for flowing conditions near critical conditions predicted by previous models (air-water, 1016 mm ID, low mixture velocities).;Flow patterns were observed in detail using wire-mesh sensor measurements. Slug-flow was observed for a narrow range of experimental conditions at low velocities. Churn-slug and churn-annular flows were observed for most of the experimental data-points. Cap-bubble flow was observed instead of bubbly flow at low vSg. Wire-mesh measurements showed that the liquid has a tendency to remain near to the walls. The standard deviation of radial holdup profile correlates to the flow pattern observed. For churn-slug flow, the profile is convex with a single maximum near the pipe center while it exhibits a concave shape with two symmetric maxima close to the wall for churn-annular flow.;The translational velocity was measured by two consecutive wire-mesh sensor crosscorrelation. The results show linear trends at low mixture velocities and non-linear behaviors at high mixture velocities. The translational velocity trends seem to be related to the flow-pattern observed, namely to the ability of the gas to flow through the liquid structures.;A simplified Taylor bubble stability model is proposed. The model allows to estimate under which conditions Taylor bubbles disappear, properly accounting for the diameter effect and velocity effect observed experimentally. In addition, annular flow distribution coefficient relating true holdup to centerline holdup in vertical flow is proposed. The proposed coefficient defines the tendency of the liquid to remain near the walls. This coefficient increases linearly with the void fraction.