Characterizations of gas-liquid interface distribution and slug evolution in a vertical pipe

Large vertical pipes are key structures connecting subsea wells to offshore platforms. However, existing studies mainly focus on small vertical pipes. In a vertical acrylic pipe with 80 mm inner diameter and 11 m height, a high-speed camera was used to visually research the influences of pipe diameters, liquid properties and inlet effect on air-water co-flow characteristic. Different flow regime maps of vertical pipes (diameters are in the range of 50-189 mm) were compared and the critical gas velocity of the transition boundary from bubble to slug flow tended to increase with the increase of diameters at D > 80 mm. Drift-flux models were established in different flow regimes and liquid properties have a significant effect on drift coefficients of bubble flow and slug flow (void fraction a < 0.4). The influence of inlet turbulent effect on the gas-liquid interface distribution gradually weakened and disappeared from the pipe base to 85D, where the flow was fully developed. Slug frequency has a trend of increase first and then decrease with the gas Weber numbers increasing at low liquid superficial velocities (JL < 0.31 m/s). And on the basis of this law, a new slug frequency correlation was proposed. It was found that there was an exponential relationship between the ratio of lengths of Taylor bubble to slug and the void fraction.(c) 2023 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Automated summary

This study investigated the influence of factors such as pipe diameter, liquid properties, and inlet effect on the air-water co-flow characteristics in large vertical pipes. It was found that increasing the diameter led to an increase in the critical gas velocity for the transition from bubble to slug flow. Flow models were established for different flow regimes, and it was observed that liquid properties significantly affected the flow velocities of bubble and slug flow. The impact of inlet turbulent effect gradually weakened and disappeared as the flow reached full development. A new correlation for slug frequency was proposed based on the relationship between gas Weber numbers and liquid superficial velocities. Additionally, an exponential relationship between the ratio of lengths of Taylor bubble to slug and the void fraction was identified.