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.