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 50e189 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(J_(L)≤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.

A volume of fluid simulation of the steady deformation and the drag of a single droplet in a flowing gas

A method is proposed to investigate the steady deformation and the drag of a single droplet in a flowing gas at a high Reynolds number.The volume of fluid(VOF)method is used to model the droplet surface structure.The direct numerical simulation(DNS)method is used to model the gas flow field.In order to avoid the effect of the droplet acceleration on the drag and reduce the computation cost,a body force is added to the droplet to make it fixed at a constant position.The body force is determined by using the Newton iteration procedure.The simulated droplet aspect ratio and the drag coefficient agree well with the published experimental data.Meanwhile,the sources of the drag are analyzed and the effect of the Reynolds number and the Weber numbers on the droplet deformation and the drag are studied.The drag mainly comes from the pressure difference between the droplet-leading zone and the trailing zone,and the turbulence wake would increase the drag.