Numerical investigation of bubble shape and flow field of gas-liquid slug flow in circular microchannels

Numerical simulations of gas liquid slug flows (also known as Taylor flows) in circular microchannels are carried out using an interface tracking method based on the volume of fluid method to investigate effects of relevant dimensionless numbers on the bubble shape and the flow structure inside and outside a bubble. Uniform slug flows are dealt with, and therefore, the motion of a single unit cell consisting of a Taylor bubble and a liquid slug is predicted. Adaptive computational cells are used to capture the thin liquid film between a bubble and the channel wall. The numerical conditions are the same as those in experiments in our previous study, i.e. two channel diameters and three liquids of different viscosities are used. The conclusions obtained are as follows: (1) the interface tracking simulation can give good predictions of the bubble shape and the relationship between the void fraction and the gas volumetric flow ratio, (2) the radius of curvature at the bubble nose can be well correlated in terms of the capillary number, whereas that at the bubble tail depends not only on the capillary number but also on the Weber number, and (3) the minimum liquid film thickness appearing in the tail region of a bubble, which is thinner than the uniform liquid film in the cylindrical bubble body region in all the numerical conditions, can be correlated in terms of the capillary number as well as the uniform liquid film thickness in the cylindrical bubble body region.