Interaction of a Taylor bubble with the liquid–liquid interface in a notched tube

Injection of air into stratified liquids for improved mixing and for the removal of oil droplets from water is some well-established applications for augmentation of heat and mass transfer and purification of water. The present study investigates the dynamics of a Taylor bubble passing through the liquid–liquid interface in a vertical tube provided with rounded notch of different radii using the Eulerian approach-based volume of fluid method. The complete bypass of the Taylor bubble across the liquid–liquid interface and the notch is observed for dimensionless notch radius, r* = 0.0388, whereas the Taylor bubble has bypassed in the form of smaller volumes periodically pinched-off near the notch for higher notch radius. The drag coefficient has significantly increased during the bypass of the bubble across the liquid–liquid interface, its peak has an order of magnitude ≅102 for r* = 0.0388, and it is ≅ 103 for a larger notch radius. This increase in the drag coefficient is also manifested in terms of significant increase in the wall shear stress and capillary pressure drop across the notch. The increase in liquid viscosity ratio has resulted in a slight increase in pinched-off bubble volumes and their surface oscillations.