Numerical Simulation Of The Mechanism Of Interactions Between Bubbles

Multiphase flows are widely existed in industry applications. These processes usually involve motions of multiple bubbles. Therefore, having knowledge of the interactions between bubbles is important for investigating multiphase flows and boiling heat transfer. A numerical simulation was performed to investigate the behaviors of two bubbles in quiescent liquid using VOSET(Coupled Volume-of-Fluid and Level Set) method and N-S equations coupled with CSF(Continuous Surface Force) model. The behaviors of two bubbles rising side by side and in axisymmetric configurations in vertical channel were studied separately. The effects of surface tension, the viscosity of the fluid, the diameter of bubble and the initial distance between bubbles were investigated in particular.This research suggests that, three types of motion were observed depending on the changing of surface tension: coalesce, two bubbles repeatedly attracted and bounced against each other, bounced and separated. With the increase of viscosity, two bubbles coalesced and the velocity of the coalescence bubble was smaller and shows less fluctuation. Two bubbles coalesced or separated for different density of the fluid. The velocity of the coalescence bubble showed fluctuation at a larger density, while that shows steady at larger density. While s, which is dimensionless initial distance, was below 2.5, two bubbles coalesce. Two bubbles had no interactions when s was above 5. The transition value of diameter was between 2 and 3mm, which determined coalescence or bouncing during the rising process.This research suggests that, two bubbles separated or coalescence. When the. Without coalescence, trajectory showed the symmetry about the channel center line, the vertical velocities of the both bubbles were almost the same while the magnitude of horizontal velocity equaled with the opposite direction. Whether the velocity of the coalescence bubble fluctuated or not depends on the Reynolds number. When the Reynolds number was below 73, the bubble had steady state. When the Reynolds number was larger than 121, the coalescence bubble showed shape fluctuation.For two bubbles placed in a vertical orientation, they coalesced when the influence on the trailing bubble exerted by the leading bubble was remarkable, the shape and velocity of the coalescence bubble mainly depended on that of single bubble. But two bubbles rose separately like an isolated bubble rose when the influence was little.This research also shows that, with the decrease of Eotvos number, the interaction between two bubbles got smaller. Two bubbles contacted earlier with the decrease of Morton number. For spherical and ellipsoid bubble, the shape of the coalescence bubble was the same with that of single bubble with the same parameter and it has no relationship with the initial distance. While for the wobbling bubble, the changing of distance would influence all the rising process.