Influence of surface tension on bubble nucleation, formation and onset of sliding

The influence of the surface tension on the bubble formation, detachment and onset of sliding underneath an inclined surface has been investigated using VOF technique in ANSYS-Fluent environment. Air is injected at a constant flow rate through a 2 mm diameter nozzle underneath an inclined plane, with varying surface inclinations ranging from 4° to 12°, submerged in viscous media. Bubbles evolve with spherical shape, underneath the inclined plane, gradually flattens and soon becomes an asymmetric shape forming two counter-rotating vortices in the surrounding fluid. The detachment of bubble from the nozzle-tip (nucleating site) is significantly influenced by the surface tension of surrounding fluid. It is predicted that the bubble holdup time at the nozzle-tip increases with increase in surface tension thereby making the bubble larger during detachment, which in turn changes the hydrodynamics of the surrounding fluid when detached. An experimental study has been performed to validate the VOF model with reference to the stretching characteristics of the bubble during initial growth. In general, the higher mass flux increases the buoyant force in the direction of sliding and at the same time the drag force that arises due to the shape opposes the sliding. The balancing act of these forces is the main cause that influences the detachment and subsequently the sliding behaviour of the bubble underneath an inclined plane.