Abstract
A local shear rate due to a local flow surrounding a small air bubble under a periodical oscillatory pressure field was derived theoretically, which is able to estimate an enhancement in removing the bubble from shear-thinning fluids. This estimation requires experimental data of changing bubble size over a cyclic period. Because the oscillation frequency was too high to record by the commercial video camera, we use a special technique. The pressure inside a closed test cell was controlled by vibrating a thin-film set on the fixed cell. We compared the observed rising velocities under oscillating pressure condition with a free rising velocity that was estimated from the shear viscosities and mean bubble sizes, which are measured by the strobe lighting technique. We also studied the bubble shape under periodical oscillatory pressure. In some cases, a cusped bubble was observed only when the diameter approached to its minimum size.
