Abstract
We have proposed a new and effective method POD (Pressure Oscillating Defoaming) for increasing the bubble rising velocity. When strong pressure-oscillation are applied to the two vertically aligned air bubbles in viscoelastic fluids, the lower-bubble are approaching the upper-bubble. In the fluid between air bubbles, hydrodynamic interaction may have complex flow structures. To clarify the flow structures, we tried measuring the retardation profile near the bubble by the high speed polarization camera, and flow visualization experiments using tracer particles. It turned out that there is a uniaxial extension behind each bubble, and strong retardation can be seen in the region. When two bubble are close, a uniaxial extension at the tail of the upper-bubble enhances rising velocity of the lower-bubble.
