Effect of the position to apply pressure oscillation for bubbles at the continuous flow channel

Abstract

We have developed a new defoaming method by applying pressure-oscillation in a continuous flow channel. Due to expansion and contraction of submillimeter bubbles, there are complex flow structures in the vicinity of bubbles in a viscoelastic fluid. We have studied the effect of a pressure-oscillation source position on the motion of submillimeter bubbles. In the previous study, submillimeter bubbles moved apart from a pressure-oscillation source position at upper stream. Horizontal moving velocity was accelerated because of negative wake at an opposite direction of bubbles motion. In this study, the motion of submillimeter bubbles was observed when we applied pressure-oscillation from lower stream. It found that submillimeter bubbles moved apart from a pressure-oscillation source position and the moving velocity of bubbles were accelerated. The moving direction of bubbles was different from the previous study. Therefore, we tried measuring the retardation and orientation distribution around the bubble by a high speed polarization camera. Strong retardation and horizontal orientation can be observed at opposite side of the movement direction of a contracting submillimeter bubble. Moreover, we observed motions of fine bubbles in the very vicinity of a submillimeter bubble as tracers. It turned out that an uniaxial extension was observed in the opposite side of the movement direction of the contracting submillimeter bubble. It was considered that strong retardation and the motion of fine bubbles were suggested to generate negative wake. The moving velocity of submillimeter bubbles was accelerated due to negative wake.