KAGAKU KOGAKU RONBUNSHU, Vol.36, No.5, 435-440, 2010
Stress Measurement around a Small Air Bubble by Flow Birefringence in a Pressure-Oscillating Field
We have developed pressure-oscillating defoaming for shear-thinning fluids. A bubble undergoes alternating expansion and contraction in a pressure-oscillating field, where the oscillating flow damps quadratically with the distance from the surface, giving biaxial elongational flow and shear flow in the vicinity of the bubble surface. In this study, a rheo-optic technique was applied to measure the stress arising from such local flow around the bubble. By using CTAB/NaSal solution with a good photoelastic correlation and rheological property similar to the UCM model, the profile of the maximum retardations was measured experimentally with respect to the distance from the bubble surface. The profile was very similar to shear stress profile around an alternately expanding and contracting bubble calculated by the unsteady state finite element analysis. Based on the stress-optic law, the thickness of stressed fluid around the bubble was estimated by comparison of the two profiles.