Experimental determination of gas-bubble breakup in a constricted cylindrical capillary

Abstract

To gain insight into the mechanisms of gas-foam generation in porous media, this work quantifies how smaller bubbles snap off from a single, larger bubble as it moves through a smooth, cylindrical constriction. Time to snap off, generated bubble size, and bubble velocity are obtained from viewing 16-mm movies taken of snap-off events. The bubble capillary number, Ca/sub GAMMA, is varied from 10/sup -5/ to 5 x 10/sup -2/. The authors study two narrowly constricted capillaries of different tube radii (neck radius/tube radius of 0.17 and 0.20) and one widely constricted capillary (neck radius/tube radius = 0.40). In the widely constricted capillary, time to breakup is proportional to Ca/sub GAMMA/sup -2/, and the generated bubble length is proportional to Ca/sub GAMMA/sup -1/. In the narrow constrictions, the same results apply above Ca/sub GAMMA = 5 x 10/sup -4/; below this critical Ca/sub GAMMA, time to breakup is independent of Ca/sub GAMMA but depends on the Ohnesorge number. Snap-off behavior with surfactant solutions is found to be similar to that in surfactant-free solutions.