LARGE AND SMALL BUBBLE INTERACTION PATTERNS IN A BUBBLE-COLUMN

A visual analysis is made on the fate of a large (or ''cap'') bubble i njected into a swarm of otherwise uniformly dispersed small bubbles; e xperiments, covering gas holdups for the swarm bubbles as high as 6%, are conducted in a two-dimensional column to ensure the distinct appea rance of a single cap throughout its rise in the swarm. Specific focus is on the stability or breakup of the large bubble induced by the ove rtaken small bubbles. The diversity of cap-bubble interactions is obse rved and classified based on the observed shape distortion and/or brea kup patterns into seven modes. The probability of occurrence of each m ode is estimated, the results of which indicate that there exists a cr itical gas holdup (e.g. similar to 0.01 for tap water) beyond which th e degree of cap-bubble interactions sharply increases. This general tr end is found for the other liquids tested (i.e. sodium sulfite and gly cerin solutions) with lower degrees of interactions and the transition being less distinct. The effects of the swarm gas holdup on the speci fic interaction properties are also studied: with increasing holdup, t he axial location of the breakup event shows a noticeable tendency of shifting from lower to higher positions; the size ratio of two daughte rs after the split tends to approach unity; the dominating breakup mec hanism shifts from the inherent instability of the cap itself to the b ubble attachment at the cap base, which triggers the ultimate necking and ''pinching-off'', to the acceleration of the cap toward (usually t wo) preceding bubbles under the influence of their wakes.