Bubble velocity and coalescence in viscoelastic liquids

Abstract

Velocity-volume data of air bubbles were collected in a Newtonian fluid [40% (wt) glycerol in water], and in two non-Newtonian fluids [1% (wt) carboxymethylcellulose in water and 1% (wt) of polyacrylamide in glycerol and water]. No velocity discontinuity was observed in the case of the log-log plots of velocity versus volume for the three fluids. Also, there was no appreciable effect of injection period of the air bubbles upon their terminal velocities. Preliminary data on the coalescence phenomena were examined for two and three air bubbles injected simultaneously in the 1% CMC and the 1% PAA solutions. In both cases, coalescence followed a regular sequence. First the trailing bubble(s) enter the wake of the leading bubble, then the bubble(s) accelerate towards the leading bubble until collision occurs. This action results in a thin film separating each, continuing with a film thinning process until complete coalescence. Some experiments were performed relating the bubble volume required to coalesce with a 1.0 × 10 −6 m 3 bubble as a function of orifice separation, illustrating the effect of elasticity upon bubble coalescence.