Effect of surfactants on hydrodynamics characteristics of bubble in shear thinning fluids at low Reynolds number

In this study, the effects of surfactants on the hydrodynamic characteristics of bubbles in shear-thinning fluids at low Reynolds number (Re<50) are investigated. The bubble terminal velocity and drag coefficient of bubble in clean and contaminated carboxymethylcellulose (CMC) solutions are obtained using a high-speed camera for examining differences. The results show that the existence of surfactant could reduce the terminal velocity of bubble at small volume (0.25wt% CMC: <100 mm³; 0.50wt% CMC: <110 mm³), attributed to stiffening the bubble interface. However, this negative effect decreases and finally disappears with increasing bubble volume. The drag coefficient curves of the bubble in contaminated CMC solution exhibit behavior similar to that exhibited by a solid sphere at Re<10, indicating that internal circulation flow is absent at the bubble interface as compared to that in clean CMC solution. However, for 10<Re<40, a transition of drag curve from 24/Re to 16/Re in contaminated CMC solution is observed, which is easy at low SDS concentrations and high CMC concentrations.