Bubble hydrodynamics and mass transfer at high reynolds number and surfactant concentration

Abstract

The interface force balance equation for a bubble rising through a liquid containing surface-active impurities that decrease the interfacial tension is shown to be incompatible with the appearance of a conventional wake. The observation of wakes is explained when the surfactant concentration is above the value required to saturate the interface. A theoretical model is developed using the integral boundary layer equations and a two-phase surfactant adsorption isotherm which divides the bubble into an upper boundary layer region where surfactant adsorbs, and a lower wake region from where it desorbs. The model predicts that, at surfactant concentrations above those that make the bubble behave as a solid sphere, the bubble interface is mobile and the flow separation point moves around to the top of the bubble. Predictions about this “large-wake” hydrodynamic regime are compared with literature data.