Effects of Surfactant on the Lift Force Acting on a Bubble in a Shear Flow

Abstract

A bubble motion in aqueous surfactant solutions is investigated with the numerical simulation. It is known that the reduction of the terminal velocity of rising bubbles is explained by the so-called Marangoni effect, which is caused by the surfactant adsorption to the air/water interface. But few studies have been done for the shear-induced lift force acting on a bubble under the presence of the Marangoni effect. Here, we conduct the simulation on the force acting on the contaminated bubble in a linear shear flow. To consider the Marangoni effect on the bubble motion, the balance equation for the concentration in liquid phase and the interfacial concentration at bubble surface are solved on the three-dimensional boundary-fitted grid system. The surfactant adsorption and desorption processes to the air/water interface are considered by the Langmuir's kinetics laws. The present simulation showed that the reduction of the lift force occurs when the surface concentration becomes sufficiently large. They also showed that the azimuthal distribution of surface concentration of surfactant gives a large influence to the lift force, although it doesn't to the drag force.