Wall effect on the behaviour of single bubbles rising in highly viscous liquids.

Abstract

The wall effect on the terminal velocity and the shape of single bubbles rising in highly viscous liquids has been investigated experimentally. The terminal velocities of single bubbles affected by the column wall are correlated with two dimensionless equations between ReM0.48/(l - λ1.5) and Eotvos number Eo, where λ is the bubble and column diameter ratio and 1 -λ1.5 is the wall effect function, which was also used for relatively low-viscosity liquids. The aspect ratio h/w defining the bubble deformation is found to be a function of Re and λ for Re ≥0.1, while it is a function of λ only for Re < 0.1. The bubble deforms from the sphere in the vicinity of Eo = 6, which corresponds to the border of dimensionless equations of bubble rising velocity.