An experimental investigation of the drag and shape of air bubbles rising in various liquids / by W. L. Haberman and R. K. Morton.

Abstract

Experiments showed that the motion of air bubbles can not be completely described by the use of dimensionless parameters containing the usual physical properties of the liquid (viscosity, surface tension, density). Three types of bubble shapes were observed in each liquid: spherical, ellipsoidal, and spherical cap. For a specific liquid, the shape of the bubble was a function of its volume. For tiny spherical bubbles, the drag coefficients coincided with those of corresponding rigid spheres. With increased bubble size, a decrease in the drag occurred in some liquids as compared to that of rigid spheres. The drag curves of the spherical bubbles rising in various liquids fell between the drag curves of rigid and fluid spheres. No criterion could be determined for the transition of the bubbles from rigid to fluid spheres. The region of ellipsoidal bubbles extended over different ranges of Reynolds numbers for the various liquids. The drag coefficients of spherical-cap bubbles were independent of bubble size and had a constant value of 2.6. An increase in drag as compared to bubbles in pure water was noted for bubbles rising in tap water or in water containing certain surface-active substances. Results are presented of tests to determine the effect of the container walls on the velocity of rise, and the experimental apparatus is described. A summary of the theoretical and experimental work of other investigators is also inlcuded.