| The motion of drops and bubbles in confined domains is encountered in several applications such as oil recovery, solvent extraction, paper-making, and microfluidics, among others. In this thesis, the motion of air bubbles in square capillaries moving under the influence of gravity is studied at finite Reynolds numbers. The steady shapes, deformations, film thickness, and velocities of the bubbles as a function of the bubble size are determined experimentally. The bulk fluid phase is either Newtonian, viscoelastic, or a surfactant solution. Bubbles rising in a Newtonian fluid are nearly spherical at lower bubble volumes and become prolate losing their fore and aft symmetry at larger bubble volumes. At lower bulk viscosities, a reentrant cavity develops at the rear of bubble. The critical viscosity at which this shape transition occurs depends on the size of the capillary. The terminal velocity of bubbles increases with volume for small bubble volumes. Even at small bubble volumes, the terminal velocity of the bubbles is much less than the Hadamard-Rybczinski velocity of a spherical bubble with the same volume. (Abstract shortened by UMI.)... |
