On motion of bubbles and drops

Dynamically interacting effects of surfactant impurities and neighbor particles on the transfer mechanism of momentum and terminal velocities of spherical bubbles, drops, or solid particle assemblages at low Reynolds numbers are analysed and formulated. The steady‐state equations of viscous fluid motion and continuity (one set for each phase) have been solved simultaneously with a conservation equation for diffusing surfactant impurities. By employing a cell model with zero vorticity at its outer boundary, and modified interfacial conditions the terminal relative velocity of an ensemble of fluid particles is evaluated and compared with some available experimental data. The analysis of solid‐fluid mixture is shown to become a special case of the analysis of fluid‐fluid mixtures where adventitious surfactant impurities stop internal circulation thereby causing drop and bubble assemblages to behave as suspension of solid particles.