The terminal velocity of rising microbubbles is a sensitive function of the bubble size and the surface concentration of mobile insoluble surfactants at the gas/liquid interface due to the Marangoni effect. With a model that allows for surface convection and diffusion, we delineate the regimes when the terminal velocity varies between the fully mobile (Hadamard-Rybczynski) and the fully immobil...

Solid exchange between the bubble wake and the emulsion phase in a gas-fluidised bed was studied both experimentally and theoretically. Measurements were made on the tracer particle concentration profile produced after a single bubble passage in a two-dimensional bed, and the solid exchange coefficients were estimated with the results of simultaneous measurements on the shape, the size and the ...