Buoyant plumes produced by a source of bubbles in a liquid medium are used for a variety of purposes. Bubble breakwaters operate because of the surface jet produced by the bubble plume. Oil slicks on water surfaces can be contained by bubble plumes. Bubble plumes have also been used to prevent parts of the surface of a river or lake from freezing. During an underwater oil-well blow-out, a plume of bubbles, oil droplets and sea water develops; the extent of the damage to marine life depends on whether all the oil rises to the surface or spreads out horizontally at some intermediate depth. In industry, bubble plumes are used with two objectives: enhancing mass transfer and mixing. As a mixing technique, the use of bubbles is attractive because it is very simple and cheap to operate. The most common applications of bubble-driven mixing are encountered in wastewater treatment, in the delicate mixing of pharmaceutical and food products, in the mixing of very hot or toxic liquids and in the destratification of lakes and reservoirs.
In this PhD project, we conducted experimental and theoretical work on the dynamics and mixing induced by a plume of small bubbles. We focused on the mixing driven by a continuous release of bubbles in a stratification consisting of two layers of liquids of different densities. We applied our model to understand the stability of LPG storage.
Prize: This project was awarded the IChemE Fluids Mixing top prize, 2001.
(click image to enlarge)
|Sequence of photographs showing the evolution of the mixing induced by a bubble plume in a two-layer stratification|