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Soutenance de Raphael Poryles

Instabilités et piégeage de bulles dans des fluides complexes
When Jul 18, 2017
from 02:30 to 04:30
Where Amphi Schrödinger
Contact Name
Attendees Raphael Poryles
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We have studied experimentally the dynamics of bubbles rising in complex fluids, from polymer solutions to immersed granular media, in a confined geometry (Hele-Shaw cell). In a first part, we considered the rise of a single bubble in a confined polymer solution. The fluid (PEO) is viscoelastic and shear-thinning. Above a critical volume, we have observed and characterized two types of instabilities : the bubble is deflected from its vertical trajectory, or fragments. The extension of this experiment to continuous air injection at of the cell bottom made it possible to quantify the coupled dynamics between bubbles and in particular their coalescence, which is highly dependent on the injection rate. In a second part, we considered the case of an immersed granular medium, in which air is injected at constant flow rate through a single nozzle at the cell bottom. In the steady state, the movement of the grains generated by the successive air pathways leads to the formation of a fluidized zone. We quantified the bubble dynamics in this zone and showed that even when varying the grains size and gas flow rate, the fraction of gas trapped in the fluidized zone remains constant. Finally, we considered the influence of a fixed obstacle on the dynamics of the central air channel. A phase diagram is established depending on the size and height of the obstacle: either the channel is stabilized by the obstacle, or it is unstable and intermittently explores each side of the obstacle.