The objective of this lab is to study experimentally a bubble column. A bubble column is a vertical cylindrical vessel containing a liquid phase where a gaseous phase is injected into the bottom by a gas distributor. This gaseous phase rises through the liquid, and finally escapes through the upper free surface. Despite their widespread use in chemical or biological industry, the modelling of such devices remains unsatisfactory due to the lack of reliable physical model describing the interactions between phases. As the void fraction of bubbles is high (up to 50%), these are opaque flows, and the standard optical used in fluid mechanics techniques (such as PIV PTV, etc…) are no longer useful at such regimes. We will therefore use an alternative state-of-the-art technique: the optical probe. This device allows to obtain time resolved 1D time signals and to measure the void fraction and the bubbles size and velocity distributions. We will therefore be able to check the different models available in the literature and to explore the complexity of two-phase flows.
This lab-course is well suited to M1 and M2 students having a background in fluid mechanics.
Single spherical bubble in a still fluid
4 hrs session
We will start with a simplified scenario: a single spherical bubble rising in a still fluid. Despite the symmetry of the problem, wake instabilities can cause the bubble to follow different paths, that includes oblique, zig-zag and chaotic trajectories. A high-speed camera will be used to acquire the images, while image processing techniques will be adapted to obtain the bubble trajectories. The goal of this module is to show the richness of the coupled dynamics of the bubble and the still fluid, and to serve as an introduction to the much more complex case of the bubble column.
4 hrs session
The bubble column available at the PEI platform allows to study of different regimes. It has an internal diameter of 0.4m and 3m height. Bubble columns present three different regimes depending on the injected flowrate of gas: homogeneous (that occurs at low flowrates, and all bubbles follow a vertical, organised path), transition and heterogeneous (large flowrates, bubbles can follow non-trivial trajectories and a recirculation pattern is observed). We will therefore use optical probes to study the transition from homogeneous to heterogeneous regime, while checking the validity of the models available in the literature to explain such transition.
Galilée building (PEI platform)
1270 rue de la piscine
(see map below)