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Mixing in a swarm of bubbles rising in a confined cell measured by mean of PLIF with two different dyes

Bouche, Emmanuella and Cazin, Sébastien and Roig, Véronique and Risso, Frédéric Mixing in a swarm of bubbles rising in a confined cell measured by mean of PLIF with two different dyes. (2013) Experiments in Fluids, 54 (6). 1-9. ISSN 0723-4864

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Official URL: http://dx.doi.org/10.1007/s00348-013-1552-0

Abstract

The present contribution reports an experimental study of the mixing of a passive scalar of very low diffusivity in a homogeneous swarm of inertial bubbles rising in a thin gap. A patch of fluorescent dye is injected within the swarm, and we observe the evolution of its mass in a given region of observation. We analyse the effect of the liquid agitation on the mixing mechanisms varying the gas volume fraction from 1.3 to 7.5 %, while the Reynolds number of the bubbles, Re = 450, their Weber number, We = 0.7, and the gapto-bubble diameter ratio, w/d = 0.25, are kept approximately constant. Here, the in-plane local mass of dye is measured by using a two-dyes planar laser-induced fluorescence (PLIF) technique that has been adapted to fix the problem of multiple light reflections at the bubble interfaces. Indeed, they induce both temporal and spatial variations of the captured light intensity that are superimposed to the effective fluorescence signal and prevent from using a standard PLIF technique. The analysis of the instantaneous concentration fields reveals the dominant role of the bubble wakes in the scalar transport. It is shown that mixing in this planar confined geometry is very efficient and enhanced by the increasing gas volume fraction. The present study also highlights that the mixing is not governed by a Fickian law of diffusion.

Item Type:Article
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Université de Toulouse > Institut National Polytechnique de Toulouse - INPT (FRANCE)
Other partners > Institut National des Sciences Appliquées de Rouen - INSA (FRANCE)
Other partners > Université de Rouen - UR (FRANCE)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UPS (FRANCE)
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Deposited By: Véronique ROIG
Deposited On:22 Nov 2013 10:47

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