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Article Dans Une Revue Chemical Engineering and Processing: Process Intensification Année : 2022

Different types of bubbly flows in a confined channel with the aim of limiting microalgae biofilm development - Part I: Hydrodynamic study

Résumé

he impact of bubble passage on wall hydrodynamics is investigated in a square channel with a cross section of 4×4 mm2. The effect of bubble size and frequency is put into evidence. Shadowgraphy, PIV and polarography are used to characterize respectively the bubbles, the liquid velocity field and the wall shear stress. The objective is to put forward the role of bubbles in limiting biofilm formation which is undesirable during microalgae culti­vation, especially with the new intensified technologies of high volume productivity photobioreactors (PBRs) with confined environment. Two types of injections are studied: capillary injection and T injection. Capillary injection generates bubbles smaller than the channel size, which are thus able to oscillate, and create greater disturbances in the hydrodynamics of the liquid phase. In fact, the streamlines and vorticity fields in the wake of the bubbles reveal the presence of small vortices, dispersed in the wake. The T injection generates Taylor bubbles followed by elongated vortices, which present the same vorticity intensity as the ones obtained with the capillary injection. Concerning the wall shear stress, the observed peaks are related to the passage of bubbles on the probe. The peak frequency increases with the bubbles passage frequency. A higher average shear stress is obtained with the capillary injection for a given air flowrate due to higher bubble frequency. The peak magnitude generated with the capillary injection shows important variations related to the bubble position in front of the probe which varies due to bubble oscillation. The T injection exhibits a constant shear stress peak magnitude regardless of the air flowrate, which shows that the thickness of the liquid film between the bubble and the wall is independent of the bubble size.

Dates et versions

hal-03973338 , version 1 (04-02-2023)

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Charlène Thobie, Walid Blel, Jean-Luc Hauser, Jérémy Pruvost, Caroline Gentric. Different types of bubbly flows in a confined channel with the aim of limiting microalgae biofilm development - Part I: Hydrodynamic study. Chemical Engineering and Processing: Process Intensification, 2022, 173 (4), pp.108844. ⟨10.1016/j.cep.2022.108844⟩. ⟨hal-03973338⟩
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