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Investigating the effects of hydrodynamics and mixing on mass transfer through the free-surface in stirred tank bioreactors

de Lamotte, A; Delafosse, A; Calvo, S; Delvigne, F; Toye, D; (2017) Investigating the effects of hydrodynamics and mixing on mass transfer through the free-surface in stirred tank bioreactors. Chemical Engineering Science , 172 pp. 125-142. 10.1016/j.ces.2017.06.028. Green open access

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Abstract

In stirred-tank bioreactors, flow structures of various length and time scales are implied in scalar transport phenomena, such as gas species transfer through the liquid free-surface and their homogenization in the bulk. A proper understanding of the underlying mechanisms, i.e. hydrodynamics, mixing and mass transfer, and of their interactions is required to design and develop reliable and efficient production-scale bioprocesses. The objective of the present work is to experimentally investigate the coupling between gas-liquid mass transfer of oxygen with mixing efficiency and circulation patterns inside an arbitrarily chosen stirred-tank configuration aerated through the liquid free-surface, a baffled 20 L-vessel agitated by two Rushton turbines. Based on global parameter values, the most appropriate rotating speed, N = 300 rpm, is selected in order to further study local hydrodynamic quantities using Particle Image Velocimetry (PIV), as well as mixing and mass transfer dynamics using Planar Laser-Induced Fluorescence (PLIF). The results obtained with these local experimental methods are analyzed in detail. Their averages are first successfully compared to global data. Statistical analysis of their spatial distributions show that large-scale flow patterns significantly influence mass transfer through the free-surface of the stirred tank. Even if global measurements show that global characteristic times for mixing and mass transfer differ by two orders of magnitude, local experimental characterization shows persistent vertical gradients of dissolved gas concentrations. So the dissolved gas concentration is not as perfectly uniform as one might expect.

Type: Article
Title: Investigating the effects of hydrodynamics and mixing on mass transfer through the free-surface in stirred tank bioreactors
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.ces.2017.06.028
Publisher version: https://doi.org/10.1016/j.ces.2017.06.028
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Stirred tanks, Hydrodynamics, Mixing, Mass transfer, PIVPLIF
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Biochemical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/10064111
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