Global characterization of hydrodynamics and gas-liquid mass transfer in a thin-gap bubble column intended for microalgae cultivation

Abstract

Global characterization of hydrodynamics and gas-liquid transfer in a 2D column with a 4 mm thickness is carried out with water and aqueous glycerol solutions. This new design can be used as a photobioreactor of low thickness to intensify the volumetric productivity by increasing microalgae concentration. To mimic the presence of algae cultures, the liquid viscosity is adjusted with glycerol. Focuses are made on flow regimes and their transitions, mixing, and gas-liquid transfer at the scale of the reactor. In comparison with conventional bubble columns lower terminal velocities are obtained. So, in homogeneous regime, the residence time of bubbles is greater than in conventional bubble columns and the gas holdup is slightly higher. However, regime transitions appear at relatively low superficial gas velocities in the confined bubble column. In addition, two transition regimes are visible and have macroscopic flow structures very similar to the ones observed for conventional columns. For the mixing time, a dependence on the viscosity is observed and whatever the solution tested, this parameter decreases very quickly with the increase of the gas superficial velocity. Finally, global gas-liquid mass transfer coefficients measurements show lower values than in classical bubble columns at the same superficial gas velocity.

Using a bio-inspired copper complex to investigate reactive mass transfer around an oxygen bubble rising freely in a thin-gap cell

“…An additional advantage of this confined configuration is to offer the possibility to cover a wide range of motion regimes for the bubbles and of subsequent mass transfer regimes. Such confined bubble reactors also find promising applications, in particular towards lightactivated reactions, such as the synthesis of added-value molecules by photochemical pathways (Oelgemöller, 2016), the cultivation of microalgae (Pruvost et al, 2017;Thobie et al, 2017) or the methane formation from carbon dioxide (Rao et al, 2017). Due to the light attenuation and to the absorbing nature of the medium, the latter applications need photoreactors with narrow geometry to be designed, while offering efficient mixing and mass transfer.…”

Measurement of Volumetric Mass Transfer Coefficient in Bubble Columns

“…Kantarci (2005) [2] reviewed several biochemical studies using bubble columns as bioreactors to produce various products, such as enzymes, proteins, antibiotics, etc. Nowadays, bubble columns are studied as an efficient photo-bioreactor for production of microalgae [5][6][7]. The supply of gas to the liquid is a crucial process to keep microorganisms alive and the knowledge of gas-liquid mass transfer rate is an important design and scale-up parameter determining the reactor efficiency [2,8].…”

Coalescence of bubbles in a high Reynolds number confined swarm

“…It is worth pointing out that this flow configuration finds promising applications in chemical engineering since it is expected to be an alternative reactor of intermediate size that takes advantage of the confinement to enhance mass transfer, as in monolith reactors, and of the intense bubble-induced agitation to develop satisfactory in-plane mixing (Roudet et al 2017;Alméras et al 2018). Some recent applications have been developed concerning light-activated reactions or cultivation of micro-algae in photo-reactors that need narrow geometries due to light absorption and attenuation, while keeping efficient mixing and mass transfer requirements (Oelgemoller 2016;Pruvost et al 2017;Thobie et al 2017).…”