Splitting of the volumetric mass transfer coefficient into a bubble–liquid mass transfer coefficient and interfacial area is essential to quantify the mass transfer rate of stirred tanks precisely. Axial distributions of the bubble–liquid mass transfer coefficient were determined in viscous Newtonian and non-Newtonian fluids using a laboratory-scale stirred tank. A detailed knowledge of the bubble–liquid mass transfer coefficient was obtained by using dedicated in situ oxygen and bubble size endoscope probes simultaneously. The volumetric mass transfer coefficient was estimated from recorded local dissolved oxygen concentrations in liquids. The interfacial area was calculated by measuring the bubble size and gas hold-up. The bubble–liquid mass transfer coefficient was then obtained by combining the estimated volumetric mass transfer coefficient and interfacial area. The bubble–liquid mass transfer coefficient was evaluated with effects of fluid rheology (concentrations of fluids), operating conditions (power input and superficial gas velocity), and axial liquid height. Bubble breakage is higher close to the stirrer due to intensive turbulence. The bubble–liquid mass transfer coefficient depended directly on operating conditions and indirectly on fluid rheology and liquid height.

Mass transfer is a crucial phenomenon in designing and scaling up chemical and biochemical stirred tanks. The literature lacks a pilot-scale study on investigating mass transfer in non-Newtonian fluids. A pilot-scale study is a prerequisite step before scaling up the process from laboratory to industrial-scale. Thus, a study using pilot-scale stirred tank was conducted to investigate bubble hydrodynamics and mass transfer in non-Newtonian fluids. This work is a scale-up study from laboratory to pilot-scale. Axial distributions of bubble–liquid mass transfer coefficient and interfacial area were obtained using dedicated in situ optical endoscope probes (oxygen and bubble size) simultaneously. Volumetric mass transfer coefficient was determined by recording local dissolved oxygen concentrations in liquid. Interfacial area was estimated by measuring local bubble size and global gas holdup. Bubble–liquid mass transfer coefficient was then deduced by combining the obtained values of volumetric mass transfer coefficient and interfacial area. Effects of operating conditions, fluid rheology, and probe axial positions (liquid height) on bubble–liquid mass transfer coefficient were considered. The operating conditions (power inputs and superficial gas velocities) were in the range of 30–250 W/m³ and 3.10–4.70 mm/s, respectively. Bubble–liquid mass transfer coefficient increased with an increase in operating conditions, whereas it decreased with an increase in fluid rheology and liquid height. Scale-up effects on mass transfer were higher for water than viscous fluids, as suggested by large deviation (9.6%) in values of bubble–liquid mass transfer coefficient.

Data obtained from large eddy simulations of single-phase, turbulent flow of Newtonian and shear-thinning fluids in a baffled stirred tank reactor are considered to identify and characterize vortical structures. The identification proceeds through an objectivized Eulerian method, accounting for the inhomogeneities in the flow, which palliates some shortcomings of previous implementations. The characterization focuses on turbulent vortices larger than the dissipative scales and, to a lesser extent, on trailing and macro-instability vortices. The characterization performed through different statistical analyses includes aspects such as size, number density, shape, distribution and organization in space, and correlation with the kinetic energy due to turbulence and the periodic passage of the blades. To the authors' knowledge, some of these representative aspects have been rarely investigated or have not been addressed at all for the turbulent flow in a stirred vessel. The influence of changing the rotational speed of the tank and the rheology of the working fluid are explored as well. Finally, considering one-way coupling, some potential and practical implications for liquid–liquid and gas–liquid dispersed systems are briefly discussed.