Bubble size and liquid-side mass transfer coefficient measurements in aerated stirred tank reactors with non-Newtonian liquids

Oxygen transfer is a key element in aerobic fermentations, especially if the culture broth's rheology is non-Newtonian, as in the case of cultures of filamentous fungi. Viscosity negatively affects the volumetric mass transfer coefficient (k(L)a), but mechanisms involved in terms of change of interfacial area (a) and liquid-side mass transfer coefficient (k(L)) have still not been clearly identified. This lack of knowledge is in part due to the difficulty in measuring bubble size in viscous fluids. In this study, an innovative technique was used to measure bubble Sauter diameter (d(32)) in water and in xanthan gum solutions. Additional experiments were carried out to obtain the volumetric mass transfer coefficient and the global gas holdup (alpha(G)). It was then possible to obtain the liquid-side mass transfer coefficient and to compare it with existing models. Finally, empirical correlations were proposed to estimate d(32), alpha(G), k(L)a and k(L) in a mechanically stirred tank. (C) 2019 Elsevier Ltd. All rights reserved.