Analysis of Scale-Up and Characterization of the Volumetric Mass Transfer Coefficient for Gas Dispersion in Yield-Pseudoplastic Fluids Using a Coaxial Mixer

Aerated mixing operations rely on the efficient distribution of the gas phase throughout the liquid, which is particularly important for many industrial processes. In this regard, coaxial mixers have been extensively investigated as energy-efficient mixing systems for complex fluids. This study addresses the challenging and unexplored analysis of scale-up on the aerated mixing performance of coaxial mixers containing yield-pseudoplastic fluids. It provides pilot-scale experimental data and proposes a modeling approach using computational fluid dynamics (CFD) and population balance equations. A coaxial mixing system furnished with an anchor and a pitched blade turbine (PBT) impeller containing 1 wt % xanthan gum solution was investigated on two mixing scales (50 and 170 L). The CFD simulations were verified against experimental data on power consumption, gas holdup, and volumetric mass transfer coefficient. Analysis of fluid flow and local performance parameters revealed a nonmonotonic effect of PBT speed on mixing performance. Additionally, the numerical simulations enabled us to evaluate the scale-up effect when maintaining a constant speed and volume of air per volume of liquid per minute (vvm). The findings demonstrated an enhancement in mass transfer parameters due to intensified flow patterns, although a significant increase in power consumption reduced the overall process efficiency. In fact, validated CFD simulations demonstrate potential for evaluating larger mixing scales, enhancing mixing performance, and verifying scale-up strategies prior to their implementation.