Abstract
Accurate understanding of gas–liquid systems involving non-Newtonian fluids is essential for the design and optimization of processes such as biomethane production. In this work, a pilot-scale stirred tank was experimentally investigated to assess the influence of non-Newtonian rheology on power consumption and bubble dynamics under gassed conditions. The system consisted of a baffled cylindrical vessel (T = 0.48 m) equipped with a Rushton turbine, using air as the dispersed phase. Carboxymethyl cellulose (CMC) solutions at concentrations of 0.25% and 0.5% w/w were employed to simulate shear-thinning fluids representative of anaerobic digestion media. Rheological measurements confirmed pronounced shear-thinning behavior, with increasing consistency index and decreasing flow behavior index at higher polymer concentrations. Power consumption was significantly affected by fluid rheology, while gas injection led to a reduction in power number for both solutions. Surface tension values remained close to those of water, indicating a limited contribution of interfacial effects. Bubble size distributions, obtained through optical imaging and image analysis, showed a clear shift toward smaller and more uniform bubbles in CMC solutions compared to water. This behavior suggests that bubble breakup and coalescence are primarily governed by rheological properties rather than surface tension variations.
