Investigating gas dispersion and solid suspension in a coaxial stirred tank containing non-Newtonian fluids using coupled tomography and pressure measurements

Three-phase agitated tanks are widely utilized across industries such as chemical processing, pharmaceuticals, wastewater treatment, and biotechnology, where precise control over gas, liquid, and solid phases is crucial for process efficiency. Despite their industrial significance, accurate quantification of local gas and solid holdups in such systems remains problematic, primarily due to the limitations of available visualization and measurement techniques. Although electrical resistance tomography (ERT) coupled with pressure measurements has shown efficacy in multiphase systems without rotating parts, its application in mechanically agitated tanks has not been reported. This study presents the first experimental integration of ERT with calibrated pressure measurements in a coaxial mixer containing non-Newtonian fluid, enabling localized quantification of gas and solid holdups under varying non-Newtonian fluid concentrations and evaluating both upward and downward pumping modes of the central impeller. Key findings show that upward pumping enhances solid suspension by promoting particle transport, while downward pumping improves gas dispersion by extending bubble residence time; moreover, liquid rheology strongly shapes holdups, highlighting the interplay between fluid properties and mixing dynamics. • ERT was integrated with calibrated pressure-drop measurements in a three-phase coaxial mixer to resolve local gas and solid holdups. • Solid suspension was enhanced by upward pumping, while gas dispersion was maximized by downward pumping. • Stronger non-Newtonian behavior led solids to suspend at higher speeds while reducing the amount of gas holdup. • Increasing the anchor impeller speed showed enhanced gas holdup in both pumping modes.