Micromixing characteristics in a gas–liquid–solid stirred tank with settling particles

The parallel-competing iodide–iodate reaction scheme was used to study the micromixing performance in a multi-phase stirred tank of 0.3 m diameter. The impeller combination consisted of a half elliptical blade disk turbine below two down-pimping wide-blade hydrofoils, identified as HEDT + 2WHD. Nitrogen and glass beads of 100 μm diameter and density 2500 kg·m− 3 were used as the dispersed phases. The micromixing could be improved by sparging gas because of its additional potential energy. Also, micromixing could be improved by the solid particles with high kinetic energy near the impeller tip. In a gas–solid–liquid system, the gas–liquid film vibration with damping, due to the frequent collisions between the bubbles and particles, led to the decrease of the turbulence level in the liquid and caused eventually the deterioration of the micromixing. A Damping Film Dissipation model is formulated to shed light on the above micromixing performances. At last, the micromixing time tm according to the incorporation model varied from 1.9 ms to 6.7 ms in our experiments.

Graphical AbstractIn a gas–solid–liquid system, the gas–liquid film vibration with damping, caused by the collisions between bubbles and particles, leads to the decrease of the turbulence level in the liquid. The higher the solid concentration or the gas flow rate, the lower the turbulence level in the liquid. The Damping Film Dissipation (DFD) model is proposed to describe the energy dissipation mechanism in the process of collisions between bubbles and particles.Figure optionsDownload as PowerPoint slide