Fractal theory provides a new strategy for the equipment design and industrial amplification. In this work we propose a novel H-like fractal (HLF) impeller to improve the distribution uniformity of hydrodynamics in stirred tanks. The impeller with two vertical blades becomes fractal impellers by designing each vertical blade as an H-shaped sub-blade (HLF-1) or uniform arrangement of H-shaped sub-blades (HLF-2). Flow characteristics including velocity and turbulent kinetic energy (TKE) distributions, vortices, power number, are predicted by large eddy simulation. Compared with Rushton turbine (RT) impeller when H/T=1 (or dual RTs when H/T=1.5, triple RTs when H/T=2), the HLF impeller can produce a flow field with more uniform distributions of larger velocities and TKE level. The HLF-2 impeller can further improve distribution uniformity of hydrodynamics in the case of high H/T. Power analysis shows that this is mainly due to the improved energy utilization efficiency by the fractal structure design.

This work aims to study the gas phase hydrodynamics in a stirred tank with a surface-aerated long-short blades agitator by the Eulerian‒Eulerian approach coupled with population balance model. Predicted local gas holdup and bubble size distribution agree well with those measured by a conductivity probe technique. The predictions demonstrate that the pressure depression in the center is the main driving force for gas suction and the downward flow carries the bubbles down to redistribute in the whole tank. The gas phase has higher gas holdup with large bubble size in the upper part and lower gas holdup but with small bubble size in the lower part of the tank. The predicted gas-liquid mass transfer coefficients agree well with our previous experimental results and just depends on the power consumption per unit volume when the aspect ratio of the liquid height to the tank diameter varies from 1.1 to 2.0.