Investigation on the Chaotic Mixing Mechanism of High-Viscosity Fluids with Laminar Flow in an Irregular Impeller Stirred Tank

In this work, an impeller with a fractal structure design was introduced in the laminar mixing of high-viscosity fluids to facilitate chaotic advection. Power consumption characteristics, mixing time, Kolmogorov entropy, and 0–1 test were applied to characterize the mixing performance and chaotic mixing characteristics. Visualization experiment, Poincaré section, and trajectories of massless particles were employed to investigate the structure of the flow field. The findings showed that the fractal structure design introduced in the impeller blades provided a reduction in power consumption, power number, and mixing time and an improvement in the Kolmogorov entropy and chaotic mixing degree, while additional energy conservation, less mixing time, and a higher chaotic mixing degree were achieved by increasing the fractal iteration number in the impeller blades. Poincaré section showed the isolated mixing regions (IMRs) and chaotic mixing regions (CMRs) in the flow field, and the phenomenon can also be confirmed by visualization experiment. The particles within the IMRs did not undergo material exchange but rather exhibited movement solely within the designated regions. In addition, the trajectories of massless particles suggested that the fractal structure design of impeller blades facilitated structural instability of the IMRs, stimulated fluid particles to escape from the IMRs into the CMRs, and induced chaotic advection in the flow field.