The flow performance of a high-viscosity fluid in novel static mixers with multitwisted leaves was investigated numerically in the range of Re = 0.1−150. The effects of mixing-segment construction, Reynolds number, and aspect ratio on the chaotic mixing characteristics of different static mixers were evaluated based on the Lagrangian tracking method. The tracer particle distributions, G values, extensional efficiency characteristics, and stretching fields were used to evaluate the dispersion and distribution mixing performances in the new static mixers. Compared with the Kenics static mixer (KSM), the static mixers with three twisted leaves (TKSM) and four twisted leaves (FKSM) achieved chaotic mixing status much earlier and could also maintain this status by successive mixing-element groups. In contrast, there were large unmixed zones in the static mixer with double twisted leaves (DKSM). Stretching rates calculated from pathlines were found to be in good agreement with results reported in the literature. The particle trajectories revealed that the logarithm of the stretching rate increased linearly with the dimensionless axial length. For a given length of static mixer, a decrease in aspect ratio benefited an increasing stretching rate. When the number of multitwisted leaves in the cross section was greater than 2, the range of the probability density curve became larger than that of the KSM. All of the static mixers were found to have small groups of material points experiencing very high stretching. The TKSM and FKSM were found to have higher mixing efficiencies than the KSM, whereas the DKSM exhibited a worse micromixing ability.
The distinction of chaotic advection and mixing of high‐viscosity fluids in tubes equipped with four different twisted tapes, including KSM, MSM, RSM, and SSM, were evaluated by Lagrangian simulation. ∼23 550 massless particle tracers marked by red and black colours were respectively released in the semicircle and concentric circles of the inlet cross‐section. Mixing performance was evaluated qualitatively by tracking Poincaré sections, and quantitatively by the variation coefficient as a function of axial position. Poincaré sections of tracers showed that KSM had the best mixing performance and RSM had two oval‐shaped segregated areas which periodically moved clockwise 90° in the cross‐sections of adjacent twisted tapes. Extensional efficiencies were computed radially and axially for all configurations. Both results showed that large dispersive mixing areas existed in the transition section. At the beginning of the first and end of the last element, the largest extensional efficiencies emerged, which were 1.07−1.21 times that at the transitions. The profiles of stretching rate showed that RSM tape had the weakest micro‐mixing ability, and the other three mixers had nearly identical stretching rates, much higher than RSM for Re < 10. With increasing Re, the mixing performance of MSM decreased first and then increased to be slightly higher than that of RSM. The secondary flows at transition regions were largely weakened for the different twist direction in the MSM. The respective roles of flow reversal and twist direction on mixing were evaluated with the stretching rates between static mixers and conventional stirred vessels.
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