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.
The laminar chaotic flow and mixing performance of a high-viscosity fluid in Lightnin static mixers (LSM) was numerically investigated via a Lagrangian particle method based on the Particle tracking technique in the range of Re=0.1−100. The numerical results of Z factor have a good agreement with the reported data from the literature. With the increase of Re in LSM, the Darcy friction coefficient values decrease and the product of fD · Re linearly increases. With the same aspect ratio (Ar), the product of fD · Re in LSM is higher by 36−57 % than that of KSM. The distribution evolution of circular group of massless particles is successfully investigated by particle distribution uniformity (PDU) in the first few mixing elements. A new ideal distribution model is proposed for structure radius (SR) which is successfully used to investigate uniform distribution of mixing process in the last few elements. The effects of Re and Ar of mixing elements on dispersive mixing performance are characterized by extensional efficiency and stretching rate. The logarithms of geometrical average stretching rate of massless particles increase linearly with the number of mixing elements. The stretching rate in LSM with Ar=1, 1.5, 2 is average higher by 45.91 %, 36.05 % and 24.32 % than that of KSM with Ar=1.5. As far as the creeping flow in LSM is concerned, the logarithm values of stretching rate are independent of Re and Ar. The mixing performance factor η is proposed to evaluate the enhancement mechanism of mixing performance based on the energy consumption. The η increases with the increasing Re and decreasing Ar. The profiles of η indicate that the mixing enhancement ability of LSM is better than that of KSM.
The circulating jet tank (CJT) has been an alternative piece of equipment for mixing instead of the bottom-stirring tank, which is widely used in industrial applications. The recurrence plots (RPs) and recurrence quantification analysis (RQA) of pressure fluctuation signals (PFS) in the novel CJT were employed to reflect the chaotic extent of jet mixing. The recurrence rate, determinism and averaged diagonal line length of PFS were evaluated at different Reynolds numbers, radial positions and axial positions. The profiles of recurrence rate, determinism and averaged diagonal line length had similar tendency with the increasing Re, which showed that the determinism of PFS increased and the randomness of the chaotic system became small. With the increase in z/H, the recurrence characteristics of PFS at θ m = π/6 gradually increased, which were smaller than that of other θ m . The results of this study provide a deep understanding of the hydrodynamics in the CJT, and thus lay a foundation for further design optimization.
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