Heterogeneous mixing characteristic of down-flush self-priming jet stirring impeller
In order to explore the mechanism of enhancing the rapid mixing of liquid-liquid heterogeneous materials by self-priming jet,the coupling model of SST k-ω turbulence model and Eulerian-Eulerian model was used to numerically simulate the oil-water mixing characteristics in a down-flush self-priming jet stirred tank.A comparative analysis was conducted on the effects of rotational speed,down-flush angle,and impeller diameter on the heterogeneous coefficient of variation and segregation strength.The mechanism of down-flush self-priming jet stirring impeller strengthening mixing was analyzed by the field synergy principle.The results indicated that the heterogeneous coefficient of variation divided the stirring process into three stages:initial oscillation,mid-term decline,and later stability.High speed,20°—30° down-flush angle,and the middle diameter of the stirring impeller effectively shortened the stirring duration of the initial and mid-term,accelerating oil-water mixing.The analysis of the phase holdup in the later stable flow field showed that a larger down-flush angle and the stirring impeller diameter resulted in uneven distribution of segregation strength along the axial and radial directions,forming a stable high oil or high water phase region.The study of the synergistic angle between velocity and concentration gradient on the longitudinal profile revealed the mechanism of enhanced mixing.The velocity difference in the jet pipe was smaller when the down-flush angle and the stirring impeller diameter were smaller.The synergistic angle of the self-priming region increased,and the oil phase accumulated.The down-flush jet impacted the wall when the angle and the diameter were relatively large.The velocity in the jet region rapidly decreased,and the synergistic angle near the wall increased,causing the water phase accumulated near the stirring shaft.In the engineering design of self-priming jet stirring impeller,the down-flush angle and the stirring impeller diameter should be reasonably set to ensure the flow space of self-priming and jet.
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