Abstract:

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.

Key words: self-priming jet, stirring impeller, heterogeneous, mixing characteristic, field synergy principle

摘要：

为了探究自吸射流强化液-液非均相物料快速混合机理，利用SST k-ω湍流模型与Eulerian-Eulerain多相流模型耦合，数值模拟研究了下冲式自吸射流搅拌槽内油水混合特性。对比分析了转速、下冲角和搅拌桨直径对非均相变异系数和离析强度的影响，运用场协同理论深入剖析了下冲式自吸射流搅拌桨强化混合机理。结果表明，非均相变异系数将搅拌过程分为初期振荡、中期下降和后期稳定三个阶段，高转速、20°~30°下冲角、搅拌桨直径居中均有效缩短了搅拌初期和中期的时长，加速了油水混合。对后期稳定流场相含率分析表明，较大的下冲角和搅拌桨直径导致离析强度沿轴向和径向分布不均匀，形成稳定的高油相和高水相区域。对纵剖面上速度与浓度梯度之间的场协同角进行了分析：下冲角和搅拌桨直径较小，射流管速度差较小，搅拌轴附近自吸区域场协同角增大，油相聚集；下冲角和搅拌桨直径较大，下冲射流冲击壁面，射流区域速度迅速下降，近壁面场协同角增大，水相在搅拌轴附近聚集。自吸射流搅拌桨在工程设计中应合理设置下冲角和搅拌桨直径，保障自吸和射流的流动空间。

关键词: 自吸射流, 搅拌桨, 非均相, 混合特性, 场协同