Establishment of a Method for Precisely Controlling Mixing/Reaction in Stirred Vessels Utilizing Dynamic Changes of Flow Patterns

本研究项目主要研究搅拌容器中流动模式的动态变化，旨在从工程角度建立一种利用这些现象精确控制混合和/或反应的方法。以圆柱形和圆锥形泰勒涡流系统为模型，研究了搅拌槽内二次循环流动的混合和颗粒分散特性。在低雷诺数下，涡胞边界附近的流体轴向混合较好，而涡核区域的流体元与外部混合较好的流动区域的交换较差。在泰勒涡流中也观察到了颗粒分级现象。大颗粒主要分布在涡旋的外围区域，粒径在50 ~ 80 μm之间;小颗粒主要分布在涡旋的核心区域，粒径在20 ~ 50 μ m之间。我们提出了一种新的颗粒分类装置，结合这些混合和颗粒分散特性。 ...更多信息 在传统的Rushton涡轮机搅拌槽中，当叶轮离底间隙C与槽内径T之比大于0.143（C/T>0.143）时，出料流水平地流向槽壁，并在槽壁分裂成上下两股流，产生两个旋涡（双环流型）。而当C/T>0.143时，由于Coinda效应，排流沿槽底向下运动，然后继续向上运动，形成一个强的旋涡（单圈型）。在低雷诺数下，没有观察到从单回路到双回路的随时间变化的过渡流态。在未来的工作中，我们将尝试通过添加适当的微扰来产生过渡流态。从反应控制的观点出发，进行了醋酸乙烯酯的连续乳液聚合。研究发现，由于耦合反应、混合和粒子聚集动力学的影响，乳胶粒子的粒径分布以很大的时间周期振荡。本研究计画成功发展了一个考虑聚合反应与乳胶粒子聚集间竞争性交互作用的随机模型。少

This research project focused on dynamic changes of flow patterns in stirred vessels and aimed to establish of a method for precisely controlling mixing and/or reaction utilizing these phenomena from engineering aspect. Characteristics of mixing and particle dispersion in cylindrical and Conical Taylor vortex flow systems were investigated as a model for secondary circulating flow in a stirred vessel. At low Reynolds numbers, the fluid flowing near the vortex cell boundary was axially well-mixed, while the fluid element confined to the vortex core region poorly exchanged with the outer well-mixed flow region. Particle classification phenomena were also observed in Taylor vortex flow. The larger particle ranging from 50 to 80 μm could be seen in the outer region of vortex, while the smaller particles ranging from 20 to 50 mm were mainly observed in the vortex core region. We proposed a new particle classification device by combining these mixing and particle dispersion characteristics. … More In a conventional stirred vessel with Rushton turbine impeller, When the ratio of the impeller off-bottom clearance, C, to the tank inner diameter, T, is larger than 0.143 (C/T>0.143), the discharged stream was directed horizontally towards the walls whre it split into two streams that moved upwards and downwards generating two vortices (a double-loop pattrn). On the other hand, when C/T>0.143, the discharged stream moved downwards the bottom of vessel owing to the Coinda effect and then continued upwards to generate a strong vortex (a single-loop pattern). No transitional time-dependent flow state from a single to double-loop pattern could be seen at low Reynolds numbers. In future work, we will try to produce the transitional flow state by adding an appropriate perturbation. From the viewpoint of reaction control, continuous emulsion polymerization of vinyl acetate was conducted. It has been found that particle size distribution of latex particles oscillates with a very large time period owing to the effect of coupling reaction, mixing and particle aggregation dynamics. This research project successfully developed a stochastic model which considers the competitive interaction between polymerization reaction and aggregation of latex particles. Less