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

本研究以搅拌釜内流型的动态变化为研究对象，旨在从工程的角度建立一种精确控制混合和/或反应的方法。作为搅拌槽内二次循环流动的模型，研究了柱形和锥形Taylor涡流系统中的混合和颗粒扩散特性。在低雷诺数下，涡胞边界附近流动的流体轴向混合良好，而局限于涡核区域的流体单元与外部均匀流动区域的交换较差。泰勒涡流中也观察到了颗粒分级现象。在涡旋的外围区域可以观察到50~80μm的较大颗粒，而在涡核区域主要观察到20~50 mm的较小颗粒。将这些混合特性和颗粒分散特性结合起来，提出了一种新的颗粒分级装置。…更详细地说，在带有Rushton涡轮叶轮的传统搅拌容器中，当叶轮离底间隙C与槽内径T之比大于0.143(C/T&GT；0.143)时，排出的气流水平地朝向壁面，同时它分裂成上下运动的两股气流，产生两个涡流(双环模式)。另一方面，当C/T&GT；0.143时，由于科达效应，排出的水流向船底下移，然后继续向上移动，形成一个强烈的涡旋(单环型)。在低雷诺数下，没有观察到从单环型到双环型的随时间变化的流动状态。在以后的工作中，我们将尝试通过添加适当的扰动来产生过渡流状态。从反应控制的角度出发，对醋酸乙烯酯进行了连续乳液聚合。研究发现，由于耦合反应、混合和粒子聚集动力学的影响，乳胶粒子的粒度分布具有很大的时间周期振荡。本研究项目成功地开发了一个随机模型，该模型考虑了聚合反应和胶乳粒子聚集之间的竞争相互作用。较少

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