Investigation of laminar flow in a stirred vessel at low Reynolds numbers
Investigation of laminar flow in a stirred vessel at low Reynolds numbers
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低雷诺数下搅拌容器中层流的研究
DOI：
10.1016/j.ces.2005.10.074
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发表时间：
2006
影响因子：
4.7
通讯作者：
M. Yianneskis
中科院分区：
文献类型：
--
作者：
M. Rice;J. Hall;G. Papadakis;M. Yianneskis
许多混合应用涉及粘性流体和层流，其中详细的以及整体的流动结构是重要的。为了了解低Re层流混合器内的流体动力学特性，对Rushton桨在Re为1、10和28时的诱导流动进行了实验和计算研究。有人发现，对于最高的Re，流动表现出熟悉的向外泵送行动与径向叶轮在湍流条件下。然而，随着Re减小，在一个叶轮旋转期间的净径向流减少，并且对于最低Re，观察到具有可忽略的净泵送的往复运动。这种行为在过去的文献中没有报道，从有效混合的角度来看，这是一种非常不理想的流型。CFD结果成功地再现了这种行为。为了阐明所观察到的流型的物理机制，在径向方向上作用在流体元件上的力进行了分析。分析表明，对于最低Re，叶尖附近径向速度的材料导数很小，因此压力和粘性力之间存在平衡，这是蠕动流的定义特征。速度和压力是同相的，因为速度由叶轮旋转产生的压力场驱动。基于这些发现，一个简化的分析模型的流量，提供了一个很好的定性和定量表示的流量。
Many mixing applications involve viscous fluids and laminar flows where the detailed as well as overall flow structures are important. In order to understand the fluid dynamic characteristics of low Re laminar flows in mixing vessels, the flow induced by a Rushton impeller for three Re namely, 1, 10 and 28, was studied both experimentally and computationally. It was found that for the highest Re, the flow exhibited the familiar outward pumping action associated with radial impellers under turbulent flow conditions. However, as the Re decreases, the net radial flow during one impeller revolution was reduced and for the lowest Re a reciprocating motion with negligible net pumping was observed. This behaviour has not been reported in the literature in the past and represents a highly undesirable flow pattern from the standpoint of effective mixing. The CFD results successfully reproduced this behaviour. In order to elucidate the physical mechanism responsible for the observed flow pattern, the forces acting on a fluid element in the radial direction were analysed. The analysis indicated that for the lowest Re, the material derivative of radial velocity near the blade tip is small thus a balance exists between pressure and viscous forces; the defining characteristic of creeping flow. The velocity and pressure forces are in phase because the velocity is driven by the pressure field generated by the rotation of the impeller. Based on these findings, a simplified analytic model of the flow was developed that gives a good qualitative as well as quantitative representation of the flow.