Computational analysis of regular and chaotic mixing in a stirred tank reactor
Computational analysis of regular and chaotic mixing in a stirred tank reactor
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DOI：
10.1016/s0009-2509(00)00407-3
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发表时间：
2001-08
影响因子：
4.7
通讯作者：
David J. Lamberto;M. Álvarez;F. Muzzio
中科院分区：
文献类型：
--
作者：
David J. Lamberto;M. Álvarez;F. Muzzio
对装有六叶径向流搅拌器的无挡板搅拌槽内的混合进行了计算研究。结果表明，叶轮恒速时产生的流动部分是混沌的。在这些条件下，位于分离环状区的流体元件所经历的拉伸以规则(非混沌)流动的线性速率特征缓慢增加。在主体流动区域内，由于流动是混沌的，拉伸以预期的指数速率增加。动态流动扰动的使用增强了混合；当应用依赖于时间的RPM时，产生了全局混沌流动。我们通过计算研究了搅拌速度在两个稳定值之间振荡时对协议混合性能的影响。比较了不同的变速频率和几种转速设置。在可变RPM方案下，分离的Torii被周期性地重新定位，流体元素有机会放弃规则区域。在这些条件下，拉伸在整个流动区域内呈指数增加。一般来说，速度波动频率较高的混合方案会产生最大的拉伸速率增长。与直觉相反的是，在给定的RPM波动频率下，较低的RPM设置的拉伸速率更高，无论是每转还是每单位消耗的能量。
Mixing in an unbaffled stirred tank equipped with a 6-blade radial flow impeller is examined computationally. Results demonstrate that the flow generated by constant impeller speed is partially chaotic. Under these conditions, the stretching experienced by fluid elements located within segregated toroidal regions of the flow increases slowly at a linear rate characteristic of regular (non-chaotic) flows. Within the bulk flow region, since the flow is chaotic, stretching increases at the expected exponential rate. The use of dynamic flow perturbations enhances mixing; when time-dependent RPM are applied, a globally chaotic flow is generated. We investigate computationally the effect on mixing performance of protocols in which the agitation speed oscillates between two steady values. Different frequencies of speed change and several RPM settings are compared. Under variable RPM schemes, the segregated torii are periodically relocated and fluid elements have the opportunity to abandon the regular regions. Under these conditions stretching increases exponentially throughout the entire flow domain. In general, mixing protocols with higher frequency of speed fluctuation produce the largest increase in stretching rates. Counter-intuitively, at a given RPM fluctuation frequency, stretching rates were higher for the lower RPM settings, either per revolutions or per unit of energy spent.