Origin of disturbances in cocurrent gas‐liquid packed bed flows
Origin of disturbances in cocurrent gas‐liquid packed bed flows
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DOI：
10.1002/aic.690410706
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发表时间：
1995-07
期刊：
影响因子：
3.7
通讯作者：
D. Krieg;J. A. Helwick;P. Dillon;M. McCready
中科院分区：
文献类型：
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作者：
D. Krieg;J. A. Helwick;P. Dillon;M. McCready
采用视觉、视频、压力和电导技术研究了垂直和水平柱充填床中共流的时变扰动。我们发现，在以往的研究中所定义的涓流脉冲跃迁，对应于行扰动最终变得可测量的条件，而不是无穷小扰动开始增长的条件。观察表明，即使液体和气体最初均匀分布，在短距离后也会形成高于或低于平均含液率的分离垂直流动区域。旨在研究不同含液率区域如何相互作用的水平填充床实验表明，第一类干扰是气体渗入液体区域。一个简单的模型表明，如果压降超过推动气体通过充满液体的孔隙所必需的值，就会发生渗透。一旦渗透足够显著，形成第三个“气泡”阶段，行波不稳定性就会形成，如果有足够的柱长，行波不稳定性就会发展成脉冲。采用三层开尔文-亥姆霍兹稳定性模型来解释水平流动中扰动的增长。对河床中小规模事件的视频观测未能发现不同区域之间的显著相关性。因此，只要考虑到分离区域的存在，就有可能用体积平均方程来描述这些系统中的流动行为。柱的直径或厚度对扰动的频率有显著影响。
Visual, video, pressure, and conductance techniques were used to study time-varying disturbances in cocurrent flow in packed beds with vertical and horizontal columns. It is found that the trickle-pulse transition, as defined in previous studies, corresponds to conditions where traveling disturbances finaly become measurable, not the conditions at which infinitesimal disturbances begin to grow. Observations demonstrate that even if the liquid and gas are uniformly distributed initially, segregated, vertical flowing regions with higher or lower than average liquid holdup form after a short distance. Horizontal packed bed experiments, designed to study how regions of differing liquid holdup interact, indicate that the first type of disturbance is infiltration of gas into the liquid region. A simple model suggests that infiltration occurs if the pressure drop exceeds a value necessary to push gas through liquid-filled pores. Once infiltration is significant enough to form a third “bubbly” phase, traveling wave instabilities form and grow into pulses if sufficient column length is available. A three-layer Kelving-Helmholtz stability model is used to interpret the growth of disturbances in horizontal flows. Video obeservations of small-scale events in the bed failed to detect significant correlations between different regions. Thus it should be possible to describe flow behaviour in these systems with volum-averaged equations, as long as the presence of segregated regions is considered. Column diameter or thickness significantly affects the frequency of disturbances.