MECHANISM OF DETACHMENT OF COLLOIDAL PARTICLES FROM A FLAT SUBSTRATE IN A TURBULENT-FLOW
MECHANISM OF DETACHMENT OF COLLOIDAL PARTICLES FROM A FLAT SUBSTRATE IN A TURBULENT-FLOW
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DOI：
10.1016/0021-9797(73)90323-8
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发表时间：
1973-01-01
影响因子：
9.9
通讯作者：
YATES, B
中科院分区：
文献类型：
--
作者：
CLEAVER, JW;YATES, B
Visser [J. Colloid Interface Sci.34，26（1970）]使用了流体动力学技术，即，旋转圆柱体，以研究从各种基材上去除亚微米颗粒。他发展了经验关系，将附着力与颗粒所经历的粘性阻力联系起来，假设颗粒嵌入稳定的粘性子层中。虽然这种技术是一种有价值的实验工具，但它回避了粒子如何运动的问题。对湍流边界层的详细研究（在流体力学文献中有报道）表明，粘性子层是不稳定的，并且不断地被湍流“爆发”所破坏。这些爆发与微型龙卷风没有什么不同，可能会产生足以分离颗粒的瞬时升力。这种非定常子层模型已被用来预测可能的升力作用在颗粒上。这些现象可能是由脉冲运动引起的，也可能是由爆发在粒子上产生的准定常上升气流引起的。从这些预测的升力中，得到了一个去除准则，对于一个给定的流体，它简化为τω d ~（4/3）π常数，其中τω为壁面剪应力，τ为颗粒直径。这一结果与以往的实证研究基本一致。去除率可以通过结合升力的分析和关于爆发的大小和频率的文献数据来预测。虽然后者的信息是从管流和平板流动的研究，预测率是定性的协议与旋转仪器的实验数据。
Visser [J. Colloid Interface Sci.34, 26 (1970)] has used hydrodynamic techniques, i.e., rotating cylinders, to study the removal of submicron particles from various substrates. He developed empirical relationships which relate the force of adhesion to the viscous drag experienced by the particle, which is assumed to be embedded in a steady, viscous sublayer. Although this technique is a valuable experimental tool, the question of how a particle is moved is evaded.Detailed investigations of the turbulent boundary layer (reported in the fluid mechanics literature) have shown that the viscous sublayer is anything but steady, and is continually disrupted by turbulent “bursts.” These bursts, which are not unlike miniature tornados, may cause instantaneous lift forces sufficient to detach a particle. This model of an unsteady sublayer has been used to predict the possible lift forces acting on the particle. These can arise either from impulsive motions or from the generation of a quasi-steady updraft over a particle by a burst. From these predicted lift forces, a removal criterion is obtained which for a given fluid reduces toτωd4/3⩾ constant whereτωis wall shear stress anddis particle diameter. This result is shown to be in general agreement with previous empirical studies. The rate of removal can be predicted by combining this analysis of lift forces with literature data on the size and frequency of bursts. Although this latter information is taken from studies in pipe-flow and flow over a flat-plate, the predicted rates are in qualitative agreement with the experimental data from rotational instruments.