Collision Frequencies between Fractal Aggregates and Small Particles in a Turbulently Sheared Fluid
Collision Frequencies between Fractal Aggregates and Small Particles in a Turbulently Sheared Fluid
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DOI：
10.1021/es960772o
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发表时间：
1997-03
影响因子：
11.4
通讯作者：
Xiao-yan Li;B. Logan
中科院分区：
文献类型：
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作者：
Xiao-yan Li;B. Logan
将胶乳微球（2.85 μm）在搅拌釜中混凝，得到分形维数分别为1.89±0.06、2.21±0.06和2.47±0.10的三组聚集体。在桨状搅拌器的湍流剪切环境中，测量了这些分形聚集体（200 ~ 1000 μm）和小颗粒（1.48 μm）在平均剪切速率为2.1、7.3和14.7 s-1时的碰撞率。碰撞频率比曲线模型预测的高5个数量级，比直线模型预测的低2个数量级。碰撞频率比曲线碰撞核预测的要高得多，这归因于通过分形聚集体内部的大量流动。流体剪切速率(G)和聚集体分形维数(D)影响分形聚集体与小颗粒碰撞频率函数（β），产生β ~ g1 -0.33 3d。根据这一关系，当D→0时，聚集体变得无限多孔，β b…
Three groups of aggregates with fractal dimensions of 1.89 ± 0.06, 2.21 ± 0.06, and 2.47 ± 0.10 were generated by coagulation of latex microspheres (2.85 μm) in a Jar-test (paddle-mixing) device. The collision rates between these fractal aggregates (200−1000 μm) and small (1.48 μm) particles were measured in the turbulent shear environ ment of the paddle mixer at mean shear rates of 2.1, 7.3, and 14.7 s-1. Collision frequencies were 5 orders of magnitude higher than predicted by a curvilinear model but 2 orders of magnitude lower than predicted by a rectilinear model. Collision frequencies much higher than predicted by the curvilinear collision kernel were attributed to significant flow through the interior of the fractal aggregates. The fluid shear rate (G) and the aggregate fractal dimension (D) affected the collision frequency function (β) between fractal aggregates and small particles, resulting in β ∼ G1-0.33D. According to this relationship, as D → 0, the ag gregates become infinitely porous and β b...