Break-Up of Aerosol Agglomerates in Highly Turbulent Gas Flow
Break-Up of Aerosol Agglomerates in Highly Turbulent Gas Flow
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DOI：
10.1007/s10494-012-9398-8
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发表时间：
2012-05
期刊：
影响因子：
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通讯作者：
Y. Ammar;A. Dehbi;M. Reeks
中科院分区：
文献类型：
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作者：
Y. Ammar;A. Dehbi;M. Reeks
紊流中的团块气溶胶可能受到非常高的湍流剪切率，通过产生升力和阻力可以克服将团块成分结合在一起的粘附力并导致其破裂。本文分析了0.1 ~ 10 μm大小的团聚体在湍流管流中破裂的实验测量结果，随后是雷诺数为105 ~ 107的膨胀区。分析表明，即使在壁面有界的湍流中，高湍流剪应力与小尺度的核心湍流相关，在壁面撞击可能发生的任何破裂之前，可能是破裂的主要来源。更重要的是，从这些结果中获得了高湍流中团聚体输运和破碎的一般动力学方程（GDE）的计算快速和有效的解。此外，气溶胶粒径分布演变的解与实验结果一致。在紊流管流段，团聚体连续暴露于紊流剪切应力下，经历了比膨胀区（跟随管流）更长的破裂时间，膨胀区暴露时间短得多，在非常高的局部湍流剪切应力作用下，团聚体瞬间发生破裂。考虑了模型中某些近似的有效性。特别是，最小颗粒的斯托克斯数为0.001,10 μm颗粒的斯托克斯数为10，团块的惯性和湍流剪切应力的波动是模型中未考虑的重要物理现象。
Agglomerate aerosols in a turbulent flow may be subjected to very high turbulent shear rates which through the generation of lift and drag can overcome the adhesive forces binding the constituents of an agglomerate together and cause it to break-up. This paper presents an analysis of the experimental measurements of the breakup of agglomerates between 0.1–10 μm in size, in a turbulent pipe flow followed by an expansion zone with a Reynolds numbers in the range 105to 107. The analysis shows that even in wall bounded turbulence, the high turbulent shear stresses associated with the small scales of turbulence in the core can be the main source of breakup preceding any break-up that may occur by impaction at the wall. More importantly from these results, a computationally fast and efficient solution is obtained for the General Dynamic Equation (GDE) for agglomerate transport and breakup in highly turbulent flow. Furthermore the solution for the evolution of the aerosol size distribution is consistent with the experimental results. In the turbulent pipe flow section, the agglomerates are exposed continuously to turbulent shear stresses and experience more longer term breakup than in the expansion zone (following the pipe flow) where the exposure time is much less and break-up occurs instantaneously under the action of very high local turbulent shear stresses. The validity of certain approximations made in the model is considered. In particular, the inertia of the agglomerates characterised by a Stokes Number from 0.001 for the smallest particles up to 10 for 10 μm particles and the fluctuations of the turbulent shear stresses are important physical phenomena which are not accounted for in the model.