Dzwinel Witold, Yuen David A
AGH Institute of Computer Science, Al.Mickiewicza 30, Kraków, 30-059, Poland.
J Colloid Interface Sci. 2002 Mar 15;247(2):463-80. doi: 10.1006/jcis.2001.8109.
The dispersion of the agglomerating fluid process involving colloids has been investigated at the mesoscale level by a discrete particle approach--the hybrid fluid-particle model (FPM). Dynamical processes occurring in the granulation of colloidal agglomerate in solvents are severely influenced by coupling between the dispersed microstructures and the global flow. On the mesoscale this coupling is further exacerbated by thermal fluctuations, particle-particle interactions between colloidal beds, and hydrodynamic interactions between colloidal beds and the solvent. Using the method of FPM, we have tackled the problem of dispersion of a colloidal slab being accelerated in a long box filled with a fluid. Our results show that the average size of the agglomerated fragments decreases with increasing shearing rate gamma, according to the power law A x gamma(k), where k is around 2. For larger values of gamma, the mean size of the agglomerate S(avg) increases slowly with gamma from the collisions between the aggregates and the longitudinal stretching induced by the flow. The proportionality constant A increases exponentially with the scaling factor of the attractive forces acting between the colloidal particles. The value of A shows a rather weak dependence on the solvent viscosity. But A increases proportionally with the scaling factor of the colloid-solvent dissipative interactions. Similar type of dependence can be found for the mixing induced by Rayleigh-Taylor instabilities involving the colloidal agglomerate and the solvent. Three types of fragmentation structures can be identified, which are called rupture, erosion, and shatter. They generate very complex structures with multiresolution character. The aggregation of colloidal beds is formed by the collisions between aggregates, which are influenced by the flow or by the cohesive forces for small dispersion energies. These results may be applied to enhance our understanding concerning the nonlinear complex interaction occurring in mesoscopic flows such as blood flow in small vessels.
通过离散粒子方法——混合流体-粒子模型（FPM），在中尺度水平上研究了涉及胶体的团聚流体过程的分散情况。溶剂中胶体团聚体造粒过程中发生的动力学过程受到分散微结构与整体流动之间耦合的严重影响。在中尺度上，这种耦合会因热涨落、胶体床之间的颗粒-颗粒相互作用以及胶体床与溶剂之间的流体动力相互作用而进一步加剧。使用FPM方法，我们解决了在充满流体的长箱中加速的胶体平板的分散问题。我们的结果表明，团聚碎片的平均尺寸随着剪切速率γ的增加而减小，符合幂律A×γ(k)，其中k约为2。对于较大的γ值，团聚体的平均尺寸S(avg)随着γ的增加而缓慢增加，这是由于聚集体之间的碰撞以及流动引起的纵向拉伸。比例常数A随着胶体颗粒之间吸引力的缩放因子呈指数增加。A的值对溶剂粘度的依赖性相当弱。但A与胶体-溶剂耗散相互作用的缩放因子成比例增加。对于涉及胶体团聚体和溶剂的瑞利-泰勒不稳定性引起的混合，也可以发现类似的依赖关系。可以识别出三种类型的破碎结构，分别称为破裂、侵蚀和破碎。它们产生具有多分辨率特征的非常复杂的结构。胶体床的聚集是由聚集体之间的碰撞形成的，这些碰撞受到流动或小分散能量下的内聚力的影响。这些结果可能有助于增进我们对微观流动（如小血管中的血流）中发生的非线性复杂相互作用的理解。
