Numerical study on rheological properties for dispersed and aggregated particle systems
Numerical study on rheological properties for dispersed and aggregated particle systems
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DOI：
10.1016/j.powtec.2019.09.041
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发表时间：
2020-02
影响因子：
5.2
通讯作者：
Hirotake Udono;K. Uruga;T. Tsukada;M. Sakai
中科院分区：
文献类型：
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作者：
Hirotake Udono;K. Uruga;T. Tsukada;M. Sakai
胶体悬浮液的剪切稀化行为是剪切引起的集合体结构变化的直接结果。本研究数值模拟了具有紧密堆积和中空结构的球形颗粒聚集体的剪切变形，以评估其对散体悬浮液的流变性影响。通过离散单元法(DEM)与直接数值模拟(DNS)相结合的方法来执行模拟，这里将其称为“DEM-DNS方法”。该方法可以结合颗粒与流体的双向相互作用，同时计算颗粒间的粘附力和接触力。颗粒间的粘附力和接触力对颗粒的破碎起着至关重要的作用。模拟结果表明，两种集料的弱剪切悬浮液在不发生结构重排的情况下，产生相同的剪切粘度。相反，在强剪切作用下，两种集料都发生了不可逆的破碎，中空集料的悬浮液表现出比紧密堆积的集料更大的剪切稀化。剪切稀化中的这种分叉表明了经常遇到的大剪切稀化背后的机制：剪切诱导的集合体的破裂使困在集合体内的流体得以释放，从而显著降低了固相的表观体积分数。因此，我们证明了DEM-DNS方法对于实验上无法实现的集合体剪切变形与宏观粘度评估的关联的复杂能力。
Shear thinning behavior of colloidal suspensions is a direct consequence of shear-induced structural variation of aggregates. This study numerically simulates the shear-induced deformation of spherical aggregates of particles with close-packed and hollowed-out structures to evaluate its rheological effects on the bulk suspension. Simulations are performed by the discrete element method (DEM) coupled with direct numerical simulation (DNS), herein referred to as the “DEM–DNS method.” This method can be used to simultaneously evaluate adhesive force and contact force acting on particles, which play an essential role in aggregate breakup, combined with the two-way particle–fluid interaction. The simulations show that the weakly sheared suspensions for both aggregates, subjected to no structural rearrangement, yield the same shear viscosity. In contrast, under strong shear where both aggregates undergo an irreversible breakup, the suspension of the hollow aggregate shows greater shear thinning than that of the close-packed aggregate. This bifurcation in shear thinning suggests the mechanism underlying the oft-encountered large shear thinning: the shear-induced breakup of aggregates enables a release of the fluid caged inside the aggregates and thus a substantial decrease in the apparent volume fraction of the solid phase. We thereby demonstrate the sophisticated capacity of the DEM–DNS method for experimentally unachievable correlation of shear-induced deformation of aggregates with a macroscopic viscosity evaluation.