粘性颗粒稀相重力驱动气固流动中的颗粒诱导解团聚
Cluster-induced deagglomeration in dilute gravity-driven gas-solid flows of cohesive grains
摘要：
由于簇内颗粒的相对速度降低，通常认为簇会导致粘性颗粒之间的团聚增强。我们对重力驱动的粘性颗粒气固流动的离散粒子模拟显示出相反的趋势，揭示了一种新的机制，我们称之为“团簇诱导的解团聚”。“具体来说，我们研究了相对稀释的气固流，并将凝聚性来源的团聚体与系统中的整体不均匀性隔离开来，即，凝聚起源的聚集体和流体动力起源的簇。我们观察到增强的集群系统的大小增加（是规范的非凝聚力系统），以及减少团聚。减少的附聚被追踪到颗粒在团簇表面处的增加的碰撞冲击速度;即，更高水平的聚集导致聚集区域和非聚集区域之间更大的相对速度，从而作为颗粒温度的附加源。这一物理图像进一步证明了一个理论模型的基础上的生成和破碎率的团聚体之间的平衡。最后，集群诱导的解聚也提供了一个令人惊讶的饱和度的团聚水平在重力驱动的，气固系统的凝聚力水平的增加，而不是单调增加的行为中看到的自由发展或驱动的颗粒系统在没有重力的解释。也就是说，更高的凝聚力导致更多的能量耗散，这与竞争效应有关：增强的凝聚和增强的集群，后者导致更多的集群诱导的解凝聚。
英文摘要：
Clustering is often presumed to lead to enhanced agglomeration between cohesive grains due to the reduced relative velocities of particles within a cluster. Our discrete-particle simulations on gravity-driven, gas-solid flows of cohesive grains exhibit the opposite trend, revealing a new mechanism we coin "cluster-induced deagglomeration." Specifically, we examine relatively dilute gas-solid flows and isolate agglomerates of cohesive origin from overall heterogeneities in the system, i.e., agglomerates of cohesive origin and clusters of hydrodynamic origin. We observe enhanced clustering with an increasing system size (as is the norm for noncohesive systems) as well as reduced agglomeration. The reduced agglomeration is traced to the increased collisional impact velocities of particles at the surface of a cluster; i.e., higher levels of clustering lead to larger relative velocities between the clustered and nonclustered regions, thereby serving as an additional source of granular temperature. This physical picture is further evidenced by a theoretical model based on a balance between the generation and breakage rates of agglomerates. Finally, cluster-induced deagglomeration also provides an explanation for a surprising saturation of agglomeration levels in gravity-driven, gas-solid systems with increasing levels of cohesion, as opposed to the monotonically increasing behavior seen in free-evolving or driven granular systems in the absence of gravity. Namely, higher cohesion leads to more energy dissipation, which is associated with competing effects: enhanced agglomeration and enhanced clustering, the latter of which results in more cluster-induced deagglomeration.
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