Application of hydrodynamic lubrication in discrete element method (DEM) simulations of wet bead milling chambers
Application of hydrodynamic lubrication in discrete element method (DEM) simulations of wet bead milling chambers
复制标题
DOI：
10.1016/j.powtec.2021.01.071
复制
发表时间：
2021-03-06
影响因子：
5.2
通讯作者：
Ness, Christopher
中科院分区：
文献类型：
--
作者：
Cabiscol, Ramon;Jansen, Tom;Ness, Christopher
湿式搅拌介质磨粉是许多工业生产过程中的关键工序。在湿磨过程中，磨珠（通常为毫米级）在快速搅拌下相互碰撞。这些碰撞将能量转移到周围的介质中，这是一种由预混浆（微米级颗粒的悬浮液）组成的进料流，导致颗粒尺寸减小。数值模拟通过模拟研磨介质、搅拌器速度和浆料流变对破碎的影响，提供了一个获得机理洞察力的机会。湿式磨粉的多相特性需要考虑固体磨珠和浆料给料的模型。现有的流体-颗粒耦合方法原则上能够做到这一点，但由于需要解决近接触珠粒之间的大流体动力润滑力，因此需要极高的流场分辨率，从而导致模拟尺寸和成本的增加。为了解决这一挑战，提出了一种实验室规模磨机的离散元法（DEM）模拟，其中磨头-磨头相互作用除了摩擦接触力外，还包括双流体动力润滑。该模型以一种简化但物理动机良好的方式解释了多相效应，避免了完全流体分辨模型的计算成本。提出了针对实验室磨机的系统模型校准，然后该模型提供了在整个转速范围内和考虑饲料粘度的经验功率消耗的良好估计。在极端粘度条件下，研究了能量耗散模式的差异和沿磨室碰撞的局部分布，揭示了大部分能量耗散是由于切向作用的颗粒间力（剪切和滚动），而依赖于自由流动和颗粒间迁移的高能碰撞（冲击和扭转）相对不重要。(C) 2021 Elsevier B.V.版权所有
Fine grinding in wet stirred mediamills is a key operation in numerous industrial processes. During wet milling, grinding beads (typically millimetre scale) collide with each other under rapid agitation. These collisions transfer energy into the surrounding medium, a feed stream comprising a premixed slurry (a suspension of micron-sized particles), leading to a reduced particle size. Numerical simulation provides an opportunity to gain mechanistic insight by modelling the influences of grinding media, agitator speed and slurry rheology on the breakage. The multiphase nature of wet milling necessitates models that account for both the solid grinding beads and the slurry feed. Established fluid-particle coupled methods are in principle capable of doing this, but the need to resolve the large hydrodynamic lubrication forces between near-contacting beads demands extremely high fluid field resolution, leading to proliferating simulation size and cost. To address this challenge, a Discrete Element Method (DEM) simulation for a lab scale mill is presented in which the bead-bead interaction includes pairwise hydrodynamic lubrication in addition to frictional contact forces. The model accounts for multiphase effects in a simplified yet physically well-motivated way, circumventing the computational cost of a fully fluid-resolved model. A systematic model calibration against the laboratory mill is presented, and thereafter the model provides a good estimation for the empirical power draw across the full range of rotation speeds and considered feed viscosities. The differences in energy dissipation modes and the local distribution of collisions along the mill chamber are examined for the extreme viscosity condition, revealing that most energy dissipation is due to inter-particle forces acting tangentially (shearing and rolling) while highly energetic collisions (impact and torsion), relying on free flows and inter-bead mobility, are relatively unimportant. (C) 2021 Elsevier B.V. All rights reserved.