离散单元法（DEM）在颗粒流动混合过程模拟中的应用

发布时间：2018-04-15 18:01

本文选题：离散单元法 + 颗粒流　；参考：《中国科学院大学(中国科学院过程工程研究所)》2017年博士论文

【摘要】：离散单元法(Discrete element method,DEM)是颗粒流模拟的主流方法,并且能够适应不同颗粒物性以及设备操作条件。但DEM方法本身存在计算量巨大、模拟时间过长等问题,因而难以针对工业规模的设备进行颗粒流动混合过程的模拟。为了克服此困难,本论文在前人工作基础上拓展并优化了基于多尺度异构超级计算系统的高效大规模离散单元模拟方法和程序,实现了胶囊和圆柱等非球形颗粒的模拟,并以此考察了滚筒混合器以及料斗内颗粒物性对其流动混合性能的影响,加深了对相应设备中颗粒流动混合机理的认识。论文研究表明在水平滚筒内采用交错抄板能够促进颗粒的径向抛洒和沿抄板的轴向导流。对所研究的滚筒,在最优抄板结构下,其轴向混合效率分别为无抄板滚筒和全抄板滚筒的16倍和5倍。模拟还表明该效应对不同颗粒物性(粒径、形状、密度和摩擦系数)和滚筒尺寸均存在,预示了其广泛的应用前景。论文研究还表明,滚筒内胶囊颗粒的形状能够影响其堆积密度和空间取向,从而影响其混合性能。而在所考察的物性范围内,颗粒密度对偏析结构的影响较形状更为显著。利用颗粒形状与密度的共同作用可进一步提高混合性能。论文通过与实验数据的对比表明,三维非规则颗粒碰撞力模型较传统的线性模型对料斗中落料过程模拟的准确性更高。以此进行的模拟表明:Beverloo方程一般能够较好地预测多粒径颗粒体系的落料行为,但在颗粒尺寸差异较大时,会高估整体落料速度。分析表明,颗粒体系的力链强度明显增加导致的内部流动阻力增大和动态拱桥的形成是其重要成因。论文最后总结了对DEM模型与模拟方法的改进,及其在颗粒流动与混合模拟研究中的应用,并展望了其后续工作与工业应用前景。
[Abstract]:Discrete element method (DEM) is the main method of particle flow simulation, and it can adapt to different particle properties and equipment operating conditions.However, the DEM method itself has many problems, such as huge computation and long simulation time, so it is difficult to simulate the particle flow mixing process for industrial scale equipment.In order to overcome this difficulty, this paper extends and optimizes the simulation method and program of high-efficient large-scale discrete element based on multi-scale heterogeneous supercomputing system, and realizes the simulation of non-spherical particles such as capsules and cylinders.The influence of particle properties in drum mixer and hopper on its flow mixing performance was investigated, and the mechanism of particle flow mixing in the corresponding equipment was further understood.In this paper, it is shown that the use of staggered plate in the horizontal drum can promote the radial sprinkling of particles and the axial flow along the plate.The axial mixing efficiency of the studied drum is 16 times and 5 times higher than that of the non-plate roller and the full plate plate roller respectively under the optimal plate reading structure.The simulation also shows that the effect exists for different particle size, shape, density and friction coefficient and cylinder size, which indicates its wide application prospect.It is also shown that the shape of the capsule particles in the drum can affect the packing density and spatial orientation, thus affecting their mixing properties.In the range of physical properties investigated, the effect of particle density on segregation structure is more significant than shape.The mixing performance can be further improved by the interaction of particle shape and density.By comparing with the experimental data, it is shown that the 3D irregular particle collision force model is more accurate than the traditional linear model in simulating the blanking process in the hopper.The simulation results show that the weight Beverloo equation can generally predict the blanking behavior of multi-particle system, but it can overestimate the overall blanking rate when the particle size is different.The analysis shows that the increase of internal flow resistance and the formation of dynamic arch bridge caused by the obvious increase of the strength of the force chain of the granular system are the important causes of its formation.Finally, the paper summarizes the improvement of DEM model and simulation method, and its application in particle flow and mixing simulation, and looks forward to its future work and industrial application.
【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ027.1

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