Computer Simulation of Powder and Particle Flow using Micro-Dynamics Approach and Validation

粉末和颗粒流动一直被认为是非常复杂的现象。对这些资本流动的研究在很大程度上依赖于经验方法。粉末和颗粒流动的计算机模拟大多基于连续介质模型。然而，随着计算机能力的不断增强，离散粒子模拟已成为预测各种情况下粒子运动的一种实用手段。本项目有两个目的：(1)发展离散粒子模拟，使之不仅在定性上，而且在定量上与实验相吻合；(2)开发实际使用的三维模拟模型。为了访问模拟模型，使用高速摄像机和数据处理设施进行了实验。将模拟结果与测量结果进行了比较。在比较的基础上，进一步建立了与实验定量吻合的模型。非球形颗粒模型是从上述比较中推导出的一个例子。在本项目中，注意到了静电引起的凝聚力。并对垂直管道内颗粒分散的气固两相流动进行了数值模拟。这项工作阐明了在循环床中观察到的颗粒团的形成可以通过考虑颗粒的重复碰撞来解释。在进行第二个目的的研究之前，对二维和三维模拟进行了比较。在本课题中，提出了一种新的准三维模拟方法。固体运动由三维计算得到，气相由轴对称二维计算得到。这种准三维模拟是预测轴对称容器喷动床层和鼓泡床层内现象的有效手段。

Powder and particle flows have been regarded as very complex phenomena. Research of those flows have been largely dependent on empirical approaches. Most of computer simulation of the powder and particle flows are based on continuum models. However, increasing computer power has made discrete particle simulation a practical means for predicting particle motion in various cases. The present project has been planned with two purposes ; (1) to develop the discrete particle simulation so that not only qualitatively but quantitatively good agreement should be obtained with experiments, (2) to develop three dimensional simulation model for practical use. To access simulation models, experiments were made using a high speed video camera and data processing facilities. Simulation results were compared with measurements. Based on the comparison, models were developed further to get quantitative agreement with experiments. A nonspherical particle model is an example which was deduced from the the above comparison. In the present project, attention was given to cohesion forces due to static electricity. Also, simulation was made of gas-solid flows where particles are dispersed in vertical duct. It was clarified in this work that formation of particle clusters observed in circulating fluidized beds can be explained by considering repeated collision of particles.Before proceeding the research to the 2nd purpose, comparison was made between 2-and 3-dimensional simulations. In the present project, a method of quasi 3-D simulation was proposed newly. The solid motion is obtained by 3-D calculation, while the gas phase is obtained by axisymmetric 2-D calculation. This quasi 3-D simulation was found to be a useful means to predict phenomena in spouted beds and bubbling fluidized beds of axisymmetrical vessel.