水平气力输送系统中颗粒波状流的模拟

On Simulating Wavelike Motion of Particles Conveyed in a Horizontal Pneumatic Pipeline

对用于两相流计算的硬球模型进行简化 ,模拟了水平气力输送系统中颗粒波的动态流型。模型中 ,气体状态由两相耦合的 Navier- Stokes方程描述 ,颗粒运动通过单颗粒的运动轨迹描述。并且 ,颗粒的碰撞运动由冲量守恒原理控制 ,颗粒的悬浮运动由力平衡方程决定 ,相间耦合作用依据牛顿第三定律处理。模拟结果从介观层次呈现了水平气力输送系统中与实验特征吻合的颗粒波状流 ,说明了颗粒波的传播速度取决于气体速度 ,它并不敏感地依赖于系统中的存料量及物料密度。

A. B. Yu, the third author in Australia, is quite interested in a deeper understanding of the pneumatic conveying process of particles in a horizontal pipeline as such pipelines already exist in Australian industry. Recent simulation advances can deal with this problem in two different ways: the soft sphere approach and the hard sphere approach. In our opinion, the hard sphere approach as developed by Ouyang, the first author, et al in Refs.8 and 9, is better suited to the simulation of wavelike motion of particles conveyed in a horizontal pneumatic pipeline due to its realistic parameters. Using this hard sphere approach, we describe the gas phase hydrodynamics by the volume averaged Navier Stokes equations for two phase flow and trace particles in meso scale while taking into account the mutual interaction between particles and between particles and fluid. In our model, the motion process of each particle is decomposed into the collision process and the suspension process. Momentum conservation of collision mechanics controls the interaction between colliding particles, while the state of each suspended particle is fully dominated by the equation of force balance taking into account the external force over that particle. The coupling relation between two phases is subject to Newton's third law of motion. The flow patterns obtained in present work appear to be realistic because calculated trajectories of individual particles are converted into the form of a video movie, which presents very realistic formation of wavelike motion in a horizontal tube, as shown in Fig.1. Figs.3, 4, 5, and 6 show the effects of three different factors on propagation velocity of particle wave: (i) gas velocity (Fig.6); (ii) solid loading (Figs.3 and 4); (iii) particle density (Fig.5). They indicate that propagation velocity of particle wave depends mainly on gas velocity and the effects of the other two factors are very small.