湿颗粒倾斜碰撞恢复系数的直接数值模拟

doi:10.11949/0438-1157.20230870

摘要/Abstract

摘要：

通过耦合VOF（volume of fluid）和重叠网格的方法，对表面附着液滴的“颗粒-颗粒”倾斜碰撞进行了直接数值模拟，获得了碰撞过程中液桥演变、颗粒运动、碰撞恢复系数的变化规律。在不同碰撞角度条件下，法向碰撞是液体对碰撞恢复系数影响最显著的情况。随着液体黏度的增加，法向恢复系数和总恢复系数降低，而切向恢复系数略微增加。随着碰撞速度的增加，法向恢复系数和总恢复系数增加，而切向恢复系数降低。在倾斜碰撞中，颗粒的旋转对于颗粒分离具有促进作用，液桥可对颗粒产生剪切作用使得部分切向动能转化为法向动能。研究结果可以为发展湿颗粒碰撞简化模型提供基础数据。

关键词: 流化床, 湿颗粒碰撞, 液桥, 碰撞恢复系数, 数值模拟

Abstract:

By coupling VOF (volume of fluid) and the overset meshing method, direct numerical simulation of “particle-particle” oblique collisions with surface-attached droplets is carried out, and the evolution law of the liquid bridge, particle motion, and collision restitution coefficient are obtained during the collision process. Under different collision angles, the effect of liquid on the collision restitution coefficient is the most significant for the normal collision. With the increase in liquid viscosity, the normal and total restitution coefficients decrease, while the tangential restitution coefficient slightly increases. With the increase in collision velocity, the normal and total restitution coefficients increase, while the tangential restitution coefficient decreases. Under the oblique collision, the rotation of particles promotes particle separation, and the liquid bridge can generate shear action, converting part of the tangential kinetic energy into normal kinetic energy. This present study can provide basic data for developing a simplified model of wet particle collisions.

Key words: fluidized-bed, wet particle collision, liquid bridge, collision restitution coefficient, numerical simulation

中图分类号:

TQ 021

刘道银, 范志恒, 马吉亮, 陈晓平. 湿颗粒倾斜碰撞恢复系数的直接数值模拟[J]. 化工学报, 2023, 74(10): 4063-4073.

Daoyin LIU, Zhiheng FAN, Jiliang MA, Xiaoping CHEN. Direct numerical simulation of restitution coefficient during oblique collision of wet particles[J]. CIESC Journal, 2023, 74(10): 4063-4073.

图/表 11

表1 颗粒-液膜平板碰撞的模拟参数

Table 1 Simulation parameters of collision of the particle-plate liquid film case

参数	数值
气体密度/(kg/m³）	1.225
气体黏度/(Pa·s）	1.789×10^-5
液体密度/(kg/m³）	827
液体黏度/(Pa·s）	0.185
液膜厚度/mm	2
表面张力系数/(N/m）	0.029
背景区域/mm	6×6×10
前景区域/mm	2.6
接触角（下落）/(°）	150
接触角（返回）/(°）	30
干颗粒碰撞恢复系数	0.853
Courant数	0.12

图1 颗粒-平板液膜碰撞的模拟和实验结果对比

Fig.1 Comparison of simulation and experiments on the oblique collision between a particle and a plate liquid film

图2 含有液滴的颗粒-颗粒倾斜碰撞示意图

Fig.2 Schematic diagram of particle-particle oblique collision with one droplet attached at the particle surface

图3 基准工况条件下颗粒和液桥的动态变化（颗粒直径2 mm，液滴直径0.4 mm，液体黏度500 mPa·s，碰撞速度1.5 m/s，碰撞角60°）

Fig.3 Dynamics of particle and liquid bridge during oblique collision at the bench condition (particle diameter 2 mm, droplet diameter 0.4 mm, liquid viscosity 500 mPa·s, collision velocity 1.5 m/s, and collision angle 60°)

图4 倾斜碰撞中颗粒分离距离随时间的变化

Fig.4 Variation of particle separation distance with time during oblique collisions

图5 不同碰撞角度下颗粒法向相对速度和切向相对速度随时间的变化（液体黏度500 mPa·s，碰撞速度1.5 m/s）

Fig.5 Variation of particle normal relative velocity and tangential relative velocity with time at different collision angles (liquid viscosity 500 mPa·s and collision velocity 1.5 m/s)

图6 碰撞角对总碰撞恢复系数的影响（液体黏度500 mPa·s，碰撞速度1.5 m/s）

Fig.6 Effects of the collision angle on the total restitution coefficient (liquid viscosity 500 mPa·s and collision velocity 1.5 m/s)

图7 倾斜碰撞中液体黏性对液桥断裂行为的影响（碰撞速度1.5 m/s，碰撞角60°）

Fig.7 Effects of liquid viscosity on the rupture behavior of liquid bridge during the oblique collision (collision velocity 1.5 m/s and collision angle 60°)

图8 不同液体黏度下倾斜碰撞中颗粒法向相对速度、切向相对速度、旋转角速度随时间的变化及液体黏度对碰撞恢复系数的影响（碰撞速度1.5 m/s，碰撞角60°）

Fig.8 Variation of particle normal relative velocity, tangential relative velocity, and rotational angular velocity with time in oblique collisions with different liquid viscosities and effect of liquid viscosity on the coefficient of restitution (collision velocity 1.5 m/s and collision angle 60°)

图9 倾斜碰撞中碰撞速度对液桥断裂行为的影响（液体黏度500 mPa·s，碰撞角60°）

Fig.9 Effect of collision velocity on the rupture behavior of liquid bridge during the oblique collision (liquid viscosity 500 mPa·s and collision angle 60°)

图10 不同碰撞速度下倾斜碰撞中颗粒法向相对速度、切向相对速度、旋转角速度随时间的变化及碰撞速度对碰撞恢复系数的影响（液体黏度500 mPa·s，碰撞角60°）

Fig.10 Variation of particle normal relative velocity, tangential relative velocity, and rotational angular velocity with time in oblique collisions with different collision velocities and effect of collision velocity on the coefficient of restitution (liquid viscosity 500 mPa·s and collision angle 60°)

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