涡流空气分级机近导叶处团聚体解团机理研究

doi:10.11949/0438-1157.20221568

摘要/Abstract

摘要：

超细颗粒往往会因为黏附力形成团聚，从而限制了通过气力分级制备粒径小且分布范围窄的超细粉体。研究团聚体解团机理可为提出解团措施提供理论依据。利用EDEM二次开发功能通过颗粒工厂生成团聚体，基于FLUENT-EDEM耦合进行涡流空气分级机环形区近导叶处区域团聚体运动及其解团过程的数值模拟，研究了不同入口风速下对团聚体解团的影响程度，并揭示了团聚体在环形区近导叶处区域的解团机理。结果表明，在导叶近壁面区域气力流场的剪切力无法使团聚体解团，流场中解团是由于团聚体与固壁面碰撞而引起的。在转笼转速为1200 r·min^-1，入口风速为6、12、18、24 m·s^-1的情况下，单颗粒占比数随入口风速由71.7%增大到88.39%，而未解团的团聚体由24.8%减少到10.51%，部分解团后形成的团聚体的占比均不超过4%，表明单个团聚体在流场中解团程度较大，入口风速增大会提高环形区近导叶处粉体分级时的分散性，引入无量纲参数——相对碰撞次数验证了这一结果。

关键词: 涡流空气分级机, 两相流, 数值模拟, CFD-DEM耦合, 二氧化硅, 团聚, 解团

Abstract:

Ultrafine particles tend to agglomerate due to adhesion, which limits the preparation of ultrafine particles with small size and narrow distribution range through pneumatic classification. Studying the mechanism of agglomeration disaggregation can provide a theoretical basis for proposing measures to disaggregate. In this paper, application programming interface (API) of EDEM is used to generate the aggregates in the particle factory, and the numerical simulation of the movement of the aggregates and their disaggregation process near the guide vanes in the annular region of a turbo air classifier is carried out in FLUENT-EDEM coupling. The influence of different inlet air velocity on the aggregates is studied and the mechanism of disaggregation of aggregates near the guide vane in the annular zone is revealed. The results show that disaggregation of the aggregates near the guide vanes in the flow field is caused by the collisions between the aggregates and the wall of guide vanes, but not the shearing force of the flow field. When the rotating velocity of the rotor cage is 1200 r·min^-1 and the inlet air velocity is 6, 12, 18, and 24 m·s^-1, respectively, the proportion of single particles increases from 71.7% to 88.39% and the proportion of the aggregates decreases from 24.8% to 10.51% with the increase of inlet air velocity, the proportion of aggregates after partial disaggregation does not exceed 4%, indicating that the increase of inlet air velocity will improve the dispersion of powder near the guide vanes in the turbo air classifier. The introduction of dimensionless parameter—relative collision number verifies this conclusion.

Key words: turbo air classifier, two-phase flow, numerical simulation, CFD-DEM coupling, silica, agglomeration, disaggregation

中图分类号:

TQ 028.8

任金胜, 刘克润, 焦志伟, 刘家祥, 于源. 涡流空气分级机近导叶处团聚体解团机理研究[J]. 化工学报, 2023, 74(4): 1528-1538.

Jinsheng REN, Kerun LIU, Zhiwei JIAO, Jiaxiang LIU, Yuan YU. Research on the mechanism of disaggregation of particle aggregates near the guide vanes of turbo air classifier[J]. CIESC Journal, 2023, 74(4): 1528-1538.

图/表 17

图1 抽取的控制体区域

Fig.1 The extracted control body

图2 涡流空气分级机原型和近导叶片控制体绝对速度云图

Fig.2 Absolute velocity contour of the air classifier prototype and control body near guide vanes

图3 原型与控制体流场对比

Fig.3 Velocities of the flow field comparison between the classifier prototype and the control body

图4 团聚体生成过程

Fig.4 Aggregation generation process

图5 获取团聚体小颗粒的坐标点信息流程图

Fig.5 Flowchart for obtaining the coordinate point information of small particles in an aggregation

表1 离散元仿真参数设置

Table 1 Parameter setting of discrete element simulation

参数	数值
小颗粒粒径d_p/μm	10
团聚体粒径D_agg/μm	30
颗粒密度 $ρ$ /(kg·m^-3)	2150^[37]
杨氏模量E	7.3
泊松比μ	0.17
颗粒间碰撞恢复系数e_p	0.75^[37]
颗粒间静摩擦因数μ_rp	0.75^[37]
颗粒间滚动摩擦因数μ_sp	0.02^[37]
颗粒壁面碰撞恢复系数e_w	0.7^[40]
颗粒壁面静摩擦因数μ_rw	0.3^[40]
颗粒壁面滚动恢复系数μ_sw	0.005^[40]
表面能参数γ/(J·m^-2)	0.0826^[38]

表1 离散元仿真参数设置

Table 1 Parameter setting of discrete element simulation

参数	数值
小颗粒粒径d_p/μm	10
团聚体粒径D_agg/μm	30
颗粒密度 $ρ$ /(kg·m^-3)	2150^[37]
杨氏模量E	7.3
泊松比μ	0.17
颗粒间碰撞恢复系数e_p	0.75^[37]
颗粒间静摩擦因数μ_rp	0.75^[37]
颗粒间滚动摩擦因数μ_sp	0.02^[37]
颗粒壁面碰撞恢复系数e_w	0.7^[40]
颗粒壁面静摩擦因数μ_rw	0.3^[40]
颗粒壁面滚动恢复系数μ_sw	0.005^[40]
表面能参数γ/(J·m^-2)	0.0826^[38]

图6 控制体内被替换单颗粒数目随时间的变化

Fig.6 The changes of replaced particle number in the control body with time

图7 控制体速度矢量图

Fig.7 The absolute velocity vector in control body

图8 控制体中单颗粒和团聚体组成占比

Fig.8 The proportion of single particles and aggregates in control body

图9 团聚体在流场中的形态

Fig.9 State of aggregations in the flow field

表2 计算团聚体在流场中临界剪切应力的参数选择［44］

Table 2 Parameter selection for critical shear stress of aggregates in flow field［44］

条件	参数
D_agg $<$ 3l_D	a₁=0.26, a₂=1, a₃=0.5, a₄=0
3l_D $≤$ D_agg $<$ 7l_D	a₁=0.068, a₂=1, a₃=1, a₄=4
7l_D $≤$ D_agg $<$ 58l_D	a₁=0.49, a₂=3, a₃=0.25, a₄=1
D_agg $≥$ 58l_D	a₁=1.9, a₂=1, a₃=2/3, a₄=0

表2 计算团聚体在流场中临界剪切应力的参数选择［44］

Table 2 Parameter selection for critical shear stress of aggregates in flow field［44］

条件	参数
D_agg $<$ 3l_D	a₁=0.26, a₂=1, a₃=0.5, a₄=0
3l_D $≤$ D_agg $<$ 7l_D	a₁=0.068, a₂=1, a₃=1, a₄=4
7l_D $≤$ D_agg $<$ 58l_D	a₁=0.49, a₂=3, a₃=0.25, a₄=1
D_agg $≥$ 58l_D	a₁=1.9, a₂=1, a₃=2/3, a₄=0

图10 24-1200工况下24 m·s-1风速时近导叶壁面流体剪切应力

Fig.10 Fluid shear stress near guide vane under 24-1200 at 24 m·s-1

图11 颗粒碰撞壁面示意图

Fig.11 Schematic diagram of the aggregate collides wall

图12 距离G面0.3 mm范围内团聚体速度分布

Fig.12 The velocity distribution of aggregates within 0.3 mm from the G-surface

图13 团聚体受力不均

Fig.13 Inhomogeneous stress on aggregates

图14 不同风速下碰撞次数

Fig.14 Collisions under different air velocity

表3 所有颗粒在X方向上的速度平均值v¯X

Table 3 Average velocity of all particles in X direction v¯X

入口风速/(m·s^-1)	$v ¯$ _X /(m·s^-1)
6	4.37
12	9.96
18	14.61
24	19.63

表3 所有颗粒在X方向上的速度平均值v¯X

Table 3 Average velocity of all particles in X direction v¯X

入口风速/(m·s^-1)	$v ¯$ _X /(m·s^-1)
6	4.37
12	9.96
18	14.61
24	19.63

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