颗粒撞击单颗粒覆层的数值计算

doi:10.16085/j.issn.1000-6613.2021-1367

摘要/Abstract

摘要：

颗粒与壁面的惯性碰撞机制是换热管壁积灰的主要原因之一，且国内外对微米级颗粒撞击壁面过程的研究较少。本文对单颗粒撞击颗粒覆层的碰撞过程进行了数值计算。首先通过建立颗粒与壁面法向碰撞的动力学模型，对颗粒与壁面（或颗粒）之间的碰撞过程进行研究。对于颗粒与壁面（或颗粒）的碰撞过程，无阻尼耗散下，理论计算结果与数值计算结果一致。相对于仅考虑黏附剥离功的情况，阻尼耗散的存在使得临界捕集速度增加。在此基础上，研究了颗粒与颗粒覆层撞击后的颗粒运动情况。颗粒-颗粒（黏附）-壁面的法向碰撞过程由于黏附颗粒的加入变得更加复杂。计算发现，对于二氧化硅颗粒-二氧化硅颗粒（黏附）-不锈钢表面的碰撞过程，当入射速度大于0.7m/s时，黏附颗粒将从壁面脱离。

关键词: 微米颗粒, 临界捕集速度, 阻尼耗散, 颗粒覆层

Abstract:

The inertial impact mechanism between particles and wall surface is one of the main reasons for ash deposition, and there are few researches on the impact process of micron particles at home and abroad. In this paper, the impact process of a single particle impacting the particle powdery layer was numerically calculated. The dynamic model of the normal collision between particles and walls was established to study the collision process between the particle and wall (or particle). For the impact process between the particle and wall (or particle), the theoretical calculation results were consistent with the numerical calculation results in the case of undamped dissipation. The existence of damping dissipation increased the critical velocity when only the work of adhesive peeling was considered. On this basis, the particle motion after particle collision with powdery layer was studied. The normal impact process of particle-particle (adhesive) -wall surface became more complicated due to the addition of adhesive particles. It was found that when the incident velocity was greater than 0.7m/s, the adhesive particles would detach from the wall surface during the collision process between silica particles-silica particles (adhesion)-stainless steel surface.

Key words: micro-particles, critical capture velocity, damping dissipation, powdery layer

中图分类号:

谢俊, 李晨曦, 朱正仁, 马昊东, 李润东. 颗粒撞击单颗粒覆层的数值计算[J]. 化工进展, 2021, 40(12): 6490-6498.

XIE Jun, LI Chenxi, ZHU Zhengren, MA Haodong, LI Rundong. Numerical study on particle impacting single particle powdery layer[J]. Chemical Industry and Engineering Progress, 2021, 40(12): 6490-6498.

图/表 17

图1 JKR接触理论中颗粒间接触示意图

图2 JKR模型的接触力随接触位移的变化曲线[18]Fn—法向力；Fc—临界接触力；δs—软卸载点S的接触位移

表1 材料参数[26- 27]

颗粒材料	密度/kg·m^-3	粒径/μm	泊松比	杨氏模量/GPa
聚苯乙烯	1040~1070	1.27	0.33	3~3.5
抛光石英	2600	—	0.17	54

表2 黏附功与赫兹刚度

壁面材料	颗粒材料	黏附功w/J·m^-2	刚度K/GPa
抛光石英	聚苯乙烯	0.052	4.563

表3 JKR模型关键点

关键点	接触位移δ/nm	接触半径α/nm
B	1.033	44.368
S	-0.853	13.437

图3 参数α与恢复系数en的关系

图4 1.27μm的聚苯乙烯颗粒撞击抛光石英表面实验结果[23]和数值计算结果的比较

图5 入射颗粒与二维颗粒覆层的碰撞[25]

图6 单层颗粒的法向碰撞

表4 颗粒与壁面(或颗粒)间的物性参数[29]

物性参数	颗粒-壁面	颗粒-颗粒
有效杨氏模量E^*/GPa	66.103	48.235
有效刚度K/GPa	88.137	64.313
有效质量m^*/kg	12.850×10^-12	6.425×10^-12
黏附功w/J·m^–2	0.197	0.078
有效半径R^*/μm	10.500	5.250
接触半径α/nm
B点	166.851	85.804
C点	105.109	54.053
S点	50.531	25.986
接触位移δ/nm
B点	0.884	0.467
C点	-0.351	-0.186
S点	-0.730	-0.386
黏附剥离功W_st/J	66.506×10^-16	6.982×10^-16
临界捕集速度v_st/m·s^-1	0.0322	0.0147

图7 接触位移随接触时间的变化关系(无阻尼)

图8 碰撞速度随接触位移的变化关系（无阻尼）

图9 参数α与恢复系数en的拟合关系

图10 接触位移随接触时间的变化关系

图11 碰撞速度随接触位移的变化关系

图12 接触位移随接触时间的变化关系

图13 碰撞速度随接触位移的变化关系

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