徐止恒, 李政权, 王贻得, 武煜坤, 李凯旋, 石昊宇

（江西理工大学 江西省颗粒系统仿真与模拟重点实验室, 江西 赣州 341000）

引用格式:

徐止恒, 李政权, 王贻得, 等. 基于 CFD-DEM 的湿颗粒气力输送数值模拟[ J] . 中国粉体技术, 2024, 30(2) : 12-23.

XU Z H, LI Z Q, WANG Y D, et al. Numerical simulation of pneumatic conveying of wet particles based on CFD-DEM[ J] .China Powder Science and Technology, 2024, 30(2) : 12-23.

DOI:10.13732 / j.issn.1008-5548.2024.02.002

收稿日期: 2023-10-17,修回日期:2023-11-20,上线日期:2023-12-28。

基金项目:国家自然科学基金项目,编号:52130001;江西理工大学高层次人才科研启动项目,编号:205200100606。

第一作者简介:徐止恒(1997—) ,男,硕士研究生,研究方向为气力输送模拟技术。 E-mail: 17852032578@163.com。

通信作者简介:李政权(1982—) ,男,副教授,博士,江西省科技领军人才,硕士生导师,研究方向为多相流仿真模拟。E-mail: qqzhengquan@163.com。

摘要: 【目的】 为了探索水平管中湿颗粒气力输送的内在机制,开发液桥轮廓由凸到凹的液桥力模型,实现对颗粒含水率的精准调控,分析不同含水率颗粒在输送过程中的动力学特性变化规律。【方法】 采用计算流体力学( computational fluiddynamics, CFD) 和离散元法( discrete element method,DEM) 双向耦合的数值模拟方法,通过对弯头外侧中心线的颗粒速度分析对比,验证数值模型的正确性以及网格的无关性。 【结果】 干颗粒沉降在管道底部,表现为管底流的运动状态,湿颗粒因液桥力的作用而形成紧密的颗粒团块,以单粒子和颗粒团 2 种形式进行运动,并且颗粒含水率越大,颗粒团聚现象越严重;湿颗粒的输送速度明显比干颗粒低,且随着颗粒含水率的增加,颗粒的平均输送速度呈下降趋势。 【结论】 相比于干颗粒输送,湿颗粒输送流动性更弱、输送效率更低以及能耗更高,在实际工业应用中,应当对湿颗粒进行前处理,以便于气力输送的无故障进行。

关键词: 计算流体力学; 离散元法; 湿颗粒; 液桥力; 流态

Abstract

Objective In order to explore the internal mechanism of the pneumatic conveying of wet particles, the flow state of the pneumatic conveying of wet particles in the horizontal pipe was studied by using periodic boundary conditions. The solid volume fraction, particle velocity and liquid bridge force of conveying particles with different moisture content were analyzed.

Methods The computational fluid dynamics ( CFD) and discrete element method ( DEM) were used for bi-directional numerical simulation, and the capillary force model of the liquid bridge contour from convex to concave was used. the particle moisture content wasprecisely controlledin the commercial software EDEM. The correctness of the numerical model and the independence of the mesh wereverified by comparing the particle velocity results of the center line outside the elbow.

Results and Discussion Through calculationin terms of conveying flow mode, dry particles settle at the bottom of the pipe, due to the friction and collision between particles ( or between particles and the wall) , the gravity of particles themselves, the decrease of gas velocity and the uneven distribution of airflow and other factors. The closer to the bottom of the pipe, the more dense the distribution of particles, which is manifested as the movement state of the bottom of the pipe. Wet particles move in two forms of single particles and clusters. The reason is that some particles are close to each other due to the pulsation between particles.When the minimum distance between particles is less than the critical rupture distance, the particles gather together under the action of liquid bridge force and gradually form larger particles. In terms of conveying efficiency, the average speed of dry particles is 3. 41 m / s, while the average speed of wet particles with 5% moisture content is 2. 83 m / s, which indicates that when the surface of the particles contains water, the conveying efficiency of materials in the pipeline will be reduced. In terms of pipewear, the particle-wall interforce of dry particles fluctuates little, while the particle-wall interforce of wet particles fluctuates greatly, and its maximum peak value increases with the increase of particle moisture content, indicating that wet particles wear the wall surface more than dry particles, and the wall wear becomes more serious with the increase of particle moisture content. In addition, wet particle transport has condensation characteristics, due to the existence of water on the surface of the particles, the adsorption force between the particles is enhanced, resulting in more collisions between the particles, which intensifies the formation of particle clusters. Inthe beginning, the percentage of colliding particles is zerodue to the relatively large spacing between particles in the initial state, andthe percentage of colliding particles increases rapidly under the action of fluidas time progresses. The average particle-particle collision percentage ( particle-particle collision as a percentage of the total number of particles) is 46%, and the average particle-wall collision percentage ( particle-wall collision as a percentage of the total number of particles)is 9%, which is consistent with the image in Figure 6.

Conclusion 1) The overall distribution of dry particles and wet particles in the pipeline is significantly heterogeneous. The dry particles settle at the bottom of the pipeline, showing the movement state of the bottom flow. However, due to the action of liquid bridge force,the wet particles form tight particle clusters and move in the form of single particles and particles. This agglomeration phenomenon become more serious with increasing water content of the particles. 2) The transport speed of wet particles is lower than that of dry particles. With the increase of particle moisture content, the average transport speed of particles shows a downward trend, indicating that the transport efficiency of particles decreases with the increase of moisture content. 3) Compared with dry particles, the particle-wall interforce of wet particles is greater and increases with the increase of particle moisture content,indicating that the impact of particles on the wall is more severe and the more serious wear of wet particles on the wall.

Keywords: computational fluid dynamics;discrete element method;wet particle; liquid bridging force; flow state.

参考文献( References) :

[1] KLINZING G E. A review of pneumatic conveying status, advances and projections[J] . Powder Technology, 2018. 333: 78-90.

[2] MIAO Z, KUANG S B, ZUGHBI H. CFD simulation of dilute-phase pneumatic conveying of powders[J]. Powder Technology, 2019, 349: 70-83.

[3] 崔益华. 水平管道负压气力输送 CFD-DEM 数值模拟[J] . 港口装卸, 2021(1) : 63-67. 

CUI Y H. CFD - DEM numerical simulation of negative pressure pneumatic conveying in horizontal pipeline [J] . PortHandling, 2021(1) : 63-67.

[4] 关佳斌, 裴旭明, 张琳荔, 等. 粮食颗粒群密相变径气力输送的流动特性[J] . 中国粉体技术, 2018, 24(2) : 38-43. 

GUAN J B, PEI X M, ZHANG L L, et al. Flow characteristics of grain particle group in dense phase change diameter pneumatic transportation[J] . China Powder Science and Technology, 2018, 24(2) : 38-43.

[5] 蔡海峰, 熊海泉, 周海军, 等. 考虑气相压缩性的高压密相气力输送数值模拟[J] . 发电设备, 2019, 33(2) : 80-85. 

CAI H F, XIONG H Q, ZHOU H J, et al. Numerical simulation of high pressure dense phasepneumatic conveying considering compressibility of gas phase[J]. Power generation equipment, 2019, 33(2): 80-85.

[6] PAN X, CHEN X, LIANG C, et al. Effect of moisture content on dense-phase conveying of pulverized coal at high pressure[J] . Korean Journal of Chemical Engineering, 2011, 28(10) : 2086-2093.

[7] ZHOU H, XIONG Y, PEI Y. Effect of moisture content on dense-phase pneumatic conveying of pulverized lignite under high pressure[J] . Powder Technology, 2016, 287: 355-363.

[8] 陈伟, 张佩, 孙永昌, 等. 基于 CFD -DEM 的非球形颗粒水力输送数值模拟[J]. 中国粉体技术, 2022, 28(5) : 82-91. 

CHEN W, ZHANG P, SUN Y C, et al. Numerical simulation of hydraulic transport of non-spherical particles based on CFD-DEM[ J] . China Powder Science and Technology, 2022, 28(5) : 82-91.

[9] 孙永昌, 张佩, 武煜坤, 等. 物料参数对立式搅拌釜混合性能影响的模拟 [J] .中国粉体技术, 2022, 28 (6) :99-106. 

SUN Y C, ZHANG P, WU Y K, et al. Simulation of effect of material parameters on mixing performance of vertical stirred tank[J] . China Powder Science and Technology, 2022, 28(6): 99-106.

[10] KUANG S B, LI K, YU A B. CFD-DEM simulation of large-scale dilute-phase pneumatic conveying system[J] . Industrial & Engineering Chemistry Research, 2020, 59(9) : 4150-4160.

[11] 宋学锋, 戴飞, 张锋伟, 等. 90° 弯管内玉米颗粒气固耦合运动特性分析[J] . 中国农机化学报, 2018, 39( 11) : 67-71. 

SONG X F, DAI F, ZHANG F W, et al. Analysis of gas-solid coupling movement characteristics of corn particles in a 90°bend[J] . Chinese Journal of Agricultural Mechanization, 2018, 39(11) : 67-71.

[12] RABINOVICH Y I, ESAYANUR M S, MOUDGIL B M. Capillary forces between two spheres with a fixed volume liquid bridge: theory and experiment[J] . Langmuir, 2005, 21(24) : 10992-10997.

[13] SUN X, SA M. A liquid bridge model for spherical particles applicable to asymmetric configurations [J] . Chemical Engineering Science, 2018, 182: 28-43.

[14] XIAO F, JING J, KUANG S B, et al. Capillary forces on wet particles with a liquid bridge transition from convex to concave[J] . Powder Technology, 2020, 363: 59-73.

[15] KANTAK A, GALVIN J E, WILDEMUTH D J, et al. Low-velocity collisions of particles with a dry or wet wall [J] . Microgravity Science and Technology, 2005, 17(1) : 18-25.

[16] XIAO F, LUO M, KUANG S B, et al. Numerical investigation of elbow erosion in the conveying of dry and wet particles[J] . Powder Technology, 2021, 393: 265-279.

[17] WANG M, ZHU W, SUN Q, et al. A DEM simulation of dry and wet particle flow behaviors in riser[J]. Powder Technology, 2014, 267: 221-233.

[18] OLALEYE A K, SHARD T O, WALKER G M, et al. Pneumatic conveying of cohesive dairy powder: experiments and CFD-DEM simulations[J] . Powder Technology, 2019, 357: 193-213.

[19] ZHANG M H, CHU K W, WEI F, et al. A CFD -DEM study of the cluster behavior in riser and downer reactors[J] . Powder Technology, 2008, 184(2) : 151-165.

[20] KUANG S B, ZHOU M M, YU A B. CFD-DEM modelling and simulation of pneumatic conveying: a review[J] . Powder Technology, 2020, 365: 186-207.

[21] 毕大鹏, 张晋玲, 谢文选, 等. 水平管稀相气力输送气-固速度关系的实验研究[ J] . 中国粉体技术, 2020, 26(2) : 1-6. 

BI D P, ZHANG J L, XIE W X, et al. Experimental study of gas - solid velocity relationship in thin phase pneumatic conveying in horizontal pipe[ J] . China Powder Science and Technology, 2020, 26(2) : 1-6.

[22] LI Z Q, ZHANG P, SUN Y C, et al. Discrete particle simulation of gas-solid flow in air-blowing seed metering device[ J] . Computer Modeling in Engineering & Sciences, 2021, 127(3) : 1119-1132.

[23] GIDASPOW D, LI F, HUANG J. A CFD simulator for multiphase flow in reservoirs and pipes[ J] . Powder Technology, 2013, 242: 2-12.