XU Zhiheng, LI Zhengquan, WANG Yide, WU Yukun, LI Kaixuan, SHI Haoyu

( Jiangxi Provincial Key Laboratory for Simulation and Modelling of Particulate Systems, Jiangxi University of Science & Technology, Ganzhou 341000, China)

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 parti-cles 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.

Get Citation: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.

Received: 2023-10-17,Revised:2023-11-20,Online:2023-12-28。

Funding Project: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。

First Author: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。

Corresponding Author: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。

DOI:10.13732 / j.issn.1008-5548.2024.02.002

CLC No: TE832; TB4         Type Code:A

Serial No:1008-5548(2024)02-0012-12