Mechanisms of dust diffuse pollution under forced-exhaust ventilation in fully-mechanized excavation faces by CFD-DEM

In order to investigate the diffuse pollution mechanisms of high-concentration dusts in the working regions of fully-mechanized excavation faces under forced-exhaust ventilation, a CFD-DEM airflow-dust coupled simulation approach was developed based on k-s two-equation turbulent model and the Hertz-Mindlin model. The diffuse pollution characteristics of the dust particles with different sizes were analyzed by combining on-site measurements with simulation. Results show that, in the region 0-15 in away from the heading face, a large horizontal-vortex field was formed due to the effect of forced jet field. Under the airflows' drag force, the dust flows were stratified in a dense strip pattern, among which the larger dust particles flew zonally at lower heights. The airflow drag force dominated the movements of the dusts with a diameter range of 2.5-20 pm, while gravity significantly affected the diffusion of the dusts with a diameter range of 40-80 mu m. The final dust emission ratio approximately decreased linearly with the increase of dust particle size. Large dust particles were more easily settled. Specifically, the dust particles with a diameter range of 7-20 pm showed long sedimentation regions, while the other dusts were intensively settled at around the head-on region. In addition, the dust particles with a diameter range of 2.5-7 mu m showed stable passing ratios during the diffusion process, and the average z value presented non-significant decrease. Finally, the dust emission ratio of 2.5 mu m reached as high as 63.4% due to the absorption of the negative pressure. Therefore, comprehensive dustproof measures should be taken by considering the diffuse pollution characteristics of dusts. (C) 2017 Elsevier B.V. All rights reserved.