Numerical Simulation Of Gas-Solid Two Phase Flow In Pneumatic Conveying Pipeline

Pneumatic conveying is a transport method of transferring particulate materials by utilizing high speed gas in pipeline. There exists problems of large energy consumption, equipment wear and pipeline blocking in engineering application.The study in pneumatic conveying process with numerical simulation can help design and optimize the system. Currently the simulations of pneumatic conveying focus on two-dimension. In this paper the related problems of gas-solid flows within the pneumatic conveying tube are simulated and analyzed based on 3D DEM-CFD. The main contents are as follows:The process of gas-solid flow within three-dimensional 90° elbow was simulated based on the Eulerien-Lagrangian coupling method. Fluid phase was solved by using FLUENT while particle phase was solved in EDEM. The normal force and the tangential force between particle to particle and particle to the wall were calculated with Hertz-Mindlin contact model. Simultaneously the resistance and rotational lift forces on particle phase by fluid are considered while the forces between the two phases are transferred in the form of momentum sink. Particle trajectories, speed, collision force, the collision frequency, fluid pressure and velocity distributions were obtained under different conditions. The formation and decomposition of the particle bunch are predicted in the elbow. The results showed that, the trajectory of particles was more disorders in the vertical section of the elbow when mass flow rate was reduced. Multiple collisions on the wall leaded the particle bunch to decomposing. The particle bunch decomposed faster with the decrease of the elbow bend diameter ratio of R/D. Increasing the flow velocity had little effect on particle bunches in the elbow.The wear on the wall of elbow by particles was simulated and analyzed with Archard Wear model. The results show that the wear was mainly in the area of 15° to 30° on the outside of the elbow, displaying in "人" distribution. Impact force, impact angle, friction, bend geometry parameters were studied in pipe wear. Increasing the mass flow rate will increase the wear volume and change wear distribution; Higher gas velocity increased the impact force which generates wear but has no effect on wear distribution. Higher R/D decreases the wear.Aiming at the problem of particle blockage inside the pipe, the dense phase pneumatic conveying process in the horizontal tube was simulated based on the Eulerian- Eulerian coupling method. Both particles phase and fluid phase were seen as continuous medium with considering the coupling of pressure and exchange coefficients of interface between two phases and turbulent transport of the solid phase and the interphase slip resistance. Results show that particles upper the plug move faster than the overall plug and reach forefront of plug, making the plug fluctuate in advance. The gas pressure drop in blanking area decreases with the particles accelerating and the pressure inside the pipe fluctuates over time. The faster airflow velocity is, the greater the pressure drop both in the blanking area and the gas plug segment are. Plug flow in horizontal pipe is more significant. Longer plug formed larger pressure drop in blanking area without effect on pressure drop of gas plug segment.