Computational Fluid Dynamics Discrete Element Method Simulation Research Articles

Analysis and modelling of bead contacts in wet-operating stirred media and planetary ball mills with CFD–DEM simulations

Wet fine grinding is an important unit process in various industries. In the present work two different stirred media mills (one with a cylindrical stirrer; one with a disc stirrer) and a planetary ball mill are investigated using coupled CFD (computational fluid dynamics) and DEM (discrete element method) simulations. While the DEM takes the grinding media into account, the CFD is used for the calculation of the fluid flow. With these coupled simulations the grinding media movement and the resulting contacts per time unit as well as their kinetic energy at the start of the contact can be tracked. In a first step these values are compared to an analytical model that was originally developed for wet operating stirred media mills. To compare different types of mills the type of contact along the stress energy spectrum, which is based on the kinetic energy of the grinding media, is important. Therefore, in the present work an extended contact analysis was developed that enables the description of normal impact and torsion, shearing and rolling induced by rotational and translational velocities. The extended analysis enables the complete characterisation of the energy spectrum for different mill types and operating conditions.

CFD–DEM simulation of the filtration performance for fibrous media based on the mimic structure

In order to obtain the comprehensive filtration information, such as the deposition morphology of particles, evolutions of the instantaneous pressure drop and efficiency, 3-D mimic models of fibrous media had been established using a stochastic algorithm and computational fluid dynamics (CFD) - discrete element method (DEM) model was adopted to simulate the gas-solid flow characteristics in fibrous media exposed to particle loading in this work. Meanwhile, the simulation results had been validated by the macro-empirical model proposed in the previous literature. In addition, the influence of various parameters including porosity, face velocity and particle size on the filtration performance of fibrous media had also been investigated. It is concluded that simulation results of the CFD–DEM model are good agreement with predictive values of the macro-empirical model. Moreover, the porosity of fibrous media, face velocity and particle size have an important effect on the filtration performance of the fibrous media.

CFD–DEM simulation of material motion in air-and-screen cleaning device

In this work, a numerical study of the gas–solid flow in an air-and-screen cleaning shoe is carried out by use of the combined Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) model where the motion of discrete particles phase is obtained by DEM which applies EDEM software and the flow of continuum fluid by the traditional CFD which solves the Navier–Stokes equations at a computational cell scale. The effect of inlet airflow velocity is studied and analyzed in terms of grains and short straws’ longitudinal velocity and vertical height, and cleaning loss. Simulation results showed that, in a certain range, different inlet airflow velocity only affects the magnitude of airflow velocity in the cleaning shoe, but does not affect the distribution regularity of flow field in the cleaning shoe. With the inlet airflow velocity increase, vibrating screen processing power improves, while grain losses increase. Grains mainly concentrate on 4–12 sections under the screen surface. Comparison of numerical simulation results with experiments has demonstrated adequate agreement. It showed that numerical simulation of material motion on vibrating screen of air-and-screen cleaning device based on CFD–DEM is feasible. The results provide a basis for improving the design on air-and-screen cleaning device of combine harvester.

Influence of rolling friction on single spout fluidized bed simulation

In this paper we study the effect of rolling friction on the dynamics in a single spout fluidized bed using Discrete Element Method (DEM) coupled to Computational Fluid Dynamics (CFD). In a first step we neglect rolling friction and show that the results delivered by the open source CFD–DEM framework applied in this study agree with previous simulations documented in literature. In a second step we include a rolling friction sub-model in order to investigate the effect of particle non-sphericity. The influence of particle–particle as well as particle–wall rolling friction on the flow in single spout fluidized bed is studied separately. Adequate rolling friction model parameters are obtained using first principle DEM simulations and data from literature. Finally, we demonstrate the importance of correct modelling of rolling friction for coupled CFD–DEM simulations of spout fluidized beds. We show that simulation results can be improved significantly when applying a rolling friction model, and that experimental data from literature obtained with Positron Emission Particle Tracking (PEPT) technique can be satisfactorily reproduced.

CFD–DEM simulation of particle transport and deposition in pulmonary airway

Including the effects of particle–particle collision and particle rotation as well as the volume of particle occupied in the fluid, the Computational Fluid Dynamics (CFD)–Discrete Element Method (DEM) approach could properly predict the behavior of gas–solid flow with strong coupling and the motion of non-spherical particle, thus show good potential in simulations of alveolar region and fibrous particle transport and deposition. CFD–DEM has been developed to investigate the particle transport and deposition characteristics in human airway. An idealized pulmonary airway model of generations 3 to 5 has been established using the same geometric parameters as previous experiment conducted by Kim and Fisher (C. S. Kim and D. M. Fisher. 1999). The predicted deposition efficiencies are in good agreement with experimental data. Thus, CFD–DEM could properly simulate the particle behaviors in pulmonary airway. Based on the simulations, particle motions are studied by analyzing the particle positions at different time intervals. The results show that the initial position of particle would notably affect its trajectory. The near wall particles distribute evenly in the daughter tubes when they cross the airway. The most centered particles at inlet travel through the model via the inner side tubes of generation 5. The trajectories of other particles would shift from the inside tubes to the lateral ones of last generation as the distance between particle initial position and tube center increases.

CFD-DEM Simulation of Minimum Fluidisation Velocity in Two Phase Medium

In this work, CFD-DEM (computational fluid dynamics - discrete element method) has been used to model the 2 phase flow composed of solid particle and gas in the fluidised bed. This technique uses the Eulerian and the Langrangian methods to solve fluid and particles respectively. Each particle is treated as a discrete entity whose motion is governed by Newton's laws of motion. The particle-particle and particle-wall interaction is modelled using the classical contact mechanics. The particles motion is coupled with the volume averaged equations of the fluid dynamics using drag law.In fluidised bed, particles start experiencing drag once the fluid is passing through. The solid particles response to it once drag experienced is just equal to the weight of the particles. At this moment pressure drop across the bed is just equal to the weight of particles divide by the cross-section area. This is the first regime of fluidization, also referred as ‘the regime of minimum fluidization’.In this study, phenomenon of ...

CFD–DEM simulation of the gas–solid flow in a cyclone separator

In this work, a numerical study of the gas–solid flow in a gas cyclone is carried out by use of the combined discrete element method (DEM) and computational fluid dynamics (CFD) model where the motion of discrete particles phase is obtained by DEM which applies Newton’s equations of motion to every individual particle and the flow of continuum fluid by the traditional CFD which solves the Navier–Stokes equations at a computational cell scale. The model successfully captures the key flow features in a gas cyclone, such as the strands flow pattern of particles, and the decrease of pressure drop and tangential velocity after loading solids. The effect of solid loading ratio is studied and analysed in terms of gas and solid flow structures, and the particle–gas, particle–particle and particle–wall interaction forces. It is found that the gas pressure drop increases first and then decreases when solids are loaded. The reaction force of particles on gas flow is mainly in the tangential direction and directs mainly upward in the axial direction. The reaction force in the tangential direction will decelerate gas phase and the upward axial force will prevent gas phase from flowing downward in the near wall region. The intensive particle–wall collision regions mainly locate in the wall opposite to the cyclone inlet and the cone wall. Moreover, as the solid loading ratio increases, number of turns travelled by solids in a cyclone decreases especially in the apex region of the cyclone while the width of solid strands increases, the pressure drop and tangential velocity decrease, the high axial velocity region moves upwards, and the radial flow of gas phase is significantly dampened.