Shear Impact Energy Research Articles

Investigation of the ball wear in a planetary mill by DEM simulation

Accurate prediction of the grinding media wear is of significant interest to optimization of the milling process. As for that, a particle wear model is proposed in this work, which connects the shear impact energy with the surface's removed volume. Experiments and simulation results in a laboratory-scale planetary ball mill verify that the particle wear model can predict the increasing trend of particle wear rate with mill speed, and has good accuracy at high mill speed. In the experiments, the grinding bowl is filled with liquid water to isolate the air and cool the grinding balls, and related modification is added to the contact model. Then, the influence of friction coefficient, fluid, and the mill speed on wear rate is explored. The results revealed the influence of friction coefficient on particle wear rate, and it is found that drag force and torque from fluid would reduce the particle wear. Also, the influence of the mill speeds the planetary ball mill is related to the rotation-revolution radius. Finally, we conducted a preliminary study on the wear of the grinding media during the ore grinding process.

DEM investigation on conveying of non-spherical particles in a screw conveyor

Screw conveyors are extensively used in modern industry such as metallurgy, architecture and pharmaceutical due to their high-efficiency in the transportation of granular materials. And substantial efforts have been devoted to the study of the screw conveyors. Numerical method is an effective way to study screw conveyor. However, previous studies have mainly focused in the regime of spherical particles while the in-depth investigations for non-spherical particles that should be the most encountered in practical applications are still limited. In view of the above situations, discrete element method (DEM), which has been widely accepted in simulating the discrete systems, is utilized to investigate the conveying process of non-spherical particles in a horizontal screw conveyor, with particles being modeled by super-ellipsoids. In addition, a wear model called SIEM (Shear Impact Energy Model) is incorporated into DEM to predict the wear of screw conveyor. The DEM simulation results demonstrate that the particle shape is influential for the flow behaviors of particles and the wear of conveyor. The conveying performance evaluated quantitatively of both mass flow rate and power consumption is subsequently obtained to investigate the effect of sphericity of particle with different operation parameters. Moreover, particle collision frequency and collision energy consumption are acquired to investigate the possible particle breakage between particles and screw blade. The comparisons between particle–particle collision and particle–wall collision reveal that particles with large shape index have more possibility to be damaged in particle–wall impingement.

Investigation of the effect of filling level on the wear and vibration of a SAG mill by DEM

Semi-autogenous grinding (SAG) mill is widely used in the grinding process of coal and ores because of its strong applicability, large capacity and low consumption of grinding media. Therefore, the research of SAG mill is still of great important practical significance. Among those parameters of the SAG mill, the filling level is very important for it is not only directly related to the processing capacity of the mill, but also affects the operation cost and stability of mill. In this paper, combined with shear impact energy model (SIEM) and discrete element method (DEM), the particle collision energy spectrum was applied to analyze the influence of ore filling level and media filling level on the power draw of the mill, the impact energy on ore, and the wear of liner and media in a slice of an industrial SAG mill. It was found that increasing the ore filling level would increase energy consumption and reduce the energy efficiency and the wear of liner and grinding media. Furthermore, the vibration of mill was explored from the collision energy on liner. The results showed that the low frequency but high energy collision between grinding media and liner was the main reason for liner wear and mill vibration.

CFD-DEM simulation of fluidized bed with an immersed tube using a coarse-grain model

The computational fluid dynamic combining the discrete element method (CFD-DEM) is widely used to comprehend the mechanism of gas–solid flow. However, as a Lagrangian method, DEM suffers from the huge cost for tracking each particle in the systems when applied to industrial applications with billions of fine particles, regardless of the great advances in computing capacity of computers. To address this issue, a coarse-grain (CG) model is proposed in this paper, where the original fine particles are represented by a small number of large-sized CG particles. In the current study, the new-developed CG model combining CFD-DEM (CG CFD-DEM) is applied to investigate the fluidized bed with an immersed tube. The applicability and accuracy of the proposed CG CFD-DEM are validated by the good agreement of the macroscopic behaviors predicted by simulations and those obtained from experiments. For the first time, the CG CFD-DEM is used to predict the erosion around the tube based on the shear impact energy model (SIEM), and the computational results calculated by CG CFD-DEM and original CFD-DEM agree well, which demonstrates that the proposed model can predict the erosion of the tube in the fluidized bed accurately and efficiently. Besides, as expected, the calculation time is drastically reduced due to the CG model, which makes the simulations of large-scale industrial applications accessible.

Multi-level DEM study on liner wear in tumbling mills for an engineering level approach

Liner wear is one of the major problems for the design and maintaining of the tumbling mills and an effective and efficient numerical approach can significantly reduce the cost for studying liner wear. To obtain an engineering level approach, a coarse grain level wear model is proposed in this paper. A multi-level study on the liner wear was conducted to assess the adequacy of the coarse grain level approach based on the simulation results of the original-level approach - Discrete Element Method (DEM) combined with the wear model Shear Impact Energy Model (SIEM). Quasi-mono-size distribution and polydisperse size distribution were used in the simulations. The reasons for the deviations of the results predicted by the coarse grain level wear model were discussed and analyzed.

Influence of particle shape on liner wear in tumbling mills: A DEM study

Tumbling mills are widely used in industry. Liner wear of the mills, which is due to the impacts of the non-spherical ore particles, can significantly affect the availability. In this research, the discrete element method (DEM) was used to predict the particle motions within the tumbling mills. Combined with the Shear Impact Energy Model (SIEM), which is a particle-scale erosion model, effect of the particle shape on the liner wear was investigated. The simulation results show that wear due to the cuboid-like non-spherical particles is larger than that due to the spherical particles, even though the primary reason for wear on the liners is not altered by the particle shape (the intense collisions in the bulk toe). Based on the results of the particle motions, it is revealed that the sliding of the particles on the lifters has large effect on wear. The reasons for the effect of the particle shape on the wear rate and distribution of the lifters are given by analyzing the sliding intensity, such as the sliding frequency, tangential stress, sliding distance and duration of the intense sliding in the toe region.

Multiscale investigation of tube erosion in fluidized bed based on CFD-DEM simulation

A multiscale analysis on the erosion of the immersed tubes in a 3-D fluidized bed is conducted using computational fluid dynamics–discrete element method (CFD-DEM) coupling a particle-scale erosion model referred to as the shear impact energy model (SIEM). Different gas velocities and tube shapes are adopted to obtain more information. Several hydrodynamic parameters, including the void and solid fraction, the average particle speed, the granular temperature and the fluctuation energy (defined as the sum of the granular temperature) have been obtained and analyzed. Since the hydrodynamic properties have great effect on erosion of the immersed tube, a quantitative analysis was carried out based on the hydrodynamic parameters around the tubes. An intrinsic relation between erosion on the immersed tube and the fluctuation energy has been revealed based on the analysis, which indicates that the fluctuation energy of the particles near the tube probably is the main reason for the erosion. Moreover, the ordered motion of the particles also has some effect on the erosion, especially on the erosion of the top and bottom of the tube when the gas velocity is high.

Numerical prediction of wear in SAG mills based on DEM simulations

Wear is a major operating problem for semi-autogenous grinding (SAG) mills. A credible and efficient numerical approach for accurately predicting wear within SAG mills can significantly reduce design time and improve grinding efficiency. In this paper, the 3D simulations were performed using discrete element method (DEM) combined with an erosion model, which is referred to as Shear Impact Energy Model (SIEM), to predict wear within a SAG mill. The approach is quantitively validated against the corresponding experiment reported by other researchers. The results show that the rotation speed significantly affects the wear rate and wear distribution on the liners. In addition, the effects of changes in lifter shape on wear within the SAG mill are also obtained and analyzed. The primary reason for wear on the liners is revealed based on the simulation results: it is the intense collisions between the particles and the liners during the acceleration of the particles in the toe region that cause the severe wear. Finally, the rotation speed and lifter shape are synthetically evaluated from the aspect of wear and energy utilization.

An erosion model for the discrete element method

A shear impact energy model (SIEM) of erosion suitable for both dilute and dense particle flows is proposed based on the shear impact energy of particles in discrete element method (DEM) simulations. A number of DEM simulations are performed to determine the relationship between the shear impact energy predicted by the DEM model and the theoretical erosion energy. Simulation results show that nearly one-quarter of the shear impact energy will be converted to erosion during an impingement. According to the ratio of the shear impact energy to the erosion energy, it is feasible to predict erosion from the shear impact energy, which can be accumulated at each time step for each impingement during the DEM simulation. The total erosion of the target surface can be obtained by summing the volume of material removed from each impingement. The proposed erosion model is validated against experiment and results show that the SIEM combined with DEM accurately predicts abrasive erosions.

Numerical prediction of erosion in elbow based on CFD-DEM simulation

A new erosion model, which is referred to as SIEM (shear impact energy model), is used to investigate elbow erosion under different working conditions using numerical simulations. The fluid motions are predicted by CFD (computational fluid dynamics), and the particle movements are calculated using DEM (discrete element method) in the simulations. Both a one-way coupling method and a two-way coupling method in CFD-DEM are adopted to calculate the gas-solid interaction. The prediction results of elbow erosion subject to a condition of dilute gas-particle flow are validated against corresponding experimental data. Because DEM and SIEM can be easily applied to dense gas-particle flows, the effect of the particle concentration on the erosion is also investigated. The simulation results show that the coupling methods have little influence on the erosion prediction when the particle concentration is low, whereas erosion in the elbow is significantly sensitive to the particle concentration. Finally, the effects of the friction coefficient, restitution coefficient and spring stiffness coefficient on elbow erosion are also investigated using simulations, and the effects were not as remarkable as the concentration.

CFD–DEM simulation of tube erosion in a fluidized bed

The erosion of the immersed tubes in a bubbling‐fluidized bed is studied numerically using an Eulerian–Lagrangian approach coupling with a particle‐scale erosion model. In this approach, the motion of gas and particles is simulated by the CFD–DEM method, and an erosion model SIEM (shear impact energy model) is proposed to predict the erosion of the tubes. The model is validated by the good agreement of the simulation results and previous experimental data. By analyzing the simulation results, some characteristics of the tube erosion in the fluidized bed are obtained, such as the distribution of the erosion rate around the tube, the variation of the erosion rate with the position of the tube, the effect of the friction coefficient of particles on the erosion, the relationship between the maximum and the average erosion rate, etc. The microscale behavior of particles around the tubes is also revealed and the linear relationship between the erosion and the shear impact energy is confirmed by the simulation results and experiment. The agreement between simulation and experiment proves that the microscale approach proposed in this article has high accuracy for predicting erosion of the tubes in the fluidized bed, and has potential to be applied to modeling the process in other chemical equipment facing solid particle erosion. © 2016 American Institute of Chemical Engineers AIChE J, 63: 418–437, 2017

A numerical 3D simulation for prediction of wear caused by solid particle impact

Discrete element method has been used to simulate the behavior of particles interacting with a flat plate in order to define a relationship between shear-normal impact energy and wear rate during mechanical erosion. The analysis was performed for various collision angles, velocities and particle concentrations and, it was found that the shear impact energy of particles with the plate was maximized at collision angles near 30° where the wear rate had its maximum value. To investigate the influence of particles accumulation on the surface, a similar simulation procedure for a single particle impacting a plate was carried out and the results demonstrated the role of particles interactions on normal-shear impact energy and consequently on the erosion mechanism. Comparison of the simulation data with experimental data indicated that the shear impact energy was mainly relevant to cutting and cracking erosion mechanism while normal impact energy was related to forging and extrusion mechanisms. The results obtained suggest that this numerical simulation method may be used in a predictive way to study practical design problems and to explain some phenomena associated with solid particle impact erosion.