This paper presents a numerical modeling on the packing densification of uniform spheres under air impact using a combined Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM). In the ...whole process, the packing structure evolution, corresponding dynamics and densification mechanism are comprehensively studied. Macro and micro properties such as packing density, coordination number, radial distribution function, as well as forces in the packings at different stages are characterized and compared. The results show that air impact can realize the transition of particle packing from random loose to random close state at appropriate conditions. In this duration, the depth-averaged normal force increases linearly with the height. Meanwhile, numerous normal forces are close to the horizontal at the final packing stage due to the effect of air impact, and their distributions indicate exponential decay law. While the distribution of the fluid-particle interaction forces increases with the height. Local packing structure evolution demonstrates that the dominating densification mechanism under the air impact is ‘pushing filling’.
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•Packing densification of equal spheres under air impact is simulated by CFD-DEM.•Macro and micro properties for different packing structures are characterized.•The forces in the packings at different packing stages are systematically analyzed.•Densification mechanism under air impact is identified by force.
In this paper, four binary hard sphere crystals were numerically constructed by discrete element method (DEM) through different packing modes under three-dimensional (3D) mechanical vibration. For ...each crystal, a modified Voronoi tessellation method (called radical tessellation) was utilized to quantitatively investigate the topological and metrical properties of radical polyhedra (RPs). The topological properties such as the number of faces, edges, vertices per RP and the number of edges per RP face as well as the metrical properties such as perimeter, surface area, volume, and relative pore size per RP were systematically characterized and compared. Meanwhile, the mechanism of the binary hard sphere crystallization was also investigated. The results show that the packing sequence and pattern of the large spheres can determine the structure of the binary hard sphere crystal. The RP structures and their metrical and topological properties of the four binary hard sphere crystals (even the packing density of the two crystals is the same) are quite different. Each property can clearly reflect the specific characteristics of the corresponding binary hard sphere crystalline structure. The obtained quantitative results would be useful for the deep understanding of the structure and resultant properties of binary hard sphere crystals.
•GPU-powered CFD-DEM model (GPU- rCFD-DEM) is developed to simulate the large-scale gas–solid reacting flow.•The coupling calculations between CFD and DEM are fully implemented on GPU.•Advanced ...coupling strategies are employed to enhance numerical stability.•Coke combustion in an industrial-scale blast furnace is simulated.
The coupling of CFD (computational fluid dynamics) and DEM (discrete element method) is extensively used for simulating gas–solid reacting flows in various industrial processes, while its high computational cost limits its industry applications, especially large-scale systems with a large number of particles and complex geometries. This paper reports a robust highly efficient GPU (graphics processing unit) − powered CFD-DEM coupling approach that is, for the first time, capable of simulating large-scale gas–solid reacting flow systems with complex geometries (GPU- rCFD-DEM). The fluid flow calculations are performed using CPU parallelization, while the particle flow simulations leverage GPU parallelization, and the coupling calculations between CFD and DEM are fully implemented on GPU. The model includes advanced coupling strategies to enhance numerical stability, especially when handling complex geometries with unstructured CFD meshes. The developed model is validated through experimental measurements and its computational performance is evaluated by comparison with previous GPU-based simulations. It shows good agreement with the experiments and superior performance compared to the traditional coupling method. The model is then applied to simulate raceway dynamics and coke combustion in an industrial-scale blast furnace, showcasing its effectiveness in handling complex geometries and a huge number of particles in gas–solid reacting flows. This work provides an efficient and robust solution for numerically simulating industrial applications of gas–solid reacting flow systems.
•A novel GPU-based DEM-CFD model was developed to simulate the gas–solid flow.•A grid-based approach was proposed to improve efficiency in simulating gas–solid systems with complex geometries.•The ...effects of tuyere angles on the raceway dynamics were analyzed.•The wear of tuyere for different tuyere angles was analyzed.
The coupling of Computational Fluid Dynamics (CFD) and Discrete Element Model (DEM) is a powerful tool for simulating dense particulate systems, yet the conventional CFD-DEM has limits for systems with large particle numbers and complex geometry. This paper reports a novel GPU-based CFD-DEM model to simulate the gas–solid flow with large particle numbers and complex geometry. A novel coupling strategy between the CFD solver and DEM solver is developed, featuring high efficiency and stability. The developed model is validated against the experimental measurements, and its efficiency is compared to the previous CFD-DEM simulations. Then, for demonstration, the model is employed to simulate the dynamic behavior of gas–solid flow in the raceway in ironmaking blast furnaces by considering complex tuyere structure details and the huge particle numbers involved. This model allows to study the effect of the tuyere angle in terms of raceway formulation and tuyere erosion. The results show that the largest and most stable raceway volume can be reached at 5° downward tuyere, although the −5° tuyere nose experiences more wear than 10° downward tuyere. The model provides a cost-effective tool to overcome the longstanding challenge of simulating dense fluid-particle systems with huge particle numbers and complex geometry.
Particle breakage during compaction affects compaction behavior and the quality of the formed compact. This work conducted a numerical study based on the discrete element method (DEM) to investigate ...the effect of particle breakage on compaction dynamics and compact properties, including particle size and density distributions, and pore properties. A force-based breakage criterion and Apollonian sphere packing algorithm were employed to characterize particle breakage behavior. The pore structures of the compacts were characterized by the watershed pore segmentation method. Calibrated with experimental data, the model was able to simulate the stress-strain relation comparable with experimental observation. During compaction, the particles were gradually broken from top to bottom with increasing pressure. Both density and pore size of the compacts had relatively uniform distribution at larger stress, while the pore size decreased sharply when the particles started to break, indicating that the smaller fragments in the compact system have a significant effect on the pore size distribution.
Effective evaluation and prediction of aerosol transport deposition in the human respiratory tracts are critical to aerosol drug delivery and evaluation of inhalation products. Establishment of an in ...vitro-in vivo correlation (IVIVC) requires the understanding of flow and aerosol behaviour and underlying mechanisms at the microscopic scale. The achievement of the aim can be facilitated via computational fluid dynamics (CFD) based in silico modelling which treats the aerosol delivery as a two-phase flow. CFD modelling research, in particular coupling with discrete phase model (DPM) and discrete element method (DEM) approaches, has been rapidly developed in the past two decades. This paper reviews the recent development in this area. The paper covers the following aspects: geometric models of the respiratory tract, CFD turbulence models for gas phase and its coupling with DPM/DEM for aerosols, and CFD investigation of the effects of key factors associated with geometric variations, flow and powder characteristics. The review showed that in silico study based on CFD models can effectively evaluate and predict aerosol deposition pattern in human respiratory tracts. The review concludes with recommendations on future research to improve in silico prediction to achieve better IVIVC.
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•The effect of particle breakage during compaction on compact structure was investigated.•A watershed segmentation method was developed to characterise pore structure of ...compacts.•Pore size and throat diameter decreased exponentially with reducing particle sizes.•Spontaneous percolation dynamics of compacts was also affected by particle breakage.•Relations between pore structure and percolation behaviour were established.
This work investigated the effect of particle breakage on the pore structure of compacts formed with the discrete element method. The watershed segmentation method was developed to quantify pore properties of the compacts. Results showed the pore size, throat diameter and throat length followed the log-normal distributions for all the compacts except for compacts in which significant particle breakage occurred. With particle breakage, the mean pore size and mean throat diameter decreased exponentially with reducing particle size. The pore structure was also explored through spontaneous interparticle percolation. Results showed that the residence time of the percolating particles followed the log-normal distributions. The coefficient of the radial dispersion increased linearly with depth for all compacts except for a compact with particle breakage. The relations between pore structure and percolation behaviour were established. With decreasing pore size and throat diameter, the mean residence time increased exponentially but the dispersion coefficient had a linear decrease.
Scale-up of mills is critical to the design and operation of industrial grinding circuits. This paper presented a scale-up model based on the discrete element method (DEM) simulation to predict the ...performance of tumbling ball mills. The mills of different sizes partially filled with steel balls and ground particles were operated at different loading and speeds. The breakage energy characterized by the damping energy on the ground particles were analysed. In particular, a breakage model was adopted to link the breakage energy with particle mechanical properties to predict particle breakage in the mills. The predicted grinding rates of the particles under different conditions were comparable to experimental measurements. Results indicated that while particle-particle contacts were dominant in the flow, particle-ball contacts were the main breakage mechanism of particles. Power draw and grinding rate were not always positive correlated. Excessive mill speeds caused more power consumption but resulted in reduced grinding rate. Based on the simulation data, two scale-up models were proposed to predict power draw and grinding rate. The models were tested with larger mills and show excellent prediction on power draw and reasonable accuracy on grinding rate.
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•Tumbling mills filled with grinding balls and particles were simulated using DEM.•The damping energy on particles is more suitable than power draw to characterise mill efficiency.•Grinding rate of mills can be calculated by linking the damping energy and powder properties.•Scale-up models to predict power draw and grinding rate of mills were developed and validated.
This work presented a numerical study based on the discrete element method (DEM) to understand the effect of particle fragmentation on compaction dynamics and the properties of formed compacts. An ...improved fragmentation model based on the force criterion and the Apollonian fragments replacement was implemented to the model to mimic particle breakage. Through growth and relaxation of progeny particles, the fragmentation model was able to significantly reduce mass loss during particle fragmentation while maintain the mechanical response of the parent particles. The model was validated by comparing with literature data in terms of compaction curve and the evolution of particle size distribution (PSD). Three stages were identified in the Hecker plot highlighting the strong effect of particle fragmentation. The effect of compact height was investigated, showing particle fragmentation decreased with increasing compact height at the early stage of compaction due to the larger degree of particle rearrangement, but the final PSD was similar for all the compacts. Analysis indicated particle fragmentation energy accounted for 2% of the total input energy while more than 50% of input energy was to overcome the friction between particles.
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•The effect of particle fragmentation on compaction was numerically investigated.•A growth-relaxation algorithm was implemented to improve the accuracy of the fragmentation model.•The variations of force and pore structures with particle fragmentation were analysed.•The compaction mechanisms were characterised through energy analysis.
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