This paper presents a CFD-DEM study of gas-solid flow in the raceway region in an ironmaking blast furnace (BF). In the simulation, 120,000 spherical particles are packed into a full-scale 2D slot BF ...geometry. Gas is injected into the geometry via tuyeres, generating raceways in different sizes and shapes under different conditions. It is observed that the raceway characteristics are much more complex under the full-scale BF than those observed under the laboratory scale in the literature. Three kinds of raceways can be identified: anti-clockwise circulating raceway, clockwise circulating raceway, and plumelike raceway. The results are analysed in terms of solid flow patterns, and flow and force structures of particles. The simulation has a good agreement with the observed in physical experiments in terms of two contrary circulating gas vortexes located upon and below tuyeres during raceway formation. Moreover, it is also indicated that operational variables have significant effect on one of the gas vortexes, which becomes the main circulating gas flow stream and determines the gas circulating direction.
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•CFD-DEM is used for raceway formation in a large scale BF.•Three types of raceways are observed and analysed by gas streamlines.•Raceway types are affected by gas velocity and tuyere length.
Effective thermal conductivity (ETC) is one of the most important thermal properties of packed granular materials, and is affected significantly by particle properties. In this work, discrete element ...method is used to study the effect of particle shape and size on the ETC of packed beds with ellipsoidal particles. The simulated ETC results are verified by experimental data with a good agreement. It is revealed that for coarse particles, the bed ETC increases with aspect ratio of ellipsoids deviating from 1.0. But for fine particles, the effect of aspect ratio becomes less significant. Such an effect is closely related to the difference of packing structures of ellipsoids at different sizes and aspect ratios. The results also reveal that at low particle thermal conductivity, the ETC is not affected much by particle size; at high particle thermal conductivity, the ETC increases with particle size. When bed temperature increases, the ETC increases markedly. The contributions of different heat conduction paths under different conditions are also quantified.
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•ETC of packed beds with ellipsoids is studied.•With aspect ratio deviating from 1.0, the ETC increases.•For coarse particles, ETC increases with particle size at high kp.•For fine particles, ETC increases with particle size and decreases with porosity.•For fine particles, contribution of the sub-conduction paths differs significantly.
The keyhole dynamics in the laser powder bed fusion (LPBF) process and its relationship with driving forces of surface tension, Marangoni force and recoil pressure have not been well addressed and ...quantified. In this work, through the modelling of melt pool dynamics, the keyhole life cycle including formation and drilling, fluctuation, and disappearance is captured. The results show that pores are sourced from the powder bed voids, the ejected keyhole protrusion, and the liquid eroded gas bubbles at the end of the track. An anticlockwise vortex is generated at the rear of melt pool, and the molten liquid travels in a clockwise path ahead of the melt pool. The variation of the powder layer thickness breaks the force equilibrium on the keyhole rim and leads to the depth fluctuation. The compressed rear keyhole is dominated by the surface tension, and the expanded front rim is controlled by the recoil pressure.
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•The keyhole lifetime includes drilling, fluctuation, and disappearance.•The variation of the powder layer thickness leads to the keyhole fluctuation.•The flow presents an anticlockwise vortex at the tail, and a clockwise path ahead.•Recoil pressure and surface tension dominate the keyhole dynamics.
Particle scale modelling of the process physics involved in laser powder bed fusion (LPBF) is a recent research hotspot, and many efforts have been made in the literature. However, a comprehensive ...review of the physics in LPBF and the effects of key variables such as powder- and operation-related parameters, and the mechanisms of defects formation is still lacking. This paper aims to offer a state-of-the-art review on multi-physics related to metal powder recoating and further melting and solidification process. The studies on powder bed recoating explored by discrete element method are presented first, including model theory and validation, effects of process parameters, and physics of particle flow and size segregation. Then powder melting approach based on computational fluid dynamics and the involved phenomena such as melt pool dynamics, keyhole dynamics, defects formation mechanisms of pores, and balling and spattering are described. The needs for future research are also discussed.
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•Powder bed recoating explored by discrete element method (DEM) is reviewed.•Physics of powder flow and size segregation in powder spreading is presented.•Powder melting based on computational fluid dynamics (CFD) is summarized.•Melt pool flow dynamics and defects formation are discussed.
Rotating drums are widely used in the industry for mixing, milling, coating, and drying processes. In the past decades, mixing of granular materials in rotating drums has been extensively ...investigated, but most of the studies are based on spherical particles. Particle shape has a significant effect on the flow behavior and thus mixing performance, but studies and understanding are still limited. In this work, discrete element method is employed to study the radial mixing of ellipsoids in a rotating drum. The effects of rotation speed and aspect ratio of ellipsoids on mixing quality and rate are investigated, and the underlying mechanisms are further developed. The results show that mixing index increases rapidly over time for both spheres and ellipsoids. Particles with various shapes of ellipsoids can reach well-mixed states after sufficient revolutions. The increase in rotation speed decreases the mixing rate for both spheres and ellipsoids. Generally, ellipsoids exhibit a higher mixing rate when the rotational speed ranges between 25 and 40 rpm. At 40 rpm, as the aspect ratio of ellipsoids deviates from 1.0, the mixing rate increases significantly and achieves the maximum when the aspect ratio is 0.75 or 1.5. A further increase in particle non-sphericity incurs a decrease in mixing rate. The increase in the deviation of aspect ratio from 1.0 contributes to stronger “slipping” of particles relative to the drum wall. Compared with ellipsoids, spheres have stronger diffusive mixing and weaker convective mixing in rolling or cascading regimes.
Facilitated by TiO2 particles absorbing La3+ in hydrosol, La-doped TiO2 was prepared by a sol-hydrothermal method. Electron paramagnetic resonance and Brunauer−Emmett−Teller (BET) surface area ...analysis showed that the obtained La-doped anatase TiO2 surface provided a higher density of oxygen vacancies without a change in the BET surface area. A theoretical calculation was carried out to explain the generation mechanism of the increased oxygen vacancies. The results showed that the La-doped anatase TiO2 (101) surface tends to engender oxygen vacancies. The photoelectric conversion efficiency of dye-sensitized solar cells fabricated from 1 mol % La-doped TiO2 reached 6.72%, which gave an efficiency improved by 13.5% compared with that of the cells fabricated from pure TiO2. The improvement in the efficiency was ascribed to more dye absorbed on the surface of TiO2.
Discrete element method is used in this work to examine the mechanisms determining powder deposition efficiency during powder spreading in powder bed fusion additive manufacturing. The results reveal ...that powder flow in the powder pile is critical for the formation and break of transient jamming. The forces on the underlying part increase first with spreading speed then decrease with a large fluctuation. For varied spreader shapes, a small inclined angle of the spreader surface makes the force barrier farther from the discharging gap, creating a larger region which ensure enough powder supply to the gap. Furthermore, a small inclined angle of the spreader surface close to the gap results in less particle motion conflicts at the gap and ensures larger discharging rate through the gap. This mechanism explains why spreaders with inclined or round surfaces help increase powder deposition efficiency.
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•Powder deposition mechanisms in powder spreading are investigated by DEM.•Load on part increases first with spreading speed and then decreases.•Advantages of inclined and round spreaders are explained.•Small inclined angles create larger regions for storing and supplying powders.•Small inclined angles have less particle motion conflicts and larger discharging rate.
Wear significantly affects equipment performance at mining sites, especially when excavating materials with diverse shapes, leading to increased bucket wear and reduced service life. This work ...combines the co-simulation of multibody dynamics and discrete element method with the Archard wear model to investigate the dynamic interactions between the bucket and non-spherical materials, and the impact of bucket wear on excavation performance. The results indicate that wear is evident on the bottom surface, side surface, and teeth of the bucket throughout the working cycle. The wear patterns observed for different teeth vary, highlighting the importance of maintenance for the middle and side teeth. Compared to spherical particles, ellipsoidal ones cause greater excavating resistance, bucket wear, and hydraulic fluctuations. As wear intensifies, the teeth become blunt, and the bottom surface exhibits unevenness, resulting in reduced payload and increased resistance and hydraulic power. Proposed wear mitigation strategies can help uphold satisfactory operating performance.
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•Bucket-material interactions are captured by MBD-DEM co-simulation.•Wear patterns on various parts of the bucket are predicted.•The effect of particle shape on excavation performance is examined.•The impact of bucket wear on excavation performance is explored.
