Extended HPM–DEM coupled simulation of drainage of square particles in a 2D hopper flow

An extended hard particle method–discrete element method coupled model (EHPM–DEM) is proposed to simulate the drainage of square particle in 2D hoppers. The EHPM extends the hard sphere model to adapt for non‐spherical shapes. A vertex‐based extension of DEM is developed to solve collisions of square particles. A new coupled method is proposed, using the EHPM to simulate binary collisions and DEM to simulate multiple contacts. The collision between two triangles and the drainage of square particles in hoppers were simulated and compared to theoretical analysis and experiments, respectively, for validation. Moreover, the advantages of EHPM over DEM and the EHPM–DEM coupled solution over the pure soft DEM solution in computational efficiency have been demonstrated. In addition, the effects of restitution coefficient, friction coefficient, and the filled height on the discharge rates are analyzed, and a uniform discharge feature is discovered, which is especially useful for scaling studies. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1863–1876, 2016     

DEM Study on the effect of particle-size distribution on jamming in a 3D conical hopper

Despite the advancement on the understanding on the unwelcome phenomenon of hopper jamming, the influence of the particle-size distribution (PSD) width of the ubiquitous continuous PSDs remains unknown. Accordingly, this study investigated using discrete element method a range of PSD widths (10%≤σ/μ≤50% ) of lognormal PSDs with a constant mean particle diameter of 10 mm in a three-dimensional hopper. Results indicate that, although the monodisperse particles of 10 mm diameters do not jam, the wider PSDs (σ/μ≥ 30%) jam. The flatter arches and higher mass-averaged force that are linked to the denser packing of wider PSDs underlie the propensity to jam. To reduce the jamming probability, the friction coefficient and initial fill height can be reduced, but not changes in particle density. The results here highlight that the mean particle diameter alone is an insufficient parameter to predict jamming and the impact of PSD width is non-negligible. © 2018 American Institute of Chemical Engineers AIChE J, 65: 512–519, 2019     

Probability-based contact algorithm for non-spherical particles in DEM

Discrete element method (DEM) is widely used in studies of particulate matter. Most of these studies are limited in the modeling of spherical particles due to contact algorithm. It is important for DEM to simulate non-spherical particles if wondering more authentic behaviors of granular materials. A probability-based contact algorithm is presented in this paper. Contacts between non-spherical particles are transferred into those between spherical particles with probability. The comprehensive mechanical behavior of granular material with a large number of non-spherical particles can be efficiently modeled because contact detection algorithm for spherical particles remains. To validate the presented algorithm, Hopper experiments for spherical and polyhedral particles are physically and numerically performed. To achieve higher accuracy of the angles of repose and profile of the stable particulate piles, a digital image processing method is adopted. The numerical results are in good agreement with the experimental observation, both in the spherical and polyhedral particles. The probability-based contact algorithm is valid in describing the behavior of polyhedral particles.     

Pulsed fluidization—a DEM study of a fascinating phenomenon

An investigation of pulsed fluidization by discrete element method simulation is presented. The particles used were 0.5 mm in diameter and 2650 kg/m³ in density. The pulsed gas flow consisted of a fluctuating component superimposed on a constant component. The effect of gas pulsation was assessed through examination of bed pressure drop and bubble patterns for a wide range of conditions. The influence on fluidized bed behaviour of frequency and amplitude of pulsation, superficial gas velocity of the base flow, and the nature (type) of pulsation was studied. Transition from chaos to ordered behaviour and formation of regular bubble patterns were reproduced. It was found that regular bubble patterns arise from periodical formation of horizontally aligned voids near the distributor plate.     

DEM study on the discharge characteristics of lognormal particle size distributions from a conical hopper

This study employs the discrete element method (DEM) to investigate the impact of the widths of lognormal particle size distributions (PSDs) with the same mean particle diameter on hopper discharge behaviors, namely, discharge rate, particle velocities, and size‐segregation. Results reveal that (i) the hopper discharge rate decreases as PSD width increases; (ii) the mean discharge rates are constant with time, but the fluctuations increase as the PSD width increases; (iii) the overall size‐segregation increases with PSD width; (iv) the overall mean particle diameters of the narrower PSDs do not exceed the initial mean of 5 mm, whereas that of wider ones do; (v) the relationship between PSD width and particle velocities is non‐monotonic with no consistent trends; and (vi) no direct correlation exists between particle velocity and size‐segregation. The results here provide valuable insights on the behavior of the prevalent polydisperse mixtures in hoppers. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1174–1190, 2018     

One-Piece Stainless-Steel 3D Printed Minichannel Evaporators using Flow Boiling Carbon Dioxide

New concepts are required for high-performance minichannel evaporators with low mass and reduced size involved in the cooling of cylindrical or conical surfaces. The development of one-piece stainless-steel evaporators using flow boiling CO₂ for the cooling of conical copper test specimens heated by a foil heater element is presented. The specimens mimic a mobile cooling device used in high-energy and particle physics. The stainless-steel evaporators were manufactured with a state-of-the-art 3D stainless-steel printer via selective laser melting. The computer-aided design and the construction of this new type of evaporators are described. A dedicated two-phase accumulator controlled loop filled with liquid CO₂ was developed, it allowed for operating four parallel connected evaporators. Cooling efficiency and manufacture reproducibility were experimentally investigated by applying different thermal loads and refrigerant mass flows.     

Hydrodynamic characteristics of a horizontal flow ejector in a rectangular chamber

The effects of the volumetric flow rate of primary motive water, water height, and the geometric parameters of the hydrodynamiccharacteristics of the gas suction rate and gas phase holdup were investigated in a rectangular chamber (0.22×0.26×1.2 m-high) with a horizontal flow ejector. Gas suction rate increased with increasing volumetric flow rate of the primary motive water, mixing tube length and diffuser length, but it decreased with increasing water height and nozzle diameter. The gas phase holdup was directly proportional to gas suction rate, indicating its corresponding increase with the volumetric flow rate of the primary motive water. Conversely, it decreased with increasing water height and nozzle diameter. However, the mixing tube length affected the gas phase holdup minimally compared to other operating parameters. Both the gas suction rate and gas phase holdup correlated with the dimensionless equations of operating parameters.     

储层流动单元研究新技术在油田开发中的应用

流动单元研究提供了精细解剖砂体,表征砂体内部非均质性的新方法。本文在传统流动单元划分的基础上应用流动带指标新方法(F z)进行储层流动单元的定量划分,为合理进行油田开发动态分析提供依据,同时开辟了一个可预测可操作的有效流动单元研究方法。     

Predicting discharge dynamics of wet cohesive particles from a rectangular hopper using the discrete element method (DEM)

Accurate prediction of the discharge rate from hoppers is important in many industrial processes involving the handling of granular materials. The present work investigates the parameters affecting the discharge rate of a wet cohesive system from a quasi-3-D, rectangular hopper using the discrete element method (DEM). The cohesion between the particles is described by a pendular liquid bridge force model and the strength of the cohesive bond is characterized by a Bond number. The Beverloo correlation is applied to cohesive systems by modifying the Beverloo constant as a function of Bond number. The predictions obtained from this modified correlation fit the simulation data reasonably well. In addition, the effect of hopper angle in cohesive systems is shown to follow a trend similar to cohesionless systems, where the discharge rate is insensitive to changes in hopper angle except below a critical angle (with respect to the vertical) where the discharge rate increases rapidly. This critical angle of flow decreases with increasing cohesion.     

Modelling of granular mixtures placing. Comparison between a 3D full-digital model and a 3D semi-digital model

This paper concerns a comparative study between a 3D full-digital and a 3D semi-digital model with the aim to represent the gravitational placing of granular mixtures with a very high number of particles. Both models use a completely digitized volume and a similar filling procedure considering ramdom local rules for the particles displacements and taking into account only steric repulsion between particles. The full-digital model is based on the digitization of the particles and their displacements. The semi-digital model takes into account the curvature of particles's surface and displacements of particles depend on real numbers instead of integers. Mono-sized spherical particles systems in homothetic conditions were firstly studied with both models. It is shown that the full digital model is very sensitive to the size of particles. Random loose packing of mono-sized systems can be stimulated correctly only when the radius of particles is equal or higher that 4 pixels. On the contrary, the semi-digital model allows a good representation of the random loose packing of mono-sized spherical particles sysytems independently of the particles radius. The comparison between the two models also concerns the study of binary mixtures with varying proportion of small particles     

三维波纹结构塔板上薄膜流体的流动特性研究

在化工传质过程中,薄膜流体(film flow)经常被用来改善液体与气体间的质量传递。填料板上的波纹结构能引起液体薄膜流动特性的改变,从而提高薄膜流体的传质效率。在本次研究中,作者对三维波纹结构塔板上的液体薄膜进行数值仿真,研究了三维波纹结构对液体薄膜流动特性的影响,并分析流动特性与气液两相间传质的联系。数值仿真中使用了开源计算流体力学软件Open FOAM中基于VOF(volume of fluid)法的多相流求解器计算薄膜流体自由表面位置。将数值仿真中的速度计算结果与文献中基于PIV(particle image velocimetry)法的测量实验结果比较后发现,两者吻合良好。在此基础上,对三维结构波纹上薄膜流体的流场进行分析。结果显示,三维波纹结构除了能在薄膜流体中引起竖直方向上的速度发生变化外,还能造成与流体流动方向垂直的横向扰动,这是二维波纹结构不具有的作用。在三维波纹结构塔板上,流体在波谷处汇聚,在到达下一个波峰时又分散。这种流动特性对不同浓度的流体进行混合非常有利,从而能大幅度提高薄膜流体与气相间的传质效率。     

非球形颗粒在矩形料斗中的流动特性(英文)

Flow behaviors of four kinds of granular particles (i.e. sphere, ellipsoid, hexahedron and binary mixture of sphere and hexahedron) in rectangular hoppers were experimentally studied. The effects of granular shape and hopper structure on flow pattern, discharge fraction, mean particle residence time and tracer concentration distribution were tested based on the visual observation and particle tracer technique. The results show that particle shape affects significantly the flow pattern. The flow patterns of sphere, ellipsoid and binary mixture are all parabolic shape, and the flow pattern shows no significant difference with the change of wedge angle. The flowing zone becomes more sharp-angled with the increasing outlet size. The flow pattern of hexahedron is featured with straight lines. The discharge rates are in increasing order from hexahedron, sphere, binary mixture to ellipsoid. The discharge rate also increases with the wedge angle and outlet size. The mean particle residence time becomes shorter when the outlet size increases. The difference of mean particle residence time between the maximum and minimum values decreases as the wedge angle increases. The residence time of hexahedron is the shortest. The tracer concentration distribution of hexahedron at any height is more uniform than that of binary mixture. The tracer concentration of sphere in the middle is lower than that near the wall, and the contrary tendency is found for ellipsoid particles.     

3D microstructure model and thermal shock failure mechanism of a Si3N4-bonded SiC ceramic refractory with SiC high volume ratio particles

In this study, an efficient method was proposed to establish 3D microstructure model of a Si₃N₄-bonded SiC ceramic refractory with SiC high volume ratio particles and its failure mechanism under thermal shock was studied based on the established microstructure model. The proposed modeling method based on modified 3D Voronoi tessellation method and “precise shrinkage ratio method” was able to establish 3D geometric model of a SiC ceramic refractory with SiC high volume fraction particles more quickly than usual methods. The modified 3D Voronoi tessellation method generated Voronoi polyhedrons (VPs) limited in finite space perfectly. The proposed “precise shrinkage ratio method” achieved a precise volume fraction of SiC particles in the established microstructure model. The crack initiation and propagation under thermal shock were calculated by employing the extended finite element method (XFEM) on the established microstructure model. The results showed the failure mode on micro-scale clearly and efforts of interface strength on the failure mode were also explored. The proposed modeling method was especially suitable for establishing 3D microstructure models of ceramic composites or isotropic metal-ceramic particle composites with high volume fraction particles and extended the use of VPs.     

乙烯气相聚合流化床反应器内Geldart B类和Geldart D类颗粒流动特性的三维数值模拟

乙烯气相聚合流化床反应器的设计、操作和优化依赖于对聚合物颗粒粒径大小和分布、气泡运动特性及聚合反应状况的准确描述。采用Eulerian-Eulerian 双流体模型和群体平衡模型耦合方法对某乙烯气相聚合中试规模的工业流化床反应器分别处于常规聚合工艺(属Geldart B 类颗粒)和免造粒工艺(属Geldart D 类颗粒)时床体的气固流动特征以及不同颗粒类型对反应器操作状态和颗粒运动特性的影响进行了三维数值模拟研究。与传统聚乙烯生产工艺相比,免造粒工艺时的Geldart D 类聚合物颗粒更易聚集于气体入口处区域,而且会产生明显的旋涡并出现较大的气泡。研究结果可为免造粒聚乙烯生产工艺的工业推广应用提供参考。     

Synthesis, 3D‐QSAR,and Structural Modeling of Benzolactam Derivatives with Binding Affinity for the D2 and D3 Receptors

A series of 37 benzolactam derivatives were synthesized, and their respective affinities for the dopamine D₂ and D₃ receptors evaluated. The relationships between structures and binding affinities were investigated using both ligand‐based (3D‐QSAR) and receptor‐based methods. The results revealed the importance of diverse structural features in explaining the differences in the observed affinities, such as the location of the benzolactam carbonyl oxygen, or the overall length of the compounds. The optimal values for such ligand properties are slightly different for the D₂ and D₃ receptors, even though the binding sites present a very high degree of homology. We explain these differences by the presence of a hydrogen bond network in the D₂ receptor which is absent in the D₃ receptor and limits the dimensions of the binding pocket, causing residues in helix 7 to become less accessible. The implications of these results for the design of more potent and selective benzolactam derivatives are presented and discussed.     

A soft‐sphere‐imbedded pseudo‐hard‐particle model for simulation of discharge flow of brick particles

A novel hybrid approach of soft‐sphere‐imbedded pseudo‐hard‐particle model is proposed to cope with the complex collision of nonspherical particles. In this approach, the boundary of a host hard particle is covered by a series of soft‐spheres, which are allowed to oscillate about the equilibrium position according to the position, orientation, and shape configuration of the host particle. The collision processes are twofold: as a predictive process, particle‐particle interaction takes place through the collision between the distributed soft‐spheres, which causes subspheres to deviate from the equilibrium positions; as a corrective process, relaxation is superposed to allow the soft‐spheres to move back toward the equilibrium positions quickly. Consequentially, this process generates the force and torque on the host particle and determines its movement. Finally, after validation, this new model is used to explore the effects of aspect ratio and base angle on the discharge of brick particles in hoppers. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3562–3574, 2016     

Uniform dispersion of nano-Al2O3 particles in the 3D graphene network of ternary nanocomposites

The interconnected 3D graphene network framework wrapping homogeneous dispersion of nano-Al₂O₃ particles was successfully designed in the phenolic resin-based ternary nanocomposite. Firstly, the solvothermal method was used to prepare graphene hybrid with highly dispersive nano-Al₂O₃ particles in a mixed solvent of ethanol absolute and deionized water. Nano-Al₂O₃ particles were homogeneously dispersed in the 3D graphene network framework when the volume ratio of ethanol absolute and deionized water was 1:1. Then the phenolic resin monomer was impregnated into the graphene hybrid by the appropriate heating process. Finally, the nano-Al₂O₃ particles/3D graphene/phenolic resin ternary nanocomposite was fabricated by in-situ polymerization. The homogeneous dispersion of nano-Al₂O₃ particles was well maintained in the nanocomposite. The nanocomposite possesses high mechanical properties. The nanocomposite leads to 35.02% and 31.50% increases in hardness and compressive strength than that directly dispersed nano-Al₂O₃ particles in the phenolic resin, respectively.     

DEM and experimental analysis of the water retention curve in polydisperse granular media

We investigate the water distribution and the link between suction and water content in granular media. Firstly, we examine the effect of suction on the shape and the volume of the liquid bridge by four different methods. Method I is based on the local expression of the capillary force coupled with the gorge method and Method II is based on the Laplace law. These two methods use the toroidal approximation. Methods III and IV are based on the integration of the differential equation that defines the liquid bridge shape (established from the Laplace law). This local behaviour is then used in a discrete element study of a sample composed of several thousands of grains. We focus our study on the pendular state. A liquid film around the grains involving the continuity of the liquid phase is assumed. The water distribution and the water content associated with a given suction are calculated. Then retention curves of the granular media are built. A parametric study is made to bring to light the effect of macroscopic parameters (grain-size distribution) and physical parameters (liquid/air surface tension and contact angle) on the water retention curve. Finally, numerical data are compared to experimental results.