Anti-shock loading capability of a fluidized-bed flocculator

The efficiency of a fluidized-bed flocculator with 800-μm particles of 1360 kg/m³ in density was studied, and the anti-shock capability of the unit was estimated for three kinds of industrial wastewater: heavy turbidity wastewater, dispersed dyeing wastewater and starch wastewater. Steady removal efficiency was contributed by the following characteristics of the flocculator: (1) the dynamic conditions, flocculation time and velocity gradient, which were stabilized at a steady level as the loading rate changed; (2) hydrodynamic characteristics, especially the considerable rise of expanded bed height with increasing superficial velocity when small and light particles were employed as the solid phase; (3) flocs growth characteristics in the fluidized bed, which caused the density and size of the flocs being maintained at a compensational relationship, resulted the stabilized settling velocity of the flocs.     

Fragmentation of metal particles during heterogeneous explosion

Shock Waves - Heterogeneous explosives contain a mixture of standard explosive material and reactive metal particles. The inclusion of metal particles alters the energy density and energy release...     

爆炸抛撒金属颗粒群的装药方式

对炸药与金属颗粒混装及炸药与金属颗粒分装方式(添加分散剂和不添加分散剂)下炸药爆炸抛 撒金属颗粒群进行了实验研究。结果表明,分装方式下颗粒容易烧结成团且在空间分布不均,添加分散剂后 颗粒的分散性较好,没有烧结成团现象。混装方式下颗粒不会烧结,空间分散性较好。在有效距离内,从颗粒 空间数密度、颗粒对靶板的侵彻能力、工艺和安全等方面来看,分装加分散剂方式优于其他2种方式。     

REVEALING MICROSTRUCTURE OF FINE PARTICLES BY TEM

This paper introduces a method of cutting nano-scaled thin films from fine particles by using the technique of metal encapsulation. The interior morphology and microstructure of fine particles are then examined by TEM or HREM.     

Thermo–elasto–plastic stresses in functionally graded materials under consideration of the fabrication process

Summary  The present study analyzes elasto–plastic thermal stresses in some particle-reinforced functionally graded material plates (FGP) by taking into consideration residual stresses of the fabrication process. For the FGP, the region near the cooling metal surface consists of distributed ceramic particles in a metal matrix, while the region near the heating ceramic surface contains distributed metal particles in a ceramic matrix. We use the thermo–elasto–plastic constitutive equation of a particle-reinforced composite, taking into consideration temperature changes and damage as well as the reinforcing effect of particles. Elasto–plastic thermal stresses are discussed here with the goal of reducing the thermal stresses. Two kinds of particle-reinforced FGP are considered: the first kind (FGP1) represents distributed ceramic particles in the metal matrix, and the second one (FGP2) represents distributed metal particles in the ceramic matrix. We modify the thermo–elasto–plastic constitutive equation of a particle-reinforced composite for the FGP2 by taking into consideration temperature changes and damage as well as the reinforcing effect of particles. Using the temperature-dependent material properties, three cases of temperature conditions are studied. The first one is the cooling from the fabrication temperature to the room temperature, the second one is the heating from the room temperature, and the last one is the heating after cooling from the fabrication temperature. The particle volume fraction is assumed to vary according to a power function in the thickness direction of the FGPs. Using the finite element method, the effects of the distribution parameter of the composition on the macroscopic stress, the stress in the matrix and the stress in the particle in the FGPs are discussed. Also, the effects of the particle volume fraction and the fabrication temperature on the maximum tensile matrix stress are discussed. Received 22 November 2000; accepted for publication 24 April 2001     

菱形颗粒冲击材料表面冲蚀磨损特性分析

基于弹射试验装置,借助高速摄像机捕捉不同入射条件下单个菱形颗粒冲击金属表面的动态过程,同时结合试验过程建立菱形颗粒冲击金属表面的FEM-SPH耦合数值模型,通过对比试验现象与仿真结果优化数值模型参数,最后借助数值模型进一步分析菱形颗粒在临界冲击、自身初始旋转以及重复冲击等工况下的运动行为及预测的凹坑轮廓形态. 结果表明:优化后的模型能够很好地捕捉颗粒冲击过程中金属表面凹坑的产生及演化规律,并能详细记录颗粒的入射行为及反弹规律,测得颗粒反弹速度和反弹角度误差均在14%以内. 临界冲击工况下颗粒动能损失最大,且冲击角越高,残余动能越少;颗粒初始旋转能够改变其反弹后的运动行为及金属表面材料的失效方式;颗粒重复冲蚀对材料表面的作用机制与后续颗粒的入射条件有密切关系,模型成功捕捉到重复冲蚀导致的材料破坏加深和破坏减缓两种特殊现象.      

FLOW BEHAVIOR AND MASS TRANSFER IN THREE-PHASE EXTERNAL-LOOP AIRLIFT REACTORS WITH LARGE PARTICLES

The flow behavior and mass transfer in a three-phase external-loop airlift reactor can be improved by adding large particles. The mass transfer and liquid dispersion behavior for a three-phase external-loop reactor with large particles are studied in terms of the effect of the diameter and loading of the large particles on the liquid dispersion coefficient and mass transfer coefficient, The results showed that increasing the diameter or loading of the large particles tend to decrease dispersion and intensify mass transfer, and that an increase in the diameter of the large particles remarkably decreases the particle loop rate, while the effect of fine particles is much less notable.     

FLOW BEHAVIOR AND MASS TRANSFER IN THREE-PHASE EXTERNAL-LOOP AIRLIFT REACTORS WITH LARGE PARTICLES

The flow behavior and mass transfer in a three-phase external-loop airlift reactor can be improved by adding large particles. The mass transfer and liquid dispersion behavior for a three-phase external-loop reactor with large particles are studied in terms of the effect of the diameter and loading of the large particles on the liquid dispersion coefficient and mass transfer coefficient. The results showed that increasing the diameter or loading of the large particles tend to decrease dispersion and intensify mass transfer, and that an increase in the diameter of the large particles remarkably decreases the particle loop rate, while the effect of fine particles is much less notable.     

Electrical Fracture Diagnostics for Metal Bodies in a Gas Flow

New results of studying the electrical aspects of metal body fracture in a gas flow are obtained. The basis of the investigations and the diagnostic method developed is a fundamentally new effect discovered by the authors: most of the microparticles formed when metal specimens (rods) fracture have the same (positive) electric charge. When the specimen is immersed in a gas flow, the charged particles formed are carried out by the flow into the ambient space and the electric field generated by the particles can be recorded by special probe-antennas. The electric signals produced by fracturing rods made of different metals immersed in a high-temperature jet of combustion products are measured. An approximate theoretical dependence of the total charge on the particles formed as a result of fracture on the strength characteristics of the rod material is obtained.     

水润滑条件下磨粒尺寸对橡胶密封副摩擦学行为的影响

磨粒磨损是各类机械橡塑密封装备的一种典型失效形式. 本文中开展了水润滑条件下磨粒尺寸对O型橡胶密封配副摩擦学行为的影响研究,分析了不同颗粒尺寸下的摩擦系数时变特性,探讨了不同运行阶段下的磨损形貌、颗粒运动特性和损伤失效机制. 结果表明:颗粒尺寸对橡胶/金属密封副的摩擦学性能有重要影响;研究发现了影响摩擦系数和损伤机制的两个颗粒尺寸临界值;当颗粒尺寸大于临界值约75 μm时,颗粒难以穿过密封界面,但少数颗粒能嵌入到摩擦副的接触区两侧,犁削作用下的金属表面产生较深的犁沟;当颗粒尺寸介于两临界值内时,接触副两侧形成“颗粒嵌入带”,颗粒以单独或颗粒群形式嵌入到橡胶内,尽管犁削了配副金属但也起到了良好的承载作用,表现出较低的摩擦系数并减缓了橡胶的磨损;当颗粒尺寸约小于另一临界值12.5 μm时,颗粒能较自由地通过摩擦界面,对配副金属表面起到了抛光效应,但也加速了橡胶的冲蚀磨损,橡胶磨损表面呈现“突脊-犁沟-突脊”交替特征,因此工程上应尽量避免此类现象的发生.      

聚合物/金属摩擦界面迁移过程的数值模拟

聚合物材料在与金属对偶件滑动接触时,会在摩擦界面上发生界面迁移,导致在金属对偶件表面形成一层转移膜.转移膜的存在能够有效地降低聚合物材料的磨损.本文基于离散单元法,利用二维颗粒流程序(PFC2D),对PTFE/45钢界面迁移过程进行数值模拟分析.模拟结果表明:PTFE与45钢组成摩擦副时,会在45钢表面形成一层转移颗粒层.一开始转移颗粒数逐渐增大,一段时间后随着转移颗粒层的形成与完整,转移颗粒数趋于一个定值且保持动态平衡,磨损颗粒增加速率显著下降,并维持在一个稳定的值.     

三维自适应FE-SPH耦合算法在多层间隔金属靶侵彻问题中的应用

鉴于有限元算法不能有效地模拟侵彻过程所产生的金属碎片, 本文中基于三维自适应FE-SPH耦合算法的基本理论, 自主开发了模拟多层间隔金属靶侵彻问题的三维FE-SPH耦合计算程序。该程序采用四面体单元对多层间隔金属靶侵彻模型进行初始离散, 计算过程中, 当四面体单元等效塑性应变超过某一设定值时, 单元自动转化为SPH粒子, 并引入有限单元-粒子接触算法和耦合算法, 实现大变形和破碎区域采用SPH方法计算, 克服有限元法单元畸变存在的问题。多层间隔靶侵彻算例分析表明, 三维FE-SPH耦合计算程序采用等效塑性应变作为转化判据计算结果较稳定, 并且能够有效地再现侵彻过程中所产生的碎片, 能够模拟侵彻碎片对后层靶的毁伤效应。     

激光选区熔化增材制造中的粉体热动力学行为

激光选区熔化(SLM)可以直接成形近全致密、性能接近锻件的复杂结构金属零件, 是金属增材制造(3D打印)领域的热点技术之一. SLM成形过程中粉末颗粒的热/动力学行为复杂, 与零件成形缺陷及力学性能紧密相关. 本文介绍了离散单元法(DEM)与计算流体力学(CFD)联合建模在SLM中的创新应用, 结合粉末床原位测试及成形在线监测, 探索SLM粉末铺设和粉末床熔融两个工艺环节的复杂粉体热/动力学行为机制. 研究发现, 粉末铺设过程中: 粉体的黏结效应、壁面效应和渗流效应3种机制相互竞争、共同支配粉末动力学行为并最终决定粉末床铺设质量. 粉末床熔融过程中: 熔池喷发的高温金属蒸汽带动环境保护气体形成内旋涡流, 由此驱动散体粉末形成复杂流固耦合运动, 导致粉末床飞溅与剥蚀现象; 热浮力效应对粉末运动不起主导作用. 文中提出了DEM-CFD双向动态耦合模型, 可以充分考虑离散粉末与熔池蒸发气体之间的热力耦合作用, 为SLM粉体熔融热/动力学行为的仿真模拟提供了一种新途径.      

FAE炸药跌落撞击安全性数值分析

提出了冲击载荷作用下燃料空气炸药(FAE)的三相混合物材料模型. 在模型中, FAE炸药被模型化为具有一定的微观结构, 其液体组分及气体组分填充于金属固相颗粒互相搭结构成的骨架孔洞内. 另外, 材料模型中引入了气体的绝热压缩模型, 使得整个模型可以给出在冲击加载条件下FAE炸药中各组分的应力状态及温度场, 从而为合理地判定FAE装药的安全性提供了条件. FAE三相混合物材料模型作为用户自定义子程序嵌入到动力学程序AUTODYN中. 最后, 应用FAE炸药材料模型对某FAE战斗部从20\,m高处垂直跌落至钢质地板的撞击过程进行了数值模拟. 基于FAE装药在这种跌落撞击过程中的应力和温度状态,对其安全性进行了评价.      

一种低附带弹药金属颗粒定向加载技术

为了实现低附带弹药金属颗粒定向可控加载,研制了采用爆轰方式驱动低附带弹药金属颗粒的发射装置,并进行了不同尺寸钨球颗粒与不同装药比的发射实验。运用高速摄影与高速红外摄影捕捉爆轰驱动过程中颗粒抛撒分布和速度,并采用CT断层扫描和三维图像重建再现了颗粒在肥皂靶中的三维空间分布。实验结果揭示了爆轰驱动下颗粒加速、减速和散落3个阶段的特征。钨球颗粒速度均值范围为689.84~889.14 m/s,最大侵彻深度为65.23~167.35 mm,颗粒加载上靶率在30%以上。发射装置中金属颗粒/装药质量比可调,能重复使用。采用肥皂靶、高速摄影、高速红外相结合的测试方法有效可行,CT图像重建用于终点弹道参数判读能提高结果分析精度。以上结果可为研究低附带弹药对生物目标的毁伤效应、致伤机理和生物损伤判定与救治提供有效可行的技术与方法。     

颗粒在大涡结构中的弥散

气相采用大涡模拟方法,颗粒相采用轨道模型研究了三维后台阶气粒两相湍流流动的大尺度涡结构的瞬时演变过程以及颗粒的瞬时弥散规律.比较了不同入流速度的颗粒在大涡结构中的瞬时弥散特性,尤其研究了高速释放大颗粒的弥散特性.三维流动中大尺度涡结构具有明显的脱离、发展、合并和破碎过程.小颗粒的分布受大涡结构的控制,其空间的弥散过程与流体 大涡结构的空间发展相一致,但是由于三维流动中大涡边缘和中心区的压力差,颗粒在大尺度 涡的边缘出现密集.而大颗粒在流场中的分布受其惯性控制,对气相的涡结构不敏感.高速释放到流场中的大颗粒受惯性影响最大,保持在其原有动量方向上运动.     

Numerical study of flows of reacting composite mixtures

A distributed mathematical model is proposed to describe a flow of a mixture of gases, fine particles of a reacting metal, and droplets of a hydrocarbon fuel. The heterogeneous chemical reaction of low-temperature oxidation of the metal, the homogeneous oxidation reaction of the reacting vaporized liquid fuel, and the difference in phase velocities and temperatures are taken into account. It is shown that this model can be used to describe the problems of detonation in a mixture of a reacting gas and reacting solid particles, and the problems of ignition of a mixture of aluminum particles and tridecane droplets. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 2, pp. 128–136, March–April, 1999.     

Numerical solution and sensitivity analysis of filter cake permeability and resistance to model parameters

The migration and capture of solid particles in porous media occur in fields as diverse as water and wastewater treatment, well drilling, and in various liquid-solid separation processes. Filter cakes are formed when a liquid containing solid particles is forced through a pervious surface which allows the liquid transport while retaining solid particles. Following a literature survey, a governing equation for the cake thickness is obtained by considering the instantaneous mass balance. Later, numerical solutions for the cake thickness, cake permeability, cake resistance, solid particle velocity (cake compression rate) and concentration of suspended particles are obtained and a sensitivity analysis is conducted. The sensitivity analysis shows that the cake permeability and cake resistance are more sensitive to the rate constant of cake erosion than they are to the rate constant of particle capture. However, the concentration of suspended solid particles, and the solid velocity are mostly sensitive to the slurry parameter and the rate constant of particle trapping. Moreover, cake permeability, compressibility, concentration of suspended particles, and the solid velocity are very sensitive to the concentration at the filter septum. Finally, as expected, with a thicker slurry, more particles are captured inside the cake, thus forming a thicker and more resistant cake. Also, as more particles are being filtered at the filter septum, a thinner cake is formed and a smaller effluent concentration is achieved.