Simulation of particle flow in a bell-less type charging system of a blast furnace using the discrete element method

A three-dimensional model was established by the discrete element method （DEM） to analyze the flow and segregation of particles in a charging process in detail. The simulation results of the burden falling trajectory obtained by the model were compared with the industrial charging measurements to validate the applicability of the model. The flow behavior of particles from the weighing hopper to the top layer of a blast furnace and the heaping behavior were analyzed using this model. A radial segregation index （RSI） was used to evaluate the extent of the size segregation in the charging process. In addition, the influence of the chute inclination angle on the size segregation and burden profile during the charging process was investigated.     

Analysis of gas–solid flow and shaft-injected gas distribution in an oxygen blast furnace using a discrete element method and computational fluid dynamics coupled model

Ironmaking using an oxygen blast furnace is an attractive approach for reducing energy consumption in the iron and steel industry. This paper presents a numerical study of gas–solid flow in an oxygen blast furnace by coupling the discrete element method with computational fluid dynamics. The model reliability was verified by previous experimental results. The influences of particle diameter, shaft tuyere size, and specific ratio (X) of shaft-injected gas (SIG) flowrate to total gas flowrate on the SIG penetration behavior and pressure field in the furnace were investigated. The results showed that gas penetration capacity in the furnace gradually decreased as the particle diameter decreased from 100 to 40 mm. Decreasing particle diameter and increasing shaft tuyere size both slightly increased the SIG concentration near the furnace wall but decreased it at the furnace center. The value of X has a significant impact on the SIG distribution. According to the pressure fields obtained under different conditions, the key factor affecting SIG penetration depth is the pressure difference between the upper and lower levels of the shaft tuyere. If the pressure difference is small, the SIG can easily penetrate to the furnace center.     

尼龙粉末在SLS预热温度下的离散元模型参数确定及其流动特性分析

尼龙粉末是增材制造中常用的粉体材料,温度对其流动性有重要影响. 探索尼龙粉末增材制造预热温度下的流动性是研究选择性激光烧结(selective laser sintering, SLS)工艺中粉体铺展成形的基础. 选取SLS技术中的尼龙粉末为原材料,采用离散元数值方法,研究尼龙粉末的流动行为,是增材制造工艺数值模拟和铺粉工艺优化的研究热点. 以Hertz-Mindlin模型为基础,基于Hamaker理论模型和库伦定律,在尼龙粉末的接触动力学模型中引入范德华力和静电力,建立预热温度下尼龙粉末流动的离散元模型(discrete element method, DEM),通过对比相应实验结果,标定了该模型的参数. 对加热旋转圆筒中尼龙粉末流动过程进行了DEM数值模拟,校核了所建模型的正确性,并研究了粉体粒径分布对尼龙粉末流动特性的影响规律. 研究表明,尼龙粉末黏附力是静电力与范德华力的共同作用结果;随着粉体粒径的增大,尼龙粉末崩塌角增大,流动性增强;相对于高斯粒径分布,粒径均匀分布的尼龙粉末颗粒流动性更强. 研究结果可指导SLS中铺粉工艺的优化.      

RESEARCH ON THE COLLISION EFFICIENCY OF NANO-PARTICLE-TO-WALL WITH EXTERNAL ELECTRIC FIELD

着重考虑了电场作用下,壁面排斥力对颗粒-壁面碰撞效率的影响. 采用Matlab 中的龙格库塔方法,对颗粒-壁面碰撞的压缩阶段及回弹阶段的动力学方程组进行求解,并对Maxwell 速度分布进行积分获得不同速度方向下的碰撞效率. 研究表明,颗粒的碰撞效率随着碰撞角度的增加而增大,并最终达到一个临界值,即完全凝并时的碰撞效率;且颗粒的碰撞效率将因壁面排斥力的影响而减小,即壁面排斥力在一定程度上阻碍了颗粒的凝并.     

竖冷设备中烧结矿石偏析行为的GPU高性能模拟

随着钢铁工业流程和技术的不断优化及节能减排要求的不断升级,如何高效回收利用各生产工序中的工业余热成为钢铁工业面临的重要课题.竖冷设备既可以有效回收烧结矿石的显热,大幅提高能源的利用率,又可以有效减少烧结工序中的粉尘,降低烧结工艺的环境污染,因此得到了高度重视.但现有竖冷设备容易出现烧结矿石的偏析问题,严重影响了显热回收的效率和设备运行的稳定性.为此,采用离散元法(discrete elementmethod,DEM)研究竖冷设备中烧结矿石的偏析,重点针对不同结构进料管对烧结矿石偏析的影响.研究发现,虽然缓冲仓内每次加入的烧结矿石皆混合均匀,但由于不同粒径的烧结矿石在进料过程中存在动量差异,导致了竖冷设备内明显的颗粒偏析,在料堆堆尖处呈现小颗粒多大颗粒少的现象,并且料层主体的偏析与进料管的结构密切相关.由于进料管的结构是进料过程的决定性因素,因此提出了通过改变进料管的结构抑制竖冷设备内烧结矿石偏析的可能途径,对提高烧结矿石的显热回收效率具有参考意义.      

THE INFLUENCE OF THE NEW TECHNOLOGY OF FIXED SURFACE PERFORATION ON CASING STRENGTH1)

用于非常规储层的定面射孔工艺可有效地降低水力裂缝的起裂压力,提高近井筒的泄油面积;但该工艺对套管强度的影响研究较少。本文基于流固耦合理论,建立了地层$\!$-$\!$-$\!$水泥环$\!$-$\!$-$\!$射孔套管的应力耦合模型,退化为裸套管与API标准进行比对,效验了模型,并发现地层约束条件下套管承受内压的能力提高了1.48$\sim$2.16倍,在此基础上,给出了套管尺寸、射孔直径及射孔相位角对套管承压能力的变化规律。计算表明：螺旋射孔方位角为45$^\circ$时,定面射孔间夹角为30$^\circ$时,套管内径越小,套管壁厚越厚,则套管的承压能力越高;相同参数下,定面射孔工艺比螺旋射孔工艺引起的套管承压能力略低。     

NUMERICAL STUDY ON THE GROWTH PROCESS OF SECONDARY AEROSOL IN THE FOG

雾环境气溶胶之间的碰撞和凝并是气溶胶迁移、生长的动力学基础. 基于颗粒群平衡方程和多重蒙特卡洛方法,针对雾环境中二次液态气溶胶生长过程开展数值研究,着重分析了湍流和布朗作用机制对单分散和指数分布的二次气溶胶碰撞凝并的影响. 结果表明:雾环境气溶胶之间的碰撞凝并使得颗粒的总数目减少,颗粒平均体积逐渐增大. 对于初始尺度为自由分子区、单分散的气溶胶,布朗运动时间为600 s时,二次气溶胶平均尺度增大至初始的202.7倍左右,数目降至初始的0.006. 对于湍流作用下有布朗运动的二次气溶胶,在较短的时间内(如100 s)气溶胶尺度增至初始的163倍,颗粒数目降至初始的0.025倍, 说明雾环境流场的湍流运动引起二次气溶胶较强的输运和聚集,导致颗粒碰撞凝并概率增加,颗粒尺度增大.     

NUMERICAL SIMULATION OF THE GROWTH OF NANOPARTICLES IN A FLAME CVD PROCESS

The growth of titania nanoparticles in a flame CVD process has been simulated by computational fluid dynamics, based on the change rate of particle number density due to their collisions calculated from an integral collision kernel. The assumptions made on constant particle volume density nv (nd^3), constant density of particle surface area ns (nd^2), and constant entity nd^2.5 in coagulation process have been examined. Comparisons have been made on particle size distribution between measurement results and predictions from present model of particle growth and Kruis model of particle dynamics for titania nanoparticles synthesized by the flame CVD process. Effects of operational parameters such as O2 mole fraction and particle number density on mean particle size and size distribution have been discussed.     

不同爆炸载荷下TA2钛合金圆管膨胀破坏过程

金属柱壳破坏过程与材料、结构及载荷等相关,断裂结果呈现多种形式,采用有限元结合实验对不同爆炸载荷作用下,TA2钛合金圆管的破坏机制开展研究。有限元结果显示:对于理想均质柱壳,由于冲击波传播使壁厚中间形成二次塑性区,圆管壁厚中部的等效塑性应变总是大于内、外壁。在较高爆压下,裂纹在加载阶段从试样壁厚中部起始,沿45°或135°向内外壁剪切扩展;而在较低爆压下,破坏发生在自由膨胀阶段,断裂从内壁起始向外壁剪切扩展,两者破坏过程和机制不同,总体来说,与实验现象符合较好。相关实验中出现的一些外壁拉伸断裂现象,可能与试样的几何、材料缺陷等因素相关,其对金属圆管爆炸破坏的影响值得进一步关注。     

混凝土中爆炸数值仿真算法研究

用AUTODYN动力学软件对装药在混凝土介质靶中爆炸作数值仿真,研究了不同的网格描述方法,以及网格划分方法对计算结果的影响。通过实际算例比较了Lagrange算法和SPH算法以及不同的网格划分细度对靶径向、轴向不同距离的最大冲击压力、靶背过载以及损伤区、炸坑大小的模拟计算结果。分析得到了混凝土介质靶中爆炸问题数值仿真的合适算法,即拉氏算法对炸点近处的较高的最大冲击压力有较好的敏感能力,SPH算法对仿真计算爆坑形态以及抛掷体速度等具有明显的优势。对于算例问题,拉氏算法10 mm网格和SPH算法3 mm粒子即可满足一定的计算精度。     

Indirect measurements of streamwise solid fraction variations of granular flows accelerating down a smooth rectangular chute

In this study, we detail a method for estimating the flux-averaged solid fraction of a steady granular flows moving down an inclined rectangular chute using velocity measurements from along the perimeter cross section, combined with knowledge of the mass flow rate through the cross section. The chute is 5 cm wide and 150 cm long with an adjustable inclination angle. Four inclination angles, from 27° to 36° at 3° intervals, are tested. This angle range overlaps the internal friction angle of the glass beads, which are 4 mm nominal in diameter. Two slender mirrors are installed at the top and the bottom of the transparent chute to reflect images of the flow down the chute of the two surfaces. This allows photographic recording of the flow with a PIV imaging system and measurement of the flow depth. The mass flow rate can be calibrated simultaneously by collecting the accumulated mass at the chute exit. A linear interpolation scheme is proposed to interpolate the volume flow rate in each section of the chute. Sensitivity analysis suggests that the relative standard deviation of this scheme is about ±6%, i.e., the resultant solid volume fraction is only moderately dependent on the interpolation scheme for the tested cases. This is further confirmed by a direct intercepting method. Compared to the sophisticated magnetic resonance imaging (MRI) or the radioactive positron emission particle tracking (PEPT) methods, the present method is verified as a cost-effective and nonhazardous alternative for ordinary laboratories. Two distinct groups of streamwise dependence of the solid fractions are found. They are separated by the inclination angle of the chute and agreed with the internal friction angle. In the experiments using the two smaller inclination angles, the solid fraction ratios are found to be linear functions of the streamwise distance, while for the two larger inclination angles, the ratios have a nonlinear concave shape. All decrease with growing downstream distance.     

MOVING MODEL ANALYSIS OF THE INITIAL COMPRESSION WAVE IN TUNNEL FOR HIGH-SPEED TRAINS1)

利用动模型实验方法,主要研究列车头型横截面变化对初始压缩波的影响。结果表明,在列车最大横截面积和流线型部分长度相同的情况下,列车头部流线型部分的平均横截面积和截面变化率均会对初始压缩波的压力峰值产生影响,平均横截面积决定了初始压缩波形成时的强度大小,截面变化率则通过影响初始压缩波的压力梯度,决定在隧道传播过程中初始压缩波压力峰值的衰减程度。     

热激励器对超声速圆管射流的控制机理

采用大涡模拟方法研究了热激励器对马赫1.3 超声速圆管射流涡结构的影响, 采用加入净热源的方法模拟了热激励器的热效应, 分析了不同激励模态(m =±1 和m =±4) 的降噪和增加射流掺混的效果. 研究发现: (1)射流在受到激励作用时, 产生了更大的径向和周向速度扰动, 这有利于流向涡的形成, m =±1 激励模态下流向涡的发展更快, 特别是在摆动面上会有更大的增长速度; (2) 气动噪声分布的频带很宽, 激励作用对抑制高频气动噪声有较强的作用; (3) 对于在喷管壁面处产生的固壁噪声, m =±4 模态下的激励作用一定程度上加强了固壁噪声.      

Stochastic many-particle model for LFP electrodes

In the framework of non-equilibrium thermodynamics, we derive a new model for many-particle electrodes. The model is applied to \(\text {LiFePO}_{4}\) (LFP) electrodes consisting of many LFP particles of nanometer size. The phase transition from a lithium-poor to a lithium-rich phase within LFP electrodes is controlled by both different particle sizes and surface fluctuations leading to a system of stochastic differential equations. An explicit relation between battery voltage and current controlled by the thermodynamic state variables is derived. This voltage–current relation reveals that in thin LFP electrodes lithium intercalation from the particle surfaces into the LFP particles is the principal rate-limiting process. There are only two constant kinetic parameters in the model describing the intercalation rate and the fluctuation strength, respectively. The model correctly predicts several features of LFP electrodes, viz. the phase transition, the observed voltage plateaus, hysteresis and the rate-limiting capacity. Moreover we study the impact of both the particle size distribution and the active surface area on the voltage–charge characteristics of the electrode. Finally we carefully discuss the phase transition for varying charging/discharging rates.     

M积分与夹杂/缺陷弹性模量的显式关系简

M积分在材料构型力学中表征着缺陷自相似扩展的能量释放率,而有效弹性模量下降量在传统损伤力学中是一个具有内变量属性的损伤参数. 探讨了两者之间的特定关系,以此为材料构型力学与损伤力学搭建桥梁.借助穆斯海里什维利（Muskhelishvili）复势函数方法获取无限大弹性平面含圆形夹杂的弹性场解,根据M 积分的复势函数解析表达式得到M 积分与夹杂弹性模量的显式表达式. 随后通过有限元分析,对含复杂缺陷群的弹塑性材料进行数值模拟,结果表明内部缺陷区域的有效弹性模量下降与M 积分存在着特定关系. 基于此,提出利用材料构型力学中的外变量参数（M 积分）来替代损伤力学中的内变量参数（弹性模量下降量）描述材料的缺陷演化.     

Analysis of residual stresses in cylindrically anisotropic materials

Metal-forming operations leave residual stresses in formed parts due to nonuniform deformation occurring during the process. An exact method of determining the longitudinal, radial and circumferential (tangential) residual stresses in axisymmetric specimens was proposed by Mesnager¹ and further developed by Sachs². The boring-out technique can be complemented by a similar procedure in which strains are measured on the inner surface of the tube when material is removed from the outer surface.The work proposed in this paper extends previous analyses of residual stresses to the case where the material exhibits cylindrical elastic anisotropy, i.e., the principal axes of anisotropy correspond to the longitudinal, radial and circum-ferential directions of the tube. In addition, the present analysis considers the case in which a residual-shear stress, developed by twisting the tube about its axis, exists in the tube. When such shearing stresses are present, the principal axes of the residual-stress distribution are not parallel to the principal axes of the tube.     

Bending of an elastoplastic strip with isotropic and kinematic hardening

Summary  We propose an exact analysis for finite bending of a compressible elastoplastic strip with combined hardening at a given stretch normal to the bending plane. We apply the self-consistent eulerian rate-type elastoplastic model based on the logarithmic rate, in conjunction with a Tresca-type loading function. Utilizing the maximum circumferential stretch at the outer surface as an independent parameter, we derive exact analytic expressions for the bending angle, the bending moment, the outer and inner radii, the radii of the two elastic-plastic interfaces and the circumferential stretches at these two interfaces, as well as the stress distributions in every current cross section. In particular, we establish an explicit relation between the two circumferential stretches at the two elastic-plastic interfaces, and we show that this relation is universal for all cases of hardening. We show also that the maximum and minimum circumferential stretches at the outer and inner surfaces obey a reciprocal relation in the course of both elastic and elastic-plastic deformations. Received 4 June 2002; accepted for publication 14 November 2002 This research was carried out under financial support from the German Science Foundation (DFG) (Contract No.: Br. 580/26-2) and from Alexander von Humboldt Foundation. We wish to express our sincere gratitude to these Foundations.     

Constraint strength and axial/radial particle velocity profiles for an integrated riser outlet

To study axial/radial profiles of particle velocity in the affected region of an integrated riser outlet,a cold model was developed for the integrated riser reactor combining the gas-solid distributor with the fluidized bed.Constraints,related to the gas-solid distributor and the upper fluidized bed,imposed on the particle flow in the riser outlet region,were investigated experimentally.The experimental results showed that with increasing superficial gas velocity,these constraints have strong influences on particle flow behavior,the particle circulation flux in the riser,and the height of the static bed material of the upper fluidized bed.When the constraints have greater prominence,the axial profile of the cross-sectionally averaged particle velocity in the outlet region initially increases and then decreases,the rate of decrease being proportional to the constraint strength.Along the radial direction of the outlet section,the region where the local particle velocity profile tends to decrease appears near the dimensionless radius r/R = 0.30 initially and then,with increasing constraint strength,gradually extends to the whole section from the inner wall.Based on the experimental data,an empirical model describing the constraint strength was established.The average relative error of the model is within 7.69%.     

MOTION OF THE ECCENTRIC ELLIPSOID: GYROSCOPIC BALANCE CONDITION AND STABILITY

本文研究了摩擦系数 和偏心距离对偏心椭球体回转平衡的影响,得到了椭球极轴与地面法向夹角 的运动方程,导出了两类稳定解.结果表明摩擦力是椭球能否旋转至直立的必要条件,当 偏心距一定, 摩擦系数 越大其运动至直立所需的时间越短.偏心距阻碍直立现象的出现,摩擦系数 一定,偏心距 越大,其运动至直立所需的时间越长.当偏心距值增大到一定程度,其将无法直立而是至一稳定的角度,并且稳定角度正比于偏心距,偏心距继续增大,将不会出现回转平衡.     

阶梯型加速段对旋流喷嘴雾化特性的影响

旋流内芯是压力旋流式喷嘴最主要的旋流发生构件, 其几何特征直接影响压力旋流式喷嘴的喷雾特性.目前采用平滑型加速段的旋流内芯导流效率较低.为减小高流量条件下的能量损失, 使喷嘴旋流内芯加速段对喷雾介质产生预旋效应, 增强旋流强度, 本文设计喷嘴旋流内芯加速段为阶梯型, 其下段阶梯相对上段阶梯旋转15°, 旋向与喷嘴旋流槽方向相同.利用粒子动态分析仪(particle dynamics analysis system, PDA) 和高速摄影(charge coupled device, CCD)系统实验研究了加速段结构改进前后喷嘴的喷雾流量、雾场索特尔平均直径(Sauter mean diameter, SMD)、雾滴速度以及喷雾锥角, 并分析了SMD、 雾滴速度的轴向和径向分布特性. 结果表明, 背压差0.08\mathrm{~} 0.46 MPa 范围内, 阶梯型加速段对喷雾介质具有较好的预旋效果.喷嘴的流量提高了48.0% ~ 51.8%; 喷雾的轴向速度提升了31.4% ~ 32.8%, 径向速度提升了1.6% ~ 16.8%; 喷雾锥角减小了4.21°~6.57°; 较高背压差下喷雾下游的SMD减小了9.8%.与平滑型加速段相比, 阶梯型加速段的设计有效地提高了喷嘴的雾化质量.