考虑地面积尘时置换通风的数值模拟

引言 置换通风系统始于北欧,较多应用于工业通风.近几年来,由于其合理的温度分布、较高的通风效率和明显的节能特性,置换通风系统已经越来越多地应用到民用建筑中.在北欧新建的办公建筑中,约有50%～70%的部分采用了置换通风系统[1].     

Numerical simulation of liquid transfer between particles

Liquid transfer between particles plays a central role in the operation of a variety of particle processing equipment, including flotation, spray-coating, flocculation, granulation, and drying. In each of these applications, the local liquid concentration within the bed dramatically affects the flow behavior of the system and can strongly impact performance. In this work, we introduce a dynamic liquid transfer model for use in discrete element modeling (DEM) of heterogeneous particle systems. We explicitly track moisture levels on individual particles and utilize an experimentally validated rule-set for liquid transfer upon forming/breaking contacts. As a test of this new model we present results from the simulation of a rotary drum spray-coating system, but expect that this liquid transfer-modified DEM is general and would be applicable to wide range of processing operations.     

Numerical simulation for the collision between a vortex ring and solid particles

This study is concerned with the numerical simulation for the collision between a vortex ring and an ensemble of small glass particles. The vortex ring, convecting with its self-induced velocity in a quiescent air, collides with the particles. The Reynolds number for the vortex ring is 2600, and the particle diameters are 50 and 200 μm. The Stokes number St for the 50 μm particle is 0.74, while the St for the 200 μm particle is 11.4. Immediately after the collision with the vortex ring, the 50 μm particles surround the vortex ring, forming a dome. It is parallel with the preferential distribution for the particle with St ? 1 around large-scale eddies, which has been measured experimentally and simulated numerically in various free turbulent flows. The 200 μm particles disperse more due to the collision with the vortex ring. This is attributable to the centrifugal effect of large-scale eddy, which has been reported by the numerical simulation for the motion of the particle with St = 10 in a wake flow. The collision between the vortex ring and the particles induces an organized three-dimensional vortical structure. It also reduces the strength and convective velocity of the vortex ring.     

Numerical simulation of the transient temperature distribution inside moving particles

This work is devoted to the two‐dimensional (2D) numerical simulation of heat and fluid flow by granular mixing in a horizontally rotating kiln. The heat and fluid flow in the gas phase are solved directly using a fixed Eulerian grid. At the same time, the particle dynamics and their collisions are solved on a Lagrangian grid. The no‐slip boundary condition on the particle surface is implemented using the fictitious boundary method. The heat transfer inside the particles is calculated utilising two models: the first is the direct solution of the energy conservation equation in Lagrangian and Eulerian space and the second is the so‐called linear model, which assumes a homogeneous distribution of the temperature inside each particle. Numerical simulations showed that if the thermal diffusivity of the gas phase significantly exceeds the same parameter of the particles, the linear model over‐predicts the heating rate of the particles. The analysis of the time‐averaged flow field inside the kiln showed that in the gas phase a double vortex structure is formed which increases the convective heat transfer in the upper part of the particulate bed. The influence of the particle size, the angular velocity of the drum and the fluid on the heating rates of particles is studied and discussed.     

Numerical simulation of the tube erosion resulted from particles impacts

In this paper,a tube erosion caused by the turbulent flow of a dilute particle-laden gas isstudied numerically.Eulerian equations are used to describe the gas-phase motion with the turbulenceviscosity evaluated from a k-ε model of turbulence.The effect of the turbulence with a stochasticdispersion model has been taken into account for the prediction of impact particle velocity and itstrajectory,The particle impact and rebound model and the erosion model of ductile alloys obtainedby Tabakoff et al.are used to predict the particle rebound phenomena and the erosion suffered bythe tubes.The results obtained in this study include the distributions of particle collision frequencyand erosion of tube surface.     

环流式旋风除尘器内颗粒运动的数值模拟

采用CFD软件Fluent提供的雷诺应力模型（RSM）和随机轨道模型,对环流式旋风除尘器内颗粒运动轨迹进行了数值模拟研究。预测了不同粒径颗粒的运动轨迹和分离效率。结果表明：颗粒在环流式旋风除尘器内的运动路径比常规除尘器长;特殊的流路设计,避免了常规旋风除尘器易产生的上灰环和颗粒短路问题,使除尘效率大幅度提高;除尘器内颗粒运动有较强的随机性,尤其对于小颗粒,受气流湍动影响显著。对不同粒径颗粒分离效率的预测表明：环流式旋风除尘器的分割粒径为1．25μm。     

Numerical simulation on mixing kinetics of slender particles in a rotary dryer

The mixing processes of slender particles in a rotary dryer fitted with lifters were simulated in three dimensions. Particle motion was modeled by the Discrete Element Method (DEM) and a three dimensional collision model for slender particles was developed. Contact force, friction force and gravitational force acting on an individual slender particle were considered when establishing mathematics models. The influences of rotational velocity on the mixing of slender particles were discussed and compared with those of spherical particles under identical operating conditions. It was found that the mixing characteristics of slender particles and spherical particles all followed a constant rate until a completely mixed state was encountered. But there were still certain differences between these two kinds of particles. The influences of the lifters with different shapes were further discussed for slender particles. Selected stimulation results were obtained and would provide consults for the further study of slender particles.     

双循环旋风分离器除尘机理的数值模拟

双循环旋风分离器通过将主进口设置在筒体中部,将顶部进气口设置为回流口,消除了进气口附近的二次流,避免了短路流,将大于3μm颗粒的分离效率提高至接近100%,并避免了少量11—15μm颗粒的短路逃逸。为了探索该设备的除尘机理,借助CFD软件,通过数值模拟研究的方式,辅助分析了2种进气口在分离性能上不同,传统旋风分离器不能完全分离3—8μm和11—15μm颗粒的机理,以及消除二次流的方法。计算结果表明:当回流气速低于主进气速时,会产生类似于顶端进气口的现象,即二次流、灰环和短路流,降低了小于6μm颗粒的分离效率。当回流气速略大于主进气速时,可以完全消除主进气口附近的二次流,使得所有粒径颗粒的分离效率都较高。模拟结果与实验结果从定性的角度符合较好。     

Numerical analysis of frictional charging and electrostatic interaction of particles

Triboelectrification due to frictional contacts between particles and surfaces is prevalent in many powder handling processes. Aiming to explore the friction-induced electrostatic charging behavior, a discrete element method (DEM) is developed for the first time in the current article, in which a frictional charging model and electrostatic interaction models are implemented. The charge accumulation on both the particles and the surface in a rotational container is then analyzed numerically and experimentally to evaluate the developed DEM. The numerical results for the frictional electrification between insulant particles and an insulant wall agree well with the experimental measurement. It is also shown that both the net charge on the particles and the degree of the particle dispersion are a function of the charging time. Moreover, it is revealed that the friction-induced particle charge enhances particle dispersion, and increases the granular temperature due to the electrostatic interactions.     

选粉机颗粒轨迹的非稳态模拟

选粉机颗粒轨迹模拟研究是分析选粉机分级效率与分级精度性能技术指标的重要基础之一。根据计算流体动力学（CFD）理论,运用DPM模型的颗粒运动方程对时间积分求解颗粒运动轨迹,阐述了颗粒的分级过程。对二维平面离散颗粒的捕集和采样结果进行分析,考察了细粉和粗粉的质量流率,并研究了不同工况下细粉颗粒粒径分布情况。对数值模拟相关工况点进行模拟结果的实验分析,结果表明：细粉颗粒质量流率模拟结果与实验结果误差为5.66%;细粉颗粒粒径分布曲线两者较吻合,100 μm颗粒含量相对误差为6.54%。研究结果为分析和预测选粉机不同工况下的成品产量和粒径分布提供了模拟方法。     

Numerical simulation of bubble and particles motions in a bubbling fluidized bed using direct simulation Monte-Carlo method

Flow behavior of bubbles and particles in a bubbling fluidized bed were numerically computed using Euler-Lagrange approach. Particle collision was simulated by means of the direct simulation Monte-Carlo (DSMC) method and hard-sphere model. The computed velocities and fluctuations of particles were in agreement with experimental data of Yuu et al. [S. Yuu, H. Nishikawa, T. Umekage, Numerical simulation of air and particle motions in group-B particle turbulent fluidized bed, Powder Technol. 118 (2001) 32-44]. The distributions of velocity, concentration, granular temperature and collision frequency of particles in a bubbling fluidized bed were analyzed. The wavelet multi-resolution analysis was used to investigate flow behavior of bubbles and particles. The bubble frequency of random-like bubble fluctuation was determined from the wavelet multi-resolution analysis over a time-frequency plane.     

淘析器内树脂颗粒运动轨迹的数值模拟及应用

采用标准模型和随机轨道模型对新型惯性撞击式淘析器内的树脂颗粒运动轨迹进行了模拟研究,预测了不同粒径颗粒的运动轨迹和速度分布。结果表明：通过在淘析段加入格栅板,使大颗粒在器内的运动路径变长,颗粒与格栅间的碰撞作用促进了粘附在粗颗粒表面上细粉尘的分离;加长对流分离段有利于提高粒料中离散的细粉尘的分离。工业规模实验验证了模拟结果。工业应用结果表明：设备投入运行后,除尘风机的能力得到发挥,没有发生堵料、不下料的状况,设备的除尘能力明显较以前增强,产品的外观质量得到根本改善。     

Numerical simulation of motion of rigid spherical particles in a rotating tumbler with an inner wavelike surface

The present work is a numerical simulation of motion of rigid spherical particles within a 2-D tumbler with an inner wavelike surface. The rotation of the tumbler is simulated as a traveling sine wave around a circle. The discrete element method (DEM, a hard sphere approach) is used. The particle-wall interactions are taken into account in a changed numerical approach of hard sphere model. The effects of two basic factors of the rotating velocity (phase velocity) and the wave numbers are separately investigated. A simple but useful method for cluster identification is provided and used. The energy-based analysis of particle clusters and the motion pattern study indicate the existence of a pulsed variation in the kinetic energy of the clusters at low wave numbers and a cyclic bulk motion of the clusters at high wave numbers. The necessary conditions for the pulsed variation of motion of particle clusters at low wave number are analyzed and a mode for industrial application, e.g. coal grinding process in power plant, is demonstrated.     

旋风分离器内颗粒质量浓度分布数值模拟

采用颗粒随机轨道模型和单元内颗粒源法,对旋风分离器内不同粒径颗粒质量浓度分布进行了数值模拟。结果表明,粒径较小的颗粒(dp≤4μm)大部分在旋风分离器分离空间锥段进行分离,而较大颗粒(dp>4μm)大部分在环形空间与分离空间筒段即被分离。随着颗粒粒径增加,分离器外壁的颗粒质量浓度逐渐呈螺旋灰带分布,内旋流夹带减小,环形空间顶板下方出现顶灰环。升气管入口0.25D(筒体直径)附近的短路流对小颗粒的影响较大。在分离空间下部排尘口附近0.5D有明显的颗粒返混,返混量随着颗粒粒径增大而减少。     

大涡模拟方法模拟鼓泡床内气固两相流动

采用大涡模拟（LES）方法模拟气相湍流,颗粒动理学方法考虑颗粒相碰撞产生的动量和能量传递和耗散,采用颗粒相大涡模拟方法（LESp）模拟颗粒脉动导致的能量耗散,同时考虑介观尺度对颗粒相压力的影响,建立了气体-颗粒LES-θ-LESp双流体模型,研究鼓泡流化床内气固两相流动的特性。数值模拟与文献实测颗粒速度和实测颗粒浓度结果具有相同的变化趋势。     

伞罩型湿式脱硫除尘器气液固三相流数值模拟

从数值模拟和试验研究的角度对新型脱硫除尘装置——伞罩型湿式脱硫除尘器气液固三相的除尘特性进行研究。利用FLUENT软件在Euler坐标系中考察气固二相,采用欧拉模型来表述气固二相的相互关系;同时在Lagrange坐标系中考察液滴的运动,并把液滴对气固二相的影响耦合于欧拉模型中,提出了气液固三相的Euler/Euler/Lagrange模型。分析了气相速度场、气相压力场、固相速度场以及液滴质量浓度等的分布情况,得到了除尘情况下装置内气液固三相的分布规律。数值模拟结果与试验结果吻合良好,对装置运行及其优化设计有一定的理论指导意义。     

磁性纤维直径对捕集Fe基细颗粒影响数值模拟

为了实现对钢铁行业微细颗粒的超低排放,提出磁性纤维提高对Fe基细颗粒物的捕集.基于计算流体力学-离散相模型CFD-DPM对比研究了传统纤维、磁性纤维直径对Fe基细颗粒捕集效率以及过滤阻力的影响.结果表明:当风速为0.10 m/s时,对于直径为35～45μm范围的纤维,直径的增大能够明显增加过滤阻力.对于粒径小于2.5 ...