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。     

基于立磨选粉机颗粒分级过程的数学建模研究

通过立磨粉磨中试试验平台开展试验,对比分析不同系统风量和选粉机转速条件下选粉机分级性能的变化规律.利用正态分布的累积分布函数,将选粉机操作参数与不同粒径颗粒的捕集概率关联.采用系统风量和选粉机转速工况变化的试验数据拟合出模型中的均值和方差,建立可定量分析系统风量、选粉机转速与颗粒部分分级效率之间关系的数学模型.经验证回...     

离心转子式选粉机的分级机理

对气相中固体颗粒的受力情况进行了分析 ,并在此基础上介绍了离心转子式选粉机的结构及工作原理 ;从理论上分析了选粉机的分级机理 ,推导了切割粒径的计算公式 ;通过模型实验 ,探讨了操作参数对选粉机分级性能的影响规律。结果表明 ,该选粉机具有良好的分级性能 ,其理论分析对选粉机的设计及性能预测具有一定的指导意义。     

基于CFD的选粉机分级过程数值模拟

为研究颗粒在选粉机内的分级过程,在对颗粒受力进行理论分析的基础上,对涡流空气选粉机SLK5500分级室平面进行了稳态和非稳态的CFD数值模拟,在稳态模拟中考察了颗粒运动轨迹和分级效率,在非稳态模拟中考察了颗粒的实时运动规律。最后得出,颗粒在选粉机内的分级过程是一个概率事件,粒径较小的颗粒进入细粉的概率大,进入粗粉的概率小,而粒径较大的颗粒进入细粉的概率小,进入粗粉的概率大。通过数值模拟对颗粒的实时运动进行了仿真,为选粉机结构改造和操作参数优化提供了模拟方法和数据基础。     

立磨选粉机分级环间距对分级性能的影响

分级环间距大小是影响选粉机分级性能指标的重要因素之一。通过构建不同分级环间距的立磨选粉机模型,采用Fluent软件对SMG5500型立磨选粉机不同分级环间距下的流场特性进行研究,对比分析间距大小对速度场、压力场和分级效率的影响规律,得出最优的分级环间距,并对整机进行实验验证。数值模拟结果表明:当分级环间距过小时,大部分大于80 μm的粗颗粒都能进入转笼,使产品极易出现跑粗现象;当分级环间距过大时,大部分小于80 μm的颗粒不能进入转笼,这使得选粉机的循环负荷加大,选粉效率受到了极大的限制;当分级环间距为110 mm左右时,SMG5500型立磨选粉机的分级性能最优。     

涡流空气选粉机分级性能的研究

利用计算流体力学CFD（Computational Fluid Dynamics）商用Fluent软件对涡流空气选粉机内部气固两相流动过程进行了数值模拟研究,采用三种方法（细粉收率法、Tromp曲线法及成品R-R粒度分布曲线法）对选粉机性能进行评价,并同实际标定结果进行比较,最后分析风量和转速对选粉机分级性能的影响.结果表明：模拟预测曲线与实践结果基本吻合,验证了CFD技术在涡流空气选粉机研究过程中提供信息的可靠性,为进一步拓展CFD技术在选粉机领域中应用提供佐证;转子转速对成品细度的影响远大于风量对成品细度的影响,同风量下,转速降低14.3％,成品中大于60μm粗颗粒增加3.42倍,同转速下,风量增加59.5％,成品中大于60μm粗颗粒增加17.9％.     

立磨选粉机叶片结构对分级区速度场影响分析

立磨选粉机分级区速度场是影响其分级性能的主要因素之一,其机内气固两相流为非理想流体。本文应用流体力学流体黏滞性与速度梯度原理,分析了速度梯度过大造成选粉机选粉精度和选粉效率下降的机理。通过构建不同叶片结构转笼的立磨选粉机模型,采用Fluent软件模拟分析了立磨选粉机不同叶片结构转笼的分级区速度场中速度流向、速度大小与速度梯度的变化规律。进行了立磨选粉机转笼叶片结构改造试验,试验表明：改造后的Z形叶片结构转笼的立磨选粉机产量在直叶片转笼结构的基础上提高了15 t/h,且0.08 mm颗粒的筛余降低了10%。     

离心式选粉机机理评析

在水泥粉磨工艺中，离心式选粉机已有几十年的历史了。由于我国水泥新标准的颁布实施，对水泥细度状态（即细度指标、颗粒分布和颗粒形状）提出了更高的要求，而离心式选粉机的内部结构及工作原理又不能适应这个要求，因此更新换代已是大势所趋。本文就此谈一些粗浅看法，供同行参考。１离心式选粉机的工艺缺陷 众所周知，选粉机的关键技术是“分散”、“分级”和“收集”。离心式选粉机在这三个方面都显得力度不够。分散靠撒料盘旋转单独完成；分级靠大风叶和回风叶形成的循环风由小风叶进行分级，能力较弱；细粉收集依靠颗粒本身在重力作…     

涡流空气选粉机分级性能模拟预测与实践结果的比较

利用计算流体力学CFD(Computational Fluid Dynamics)商用Fluent软件对涡流空气选粉机内部气固两相流动过程进行了数值模拟研究,采用三种方法(细粉收率法、Tromp曲线法及成品R-R粒度分布曲线法)对选粉机性能进行评价,并同实际标定结果进行比较,最后分析风量和转速对选粉机分级性能的影响。结果表明:(1)模拟预测曲线与实践结果基本吻合,验证了CFD技术在涡流空气选粉机研究过程中提供信息的可靠性,为进一步拓展CFD技术在选粉机领域中应用提供佐证;(2)转子转速对成品细度的影响远大于风量对成品细度的影响,同风量下转速降低14.3%,成品中大于60μm粗颗粒增加3.42倍,而同转速下风量增加59.5%,成品中大于60μm粗颗粒仅增加17.9%。     

高细转子选粉机在球磨机节能高产中的作用

0 前言 在工业生产中,按一定的生产工艺要求,将物料中不同粒径大小的颗粒分离开的过程称之为分级。在水泥生产中又称为选粉。利用空气作为分级介质的选粉机已有几十年的历史了。由于我国水泥新标准的颁布实施,对水泥细度状态(即:细度指标、颗粒分布和颗粒形状)提出了更高的要求,现有选粉机的     

Enhancement of Hydrocyclone Classification Efficiency for Fine Particles by Introducing a Volute Chamber with a Pre‐Sedimentation Function

A new hydrocyclone was designed with a volute chamber positioned prior to the inlet. Since the volute chamber prior to the inlet has a pre‐sedimentation function due to the centrifugal sedimentation effect, coarse particles are concentrated on the outer side and fine particles are concentrated on the inner side as the particles reach the entrance of the hydrocyclone. Consequently, coarse particles in the hydrocyclone are easily separated into the underflow and fine particles are easily transferred into the overflow. As a result, the separation or classification performance of the hydrocyclone was improved effectively. Compared with the traditional type of hydrocyclone, this new type of hydrocyclone with a volute chamber before the inlet was shown to possess a much higher classification efficiency for fine particles.     

“L”形涡流分级机导流叶片的数值模拟与试验

导流叶片是涡流分级机分级区的重要部件,本文设计了一种其凹槽面向转子的"L"形导流叶片,并以该叶片与转子组成的分级区域为气一固两相湍流理论模型,采用RSM应力方程模型和随机颗粒轨道模型进行了数值模拟.结果表明:"L"形导流叶片能实现迅速分级,减少颗粒在分级区的团聚;粗颗粒受到较大的离心力被抛向导流叶片凹槽内碰到导流叶片背风面失去动量后由于受到气流干扰很小,在自身重力作用下迅速下掉入粗粉斗,很大程度上避免了传统平板导流叶片易产生的颗粒返混现象,减少了已分级的粗颗粒对后续待分级颗粒的干扰,使分级过程更加稳定.根据数值模拟结果结合经验,"L"形导流叶片安装时的径向倾角取55°为宜.试验结果表明,使用该"L"形导流叶片有利于提高分级效率和分级精度.     

Computational simulation of the dynamics of secondary organic aerosol formation in an environmental chamber

A key atmospheric process that is studied in laboratory chambers is the oxidation of volatile organic compounds to form low volatility products that condense on existing atmospheric particles (or nucleate) to form organic aerosol, so-called secondary organic aerosol. The laboratory chamber operates as a chemical reactor, in which a number of chemical and physical processes take place: gas-phase chemistry, transport of vapor oxidation products to suspended particles followed by uptake into the particles, deposition of vapors on the walls of the chamber, deposition of particles on the walls of the chamber, and coagulation of suspended particles. Understanding the complex interplay among these simultaneous physicochemical processes is necessary in order to interpret the results of chamber experiments. Here we develop and utilize a comprehensive computational model for dynamics of vapors and particles in a laboratory chamber and analyze chamber behavior over a range of physicochemical conditions.

Copyright © 2018 American Association for Aerosol Research     

淘析器内气固两相流动的数值模拟

针对现有淘析器存在分级效率低,粒料中夹带塑料粉尘和部分粒料随气流溢出的问题,采用CFD模拟软件FLUENT6.2对现有淘析器及其改进型淘析器内部的气相流场和粒子运动轨迹进行了数值模拟.气相控制方程采用标准湍流模型,颗粒运动控制方程采用随机轨道模型.模拟结果表明:改进型淘析器可消除现有淘析器出口附近的短路流:加长对流直管段,增加了气固对流时间,强化了气流对粒料表面的剪切作用;淘析区加入格栅,既规整流场,消除静电吸附,又通过碰撞振动提高了粒料表面粉尘的分离程度.     

Description of dynamic processes in two-phase colliding media with the use of molecular-kinetic approaches

A model of a reacting two-phase medium consisting of a gas and incompressible particles, which takes into account the collisional dynamics of random motion of particles, is presented. Molecular-kinetic approaches of the theory of granular media are applied. Shock wave patterns are analyzed, and conditions on strong discontinuities in the two-phase mixture are obtained. Two types of discontinuities are identified: without and with generation of the random energy on the shock wave. For shock waves of the second type, the amplitude of the particle concentration is independent of the wave propagation velocity. The model is verified against the results on the velocity of sound measured in mixtures ejected from a high-pressure chamber of a shock tube.     

Effect of distributed injection of air into the afterburning chamber of a ram-rocket engine on the efficiency of combustion of boron particles

A mathematical model of combustion of boron particles in a ram-rocket engine is developed. The boron combustion efficiency for one-stage and two-stage injection of air into the afterburning chamber is calculated. It is demonstrated that two-stage injection of air sometimes allows the time of complete combustion of boron particles to be significantly reduced (by a factor of 1.5–3); thus, the fuel combustion efficiency in the ram-rocket engine can be increased. The simulated results are consistent with available experimental data.     

螺旋并联分配管对旋风分离器分离性能的影响

为兼顾高分离精度及大处理量的要求,微小型旋风分离器并联得到越来越多应用。运用离散相模型和实验研究了螺旋并联分配管对旋风分离器分离性能的影响,分析了螺旋分配管分级和改变“序态”特性。结果表明,大颗粒易于从分配管前端出口逸出,依次进入旋风分离器固体颗粒呈现不同粒径分布,总体呈现分级特性;螺旋管对细颗粒物具有改变“序态”作用,进入旋风分离器颗粒粒径呈现外小内大趋势,内部相比外部颗粒浓度更高;内侧大颗粒构成的粒子环促进细小颗粒的去除,从而提高旋风分离器分离效率。实验进一步验证螺旋分配管分级和改变“序态”特性。研究结果对微小型旋风分离器并联设计具有指导意义。     

燃油锅炉油雾燃烧过程中碳烟的排放特性

针对2 t/h卧式锅壳锅炉炉膛结构及换热特点,建立了炉膛换热条件下油雾燃烧的非预混燃烧模型,研究了风速对炉内燃料燃烧及碳烟颗粒物排放特性的影响. 结果表明,炉内燃料浓度在炉膛轴向0.3~0.7 m的范围内快速降低,碳烟颗粒物主要在距炉膛燃料喷口0.3~1.5 m的混合燃烧区内迅速生成,并随风速增大而远离喷口,生成速率在着火点位置最大. 风速过大或过小都会增加碳烟颗粒物的生成,风速7.5 m/s时炉膛碳烟排放浓度最小,出口浓度分布更均匀,约为0.042%(w).     

Numerical and experimental investigation of a fluidized bed chamber hydrodynamics with heat transfer

The hydrodynamics and heat transfer of a gas-solid fluidized bed chamber was investigated by computational fluid dynamic (CFD) techniques. A multifluid Eulerian model incorporating the kinetic theory for solid particles was applied to simulate the unsteady state behavior of this chamber. For momentum exchange coefficients, Syamlal-O’Brien drag functions were used. A suitable numerical method that employed finite volume method was applied to discretize the equations. The simulation results also indicated that small bubbles were produced at the bottom of the bed. These bubbles collided with each other as they moved upwards forming larger bubbles. Also, the solid particle temperature effect on heat transfer and hydrodynamics was studied. Simulation results were compared with the experimental data in order to validate the CFD model. Pressure drops and mean gas temperature predicted by the simulations at different positions in the chamber were in good agreement with experimental measurements at gas velocities higher than the minimum fluidization velocity. Furthermore, this comparison showed that the model could predict hydrodynamics and heat transfer behaviors of gas solid fluidized bed reasonably well.     

A density based segmentation method to determine the coordination number of a particulate system

The coordination number is an important parameter for understanding the particulate systems, especially when agglomerated particles are present. However, experimental determination of the coordination number is not trivial. In this study, we describe a 3D classification method, which is based on the revised DBSCAN (Density-Based Spatial Clustering of Applications with Noise) and its application to X-ray micro-tomographic (XMT) images to determine the coordination number distribution. Pellets of micro-crystalline cellulose were used as model particles. The validity of the segmentation was checked by comparing the particle size distribution (PSD) obtained by XMT-DBSCAN with PSD obtained by optical microscopy. The results were found to be in good agreement, demonstrating the suitability of the DBSCAN method. The means and standard deviations of coordination numbers were (8.2±1.7, n=994 particles), (8.1±1.5, n=904) and (6.2±1.2, n=159) for pellets with length based mean sizes of 157, 307 and 437 μm, respectively. The coordination number distribution was in line with previous finding in mono-sized acrylic beads.