灰斗抽气对旋风分离器分离性能影响数值模拟研究

 利用计算流体动力学软件FLUENT对旋风分离器内气固两相流动特性进行三维数值模拟,模拟气相流场采用雷诺应力模型,应用随机轨道模型模拟湍流流场中颗粒的运动轨迹,同时给出了不同抽气率下旋风分离器的速度、压力分布,计算出旋风器分级效率,模拟结果与文献实验数据吻合较好.结果表明,灰斗抽气可以提高锥体内旋转气流切向速度,轴向速度减少能够降低气流携带颗粒返混能力,并减小排气芯管下口短路流,提高旋风分离器分离效率.对于给定的旋风分离器,抽气率应有一最优值.     

PM2.5细颗粒物分离技术的数值模拟和性能改进

旋风切割器是分离细颗粒物的主流技术,为了提高其分离效率并减少能耗,本文分析了切割器参数对粒子分离的影响.基于计算流体动力学数值模拟的方法,分析了VSCC型旋风切割器的内部湍流流场,比较15~25L/min范围内不同流速下的涡流变化情况;基于"逃逸率"概念,模拟1~6μm内不同粒径的细小粒子逃逸率随流速的变化曲线,考察临界粒径dc并结合气溶胶实验进行验证,分析流速对分离性能的影响程度;之后考察了流速对压降的影响,提出一种几何参数改进方案,在避免压降升高的前提下提高分离性能.研究表明:流速影响旋风切割器内的湍流分布,随着流速增大,临界粒径变小,分离性能得到提升,模拟结果在16 L/min的流速下,临界粒径约为2.5μm,与实验结果基本一致,并且利用曲线给出计算总分离效率的思路;调节几何参数可以实现在低能耗的前提下,将临界粒径进一步降低为1.1μm,收集效率更高.研究结果可为PM2.5切割器的商业选择或工程设计提供理论参考.     

煤粉气-固两相流的超声衰减特性

以颗粒相在整个检测空间内均匀分布为前提,采用McClements理论和Bouguer-Lambert-Beer定律共同描述煤粉气-固两相流中超声衰减特性,建立超声衰减系数与气-固两相流相关参数的理论关系,通过数值模拟,分析超声衰减随着颗粒相体积分数、超声频率、颗粒粒径变化的规律。结果表明,超声频率越高衰减系数越大;声衰减系数随着颗粒相体积分数的增大线性递增;选用某固定频率检测,测得2个体积分数下的声衰减系数即可确定衰减-体积分数曲线斜率,从而实现任意衰减系数对应的颗粒相体积分数测量;在相同的体积分数下,煤粉颗粒粒径为10～200μm,声衰减系数随着颗粒粒径的增大单调递减,当煤粉颗粒粒径大于200μm时,声衰减系数对煤粉颗粒粒径不再敏感。     

双锥旋流分离器内固-液分离过程的数值模拟

为了进一步认识双锥旋流分离器的固-液分离过程,利用基于计算流体动力学的多相流模型对直径100 mm双锥旋流分离器内粒径为5~50μm的颗粒的分离过程进行数值模拟,比较模拟所得颗粒的分离效率与实验结果的一致性。结果表明:粒径为5μm的颗粒进入内旋流后紧靠空气芯快速上升;粒径为25μm的颗粒进入内旋流后上升速度较慢,且在上升过程中逐渐远离空气芯;粒径为50μm的颗粒偶有进入内旋流的现象,但最终仍从底流排出;颗粒在分离器内的分布规律是,颗粒越小越趋向于分布于整个分离器内,随着粒径的增大,颗粒的分布先后出现浓度偏移及空间偏移,颗粒越大越趋向于分布于壁面附近及锥底部分。     

分级轮叶片结构和转速对分级性能影响的仿真

运用Fluent软件,采用液-固两相流的数值模拟方法,对超细粉体湿法离心分级机分级腔内流场进行数值模拟仿真;选用重整化群k-ε湍流模型和欧拉多相流模型,利用多重参考坐标系法,在稳态条件下,分析不同形状分级轮叶片分级腔内流体的速度分布情况,研究不同形状分级轮叶片对分级机分级性能的影响;选用离散相模型,在非稳态条件下,分析分级腔内颗粒轨迹的规律,研究分级轮转速对分级粒径的影响。结果表明:相比于直叶片和斜叶片,弧形叶片分级效果更好;采用弧形叶片结构,当分级轮转速为1 000 r/min时,分级粒径大于1μm,分级轮转速为2 000 r/min时,分级粒径接近1μm,当分级轮转速为3 000 r/min时,分级粒径小于1μm,增大分级轮转速有利于减小分级粒径。     

基于CFD的双锥角微型旋流器分离性能的数值模拟

针对常规单锥角微型旋流器难以分离超细粉体的难题,提出一种Φ8 mm双锥角微型旋流器,通过CFD软件FLUENT 14.5对2种微型旋流器进行模拟,对比分析单锥与双锥旋流器内部流场和各自的分离性能,并进行实验验证。结果表明:双锥角微型旋流器分离粒径更小;溢流中粒径为小于1μm的质量分数提高6.13%,小于2μm的提高3. 6%;底流中粒径为小于4.5μm的质量分数提高5. 21%;底流夹细和溢流跑粗现象得到明显改善。     

高温高压旋风分离器流场模拟及性能试验

提出一种圆形径向进口、筒体段扩径的拱顶旋风分离器新结构;并与PV型分离器进行了流场和分离性能对比。结果表明:在相同处理气量下,新型分离器外旋流区切向速度显著大于PV型,中心涡核区轴向速度小于PV型;用中位粒径为9μm的滑石粉进行冷模试验,新型旋风分离器分离效率比PV型高约1%;新型旋风分离器结构强度和分离性能优良,适合高温、高压的工况下应用。     

基于计算流体动力学的颗粒磨蚀管道弯头研究

为了探究气-固两相流中颗粒对管道弯头的磨蚀机理,采用计算流体动力学软件对90°弯头进行磨蚀模拟研究。结果表明:颗粒在弯头内的轨迹是先汇聚、后发散的过程,弯头壁面上颗粒汇集程度最大的位置也是磨蚀最严重的地方;随着气流速度与颗粒粒径的改变,最大磨蚀点分布在与x=0坐标面夹角为70~90°的截面之间,并且分布在z=0平面的一侧;最大磨蚀率与颗粒流量成正比;在颗粒质量流量为0.1 kg/s的条件下,当颗粒粒径小于45μm时,气流速度对最大磨蚀率影响不大,当颗粒粒径大于45μm时,最大磨蚀率与气流速度接近二次多项式关系;当气流速度为20 m/s时,粒径介于45~75μm的颗粒的磨蚀率最大,而且颗粒流量越大,这种趋势越明显。     

雾化焙烧制备超细颗粒用旋风分离器优化模拟

旋风分离器是雾化焙烧制备稀土氧化物工艺中的常用分离设备之一。为了提高焙烧产物中超细颗粒的分离效率，采用Fluent数值模拟和实验验证相结合的方法，得到旋风分离器的优化构型，利用颗粒分离效率和流体压降2项指标进行评价，以探讨扩张结构旋风分离器的优化效果。结果表明：在锥筒高度为距旋风分离器顶板370 mm处，进行角度为10°的扩张改进后，分离器对粒径为1、 3、 5μm的颗粒分离效率分别提高13.25%、 42.33%、 44.02%,阻力系数减小3.6%;新改进结构旋风分离器在降低能耗的同时提高分离效率。     

管内Cu-水微米颗粒流湍流强化传热研究

传统光管在高雷诺数下的传热效果不理想,因此提出在水介质中添加微米Cu颗粒作为工作介质来强化管内换热的方法。建立了Cu-水微米流的多相流传热物理模型,采用基于颗粒动力学的欧拉-欧拉双流体模型,对粒径分别为10μm、50μm、100μm和500μm,流速分别为1 m/s、1.5 m/s、2 m/s和2.5 m/s,颗粒体积分数分别为5%、10%、15%和20%进行了传热Nu和阻力损失f数值计算,结果表明:Cu-水微米流的努塞尔数Nu随雷诺数Re和颗粒体积分数的增大而增大,而随粒径的增大而总体趋势减小;摩擦因子f随颗粒体积分数的增大而增大,而随雷诺数Re增大而增小;传热综合性能评价因子η随颗粒体积分数的增大而增大,随着粒径的增大而总体趋势减小。粒径10μm的传热综合性能在研究的粒径范围内最佳,η达到1.1~2.3。     

Performance evaluation of industrial large-scale cyclone separator with novel vortex finder

This paper presents an experimental and numerical study on an industrial large-scale tangential-inlet cyclone separator with a novel and easy-to-implement vortex finder. The vortex finder was designed with slots on the side wall to improve cyclone performance. The collection efficiency, pressure drop, and interior flow field were analyzed. The proposed device provides an effective gas flow pathway and a coupled swirl-inertia separation mechanism, which eliminates short circuit flows under the bottom inlet of the slotted vortex finder to reduce the swirling intensity and minimize the flow instability in the separator. The pressure drop was reduced up to 27.9% compared to the conventional separator and the maximal increase in collection efficiency was 5.45%. The results presented here may provide a workable reference regarding the effects of vortex finders on improving flow fields and corresponding performance in industrial large-scale cyclone separators.     

出口结构对双蜗壳式旋风分离器内流场的影响

用智能七孔球探针测试仪对不同出口结构的双蜗壳式旋风分离器内不同位置的三维速度及压力进行测量,从而获得不同结构参数对流场的影响。实验结果表明,排尘锥结构具有一定的稳流作用,有利于分离器的分离;分流型芯管的开缝有分流的作用,降低了芯管内的气流旋转强度,使上下行流都有所减少,旋风管中心附近以及边壁附近的切向速度都有所减小;分流型芯管的特有的缩口结构使不同截面上的切向速度的最大值都有所增加,距离缩口越近增加越强烈。     

一种新型的旋风分离器

介绍了旋风除尘器的一种新的改进方法,即在旋风除尘器的排气管处加二次流,通过控制二次流的大小及进风方向,可以改变旋风分离器内部流场分布,从而减少上灰环和短路流的产生,提高旋风除尘器的分离效率,尤其是提高其对微细粉尘的分离能力。     

Study and optimization of flow field in a novel cyclone separator with inner cylinder

This paper presents a study of gas-solid flow in a novel cyclone separator with inner cylinder, compared with that in a conventional cyclone. The Reynolds stress model (RSM) is used to simulate fluid flow, and the discrete phase model (DPM) is selected to describe the motion behavior of particles. The experimental data measured by particle image velocimetry (PIV) is used to verify the reliability of the numerical model. The results show that in the novel cyclone, the cleaned gas can be quickly discharged from the vortex finder, the movement distance and residence time of fine particles are prolonged, the short-circuit flow and vertical vortex under the vortex finder are eliminated, the mutual interference between upflow and downflow in the cylinder is eliminated, and the region of quasi-free vortex in the cone is enlarged. Compared with the conventional cyclone, the novel cyclone has higher collection efficiency and lower pressure drop.     

Effect of the inlet angle on the performance of a cyclone separator using CFD-DEM

Hydrodynamic characteristics in a cyclone separator are simulated by means of DEM-CFD. Reynolds stress turbulence model (RSM) is used to capture gas turbulence. By changing the inlet angle, the distributions of pressure drop, tangential and axial velocity of gas phase are obtained within the cyclone. Simulated results indicate that the flow pattern consists of two regions: loss-free vortex region and forced vortex region. The negative inlet angle brings about a larger pressure drop comparing to positive inlet angle. The separation efficiency and trajectory of particles from simulation are obtained. The effects of inlet angle and particle size on separation efficiency are quantified. The separation efficiency is increased with an increase of particle size, while the separation efficiency firstly increases and then declined as inlet angle changes from negative to positive. An agreement between the numerical simulation and experimental results has been achieved in a cyclone separator.     

Effects of helical fins on the performance of a cyclone separator: A numerical study

This study aimed to investigate the separation performance of a cyclone separator after reshaping its cylindrical body by installing the helical triangular fins. A numerical simulation based on Fluent was adopted to perform an orthogonal test to optimise the structure of the cyclone separator with helical triangular fins. Three structural parameters of the helical triangular fins were selected as optimisation variables: base width, fin size, and fin pitch, and their influences on the evaluation indices of the cut-off diameter were investigated. The optimal combination scheme was determined by range analysis, and the cyclone separator performances before and after optimisation were compared and analysed. The significant influence of the structural parameters on the cut-off diameter was in descending order as the fin pitch, fin size, and base width. For particles with diameter of 0.1, 0.5, 1, 2, and 3 μm, the separation efficiency of the cyclone separator with optimized helical triangular fins increased by 7.4 %, 15.9 %, 20.1 %, 10.9 % and 14.8 % respectively. Moreover, the cut-off diameter of the finned cyclone separator is reduced by 30.7 %, while the pressure drop is only increased by 6.6 %. The short circuit flow and back-mixing were alleviated, thereby considerably enhancing the stability of the flow field. Therefore, the finned cyclone separator was found to play a critical role in increasing the separation of fine particulate matter.     

多效旋风分离器压降的实验研究

为了有效提高新型多效旋风分离器对粒径为0.1~3μm颗粒的分离效率,获取该设备的阻力性能,采用实验方法研究该新型多效旋风分离器压降与进口气速的关系,并与Lapple型旋风分离器进行比较。结果表明:进口风速为5~30m/s时,主体直径为0.25m的多效旋风分离器总阻力系数为7.29,其中,一级和二级预分离螺旋管的阻力系数分别为1.04和1.73;主体的阻力系数为4.52。直径为0.25m的Lapple型旋风分离器的阻力系数为7.21。     

多联机旋风式油气分离器内管与进气碰撞的数值模拟

以小型多联机用旋风式油气分离器为研究对象,建立三维稳态数值模型。气流场选用重整化群湍流模型(RNGk-ε),油滴轨迹采用随机轨道(DRW)模型,研究内管长度、筒体高度和进气碰撞程度对油气分离器内部流场分布、分离效率和压降的影响。发现大部分油滴在内管截面以上的筒体空间内完成分离;油气分离器所需内管长度与筒体高度比值随进气速度的增加而减小;进气碰撞程度(油气分离器横截面上内管下边缘与进气管上边壁的垂直距离与进气管径的比值,即h1/di)小于26.57%,进气速度大于23.09 m/s时,更容易获得稳定的旋流流场。     

The impact of cylinder vortex stabilizer on fluctuating turbulence characteristics of a cyclone separator based on Large Eddy Simulation

The main purpose of present study is to comprehensively clarify the impact of cylinder vortex stabilizer on fluctuating turbulence structure of a Stairmand cyclone separator on basis of Large Eddy Simulation. The cylinder vortex stabilizer is easy and could be applied to any existing cyclone model without any major replacement. This novel modification in cyclone body is considered to alleviate the negative effect of entrainment of particles from the ash hopper and swing of the vortex end in swirling flow. The numerical simulations were conducted based on Stairmand cyclone separator and three new models with variation of vortex stabilizer length and diameter. The results showed that the cylinder vortex stabilizer could enhance flow instability and improve fluctuating turbulence structure to some extent. It is confirmed that cylinder vortex stabilizer could significantly reduce the tangential velocity in the inner quasi-forced vortex region of the cyclones. Comparing with Stairmand cyclone, the swirling first and second peak frequency of cyclone model with vortex stabilizer (Length L/D: 6.5, diameter d/D: 0.12) have been confirmed to get considerable reduction of 11.54% and 10.86%, respectively. This modified cyclone model is comparatively better for enhancement of flow stability, providing about 18.4% maximum reduction of normalized flow angle, 24.8% of rotational kinetic energy in dust collector and 14.2% in the main body of cyclone.