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35~45 μm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 μm的颗粒,磁性纤维直径的增加对捕集效率提高的影响相对较小,当颗粒粒径大于2.5 μm时,增大纤维直径能够显著提高捕集效率。风速处于0.01~0.05 m/s范围时,增大纤维直径对提高磁性纤维捕集效率作用明显;当风速为0.08~0.10 m/s时,纤维直径变化对捕集效率的影响较小。磁性纤维质量因子随纤维直径增大而下降。     

并列和错列纤维过滤器稳态除尘过程的 格子Boltzmann模拟

大部分纤维捕集效率和压降的理论模型认为纤维性能仅取决于来流速度、颗粒粒径、纤维体积分数、过滤层厚度、纤维直径等因素。实际上,布袋除尘器的性能还与纤维配置方式直接相关。利用LB(lattice Boltzmann)两相流模型对多层纤维捕集颗粒物过程进行了数值模拟,研究了不同纤维配置方式下系统压降与捕集效率的变化。结果表明,错列纤维的性能参数优于并列纤维;纤维排列间距增大,压降增幅大于捕集效率,导致性能参数下降。通过比较不同位置纤维的捕集能力发现,在布朗扩散和拦截捕集机制主导下,前方纤维捕集能力略强于后方纤维;而在惯性碰撞捕集机制主导时,对捕集贡献最大的主要是前两排纤维,后方纤维对捕集效率的贡献非常小,可以忽略。这些研究结果可以对布袋除尘器的多层纤维配置方式的优化提供理论依据和工程建议。     

超薄ePTFE纳米纤维膜用于PM2.5的高效治理

针对中高浓度PM2.5的高效过滤问题,选取颗粒粒径与膜孔径比值(dP/dm)范围为0.86~4.46,厚度小于等于1 μm的三种不同结构的超薄ePTFE纳米纤维膜展开应用性能研究。考察了过滤速度、PM2.5浓度和膜结构对过滤性能的影响以及膜的再生性能。得益于纳米纤维堆叠的网状结构,在过滤速度为1.2~4.8 m/min,进口浓度为200~1000 mg/m3的范围内,三种超薄ePTFE纳米纤维膜均能实现PM2.5的高效截留(>99.5%),其稳定压降和压降增长速度均随过滤风速和进口PM2.5浓度增加而增加,但初始压降和出口浓度仅随过滤风速增加而增加,与进口浓度关系不大。超薄ePTFE纳米纤维膜层数少、过滤阻力低(≤130 Pa)且膜表面光滑(表面粗糙度小于1 μm),降低了滤饼与膜表面附着力,使滤饼易于脱落,在4次循环实验中展现出良好的再生性能。横向对比结果显示,dP/dm为0.86,膜厚度为0.5 μm的超薄ePTFE纳米纤维膜兼具最低的过滤压降(30 Pa)、良好的过滤效率(99.93%)及再生性能好的优势,在中高浓度PM2.5空气净化领域表现出较好的应用前景。     

方形截面纤维表面气溶胶粒子多机理过滤性能数值分析

采用数值方法求解绕方形截面纤维流场，考虑粒子布朗扩散、拦截效应和惯性碰撞捕集机理的联合作用，用布朗动力学方法研究方形截面纤维的过滤性能，考察了纤维迎风角(θ)、填充率(C)和过滤风速(u?)对捕集效率、质量因子及粒子沉积分布的影响。结果表明，小粒子的扩散捕集或大粒子的惯性捕集在方形纤维表面的粒子沉积行为均表现出显著的局部沉积特征，且与粒子捕集机理和迎风角有关。方形纤维质量因子的分析结果表明，在高填充率下，方形纤维的过滤压降虽高于圆截面纤维，但具有较高的捕集效率，综合过滤性能仍明显优于圆截面纤维，但在低填充率下，方形纤维综合过滤性能劣于圆截面纤维。     

纤维对PM_(2.5)过滤性能的影响

在日常的生产和生活排放的残留物中存在许多有毒的PM2.5细颗粒物,对人体呼吸功能损害大,因此研究如何有效去除PM2.5细颗粒物具有十分重要的意义。对不同尺寸"Y"形截面和圆形截面的单纤维丝对烟气中PM2.5颗粒物的过滤性能进行实验,分析不同烟气流速和颗粒物浓度对颗粒物截留率的影响,进而研究纤维集合体在不同单丝线密度和孔隙率的条件下对烟气中PM2.5颗粒物过滤性能的作用。结合Euler法和Lagrange法对上述单纤维丝和纤维集合体实验工况进行数值模拟,将其结果与实验数据进行对比发现实验与数值模拟结果吻合较好。研究结果表明,同一时刻"Y"形截面的单纤维丝比圆形截面单纤维丝对颗粒物截留率更高。对于纤维集合体,单丝线密度为0.27 tex和孔隙率为0.88工况下,纤维集合体对颗粒物PM2.5的捕集性能最好。     

数值研究壁面参数对单纤维捕集效率的影响

基于开源OpenFOAM软件模拟单纤维过滤介质内气-固两相流运动,着重研究了单纤维过滤介质壁面参数与捕集效率之间的关系,即为纤维过滤介质的碰撞恢复系数和碰撞阻尼系数的变化对捕集效率的影响。将模拟结果与经验关联式进行对比验证,且具有很好的一致性。模拟结果表明:固体颗粒物的捕集效率随着碰撞恢复系数的增大呈现先减小后平稳的变化趋势,而碰撞恢复系数为0.5之后捕集效率基本保持稳定;颗粒物捕集效率随着碰撞阻尼系数的增加,固体颗粒物的捕集效率呈现先增大后平稳的趋势,且在碰撞阻尼系数在0.7以后,捕集效率基本趋于稳定。     

纤维对PM2.5过滤性能的影响

在日常的生产和生活排放的残留物中存在许多有毒的PM_2.5细颗粒物,对人体呼吸功能损害大,因此研究如何有效去除PM_2.5细颗粒物具有十分重要的意义。对不同尺寸“Y”形截面和圆形截面的单纤维丝对烟气中PM_2.5颗粒物的过滤性能进行实验,分析不同烟气流速和颗粒物浓度对颗粒物截留率的影响,进而研究纤维集合体在不同单丝线密度和孔隙率的条件下对烟气中PM_2.5颗粒物过滤性能的作用。结合Euler法和Lagrange法对上述单纤维丝和纤维集合体实验工况进行数值模拟,将其结果与实验数据进行对比发现实验与数值模拟结果吻合较好。研究结果表明,同一时刻“Y”形截面的单纤维丝比圆形截面单纤维丝对颗粒物截留率更高。对于纤维集合体,单丝线密度为0.27 tex和孔隙率为0.88工况下,纤维集合体对颗粒物PM_2.5的捕集性能最好。     

多通道PM2.5化学物种采样器的研制与应用

利用自行开发的设计计算软件,完成了PM2.5切割器特性尺寸的精确设计及其切割性能对喷嘴尺寸、采样流量和环境因素的敏感性分析.铝质切割器的切割粒径为2.42 μm,捕集的颗粒物质量浓度与"理想采样器"相差8.1%;采样系统的气密性良好,1 min内压力下降小于0.005 MPa;累积采样流量偏差小于±5%.实验室验证、与美国同类商业化采样器的平行采样对比以及在三个城市的现场运行均表明,研制的多通道PM2.5采样器的性能满足一次采样供质量浓度、化学物种及单颗粒特征等分析的实际应用需要.     

高效捕集PM2.5的静电器及其W型极板结构的数值模拟分析

高压静电与催化模块的耦合技术，是协同净化大气复合污染物的有效方法。通过实验比较W板静电器和平板静电器对于亚微米颗粒的捕集性能，采用计算流体力学方法构建双级静电器内静电场、流场、颗粒场的多物理场耦合模型，重点研究收尘区W型极板的角度对亚微米颗粒捕集性能的影响机制，获取双级静电器内部的流场、静电场分布特性，并针对不同角度W板双级静电器中0.1μm、1μm、2.5μm颗粒的荷电特性及捕集效率展开研究。结果表明，相较于传统的平板静电器，W板静电器具有更高的捕集效率，在1 m·s^-1的风速下，W板静电器对亚微米颗粒的捕集效率提升约10%。W板静电器之所以能明显提高对亚微米颗粒物的去除效率，可归因于收尘区的W型结构内易形成漩涡，导致亚微米颗粒物碰撞和凝并，因此提高了对亚微米颗粒物的捕集性能。     

碰撞恢复系数对单纤维颗粒捕集特性的影响

利用CFD-DEM耦合方法对单纤维过滤介质进行了气-固两相流的数值模拟,研究了颗粒和纤维体间碰撞恢复系数的变化对颗粒在单纤维体上的沉积及捕集特性的影响。结果表明,颗粒的粒径较小时,纤维体捕集颗粒数量较少,且颗粒较为发散,而当颗粒的粒径较大时,颗粒被纤维体捕集的数量明显增加。颗粒的捕集数量随颗粒与纤维体间的恢复系数呈先增加后减少,然后达到平稳状态的趋势,颗粒与纤维体间的恢复系数超过0.3时,颗粒的捕集效率趋向于一个稳定值。     

一种新型受热面飞灰颗粒的沉积特性

以一种余热锅炉中新型的受热面为研究对象,采用实验研究和数值模拟的方法研究其飞灰沉积特性。建立了菱形受热面飞灰颗粒的沉积模型,对飞灰颗粒的反弹、黏附及脱落过程进行预测,并与叉排管束和顺排管束的含灰烟气流的速度场、温度场和飞灰颗粒沉积率进行比较。结果表明,菱形受热面在换热和飞灰沉积方面优势明显。沉积主要集中于受热面左上部,颗粒由于惯性碰撞在迎风侧沉积。相同速度下,随颗粒粒径增加沉积率先增大后减小,在3 m·s^-1的烟气流速下颗粒直径为5 μm时飞灰颗粒沉积率最高,为9.49%。保持粒径不变,随速度增大沉积率逐渐降低。     

聚结层排布对高压天然气净化用滤芯过滤性能影响的实验研究

本工作利用聚结滤芯过滤性能实验装置,通过改变滤芯内部的滤材排布,研究了聚结层为单一滤材以及由不同滤材排布组合的滤芯过滤性能,分析了聚结层排布方式对过滤效率、压降、饱和度及液体分布的影响。结果表明,由单一滤材组成的滤芯过滤效率随滤材孔径减小而增大,但孔径最小时由于压降较高,导致滤芯综合过滤性能反而最差。疏油在前、亲油在后的聚结层排布方式可提高滤芯过滤效率、减少液滴二次夹带,且以两层相同滤材交错排列的滤芯过滤效率比单层滤材交错排列明显更高,压降也相对较低,使得综合过滤性能显著提升。继续增加进气侧的疏油滤材层数可延缓压降增长、提高运行寿命,滤芯稳态品质因子达到最大值(0.30 kPa-1)。聚结层排布方式对滤芯过滤性能的影响主要通过改变液体分布形式而实现,且末层滤材的通道结构变化是导致不同聚结层排布方式的滤芯过滤性能出现差异的主要原因。     

Prediction for particle removal efficiency of a reverse jet scrubber

Numerical computation was conducted to predict the collection performance of a reverse jet scrubber for polydisperse particles. The particle size distribution of polydisperse particles was represented by a lognormal function, and the continuous evolution of the particle size distribution in a reverse jet scrubber is taken into account with the first three moment equations. Numerical results were compared with the analytic results using average relative velocity in all zones and experimental results.

In a reverse jet scrubber, the impaction is the main particle collection mechanism because of high relative velocity and short collection time. The particle collection by impaction increases with an increase in particle size, and geometric mean diameter and geometric standard deviation decrease as time goes on. High droplet velocity and gas velocity increase the particle collection efficiency, and the small droplet size also increases the collection efficiency because smaller droplet size provides broader surface area. The packing density is a factor affecting particle collection efficiency in a scrubbing process. The dense packing density also provides large surface area and leads to high collection efficiency.     

Analytic solutions for filtration of polydisperse aerosols in fibrous filter

In this study, analytical solutions for penetration efficiency of a polydisperse aerosol in fibrous filter were derived employing Brownian diffusion and inertial impaction as removal mechanisms. Size distribution of aerosol particles was assumed to be represented by a log-normal function during the filtration. Derived solutions were compared with the exact solution, which is not based on the log-normal assumption, showing good agreement. Error resulting from the log-normal assumption was shown to be greater in the impaction-dominant regime than in the diffusion-dominant regime due to higher size dependency of collision kernel which destructed log-normal shape of size distribution. The penetration efficiency of the analytic solution initially decreases faster and then decreases slower than that of the exact solution in the diffusion-and intermediate dominant size regimes due to its polydispersity of particle distribution, while it overpredicted the particle removal in the impaction size range because of neglect of polidispersity effect. A new solution for the most penetrating particle diameter was also provided showing the dependence on filtration velocity, fiber volume fraction, and fiber size.     

多孔介质内颗粒流动特性的格子Boltzmann模拟

地下岩石孔隙中小颗粒的运移和沉积会使得储层渗透性能降低,影响石油开发。为了探究悬浮颗粒在多孔介质中的流动过程,采用格子Boltzmann方法对三维多孔介质内流体和颗粒的运动过程进行了数值模拟,采用有限体积颗粒法构建多孔介质中骨架颗粒和悬浮颗粒。通过Half-Way反弹格式实现流体与颗粒间的相互作用,考虑孔隙结构、入口流速、孔隙率和颗粒直径对颗粒流动特性的影响,探究颗粒的运移和沉积规律。结果表明,入口速度对不同孔隙结构下颗粒的运动作用显著。随着入口速度增大,颗粒与颗粒、孔隙壁面以及流体之间的动量和能量交换作用增强,缩短了颗粒的运移路径,颗粒沉积率逐渐变小,颗粒拟温度增大。孔隙率的下降强化了颗粒间的碰撞,孔隙率由0.581降低至0.400,使得颗粒拟温度提升至9倍。颗粒拟温度随颗粒直径的增加而增加。但随着孔隙率增加,颗粒轴向速度增加,颗粒最高轴向速度可达入口流速的11倍,而颗粒接触力降低。     

Numerical Study of an Electret Filter Composed of an Array of Staggered Parallel Rectangular Split-Type Fibers

The flow field through a staggered array of parallel, rectangular split-type electret fibers was numerically modeled. The particle trajectory and the collection efficiency were simulated by solving the equation of particle motion, taking into account the effects of diffusion, interception, inertial impaction, and electrostatic forces. The model was validated against results calculated from semiempirical expressions. The model was applied to investigate the role of the inertial impaction and the interception mechanisms in the particle collection by an electret fiber, the particle trajectories under various filtration conditions, the effect of the aspect ratio of the rectangular fiber on the filter penetration, and the distribution of the deposited particles on the surface of the fiber. The simulated results indicate that the inertial impaction and interception mechanisms account for a major portion of neutral particles collected by an electret fiber when the Stokes number is higher than 0.5. For neutral particles, fibers with an aspect ratio of 38/10 have almost the same penetration as fibers with an aspect ratio of 10/38; while for singly charged particles, fibers with an aspect ratio of 38/10 achieve a much lower penetration when the electrophoretic collection mechanism dominates. In addition, it is predicted that a filter composed of fibers with an aspect ratio of 38/10 will result in a lower flow resistance and thus a slower clogging process when the dielectrophoretic collection mechanism dominates.     

Retracted: Effects of the Operating Conditions and Geometry Parameter on the Filtration Performance of the Fibrous Filter

The gas‐solid two‐phase flows in fibrous filters were simulated by computational fluid dynamics (CFD) technology. The pressure drops and filter efficiencies with different operating conditions and geometry parameter, including face velocity, particle size, and solid volume fraction (SVF) were calculated. The effects of the operating conditions and geometry parameter on the filter performance of the fibrous filter were obtained. The results indicate that the pressure drop increases linearly with the face velocity and the predicted values of the pressure drops are in excellent agreement with the experimental correlation. Filtration efficiency decreases with the face velocity for submicrometer particles (0.1 μm) and, for larger particles (1 μm) the tendency is just the opposite. The filtration mechanism is different for different particle sizes. For the filter in this paper, when the particle size is smaller than 0.2 μm, Brownian diffusion plays a significant role in the filtration process. When the particle size is greater than 0.5 μm, inertial impaction becomes an important capture mechanism. For particle sizes in the range of 0.2–0.5 μm, the Brownian diffusion and inertial impaction are both relatively weak and, therefore, the filtration efficiency has the least value in this range. Additionally, the SVF distribution is an important geometry parameter in the filter. The filtration efficiency of the filter with a decreased SVF (geometry B) along the thickness of the filter is higher than that of the filter with the even SVF (geometry A), while maintaining a low pressure drop.     

外二次旋流风对旋流煤粉燃烧及NO生成的影响

对旋流煤粉火焰在两种分级进风的情况下用PIV（particle image velocimetry）测量了燃烧室内的速度分布,研究了湍流拟序结构对旋流火焰的燃烧特性及NO排放的影响。燃烧室进口附近,当外二次风率较大时,其拟序结构沿横向的扩散较早,大量小颗粒被裹入涡结构中参加反应,因此中心区域温度较高;外二次风率较小时,一次风外侧的涡结构使得更多的大颗粒在惯性离心力作用下运动到了近壁区域,因此近壁区温度更高。在本文的实验范围内,保持其他条件不变,增加外二次旋流风,有利于剪切层纵向涡结构的形成,也有利于横向涡的形成,促进了小颗粒煤粒燃烧和大颗粒煤粒挥发分析出,从而促进NO的提前生成以及燃烧中间产物对NO的还原,最终减少NO的生成。