Collection Efficiency of Rectangular Slit-Nozzle Inertial Impactors with Impaction Plates of Elliptical Concave Curvature

In this study, the impaction plate with an elliptical concave groove was employed in an effort to enhance the collection efficiency of the slit-nozzle inertial impactor. The major axis length (A) and the minor axis length (B) of the elliptical concave curvature were varied. The effect of the ratio of A to B on the collection efficiency of slit-nozzle inertial impactors was investigated both numerically and experimentally. The numerical results were in good agreement with the experimental data for different values of A/B ratio. The elliptical concave impaction plates were useful in not only reducing the particle bounce but also lowering the cut-off size. The optimum range of the A/B ratio was found to exist for minimizing the cut-off size. When the elliptical concave impaction plates with the A/B ratio of 2 were used for the slit-nozzle inertial impactors, the square-root of the Stokes number was estimated to be lowered from 0.77 to approximately 0.6, resulting in the decrease of the cut-off size by 22% compared with the typical flat impaction plates.

Copyright 2013 American Association for Aerosol Research     

Use of Polyurethane Foam as the Impaction Substrate/Collection Medium in Conventional Inertial Impactors

Open pore polyurethane foam (PUF) can be used effectively as a substrate for conventional inertial impactors with both high particle collection efficiency and minimal vaporization of semi-volatile particle components. The collection characteristics of PUF as an impaction substrate were studied as a function of PUF density, Reynolds number, impaction substrate diameter, and nozzle-toplate distance. The conventional impaction substrate of the PM_2.5 Harvard Impactor sampler was replaced with the PUF substrate. The use of PUF resulted in significant changes in the collection efficiency curve, with the 50% cut-off size (     

Effect of Coating Thickness on Particle Bounce in Inertial Impactors

A coating technique for applying uniform, thin layers of grease onto impactor substrates is described. The technique involves dissolving or diluting the grease in a solvent, applying the grease solution to the substrate, the spinning the substrate at a high speed. The coating thickness is controlled by the concentration of grease in the solution and by the spin speed. Apiezon-L vacuum grease and silicone oil were tested with this technique. Coating thicknesses between 0.3 and 9 μm were successfully generated on the polycarbonate film. The coated substrates and uncoated polycarbonate were tested for particle collection efficiency with polystyrene latex in two stages (0.56- and 1.0-μm cut-size) of a microorifice uniform deposit impactor. In the range of coating thicknesses tested, the collection efficiency of Apiezon-L was strongly related to the coating thickness; large coating thicknesses greatly improved particle collection. For the silicone oil, collection efficiency was high for all the coating thicknesses. The thinnest coating of silicone oil performed as well as the thickest coating of Apiezon-L grease.     

Mechanism of Particle Impaction and Filtration by the Dry Porous Metal Substrates of an Inertial Impactor

This study has investigated numerically the particle collection efficiency curves of inertial impactors with a dry porous metal substrate covering a wide range of particle diameters. The results show that the penetrating air causes higher inertial force for particles near the surface of the dry porous metal substrate than that of the flat plate, which increases the collection efficiency due to inertial impaction mechanisms. The calculated collection efficiency curve will be sharper than that assuming 100% filtration efficiency (ideal filtration) and there is a minimum value of <2% at $sqrt {bf St}$ = 0.05 ～ 0.07 (corresponding to d p = 0.1 ～ 0.5 w m) for different Re and K. The collection efficiency increases to 15% for the ultrafine particles with a diameter of 0.01 w m when Re = 3,000 and K = 568,000 cm m 2 . When $sqrt {bf St}$ M 0, the collection efficiency will approach the curve considering ideal filtration due to diffusion mechanisms.     

Effect of Agar Plate Volume on Accuracy of Culturable Bioaerosol Impactors

Agar plate volume in bioaerosol impactors affects collection efficiency, but it is often overlooked in practice. This study investigated the effect of agar volume (20, 35, and 50 mL) and, consequently, jet-to-plate distance on accuracy of culturable impactors. Laboratory experiments investigated sensitive Escherichia coli and hardy Bacillus atrophaeus bacteria with a BioStage impactor. Outdoors bacterial and fungal sampling assessed effects of varying agar volume in BioStage, Sampl’air Lite, and SAS Super 180 multinozzle impactors relative to a reference BioStage with 35 mL agar. The results demonstrate that agar plate volume affects not only overall collection efficiency, but also species selection and colony masking. Culturable concentrations of E. coli in laboratory were underestimated by 35% when using 20 versus 35 mL agar volume (p < 0.001). However, data indicate selection of healthier bacteria, as E. coli colonies were significantly larger on 50 versus 20 mL agar plates (p < 0.001). For outdoors, lower agar volume significantly improved accuracy of Sampl’air relative to the reference BioStage for bacterial (p < 0.001) and fungal (p = 0.03) aerosols. Changes for other samplers were not statistically significant, likely due to wide variability in microbial profiles. Outdoors data indicate that culturable concentrations may be positively correlated with increasing dimensionless jet-to-plate distance, especially for bacteria (p = 0.04). This effect may be attributable to sampler jet dissipation with lower nozzle number impactors (i.e., the Sampl’air) being more sensitive. This study demonstrates that bioaerosol impactor agar plate volume should be considered prior to sampling.

Copyright 2013 American Association for Aerosol Research     

Aerosol Particle Collection Efficiency of Holey Carbon Film-Coated TEM Grids

A simple sampling method to collect aerosol particles for transmission electron microscope (TEM) analysis was developed by R’mili and others in 2013. The method involves passing air through a holey carbon film-coated copper mesh TEM grid (holey carbon grid) and sampling particles by filtration. In this study, we proposed a modified calculation method to represent the collection efficiencies of holey carbon grids, taking into consideration the porosity of the copper mesh. We then evaluated the particle collection efficiencies of holey carbon grids both theoretically and experimentally. We tested the collection efficiency of two types of holey carbon grids, with nominal pore sizes of 1.2 and 0.6 μm, using particles of monodispersed polystyrene latex (PSL) and potassium chloride. The overall collection efficiency of each grid (E_grid) was determined by the downstream/upstream concentration ratio measured by condensation particle counters (CPCs). In addition, for PSL particles, the collection efficiency of the holey carbon film (E_film) was determined by the ratio of the number of particles on the film (counted on a scanning electron microscope) to the number of inflow particles (counted by a CPC). We compared model calculations against the experimental results obtained in this study and those reported by R’mili and others in 2013. These data showed that the calculated E_grid values were in reasonably good agreement with the experimental E_grid values. However, although the model calculation indicated that E_film ≈ E_grid, there was an inconsistency between the experimental E_film and E_grid, which requires further investigation in order to determine its cause.

Copyright 2014 American Association for Aerosol Research     

An Experimental Study of the Performance Factors Affecting Particle Collection Efficiency of the Electrocyclone

An electrocyclone designed with a central discharge wire was built and used to investigate the performance factors affecting its particle collection efficiency by varying the operational conditions and parameters in the particle size range of 0.5 to 10 w m. A voltage of 0 to 9 kV was applied to the discharge wire varying in terms of diameter and length. Two types of vortex finder materials, aluminum and acryl, in three lengths, 2.5, 3.5, and 4.5 cm, were employed to examine the effects of electrostatic force. An increase in applied voltage and a decrease in wire diameter were found to boost collection efficiency, particularly at low flow rates for small particles. Many small particles induced in the cyclone were collected at the bottom of the cyclone cone and in the vortex finder that was situated close to the discharge wire. It was also found that the aluminum vortex finder yields higher collection efficiency than the acryl vortex finder and that the length of vortex finder plays a more important role in particle collection efficiency of the electrocyclone than that of an ordinary cyclone.     

基于颗粒直径大小对环形空间携屑影响的数值模拟

钻井是开发石油资源一个非常重要的环节和技术手段,井中岩屑易在井眼底部形成岩屑床,导致下钻遇阻、蹩泵甚至卡钻,因此岩屑运移机理的研究对钻井作业来说至关重要。通过对现场实际情况的调研,得到井下上返颗粒的直径范围,进行数值模拟。运用Solid Works对井下环形空间进行建模与装配,得到井下环形空间的三维模型。使用软件建立井下环形空间的简化模型,通过应用FLUENT中动网格部分的UDF编写成功地实现了钻杆的旋转。运用FLUENT数字模拟软件,通过对流体非定常流的数值模拟,对岩屑在环形空间的运移规律进行研究,模拟条件更加接近实际情况,结果更加精确,可以为钻井井眼清洁工作提供科学参考。     

硬球链流体在平板和硬球表面分布的密度泛函理论

采用Yethiraj和Woodward的密度泛函理论方法,结合胡英和刘洪来等发展的硬球链流体状态方程,得到了自由连接硬球链流体在平板狭缝中和球形固体颗粒表面附近的密度分布表达式,并计算了在两平行壁所组成的狭缝中和直径大小不同的球形固体颗粒周围硬球链分子的链节密度分布.理论计算结果与作者采用Dickman 和Hall 的方法进行Monte Carlo计算机模拟结果非常吻合.颗粒直径对链状分子的密度分布有一定的影响,随着固体颗粒直径的增加,靠近颗粒表面附近的链节密度降低.     

Influence of the Marangoni Effect on the Efficiency of Plate Columns for Binary Distillation

The main feature of a distillation process is its efficiency. The gas‐liquid bubbling layer formed on the trays and the ongoing mass‐exchange process during distillation is influenced by the change of the surface tension gradient during this mass‐exchange procedure. Binary mixtures with respect to the change of the surface tension effect can be divided into positive, negative, and neutral ones. In order to assess the effect of surface tension on mass transfer, the stabilization index quantity is applied, representing the product of the liquid phase process momentum and the surface tension gradient in the mixture of the liquid phase. One possibility to express the Marangoni efficiency enhancement ratio by experimental distillation data obtained under identical hydrodynamic conditions in two binary systems, i.e., a positive (methanol‐water) and a neutral one (methanol‐ethanol), is presented.     

Particle Deposition on Spheres by Inertial and Electrostatic Forces

The theoretical collision efficiency of a sphere is examined considering the simultaneous effects of inertial impaction and electrostatic attraction. The competition between these two mechanisms is discussed. Electrostatic attraction is found to be much more effective in terms of energy consumption than inertial impaction. Also the effects of the use of a more accurate non-Stokesian drag and interception are examined under typical industrial conditions. A well-defined experimental system was designed and constructed to investigate the combined effects of inertial impaction and electrostatic attraction on particle collection by spheres. The experimental results were compared with theoretical predictions with and without the non-Stokesian drag correction. Good agreement between experiment and the model with the non-Stokesian drag correction was obtained.     

溢流管直径对旋流器分离效率影响的数值模拟

在溢流管长度L0均分别设定为10mm、15mm、20mm条件下,应用Fluent软件对不同直径的直筒式水力旋流器进行了数值模拟,得到了不同入口速度下的压降和分离效率。结果表明,当溢流管直径为3mm时,旋流器的分离效率最大。旋流器主直径D一定时,使旋流器分离效率最高的直径也是一定的,一般溢流口直径选择经验值为D/(5~8.5)。     

Comparison of Coal Ash Particle Size Distributions from Berner and Dekati Low Pressure Impactors

This article presents the differential mass size distributions of coal combustion particulate matter (PM) determined with the Berner low-pressure impactor (BLPI, Hauke Model 25-4/0.015) and a newer generation of low pressure impactor, the Dekati low-pressure impactor (DLPI, Dekati Ltd Model 6281). The collection characteristics of the BLPI and DLPI are compared and cutoff diameters are calculated. Samples were collected in the post-combustion zone of a 19 kW vertical downflow combustor from two coal types. Both BLPI and DLPI represent a tri-modal distribution and give statistically similar characterizations of the coal ash particle size distribution. Distributions generated from DLPI data have higher fractions of submicron particles compared to those generated from BLPI data. The DLPI's two additional stages may provide greater resolution in the submicron region than the BLPI.     

Influence of the Impaction Angle on the Triboelectric Charging of Aerosol Nanoparticles

A low pressure impactor is used to measure triboelectric charging behavior of metallic nanoparticles. Ag nanoparticles, produced by spark discharge, were impacted onto Pt sputtered targets. The influence of the impaction angle and impaction velocity on the triboelectric charging was investigated. While for perpendicular impaction the charge transfer behavior of previous work was confirmed, the oblique impaction revealed new phenomena. Additional charge transfer was observable, which increases with obliqueness. The possibility of mass transfer between particle and target due to the high-energy collisions was also investigated. SEM characterization and Auger spectroscopy indicate mass transfer from the particle to the target surface.     

加热器直径对200 mm太阳能级单晶硅加热效率、能耗和氧含量的影响

大幅降低单晶硅的生产成本是光伏行业急需解决的难题之一.本文采用CGSim晶体生长软件,对现有工业单晶炉的热场结构进行了优化并分析了其对加热效率、单晶炉能耗和晶体氧含量的影响.结果表明,随加热器内径的减小,加热器对石墨坩埚的加热效率逐渐提升,进而使加热器的功率大幅下降;同时,熔体中的对流也受到抑制,减小了对流对坩埚壁的冲刷,降低了晶体中的氧含量.当加热器内径为550 mm时,单晶炉的功率降低了25.7％,晶体中的氧含量降低了27.1％,为进一步降低单晶硅的生产成本提供了依据.     

阿司匹林明胶微球粒径分布及其影响因素的研究

采用W／O型乳化一固化聚合方法制备了阿司匹林明胶微球（AIGM）,通过单因素试验和正交设计试验研究制备条件对AIGM平均粒径的影响,并采用粒度分析仪、扫描电镜等分析手段对其结构进行了表征。结果表明,反应条件对AIGM的形成及粒径影响很大,溶液pH=5．0以及乳化剂用量小于临界胶束浓度是形成复合微球的必要条件;AIGM粒径随戊二醛量增加、反应时间的增长、阿司匹林与明胶配比的增加而增大;pH值和阿司匹林与明胶配比是影响微球平均粒径的主要因素。     

High-Volume Aerosol Filtration and Mitigation of Inertial Particle Rebound

The performance of electrostatically charged blown microfiber filter media was characterized for high-volume sampling applications. Pressure drop and aerosol collection efficiency were measured at air pressures of 55.2 and 88.7 kilopascals (kPa) and filter face velocities ranging from 2.5 to 11.25 meters per second (m/s). Particle penetration was significant for particles above 0.5 micrometers (μm) in aerodynamic diameter where the onset of particle rebound was observed as low as 200 nanometers (nm). Particle retention was enhanced by treating filters in an aqueous solution of glycerol. Adding this retention agent eliminated electrostatic capture mechanisms but mitigated inertial rebound. Untreated filters had higher nanoparticle collection efficiencies at lower filter face velocities where electrostatic capture was still significant. At higher filter face velocities, nanoparticle collection efficiencies were higher for treated filters where inertial capture was dominant and particle rebound was mitigated. Significant improvements to microparticle collection efficiency were observed for treated filters at all air flow conditions. At high air pressure, filter efficiency was greater than 95% for particles less than 5 μm. At low air pressure, performance enhancements were not as significant since air velocities were significantly higher through the fiber mat. Measured single fiber efficiencies were normalized by the theoretical single fiber efficiency to calculate adhesion probability. The small fiber diameter (1.77 μm) of this particular filter gave large Stokes numbers and interception parameters forcing the single fiber efficiency to its maximum theoretical value. The adhesion probability was plotted as a function of the ratio of Stokes and interception parameter similar to the works of others. Single fiber efficiencies for inertial nanoparticle collection were compared to existing theories and correlations.

Copyright 2014 American Association for Aerosol Research     

Electrostatic and Inertial Collection of Aerosol Particles by Water Droplets

Inertial impaction and electrostatic attraction are generally the two most important mechanisms for the collection of charged micron-sized particles by charged droplets. An experiment was carried out to determine the collision efficiencies of charged 142-μm-radius water droplets for charged micron-sized particles under different values of the electrostatic force. Experimental results agree well with a trajectory model that used a numerically derived flow field for the 142-μm-radius droplets.     

影响乳化硅油颗粒度因素的考察

以二甲基硅油为主要原料,非离子表面活性剂复配制备乳化硅油,考察了乳化剂用量、乳化时间、乳化温度、pH、搅拌速度、乳化水温度和乳化方法等工艺条件对乳化硅油颗粒度的影响。结果表明,在50～90℃,乳化温度对乳液粒径影响不显著;乳化剂用量、乳化时间、pH、搅拌速度和乳化方法对乳液的粒径均有影响。w(乳化剂)=7%,乳化时间45min,乳化温度80℃,乳化体系的pH≈6,在1200r/min的搅拌速度下采用乳化剂在油中法,制得了平均粒径为1.561μm,折光率为1.403,表观黏度216mPa.s的固体份质量分数为30%的硅油乳液。应用文中所述的工艺条件,脱膜剂厂家制备出了性能优良的乳化硅油脱模剂产品。