Size Characterization of Carbonaceous Particles Using a Lovelace Multijet Cascade Impactor / Parallel-Flow Diffusion Battery Serial Sampling Train

A serial sampling train consisting of a Lovelace multijet cascade impactor (LMJI) and a seven cell parallel-flow diffusion battery (PFDB) has been used to provide a comprehensive method for sizing aerosols with a wide size distribution ranging from less than 0.01 μm to over 10 μm. The fraction of the aerosol greater than 0.7 μm is collected by the impactor. The remaining fraction of the aerosol is sampled by the PFDB. Design of the PFDB is based on the theory of a screen-type diffusion battery. The concept of parallel flow is employed to provide a method for sampling aerosols that fluctuate too rapidly in concentration and size distribution to be measured by conventional methods. The LMJI/PFDB sampling system is useful for characterizing multimodel size distributions such as those that occur in ambient aerosols. It can also be used to determine the chemical composition of collected samples as a function of particle size. This sampling system has been used to size classify diesel and diesel-oil shale exposure atmospheres, and benzo(a)-pyrene-coated carbon black aerosols. The diffusion equivalent diameter (D _de) of the diesel exhaust was 0.07–0.08 μm, and the oil-shale dust had a mass median aerodynamic diameter (MMAD) of 2.6–2.9 μm. The size distribution of the carbon black aerosol was bimodal, with the fine fraction having a D _de of 0.2 μm, and the coarse fraction having a MMAD of 2.0 μm.     

Effect of Flow-induced Relative Humidity Changes on Size Cuts for Sulfuric Acid Droplets in the Microorifice Uniform Deposit Impactor (MOUDI)

The effect of flow-induced relative humidity changes on cut sizes of aqueous sulfuric acid particles in a multi-nozzle microrifice uniform deposit impactor (MOUDI) was studied theoretically and experimentally. In the theoretical study, the differential equation of vapor transport to particles including the Fuchs correction, the Kelvin effect, sulfuric acid solution properties, and temperature depression was integrated along the particle critical trajectory to determine the cut size at various relative humidities. Results show that aqueous sulfuric acid particles first shrink owing to evaporation caused by pressure drop, then grow in the jet owing to condensation caused by aerodynamic cooling. The study was confined to stages 7 (50% cut size = 0.122 μm) and 8 (50% cut size = 0.047 μm) where humidity variations are greatest. It was found that the net size change of aqueous sulfuric acid droplets is negligible when the inlet relative humidity is < 80% because of the moderate pressure drop across nozzles and the extremely short residence time the particles spend in the jet. The agreement between theory and experiment is good     

Simultaneous Elemental Composition and Size Distributions of Submicron Particles in Real Time Using Laser Atomization Ionization Mass Spectrometry

Composition and size of individual submicron particles have been measured using a laser atomization ionization mass spectrometry technique, the Particle Blaster. Individual particles are quantitatively converted to atomic cations, providing information on both their complete elemental composition and particle size. Measured average atomic ratios for 100 nm particles of sodium chloride is 1.12 +- 0.36 (Cl:Na), for 50 nm particles of silica is 1.93 +- 0.52 (O:Si), and for 64 nm polystyrene latex spheres (PSL) is 1.13 +- 0.19 (H:C), in excellent agreement with the empirical formulae. Calculated particle sizes agree well with electrostatic classifier or TEM measurements in the size range of 17-900 nm diameter for particles of sodium chloride, silicon, and PSL. Size distributions are also obtain able, giving narrower distributions than are measured with an electrostatic classifier, for particles of alumina, silica, sodium chloride, and PSL spheres. Comparison with TEM data shows comparable primary particle sizes, but numerous particle aggregates are detected by the Particle Blaster which are unreported by the TEM measurements.     

High-Volume Dichotomous Virtual Impactor for the Fractionation and Collection of Particles According to Aerodynamic Size

A prototype dichotomous virtual impactor (DVI) using a single acceleration nozzle, operating at approximately 500 1/min, and having an aerodynamic particle outpoint diameter of about 2–3 μm has been constructed and tested. Under these conditions the flow through the acceleration nozzle is calculated to be turbulent. This sampler was calibrated with a monodisperse aerosol, and the measured particle size-dependent collection efficiencies demonstrate that the sampler size fractionates atmospheric particulate matter as efficiently as the low-volume dichotomous virtual impactors. Analysis of test data indicates that the high-volume sampler can be described by classical impaction theory. These data also indicate that over the range of Reynolds numbers from 24,000 to 81,000 there is little, if any, dependence of inferred acceleration nozzle turbulence on the performance characteristics of the sampling system. A comparison of the concentration of atmospheric particulate matter, sulfate, and calcium on the fine filter samples collected with colocated high- and low-volume virtual impactors also shows that the two samplers are operating with similar performance characteristics. Additionally, the high-volume DVI collects at least 10–30 times the mass of particulate matter that the presently available virtual impactors collect and thus allows one to obtain improved precision in the measurement of those airborne species that are near the minimum detectable level of current analytical methods.     

Evaluation of Aerodynamic Particle Sizer and Electrical Low-Pressure Impactor for Unimodal and Bimodal Mass-Weighted Size Distributions

The objective of this study was to investigate the feasibility of the Aerodynamic Particle Sizer (APS) and the Electrical Low-Pressure Impactor (ELPI) to study mass weighted particle size distributions. Unimodal and bimodal liquid test aerosols were produced to a small chamber. Simultaneous measurements were performed with an APS 3320, an APS 3321, an ELPI and a Dekati Low-Pressure Impactor (DLPI) analyzed gravimetrically. ELPI current and mass responses were simulated for lognormal size distributions using a parameterization of the impactor kernel functions. In experiments with a single coarse mode, the mass ratio to the DLPI was between 0.75 and 1.15 for both APS models up to 5 μ m and for the ELPI up to 3 μ m. For larger sizes the ELPI and APS 3320 overestimated and the APS 3321 underestimated the concentration. In experiments with a single fine mode, submicrometer ELPI and DLPI results were in good agreement. However, in contrast to the DLPI all three spectrometers showed a significant mass fraction above 1 μ m. In experiments with a bimodal size distribution, the mass ratios were altered compared to single coarse mode experiments. Simulations showed that uncertainties in ELPI measurements of larger particles occur when concentrations of small particles are high. Several mechanisms that may bias ELPI and APS measurements are described. With knowledge of these, ELPI and APS 3321 can, under many circumstances give accurate time-resolved mass size distributions for particles smaller than 3 and 5 μm, respectively.     

Measurement of the Size of Fine Nonspherical Particles with a Light-Scattering Particle Counter

To characterize flow separation and classification processes, particle size distributions must be measured in the airborne state without affecting the state of dispersion or disturbing the flow. Light-scattering devices with an optically defined measuring volume are specially designed for this purpose. However, the light-scattering device must be calibrated using nonideal particles which are present within the multiphase flow, preferably on an equivalent diameter based on settling rate. The cyclone cut size calibration can solve this problem. By means of this aerodynamic calibration technique, it is possible to measure size distributions of nonspherical particles with a light-scattering particle counter in industrially relevant cases.     

Size Distribution Measurement of Carbonaceous Particulate Matter Using a Low Pressure Impactor with Quartz Fiber Substrates

The collection characteristics of a small deposit area low pressure impactor (SDI) were studied in order to employ the impactor for size distribution measurements of carbonaceous matter. In this work, the SDI was calibrated for soft and porous quartz substrate material in a series of laboratory experiments. The collection efficiency curves were measured by using monodisperse dioctyl sebacate particles and by applying two different detection methods. One method was based on the detection of current carried by charged test particles, and the other measured number concentrations of particles in bipolar charge equilibrium by two condensation particle counters. Concerning the particle size corresponding to a 50% collection efficiency (D ₅₀ ), significant shifts toward smaller particle sizes were found for the quartz fiber substrates compared with the flat plates. Also the shapes of the collection efficiency curves differed considerably: quartz substrate gave less steep curves than plain impaction plates. The new calibration was applied to field data from urban and rural sites. Compared with the original calibration of the SDI, the new calibration changed the measured size distributions of organic and elemental carbon. In addition, a reasonable size-segregated mass closure was achieved by combining data from thermal-optical analysis and ion-chromatography.     

Measuring Particle Size Distributions in Multiphase Flows Using a Convolutional Neural Network

The efficiency of many chemical engineering applications depends on the surface/volume ratio of the dispersed phase. Knowledge of this particle size distribution is a key factor for better process control. The challenge of measurements acquired by optical imaging techniques is the segmentation of overlapping particles, especially in high phase fraction flows. In this work, a convolutional neural network is trained to segment droplets in images acquired by a shadowgraphic approach. The network is trained on artificial images and implemented into a droplet size algorithm. The results are compared to an OpenSource segmentation approach.     

利用胶质气体泡沫分离细微颗粒

This paper presents a method of separation of fine particles, of the order of a few microns or less, from aqueous media by flotation using colloidal gas aphrons (CGAs) generated in aqueous solutions. More than 150 experiments were conducted to study the effects of surfactant type, surfactant concentration, CGAs flow rate, and particle concentration on the removal efficiency (fine particles of polystyrene were used as a target compound). The results indicate that CGAs, generated from cationic surfactant of hexdecyltrimethyl ammonicum bromide (HTAB) and anionic surfactant of sodium dodecylbenzne sulfonate (SDBS), are an effective method for the separation off ine particles of polystyrene from wastewater. The flotation yields are higher than 97%.     

Design and Testing of the NCTU Micro-Orifice Cascade Impactor (NMCI) for the Measurement of Nanoparticle Size Distributions

Soot processes within a turbulent nonpremixed flame burning acetylene/air were investigated by conducting thermophoretic sampling experiments at various axial and radial locations. Analyses of transmission electron microscope images yielded the mean soot spherule diameter, number of spherules per aggregate, and fractal morphology within this highly luminous turbulent flame. Specifically, translucent particles were observed at low-to-intermediate heights above the flame with the formation and evolution of young soot precursors. The soot spherule diameter peaked at 34 nm halfway along the centerline, identifying the flame regions of surface growth and oxidation processes. In the meantime, the aggregation was continuous along the flame axis with the mean number of spherules per aggregate reaching 150 at the highest sampling location. Size ranges of spherules and aggregates were narrow and broad, respectively, while the relative widths of both size distributions remained similar throughout the flame. In contrast to the observed axial variations, the radial changes of the mean spherule and aggregate sizes appeared to be small. Aggregate morphologies were universally characterized by a fractal dimension of 1.82 and a fractal prefactor of 1.9 for all the flame positions. In comparison to a lightly sooting ethylene flame, these measurements in the acetylene turbulent flame revealed that the fuel type mainly affected the axial evolution of spherule diameters but not their range, and enhanced the aggregate sizes but not their morphology. The effective decoupling of spherule and aggregate sizes permitted the separation of soot surface growth and oxidation from aggregation. This key aspect provided a stringent test for the existing particulate diagnostics and predictive models in their ability to quantify the actual particle surface area, particularly in optically thick conditions that are encountered in many practical combustion environments.     

Capillary Impactor with Optical Detection in Collection of Carbonaceous Particles

A new single-orifice capillary system for optical analysis of carbonaceous matter is reported. The special feature of this system is the use of long, flexible capillary tubing for sampling.     

用电导探针测定气-液多层桨搅拌槽内气泡尺寸分布

在直径0.48 m的椭圆底三层组合桨搅拌槽中,使用双电导探针测定常温24℃及热态81℃通气条件下,空气-去离子水体系的局部气泡尺寸分布,分别利用标定法及数学重构法进行数据处理,得出适宜方法为数值解析的重构法.采用以半椭圆管盘式涡轮(HEDT)为底桨,上两层分别为四叶轴流桨下压(WHD)及上提(WHu)操作的HEDT+2...     

Classification of Fine Particles Using the Hydrodynamic Forces in the Boundary Layer of a Membrane

The wet classification of particles < 10 μm is a complex process that has been researched for many years. In this study, the usage of a modified cross‐flow filtration process as a classification process was investigated. With this process, particles in a fine micrometer range can be separated from suspensions. The upper particle size is dependent on hydrodynamic forces. The experimental results were compared with different hydrodynamic force models to predict upper size. The influence of the permeate flux and the particle concentration in the feed on the upper particle size is studied.     

Unipolar Charging of Fine and Ultra-Fine Particles Using Carbon Fiber Ionizers

A simple and novel unipolar charger using carbon fiber ionizers was developed to effectively charge fine and ultra-fine aerosol particles without the generation of ozone. The particle penetration in the charger was investigated for non-charged, neutralized, and singly charged particles in the size range of 20–200 nm. Particle loss and the intrinsic, exit and extrinsic charging efficiencies of fine and ultra-fine particles were also investigated for non-charged particles at different applied voltages to the charger. Particle penetrations in the charger were nearly 100% for particles larger than 20 nm, irrespective of the initial particle charging state. Particle losses in the charger could be decreased by decreasing the applied voltage to the charger from 4.0 kV to 2.3 kV. The intrinsic charging efficiencies were proportionally increased with the applied voltage, whereas the exit charging efficiencies were almost independent of the applied voltage. Therefore, the extrinsic charging efficiency of the charger becomes higher for the lower applied voltage (2.3 kV), at which about 60% of 20 nm particles were charged. Little (less than 4 ppb) to no ozone was generated under all operation conditions. It can be concluded that the newly developed unipolar charger using carbon fiber ionizers can charge fine and ultra-fine particles at least as effectively as currently available unipolar chargers, but with the major advantage of negligible ozone generation, a highly desirable feature if the charged particles are to be used for chemical or biological analysis.     

A Study of the Size Distributions and the Chemical Characterization of Airborne Particles in the Vicinity of a Large Integrated Steelworks

An atmospheric measurement campaign took place in the spring of 2006 to characterize the emission of particles from an integrated iron and steelmaking site. During the measurement campaign, the PM ₁₀ daily limit value of 50 μ g m ^{? 3} was not exceeded during any day. However, excursions in PM ₁₀ concentrations occurred over periods of a few hours which were associated with wind passing over the steelworks' site. Measurements with an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) showed six particle classes associated with emissions from steelmaking processes. Two of these were iron-rich, one showing internal mixing with nitrate, the other internally mixed with phosphate, which subsequent analysis identified as arising from the ironmaking sector and the hot and cold mills as the dominant sources, respectively. Other ATOFMS classes were rich in lead, zinc, and nickel, which were also associated with steelmaking sources. A Micro Orifice Uniform Deposit Impactor (MOUDI), used to measure particle size distributions over periods of 19–42 hours, showed two characteristic size distributions for iron, one bimodal with modes at 0.45 μ m and 4 μ m, the other unimodal centered at 6 μ m. In the former case, the smaller mode exhibited a peak for lead at the same particle size and in the case of the larger mode, phosphate and calcium also showed a peak at 4 μ m diameter, consistent with the ATOFMS findings. An additional particle type with a unimodal size distribution centered at about 1.2 μ m, with internally mixed Pb, Zn, and Cl but not Fe was also found.     

微细粉振动流化床的团聚模型

微细粉振动流化床的团聚模型唐洪波赵王君（天津大学化学工程研究所,天津３０００７２）（天津大学化学工程系,天津３０００７２）关键词微细颗粒振动流化床团聚物团聚模型１实验１．１实验装置及流程本实验所用装置及实验流程如图１所示,流化床内径为１９ｍｍ,高４...     

Adhesion of Fine Particles in Dispersions

When a dispersion of fine particles is concentrated, the product can contain clumps which arise from the aggregation of the particles. There are several drivers: sedimentating, drying, filtration, forcing the particles together to produce agglomerated structures which are much larger than the primary particles. The problem of understanding this phenomenon is twofold: on the one hand, it is difficult to measure aggregates in a concentrated slurry; on the other, there is no theory to predict when aggregates should form in an apparently-stable dispersion. This paper describes a new experimental method for measuring aggregates in concentrated suspensions, showing that the aggregation phenomenon can be followed over a wide range of experimental conditions. In particular, the results show that the aggregates exist at small concentrations in ostensibly stable dispersions even before concentrating takes place. Colloids based on polymers, ceramics, biological cells and emulsions all showed this aggregation effect. We have called these aggregated structures “multiplets” to distinguish them from the more normal flocs produced by destabilising the colloid. A theory of aggregation is proposed to fit the experimental results. This theory is based on the idea that multiplets form as a consequence of small adhesion forces between particles immersed in liquid; a molecular dynamics simulation using this concept of adhesion forces is used to demonstrate the formation of multiplet material at low concentrations. The theory seeks to show how the size of multiplets should vary with adhesion and with particle concentration.     

细颗粒振动流态化研究进展

概括了细颗粒在振动流化床中的流态化实验研究和理论模型,着重介绍了振动场对细颗粒流化行为的影响,综述了振动场中粘性颗粒的运动,有利流化的振动参数以及聚团尺寸测量和计算的研究现状。     

Particle Size Distributions in Calcined Powders

The changes in particle size distributions in bayerite and magnesium hydroxide on calcination are reported. In general, size distributions in calcined powders very closely resemble those obtained before calcination. Theoretical changes in particle volume, and hence in volume equivalent diameter, can be calculated from weight-loss data and corresponding densities. Possible reasons for deviation from the theoretical size reduction ratio are also discussed.