Modification of Laminar Flow Ultrafine Condensation Particle Counters for the Enhanced Detection of 1 nm Condensation Nuclei

This paper describes simple modifications to thermally diffusive laminar flow ultrafine condensation particle counters (UCPCs) that allow detection of ～1 nm condensation nuclei with much higher efficiencies than have been previously reported. These non-destructive modifications were applied to a commercial butanol-based UCPC (TSI 3025A) and to a diethylene glycol-based UCPC (UMN DEG-UCPC). Size and charge dependent detection efficiencies using the modified UCPCs (BNL 3025A and BNL DEG-UCPC) were measured with high resolution mobility classified aerosols composed of NaCl, W, molecular ion standards of tetra-alkyl ammonium bromide, and neutralizer-generated ions. With negatively charged NaCl aerosol, the BNL 3025A and BNL DEG-UCPC achieved detection efficiencies of 37% (90× increase over TSI 3025A) at 1.68 nm mobility diameter (1.39 nm geometric diameter) and 23% (8× increase over UMN DEG-UCPC) at 1.19 nm mobility diameter (0.89 nm geometric diameter), respectively. Operating conditions for both UCPCs were identified that allowed negatively charged NaCl and W particles, but not negative ions of exactly the same mobility size, to be efficiently detected. This serendipitous material dependence, which is not fundamentally understood, suggests that vapor condensation might sometimes allow for the discrimination between air “ions” and charged “particles.” As a detector in a scanning mobility particle spectrometer (SMPS), a UCPC with this strong material dependence would allow for more accurate measurements of sub-2 nm aerosol size distributions due to the reduced interference from neutralizer-generated ions and atmospheric ions, and provide increased sensitivity for the determination of nucleation rates and initial particle growth rates.

Copyright 2012 American Association for Aerosol Research     

Moderated,Water-Based,Condensational Particle Growth in a Laminar Flow

Presented is a new approach for laminar-flow water condensation that produces saturations above 1.5 while maintaining temperatures of less than 30°C in the majority of the flow and providing an exiting dew point below 15°C. With the original laminar flow water condensation method, the particle activation and growth occurs in a region with warm, wetted walls throughout, which has the side-effect of heating the flow. The “moderated” approach presented here replaces this warm region with two sections—a short, warm, wet-walled “initiator,” followed by a cool-walled “moderator.” The initiator provides the water vapor that creates the supersaturation, while the moderator provides the time for particle growth. The combined length of the initiator and moderator sections is the same as that of the original, warm-walled growth section. Model results show that this new approach reduces the added heat and water vapor while achieving the same peak supersaturation and similar droplet growth. Experimental measurements confirm the trends predicted by the modeling.

Copyright 2014 American Association for Aerosol Research     

激光粒度仪分级测定水煤浆粒度分布的研究

为确定多种磨矿产品级配制得水煤浆样品的粒度分布,文章提出了分级测定水煤浆粒度的方法,已知各磨矿产品的粒度分布,通过分级拟合的方法得到不同质量比级配样品的粒度分布。结果表明:分级计算方法得到的煤样粒度分布可以准确反映出级配样品的峰型,且粒度测试结果较为准确。     

A New Coincidence Correction Method for Condensation Particle Counters

A new method for solving the theoretical rate of coincidence in a condensation particle counter (CPC) using the Lambert W function is described. The method, based on a Poisson process, corrects for the inherent effects of coincidence in particle counters, and provides an accurately determined true counting rate. Using an experimentally determined dead time for MSP Model 1110 and TSI Model 3760A CPCs, the method provided correction of up to 99% of the maximum count rate allowed by this method, with an average discrepancy of less than 4% when compared with a reference number concentration standard. The new coincidence correction method can be applied to any CPC with a known per-event dead time, extending its upper concentration measuring range by nearly one order of magnitude.

Copyright 2013 American Association for Aerosol Research     

Particle Size Modification of Thermally Stable Secondary Explosives for IM Applications

As well as improving the survivability of weapons and platforms, insensitive munitions (IM) reduce both casualty rates and mission losses. Their use also leads to improved safety during storage and transportation. For a munition to fulfil IM criteria, each of its energetic sub‐sections must be IM compliant. The initiator and explosive train are the most critical of these sub‐systems as their safety and reliability are of paramount importance if the weapon is to be suitable for service use, yet they are generally the most difficult part of a weapon to protect from inadvertent initiation. As part of an ongoing study into initiation methods suitable for use in IM systems, an investigation into the behaviour of energetic materials when impacted by laser‐driven flyers was performed. Laser‐based detonators exhibit increased safety characteristics over conventional initiation methods as they can be based on insensitive secondary explosives rather than sensitive primary explosives. Also, they are less susceptible to accidental initiation due to an external hazard threat. Single pulses from a high‐powered Q‐switched Nd:YAG laser were used to launch flyers from substrate‐backed aluminium films to velocities up to 6 km s⁻¹ across a short stand‐off to impact explosive targets. Several novel energetic materials have been selected for investigation as potential candidates for inclusion within flyer‐based initiation systems and explosive train applications. The materials are of interest due to their increased thermal stability and power output over conventional explosives currently in service. Attempts were made to increase the flyer responsiveness of the materials by tuning their particle size using ultrasound. The effect of particle size on the initiation threshold energy was investigated for three materials.     

粒度测试及激光衍射粒度测试法在涂料工业中的应用

介绍了涂料工业中常用的几种测量粒度及粒度分布的方法及适用范围,并从几个方面阐述了激光衍射粒度测试法作为一种新颖的颗粒粒度测量技术在涂料工业中的应用。     

Characterization of Mixing and Size Segregation in a Rotating Drum by a Particle Tracking Method

The mechanisms of segregation in solids mixing, even in simple rotating drums, are not clearly understood. Although most past studies have focused on binary mixtures, this work investigates the effect of polydispersity on granular flow, mixing, and segregation in a rotating drum operated in rolling regime through particle trajectories obtained from the radioactive particle tracking technique. Velocity profiles, radial segregation, and axial dispersion coefficients for monodisperse and polydisperse systems of glass beads are analyzed with respect to rotational speed and particle size. A model is introduced to predict the residence times along streamlines and evaluate the rate at which the material renews at the free surface and within the inner layers of the bed. Our results reveal similar velocity profiles and residence times for monodisperse and polydisperse systems. They also indicate that the particles distribute along the radial direction of the drum, although not necessarily in a core/shell configuration. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1894–1905, 2013     

A Laminar-Flow,Water-Based Condensation Particle Counter (WCPC)

A new water-based condensation particle counter (WCPC) is presented. The WCPC is a thermally diffusive, laminar flow instrument. Condensational enlargement is achieved through the introduction of a saturated airflow into a “growth tube” with wetted walls held at a temperature higher than that of the entering flow. An unsheathed, 1 L/min instrument utilizing this principle has been evaluated with various aerosols. The particle size detected with an efficiency of 50% is at or below 4.8 nm for particles sampled from vehicular emissions or ambient air, and for various laboratory-generated inorganic salts. The cut point is higher for the organic materials tested, ranging from 8 nm to 30 nm depending on the compound and purity level. An empirically determined dead-time correction factor is applied to the coincidence correction, which allows extension of the single-count mode to higher concentrations. The counting efficiencies for 80 nm oil and salt aerosols are equal, and above 97% for concentrations approaching 10 ⁵ cm ^?3 . When subject to a step-fucntion change in input concentration the time required to attain 90% of the final value, including a 0.5 s lag, is 1.3 s. The corresponding exponential time constant is 0.35 s. The WCPC evaluated here is marketed as the TSI Model 3785.     

SA-3100离心粒度分析条件对粒径真实测定的影响

用SA-3100型离心粒度分析仪测试粉体的粒度时,对同一样品的分析,往往会有不同的结果.通过对沉降介质和分散剂、最大粒径值的设定、以及测量模式的选择等影响因素作比较试验,寻求准确使用该仪器进行粒度分析的方法.     

Liquid Jet Stability in a Laminar Flow Field

The breakup of a Newtonian liquid jet into droplets injected horizontally into another flowing immiscible Newtonian fluid was studied experimentally under creeping flow conditions. Different breakup mechanisms take place in different flow regions. No filament is generated at very low velocities of the continuous phase when the droplets peel off directly at the nozzle tip. As soon as the flow rate of the continuous phase exceeds a critical value, a filament of a characteristic length begins to grow. The filament breaks up due to instabilities in terms of developing interfacial waves. The laminar breakup length of the filament is found to correlate with the flow rates of both phases and their viscosity ratio. The impact of the capillary diameter, through which the disperse phase is injected, on the filament length was investigated and the maximum droplet size was estimated.     

Water Adsorption in Feed Ingredients for Animal Pellets at Different Temperatures,Particle Size,and Ingredient Combinations

Production of animal feed pellets with uniform, predictable, and good technical pellet quality is challenging. The objective of this work was to investigate water adsorption in dry ingredients and in mixture of dry ingredients commonly used in animal feed. Rehydration at 20 and 80°C and water adsorption in moist air at 80°C were studied. Ingredients studied were soybean meal, wheat, barley, dehulled oats, rapeseed cake, sugar beet pulp, maize, and wheat bran. The ingredients were milled fine (< 0.5 mm) or coarse (> 0.5 mm).

Results show that the chemical composition of ingredients and the physical state of water affect water adsorption. A combination of steam and water should be used to optimize production of pelletized feed. The combination of a fine degree of milling, high temperature, and a long residence time favor the water adsorption process for most of the dry ingredients. For mixtures of dry ingredients, the individual chemical composition of each ingredient could be as important as physical factors such as particle size, temperature, and residence time in water.     

A Fast Scanning Mobility Particle Spectrometer for Monitoring Transient Particle Size Distributions

The Scanning Mobility Particle Spectrometer (SMPS) is a key tool for measuring particle size distribution. The application of the instrument to obtain size distributions throughout a wide range of particle sizes for transient systems, such as motor vehicle emissions, has been limited by the time resolution of the SMPS. In this paper, we present a fast-SMPS (f-SMPS) that utilizes a Radial Differential Mobility Analyzer (rDMA) and a Wixing Condensation Particle Counter (mCPC). The combination of these two components allows for the acquisition of particle size distributions on the time scale of several seconds. The Instrument has an operating range of 5–98 nm and can obtain particle size distributions at rates of up to 0.4 Hz. This paper presents the initial construction and calibration of the instrument followed by its application to several sampling scenarios. Samples from the on-road testing of a heavy-duty diesel (HDD) vehicle demonstrate the utility of this instrument for momtor vehicle emissions measurements as size distributions can now be associated with discrete events taking piace during vehicle onroad operation. For instance, these data indicate the presence of a number peak at 15 nm during transient vehicle operation. Previous work indicates that these particles are associated with the loss of engine lubricating oil.     

快速测定工业水煤浆粒度组成的方法

提出了一种快速测定工业水煤浆粒度组成的方法 ;工业生产证明 ,该方法所测结果与激光粒度分析仪所测结果吻合较好 ,能满足实际生产的需要。     

不溶性硫黄的粒度分布测试方法研究

研究不溶性硫黄粒度分布的测试方法。结果表明:激光衍射法干法测试无法得到真实的粒度分布,采用激光衍射法湿法测试,以无水乙醇为分散剂,结合纯搅拌处理工艺,测试结果更符合实际情况;该方法测定的粒度分布结果重复性好,且与扫描电子显微镜照片相符合,说明了该方法的可靠性。     

LiFePO_4材料的溶胶凝胶法合成及其粒度研究

采用溶胶凝胶法合成了橄榄石型LiFePO4材料。运用XRD、SEM和激光粒度分布仪等手段对材料进行表征。研究了反应体系pH值、煅烧温度、煅烧升温速率和柠檬酸用量等工艺参数对LiFePO4粒径和粒度分布、物相组成和结构等物性的影响。得到的适宜工艺条件为：反应体系pH值为3.57,煅烧温度800℃,煅烧升温速率7℃/min,柠檬酸用量3.5∶1.0。同时分析了各因素对LiFePO4材料粒度分布的影响机制,重点讨论了反应过程机理和煅烧过程机理。     

光透射法测定阴极电泳漆乳液粒径

介绍了测定光直接透过被测溶液时强度之衰减，即透射法来测定阴极电泳漆乳液的粒径大小的一种方法。     

大颗粒、高浓度硅溶胶的制备新方法

以水玻璃为原料,采用滴加工艺制备一定粒径大小的二氧化硅作为母核;采用在催化剂和分散剂共同作用下水解硅粉的方法使母核二氧化硅颗粒进一步增长,得到了高均匀分布的平均粒径在100nm以上、浓度可达50％的二氧化硅溶胶。并对新方法下pH值、温度以及母核SiO2的浓度、粒径大小对二氧化硅平均粒径及其均匀性的影响进行了分析。研究结果对制备大颗粒、高浓度的硅溶胶具有积极意义。     

A Scanning Transmission Electron Microscopy Method for Determining Manganese Composition in Welding Fume as a Function of Primary Particle Size

Increasing evidence suggests that the physicochemical properties of inhaled nanoparticles influence the resulting toxicokinetics and toxicodynamics. This report presents a method using scanning transmission electron microscopy (STEM) to measure the Mn content throughout the primary particle size distribution of welding fume particle samples collected on filters for application in exposure and health research. Dark field images were collected to assess the primary particle size distribution and energy-dispersive X-ray and electron energy loss spectroscopy were performed for measurement of Mn composition as a function of primary particle size. A manual method incorporating imaging software was used to measure the primary particle diameter and to select an integration region for compositional analysis within primary particles throughout the size range. To explore the variation in the developed metric, the method was applied to 10 gas metal arc welding (GMAW) fume particle samples of mild steel that were collected under a variety of conditions. The range of Mn composition by particle size was -0.10 to 0.19 %/nm, where a positive estimate indicates greater relative abundance of Mn increasing with primary particle size and a negative estimate conversely indicates decreasing Mn content with size. However, the estimate was only statistically significant (p<0.05) in half of the samples (n=5), which all had a positive estimate. In the remaining samples, no significant trend was measured. Our findings indicate that the method is reproducible and that differences in the abundance of Mn by primary particle size among welding fume samples can be detected.     

Minimizing Concentration Effects in Water-Based,Laminar-Flow Condensation Particle Counters

Concentration effects in water condensation systems, such as used in the water-based condensation particle counter, are explored through numeric modeling and direct measurements. Modeling shows that the condensation heat release and vapor depletion associated with particle activation and growth lowers the peak supersaturation. At higher number concentrations, the diameter of the droplets formed is smaller, and the threshold particle size for activation is higher. This occurs in both cylindrical and parallel plate geometries. For water-based systems, we find that condensational heat release is more important than vapor depletion. We also find that concentration effects can be minimized through use of smaller tube diameters, or more closely spaced parallel plates. Experimental measurements of droplet diameter confirm modeling results.

© 2013 American Association for Aerosol Research