Design and performance test of a multi-channel diffusion charger for real-time measurements of submicron aerosol particles having a unimodal log-normal size distribution

It is important to develop a simple and fast method for measuring the sizes of submicron particles in both laboratories and fields. In our previous studies, Park, An, and Hwang [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420–430] and Park, Kim, An, and Hwang [(2007). Real-time measurement of submicron aerosol particles having a log-normal size distribution by simultaneously using unipolar diffusion charger and unipolar field charger. Journal of Aerosol Science, 38, 1240–245], we introduced methodologies that our lab made unipolar charger could lead to detection times of under 5 s in conjunction with an electrometer and a condensation particle counter (CPC), and under 3 s with two electrometers.However, both methodologies require an appropriate assumption of the geometric standard deviation of particle sizes. In this paper, we introduce a methodology for determining the geometric standard deviation of particle sizes as well as the geometric mean diameter and the total number concentration of particles. For this purpose, a diffusion charger that consisted of discharge zone, mixing and charging zone, and three flow channels for obtaining three different residence times and average charges of particles in the channels, was designed and tested. For determining the average particle charge, various methods including theoretical calculations and the tandem differential mobility analyzer (TDMA) method were used. The results obtained from the different methods agreed well with each other. To compare the size distribution with the data that were measured through a scanning mobility particle sizer (SMPS), sodium chloride (NaCl) particles were used. The estimated results by using a data inversion algorithm were less than those measured by SMPS by around 22% for the total number concentration and 10% for both the geometric mean diameter and the geometric standard deviation. Furthermore, the detection time was under 3 s.     

The effect of ion and particle losses in a diffusion charger on reaching a stationary charge distribution

Bipolar charging of nanometer-sized aerosol particles in a tube containing a radioactive source has been investigated theoretically. A model has been developed which accounts for diffusion losses of particles and ions to the tube wall, as well as for the spatial dependency of the ion-pair generation rate. The ion generation rate profile along the tube axial direction as a function of the source size and of the tube length and radius has been evaluated and, subsequently, used to examine the aerosol charging process. Comparative calculations were also performed for uniform ion generation and negligible diffusion losses. In a real charger, where diffusion losses are unavoidable, particles cannot attain a steady charge distribution. On the contrary, provided the nt product (ion mean concentration × mean aerosol residence time) is large enough, the number concentration of charged particles of a given size reaches a maximum at a certain axial location and thereafter decreases. The extrinsic charging efficiency (fraction of originally neutral particles which carry a net charge at the ionizer outlet) depends in a complex manner on a number of parameters: particle size and polarity, tube length and radius, nt product, and relative aerosol-to-ion concentration.     

CCD法测量精馏设备中气泡尺寸分布

气泡的尺寸及其分布是精馏操作,精馏设备设计的重要参数,因此精确的测量气泡的尺寸是每一个研究者所追求的目标。为此人们开发出多种测量气泡尺寸的方法,这些方法各有其优缺点以及适用范围。对主要的气泡尺寸的测量方法进行了总结,并应用CCD法对精馏塔中的气泡尺寸分布进行了测量。     

数字全息在线测量煤粉粒度分布

煤粉粒度是燃煤电厂的重要指标,在线测量煤粉粒度能够即时指导锅炉优化运行,对节能减排具有重要意义。搭建了一套模拟一次风粉管道的煤粉粒径在线测量的装置,解决了传统取样方法堵塞和测量实时性差的问题,并设计实验研究数字全息在线测量煤粉粒度的可行性和可靠性。实验结果表明,数字全息在线测量煤粉粒度分布曲线与激光粒度仪的测量曲线趋势一致,平均粒径相对误差为5.6%,表征粒度分布的关键参数d₅₀和d₉₀的相对误差均低于2%,满足工业应用的需求。数字全息技术对稀释前后不同浓度的煤粉粒径关键参数的测量相对误差均低于7%,稀释前后的煤粉粒度的数量分布和体积曲线的趋势一致,验证了数字全息技术在线测量煤粉粒度分布的可靠性,为整体测量装置的开发奠定了基础。     

New measurement of particle size distribution by a buoyancy weighing-bar method

The rates which particles from JIS Test Powders 1, Class 2 (silica sand), Class 3 (silica sand), Class 16 (calcium carbonate, heavy), and JIS Test Powder 2, Class GBM-20 (barium titanate glass) settled out of homogenous suspensions were determined using the principles of the buoyancy weighing-bar method as well as a sedimentation balance. Samples were standardized by Japanese Industrial Standard, and the dispersing agent was NaPP or NaHMP, while the viscosity improver was a starch syrup solution. Although constructing a handmade sedimentation balance is difficult, developing a handmade weighing tool capable of measuring particle size distribution is easy. Herein three weighing-bars, which were composed of aluminum, stainless steel, and copper, were used to measure the particle size distribution. However, an aluminum slit-cylinder occasionally replaced the weighing-bars. The weighing data obtained via an analytical balance were controlled by connecting the balance to a personal computer with an RS-232C interface, and the determined particle size agreed well with the data obtained by Andreasen analyses and the sedimentation balance.     

大型喷雾粒径分布的图像法测量

雾化技术在能源、化工等领域应用广泛,研究雾化机理和优化雾化喷嘴性能的前提是对其雾化液滴尺寸及粒度分布进行准确有效的测量和表征。目前常用的雾化液滴粒度测量技术,如基于光散射或衍射原理的激光粒度仪和相位多普勒分析仪等,能够较准确地测量粒径分布比较窄、最大粒度在2000 μm以下的喷雾,但对含特大颗粒且粒径分布很宽的喷雾,往往难以得到可靠结果甚至不可能进行测量。本文提出了用图像法测量这类大流量喷雾,构建了图像法测量系统,编写了图像处理程序,经标定实验后,采用该系统对某喷嘴喷雾液滴粒径分布及规律进行了测量研究。研究结果表明图像法可用于大型喷雾液滴粒度及分布的测量。     

Formation of monodisperse polyacrylamide particles by dispersion polymerization: particle size and size distribution

Highly monodisperse polyacrylamide microparticles were directly prepared by dispersion polymerization in aqueous alcoholic media initiated by 2,2′‐azobisisobutyronitrile using poly(N‐vinylpyrrolidone) as a steric stabilizer. Monomer conversion was studied dilatometrically and polymer molecular weight was determined viscometrically. The hydrodynamic diameter of polymer particles and its distribution were measured with a dynamic laser light scattering spectrometer. The number of the nuclei produced in the early stage of the polymerization was found to be constant during the remainder of the polymerization. The influences of various polymerization parameters, such as initiator concentration, monomer concentration, stabilizer content, medium polarity, and polymerization temperature on the particle size and size distribution were systematically investigated. Copyright © 2003 Society of Chemical Industry     

二项式分布在种群平衡模型模拟粒度分布中的应用

提出了一种适用于几何网格的子粒子二项式分布函数,并应用于种群平衡模型模拟活性污泥絮凝后的粒度分布。结果表明：与二元分布相比,该二项式分布可以得到更准确的粒度分布和平均粒度模拟值;通过校核二项式分布参数C_p的取值,可以提高粒度分布和平均粒度的模拟精度。相比于二元分布或正态分布只能描述一种类型的子粒子分布,该二项式分布具有较强的适应性,调整参数C_p的取值,可以得到更多可能的子粒子分布;参数C_p还可以表征粒子的破碎方式--较小的C_p值表征粒子具有较强的稳定性,易破碎生成较大的子粒子;较大的C_p值表征粒子具有较弱的稳定性,易破碎生成较小的子粒子。     

Numerical study on particle size distribution in the process of preparing ultrafine particles by reactive precipitation

Based on the population balance and mass balance in a reactive precipitation process, a numerical simulation model was developed to predict the particle size distribution (PSD) in the reactive precipitation process. The precipitation system of BaCl₂ with Na₂SO₄ to prepare BaSO₄ in aqueous solution was adopted to obtain ultrafine particles in a stirred precipitation reactor and the particle size distribution and the morphology of the particle were observed under transmission electron microscope. It was illustrated by the experimental observation of the micrographs of BaSO₄ particles obtained that apparent agglomeration occurred between the particles, which phenomenon must be taken into consideration in PSD modeling. The population balance equation was calculated by discretization method to obtain particle number and particle size distribution. By implementing the model, the reactive precipitation process in a batch reactor including reaction, nucleation, growth and agglomeration was simulated. The simulation results were validated by the experimental data of BaSO₄ precipitation. Further analysis was endeavored to explore the effects of some important factors such as the supersaturation degree and agglomeration on the evolution of the volume-based characteristic particle size and the variance of volume-based characteristic size of the particles. It was depicted that particle size and particle size distribution are controlled by the supersaturation degree and agglomeration between the particles. Stemming from the analysis in the context, the disciplinarian of the influences of these factors and the method for controlling particle size distribution were presented for the reactive precipitation process.     

超声法在线测量烟气脱硫浆液粒度分布、密度方法和装置

针对烟气脱硫工艺中石灰石/石膏浆液粒度、密度（浓度）在线测量需求,研究了基于超声衰减法的浆料多参数在线测量方法和装置。改进了一种自适应控制参数的差分进化算法用于颗粒粒径反演,模拟算例显示,改进差分进化算法求解精度更高;设计了非接触式测量管段,采用换能器一发一收模式,实现非接触式无损测量;开展了温度变化对声衰减影响实验,提出了声衰减量的温度修正方法。通过实验室结果验证,文中方法浓度测量结果与取样法浓度分析结果最大偏差为1.75%,最小偏差为0.59%。通过电厂测试结果验证,文中方法的粒度测量结果与显微镜图像法、激光粒度仪三者测量结果具有较好的一致性,最大偏差小于17%;密度测量结果与取样法吻合度高,最大重复性偏差仅为0.23%,单次测量结果与取样法最大偏差为0.26%,两项指标均优于差压密度计测量结果,可满足烟气脱硫工艺中石灰石/石膏浆液粒度、密度（浓度）在线测量需求。     

Measurement of number and size distribution of particles emitted from a mid-sized transportation multipoint port fuel injection gasoline engine

This study was carried out to characterize the engine-exhaust particulate emissions from a typical multipoint port fuel injection gasoline engine used in transportation sector. Though gasoline engine showed no visible tail pipe emissions yet its particle concentrations were comparable to mineral diesel, particularly at high engine loads. Average sizes of particles emitted in gasoline exhaust are found to be way smaller than particles emitted in diesel exhaust under similar operating conditions. The peak particle concentrations for mineral diesel never go below 40 nm size however for gasoline engine, it was as low as 20 nm for most engine operating conditions. Within a very limited operating range, gasoline engine performance was superior to its diesel counterparts in terms of particulate size and number distribution however it deteriorates very quickly as soon as the fuel-air mixture becomes closer to stoichiometric ratio, typically under high engine load and speed conditions.     

二氧化硅纳米颗粒对冰浆中冰晶粒径分布及存储演化特性的影响

分别以乙二醇水溶液和氯化钠水溶液为基液配制不同浓度的二氧化硅纳米流体并以此制备冰浆,通过显微装置获得冰晶图像,将实验得到的粒径分布与正态分布、对数正态分布、Gamma分布和Weibull分布进行对比,探讨纳米二氧化硅对冰晶平均粒径与分布特性的影响,同时观测储存过程中冰晶粒径演化规律。结果表明：加入纳米二氧化硅前后冰晶粒径分布均可用Gamma分布描述;纳米二氧化硅可起到细化晶粒的作用,而且添加浓度越高冰晶颗粒越小;当基液为乙二醇水溶液时,加入纳米二氧化硅可较好地抑制储存过程中的冰晶粒径增长,但基液为氯化钠水溶液时,纳米二氧化硅浓度需达到0.75%,才可抑制冰晶增大。研究结果证明,一定浓度的纳米二氧化硅流体可作为制冰溶液,起到减小冰晶粒径并控制冰晶生长的作用,这对冰浆流动和传热性能的改善具有重要的应用价值。     

Measurement of particle size distribution of tripalmitin crystals in a model solution using a laser diffraction method

The form and size distribution of tripalmitin (PPP) crystals formed by quenching a solution in a batch crystallizer have been studied using scanning electron microscopy and a laser diffraction technique. Although the accuracy of the laser technique for particle sizing was affected by the nonsphericity of the crystals, the technique proved to be effective and very reproducible. Crystals recovered by filtration and sonication for laser sizing exhibited markedly different particle size distributions (PSD) and shapes compared to those prepared using another standard route, namely, suspension in butanol and centrifugation. Solutions of 2–10 wt% PPP in a paraffin solvent were crystallized at 25–40°C and displayed two ranges of behavior: (i) rapid growth under strongly supersaturated conditions, yielding narrow PSD of plate and needle-like crystals; and (ii) slow growth in the metastable regime, yielding spherulitic aggregates of platelets that broke down under sonication during preparation for laser sizing. Suspension in alcohol followed by centrifugation yielded aggregates that did not break down under sonication, indicating that the sample preparation route affected the result of the analysis.     

Machine vision based particle size and size distribution determination of airborne dust particles of wood and bark pellets

Dust management strategies in industrial environment, especially of airborne dust, require quantification and measurement of size and size distribution of the particles. Advanced specialized instruments that measure airborne particle size and size distribution apply indirect methods that involve light scattering, acoustic spectroscopy, and laser diffraction. In this research, we propose a simple and direct method of airborne dust particle dimensional measurement and size distribution analysis using machine vision. The method involves development of a user-coded ImageJ plugin that measures particle length and width and analyzes size distribution of particles based on particle length from high resolution scan images. Test materials were airborne dust from soft pine wood sawdust pellets and ground pine tree bark pellets. Subsamples prepared by dividing the original dust using 230 mesh (63 μm) sieve were analyzed as well. A flatbed document scanner acquired the digital images of the dust particles. Proper sampling, layout of dust particles in singulated arrangement, good contrast smooth background, high resolution images, and accurate algorithm are essential for reliable analysis. A “halo effect” around grey-scale images ensured correct threshold limits. The measurement algorithm used Feret's diameter for particle length and “pixel-march” technique for particle width. Particle size distribution was analyzed in a sieveless manner after grouping particles according to their distinct lengths, and several significant dimensions and parameters of particle size distribution were evaluated. Results of the measurement and analysis were presented in textual and graphical formats. The developed plugin was evaluated to have a dimension measurement accuracy in excess of 98.9% and a computer speed of analysis of < 8 s/image. Arithmetic mean length of original wood and bark pellets airborne dust particles were 0.1138 ± 0.0123 and 0.1181 ± 0.0149 mm, respectively. The airborne dust particles of wood and bark pellets can be described as non-uniform, finer particles dominated, very finely skewed with positive skewness, leptokurtic, and very well sorted category. Experimental mechanical sieving and machine vision methods produced comparable particle size distribution. The limitations and merits of using the machine vision technique for the measurement of size and size distribution of fine particles such as airborne dust were discussed.     

Calculation of the particle size distribution in suspension polymerization using a compartment-mixing model

A modelling strategy for effective estimation of the particle size distribution (PSD) in suspension polymerization is presented. The strategy consists of coupling a population balance equation (PBE) and a compartment-mixing (CM) model to account for the non-homogeneous mixing in the tank reactor. The values for the rate of energy dissipation of each compartment are estimated from Computational Fluid Dynamics (CFD) calculations and experimental reports on systems with the same agitator and geometric characteristics. Model predictions using the CM model are compared with predictions that assume homogeneous mixing and experimental data on PSD from styrene and divinylbenzene pilot-plant suspension polymerization reactors of 1 and 5 L with Rushton and PBT impellers.     

Emulsification of a viscous monomer mix: Particle size and size distribution

A non-Newtonian mixture of monomers, their copolymer and pigment was dispersed into water with emulsifier by a rotor-stator homogenizer (Brinkmann Polytron). Volume median diameters d₅₀ of the droplets, measured by Coulter Counter or optical microscopy, were typically 4–20 μm; d₅₀ was about inversely proportional to monomer fraction (0.2 to 1.0), or to rotor speed (4000 to 11000 rpm). Increasing the emulsifier from 0.1 % to 3% roughly halved d₅₀; volume fraction of organic phase had little effect. Turbulent dispersion theory (Calabrese et al., 1986a, b), adapted to non-Newtonian drops, represented the data but with different numerical constants. A high geometric standard deviation, around 1.7 but increasing slightly as monomer fraction decreased, may be due to non-uniform turbulence and to the complexity of breakup at high viscosity.     

Measuring the particle size of a known distribution using the focused beam reflectance measurement technique

The accuracy of the focused beam reflectance measurement (FBRM) probe, which measures a chord length distribution, from Mettler-Toledo Lasentec^® has been explored. A particle video microscope (PVM) probe, which provides in situ digital images, was used as a direct visual method to test the reliability of the FBRM results. These probes can provide in situ particle characterization at high pressures. The FBRM has been used to study emulsions and ice and clathrate hydrate formation. The ability of the FBRM to accurately characterize unimodal and bimodal distributions of particles and droplets and to measure agglomeration events was investigated. It was found that while the FBRM can successfully identify system changes, certain inaccuracies exist in the chord length distributions. Particularly, the FBRM was found to oversize unimodal distributions of glass beads, but undersize droplets in an emulsion and was unable to measure full agglomerate sizes. The onset of ice and hydrate nucleation and growth were successfully detected by the FBRM, but quantitative analysis of the particle and agglomerate sizes required simultaneous PVM measurements to be performed.