Comment on the Calculation of the Steady-State Charge Distribution on Aerosols < 100 nm by Three Body Trapping Method in a Bipolar Ion Environment

The theory of Fuchs (1963) Fuchs, N. 1963. On the Stationary Charge Distribution on Aerosol Particles in a Bipolar Ionic Atmosphere. Geofis. Pura Appl., 56: 185–192. [Crossref] , [Google Scholar] is widely used for calculation of the steady-state charge distribution on (submicron) aerosol particles in a bipolar ion environment. Hoppel and Frick (1986) Hoppel, W. and Frick, G. 1986. Ion-Aerosol Attachment Coefficients and the Steady-State Charge Distribution on Aerosols in a Bipolar Environment. J. Aerosol Sci., 5: 1–21. [Taylor & Francis Online] , [Google Scholar] and others showed that the Fuchs theory is no longer valid for particle diameters in the order of magnitude of the ionic mean free path. In their 1986 and 1990 papers, Hoppel and Frick published a new calculation method based on the concept of thee-body trapping, which is applicable for small particles down to the size of ions. Some print and procedure mistakes were made in the named publications. Additionally some important calculation information was not given. In this article, the relevant equations are shown, corrected and appended. A recalculation of the charge distributions for small particles based on three-body trapping shows a pronounced difference in comparison to data calculated according to the theory of Fuchs.     

Modeling Entry of Micron-Sized and Submicron-Sized Particles into the Indoor Environment

A theoretical approach, based on particle dynamics, was used to examine the outdoor-to-indoor penetration coefficient ( P ) of fine particles inside thin rectangular cracks. Parallel-plate flow theory indicates that crack infiltration flow can be assumed laminar for long, thin rectangular cracks. Considering laminar crack flow, three particle penetration models were used to estimate P . They are the Licht model, the Fuchs model, and the Taulbee model. The first two models consider gravitational sedimentation as the particle deposition mechanism, while the third model considers particle deposition induced from both gravitational sedimentation and Brownian diffusion. Modeling results indicate that gravitational sedimentation governs particle deposition behavior for micron-sized particles, and that all three models can be used to model penetration for these particles. For submicron-sized particles, Brownian diffusion becomes the major deposition mechanism, and only the Taulbee model is suitable to model particle penetration. The Taulbee model was validated using published experimental results of other researchers. Model validation indicated that the Taulbee model satisfactorily estimates particle penetration for micron-sized and submicron-sized particles. Application of the three models to actual building penetration is discussed.     

Modeling of Mixing and Precipitation Using CFD and Population Balances

Simulations of particle size distributions in technical precipitation reactors require the consideration of turbulent mixing and precipitation kinetics. For that, spatially resolved population balances have to be evaluated. In turbulent flows these balances cannot be solved directly, instead either Reynolds averaging or Large Eddy Simulations have to be applied, while unresolved fluctuations need to be modeled. Reynolds averaging of the population balance leads to a turbulent growth dispersion term which has to be modeled. As no theoretically founded approach is available, an assumption was made in analogy to the turbulent diffusion, which improves the prediction of the size distribution shape compared to experiments.     

Theoretical Study of Equilibrium Bipolar Charge Distribution on Nonuniform Primary Straight Chain Aggregate Aerosols

A general theory describing the equilibrium bipolar charge distribution for straight chain aggregate aerosols consisting of primary spheres of different diameters was derived from a theory previously developed for linear chain aggregate of uniform spheres. The present theory is based on the assumptions that (1) the individual primary particles of a straight chain aggregate are charged independently, (2) the probability that a particular primary particle has acquired q elementary charges is governed by the Gaussian distribution predicted by Boltzmann's law, based on particle size; and (3) the resultant charge of a straight chain aggregate is the algebraic sum of the charges carried by the constituent primary spheres. The present theory can be stated as follows: The equilibrium bipolar charge distribution of straight chain aggregate aerosols with nonuniform primary spheres can be expressed by Boltzmann's law with an equivalent diameter such that d_eL = Σ ⁿ _i=1 d_i . The limitations imposed by the assumptions are also discussed.     

Adhesion of Micron-Sized Limestone Particles to a Massive Coal Substrate

The force of adhesion was measured between limestone (calcite) particles with a mass mean diameter of 1.6 μm resting on a massive coal substrate under ambient conditions where the relative humidity was controlled from test to test between the limits of 18 and 93.5%. The force of adhesion for these particles was less than 0.1 millidyne for relative humidities less than 72% and increased to greater than 0.8 millidyne above 93% relative humidity. A model for this variation is proposed which suggests that the Van der Waal's forces are operative between the particle and substrate below 72% relative humidity and that the adsorbed water film on the limestone interacts with capillary water in the porous coal structure when the relative humidity is above 75 %.     

Adhesion of Micron-Sized Limestone Particles to a Massive Coal Substrate

The force of adhesion was measured between limestone (calcite) particles with a mass mean diameter of 1.6 μm resting on a massive coal substrate under ambient conditions where the relative humidity was controlled from test to test between the limits of 18 and 93.5%. The force of adhesion for these particles was less than 0.1 millidyne for relative humidities less than 72% and increased to greater than 0.8 millidyne above 93% relative humidity. A model for this variation is proposed which suggests that the Van der Waal's forces are operative between the particle and substrate below 72% relative humidity and that the adsorbed water film on the limestone interacts with capillary water in the porous coal structure when the relative humidity is above 75 %.     

水环境监测中离子色谱的应用

离子色谱技术出现之后,即得到了广泛的运用。实践研究表明,将离子色谱技术运用于水环境监测中,可以对水中的有机酸、阴阳离子、过渡金属等有效分析,灵敏度较高、效果较好,具有较大的研究价值。     

浅谈30DD350型离子膜电解槽的损坏和维修

介绍了30DD350电解槽的基本结构,总结了其损坏形式及维修方法。     

卤水环境下离子侵蚀对HPC强度的影响研究

本文针对青海省西宁市兴建轨道交通工程中混凝土耐久性的研究,配制了不同配合比的HPC,记录并分析了其在2年腐蚀期内的抗压与抗折强度随腐蚀龄期的变化规律.结果表明:在卤水腐蚀环境下混凝土的抗折与抗压强度在0.5-1.0a、1.0-1.5a、1.5-2.0a这3个时间段内的变化与离子侵蚀密切相关,抗折强度在龄期内表现为增强,抗压强度表现为降低;标号为Ca50z的HPC试件为最佳配合比,表现了良好的抗腐蚀性;矿物掺合料的掺加能有效的提高混凝土的抗腐蚀性能;硫酸根离子侵蚀导致混凝土的损伤是其抗压强度下降的原因之一,且氯离子能够减缓硫酸盐侵蚀破坏的速度.     

Deposition of Ultrafine Aerosols in a Human Oral Cast

This paper reports experimental measurements of the total deposition of ultrafine aerosols in a human oral airway cast. A clear polyester resin cast of the upper airways of a normal human adult, including the nasal airways, oral cavity, tongue, nasopharynx, and larynx, was made from a postmortem solid cast. Measured pressure drop in the oral airway was slightly lower than in the nasal airway. The measured oral flow resistance was similar to the values reported for human volunteers breathing through the mouth at rest and for spontaneously opening of the mouth. Aerosol deposition data in the cast for monodisperse NaCl aerosols between 0.2 and 0.005 μm in diameter deposited in the cast were obtained for inspiratory and expiratory flow rates of 4, 20, and 40 L/min. Deposition efficiency increased with decreasing particle size and flow rate indicating that turbulent diffusion was the dominant mechanism for deposition. Higher deposition efficiency was observed for inspiratory flow in the oral airway than for expiratory flow. Oral deposition and nasal deposition for inspiratory flow were similar, but oral deposition was lower for expiratory flow. Deposition efficiency can be expressed as a function of the flow rate and diffusion coefficient of the particle.     

Scale‐up of Mini‐Plant Extractors on Energy Dissipation‐Based Population Balances

The new scale‐up concept for extraction columns relies on three identities being kept idem, as is the total specific flow rate, energy dissipation, and mean droplet residence time in a compartment. The droplet population balance‐based model allows maintaining hydrodynamic similarity in different geometries, as is in a mini‐ or a pilot plant. This leads to similar breakage and coalescence probabilities giving comparable droplet size distributions, thus mass transfer area and extraction efficiency. A new breakage frequency term has been developed relying on the energy dissipation rate and is thus independent from geometric constraints. The traditional scale‐up rules are based either on a constant tip velocity (≈ N) or on a constant energy input (≈ N³), whereas here it follows a constant energy dissipation (≈ N²). A step‐by‐step approach to the new procedure proved by case samples is given. Data from literature pilot experiments could be verified by computer simulations, without using adaptable parameters. All parameters in the correlations where derived in a lab‐scale apparatus and the coalescence parameters were obtained in the mini‐plant experiments. Derivation between simulated and experimental pilot data for stage numbers was less than 14 %, operating parameters (rotational speed N, throughput) were underestimated by 4 % leading to a slightly smaller HETS (Height Equivalent of Transfer Stages) value as measured, affecting the column height with less than 1 %.     

Electrically Produced Standard Aerosols in a Wide Size Range

Non-uniformly charged particles cause a major problem in electrical methods for producing standard aerosols, imposing strict limitations on the usability of the obtained standard aerosols. This article gives a quick overview of this problem, examining the ways how differently charged particles affect the generation of standard aerosols, and presenting a new method for producing standard aerosols and avoiding the effects of multiply charged particles, with the key idea that the probability for small particles to have more than one charge is very low. A two-stage aerosol generator is used. Small silver particles (d< 40 nm) generated by homogeneous nucleation of silver vapors obtain in bipolar charger not more than one elementary charge. These condensation nuclei are enlarged by a condensational growth device. Big particles are now also not more than singly charged, and narrow size distribution can be obtained by electrical separation. Properties of standard aerosols produced experimentally by both the conventional and the new method, are compared and the validity of the new idea behind the new method is confirmed.     

海洋大气区预应力混凝土氯离子传输时间相似关系研究

海洋大气区预应力混凝土内氯离子在现场环境与实验室内传输的过程有所不同.为探究二者的时间相似关系,本文基于相似理论,以连云港某港区在役混凝土构件为参照物,制定室内人工气候模拟加速试验制度,并浇筑12根与现场构件材料、受力相似的试验梁进行盐雾喷淋侵蚀.通过检测现场和室内试验构件中的自由氯离子含量并计算其表观氯离子扩散系数,以时间衰减系数为工具,分析水胶比、预应力张拉水平、粉煤灰掺量对氯离子扩散的影响,得出预应力混凝土内氯离子传输的时间相似系数表达式,并利用实际工程验证该表达式的准确性,说明基于相似理论的预应力混凝土内,氯离子传输的时间相似关系可用来研究海工预应力混凝土结构耐久性寿命预测问题.     

Numerical Analysis of the Vertical Motion of a Single Micron-Sized Particle in a Thermal Gradient Diffusion Chamber with Electrostatic Levitation

A model to describe the vertical motion of a single micron-sized insoluble particle electrically suspended in an upward thermal gradient diffusion chamber is developed. Motion of the particle is determined by five forces: gravitational, electrostatic, aerodynamic drag, thermophoretic, and diffusiophoretic. Condensation/evaporation effects are taken into account. The model predicts the behavior of an aerosol particle with specified characteristics in a diffusion chamber. The use of an aqueous salt solution as the lower pool establishes two regions in the chamber: an undersaturated region with respect to water vapor in the lower portion of the chamber and a supersaturated region in the upper portion. This unique saturation profile combined with certain operating conditions of the chamber leads to an oscillatory motion of the particle.     

Ti-6Al-4V在氯离子环境中的耐蚀性研究

针对腐蚀性环境油气田开发实际,利用高温高压釜,研究Ti-6Al-4V在盐酸溴化锌加重溶液中的失重腐蚀速率,并利用体式显微镜及扫描电镜对试样进行腐蚀形貌观察和腐蚀膜成份分析,试验结果表明:在本文试验条件下,Ti-6Al-4V的腐蚀速率为0.1089mm/a;Ti-6Al-4V蚀坑较浅且呈开放式,未被腐蚀产物所覆盖;腐蚀膜中含有一定量Cl元素,表明Cl-是参与腐蚀反应的主要元素。     

Collection and Generation of Sulfuric Acid Aerosols in a Wet Electrostatic Precipitator

Wet electrostatic precipitators (WESPs) are considered to be a possible technology for the control of sulfuric acid mist. The performance of a lab-scale WESP was investigated as a precipitator for sulfuric acid aerosol droplets produced under controlled conditions in a pilot plant. It was found that for higher levels of residual SO₂ in the flue gas, WESP collection efficiencies were greatly reduced due to aerosol formation inside the WESP. Investigations showed a strong correlation of aerosol emission from the WESP with incoming SO₂ concentration and operating voltage. It is suspected that the reactive species produced in the nonthermal plasma of the corona discharge oxidize the SO₂ to SO₃ which forms sulfuric acid. This causes supersaturation with subsequent homogeneous nucleation and thus aerosol formation.

Copyright 2015 American Association for Aerosol Research     

Electro-optical Detection of External Mixtures in Aerosols

A measurement technique was developed that has the capability to resolve externally mixed particles of different refractive indices within the range expected for and observed in atmospheric aerosols. Measurements of laboratory aerosols showed that for a specified geometric size, absorbing particles could be sized either larger or smaller than nonabsorbing particles by an optical particle counter and that the difference was in reasonable agreement with theoretical calculations. Atmospheric measurements showed that there was a range of refractive index present in particles of a specified geometric size from which we conclude that the aerosol was externally mixed chemically with respect to light-absorbing compounds. On some occasions, primarily during times of strong combustion source emissions, the degree of external mixing was large; the percentage of particles in the externally mixed, absorbing subpopulation that we measured ranged from about 20% to 50% of the total at that size. We conclude that the external mixing was largely between soot (or other light absorbing compounds) and inorganic (sulfate and nitrate compounds).     

Aerosol Charge Fractions Downstream of Six Bipolar Chargers: Effects of Ion Source,Source Activity,and Flowrate

Bipolar diffusion charging is used routinely in aerosol electrical mobility size distribution measurements. In this study, aerosol charge fractions produced by six bipolar chargers (neutralizers) were measured using a tandem differential mobility analyzer system. Factors that were studied include the type of ion source (²¹⁰Po, ⁸⁵Kr, ²⁴¹Am, and soft X-ray), source activity, charger design, and aerosol flowrate. It was found that all six types of neutralizers achieve stationary state charge distributions when the source activity is sufficiently high. For ²¹⁰Po neutralizers with an initial radioactivity of 18.5 MBq (0.5 mCi), stationary state charge distributions are achieved when the source is less than 3.25 years old (residual activity no less than 0.0527 MBq). Stationary state was achieved for ⁸⁵Kr neutralizers having residual radioactivity greater than 70 MBq. Source activities of ²⁴¹Am and soft X-ray neutralizers are discussed. Aerosol charge fractions for six neutralizers remain reasonably invariant over a wide range of flowrates. The positive charge fractions achieved by the soft X-ray neutralizer are higher than those by the other five neutralizers using radioactive sources while negative charge fractions for all neutralizers studied are all in a similar range. This study also raises questions about bipolar charging fractions used for data inversion in some scanning mobility particle spectrometer (SMPS) systems, and underscores the need to better understand bipolar charging to achieve more accurate measurements of particle size distributions.

Copyright 2014 American Association for Aerosol Research