Electric Field-Enhanced Coalescence of Liquid Drops

Abstract

A fundamental understanding of drop coalescence and growth is of importance to separations and materials processing. Under external driving forces, drops dispersed in an immiscible fluid collide and coalesce with each other due to their relative motion. As a result of drop coalescence, the average drop size in the dispersion increases over time, improving the separation process. Collision and coalescence of spherical, conducting drops bearing no net charge in dilute, homogeneous dispersions are considered theoretically under conditions where drop motion results from gravity settling and electric field-induced attraction. A trajectory analysis is used to follow the relative motion of two drops and predict pairwise collision rates. A population dynamics equation is then solved to predict the time evolution of the size distribution and the average size of drops. The results show that the rate of drop collision and growth can be increased significantly by applying an electric field, in accord with fundamental experiments and patents on electrocoalescence.     

Use of Ambient Aerosols for Measuring Filter Efficiencies

For the evaluation of high-efficiency air filters, it is possible to dispense with aerosol generators and instead use ambient air as a test aerosol, since it contains large numbers of particles up to 0.5 μm. Some instances of such use are described.     

Collection Efficiency of the Aerosol Mass Spectrometer for Chamber-Generated Secondary Organic Aerosols

The collection efficiency (CE) of the aerosol mass spectrometer (AMS) for chamber-generated secondary organic aerosol (SOA) at elevated mass concentrations (range: 19–207 μg m^?3; average: 64 μg m^?3) and under dry conditions was investigated by comparing AMS measurements to scanning mobility particle sizer (SMPS), Sunset semi-continuous carbon monitor (Sunset), and gravimetric filter measurements. While SMPS and Sunset measurements are consistent with gravimetric filter measurements throughout a series of reactions with varying parent hydrocarbon/oxidant combinations, AMS CE values were highly variable ranging from unity to <15%. The majority of mass discrepancy reflected by low CE values does not appear to be due to particle losses either in the aerodynamic lens system or in the vacuum chamber as the contributions of these mechanisms to CE are low and negligible, respectively. As a result, the largest contribution to CE in the case of chamber-generated SOA appears to be due to particle bounce at the vaporizer surface before volatilization, which is consistent with earlier studies that have investigated the CE of ambient and select laboratory-generated particles. CE values obtained throughout the series of reactions conducted here are also well correlated with the f ₄₄/f ₅₇ ratio, thereby indicating both that the composition of the organic fraction has an important impact on the CE of chamber-generated SOA and that this effect may be linked to the extent to which the organic fraction is oxidized.

Copyright 2013 American Association for Aerosol Research     

An Experimental Investigation for Agglomeration of Aerosols in Alternating Electric Fields

Electrostatic precipitators have a relatively low efficiency for the collection of submicron particles. One way to increase their efficiency is to enforce the agglomeration and thereby form larger particles. In this work, a study has been initiated for enhancing the agglomeration between oppositely charged particles by using an alternating electric field to increase the relative motion between such particles. A simple first order computer model was developed for establishing the magnitude of agglomeration and for characterizing the interdependence of different parameters of importance. A laboratory experimental unit was established for studying various practical configurations for agglomeration in alternating electric field, using finely dispersed limestone powder. For the measurements of particle size distributions, a Berner Low Pressure Impactor was used. The preliminary results have shown a 50% reduction in the mass concentration of submicron particles, for oppositely charged particles in an alternating electric field. On the other hand, no agglomeration was measured by the use of a quadrupole field.     

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     

Generation of Radiolabeled Soot-Like Ultrafine Aerosols Suitable for Use in Human Inhalation Studies

We have developed a method for radiolabeling ultrafine carbon particle aggregates with technetium-99m. The carbon aggregate aerosol was chosen to mimic the physical properties of urban combustion or ''soot-like'' particulate. The radioisotope is a short lived (t_1/2 = 6.02 h) gamma emitter commonly used in human studies where scintigraphic methods are employed. Primary carbon parti cles, the aggregation of which is controlled by concentration and time, were produced by arcing between graphite electrodes under an argon atmosphere. Radiolabeling of particles was accomplished by applying a pertechnetate solution onto the tips of electrodes prior to arcing. The activity median diameter of experimental aerosols could be varied from 50 to 150 nm. The specific activity of aerosols increased with the amount of activity applied to the electrodes and decreased with time of generator operation. In-vitro leaching of the radioisotope from particles into solution was also measured. Leaching appeared to increase with the specific activity of the aerosol but was not affected by particle size.     

Collection Efficiencies in an Aerodyne Aerosol Mass Spectrometer as a Function of Particle Phase for Laboratory Generated Aerosols

The Aerodyne Aerosol Mass Spectrometer (AMS) is a useful tool to study ambient particles. To be quantitative, the mass or (number) of particles detected by the AMS relative to the mass (or number) of particles sampled by the AMS, or the AMS collection efficiency (CE), must be known. Here we investigated the effect of particulate phase on AMS CE for ammonium nitrate, ammonium sulfate, mixed ammonium nitrate/ammonium sulfate, and ammonium sulfate particles coated with an organic liquid. Dry, solid ammonium sulfate particles were sampled with a CE of 24 ± 3%. Liquid droplets and solid particles that were thickly coated with a liquid organic were collected with a CE of 100%. Mixed phase particles, solid particles thinly coated with liquid organic, and metastable aqueous ammonium sulfate droplets had intermediate CEs. The higher CEs for liquid particles compared with solid particles were attributed to wet or coated particles tending to stick upon impact with the AMS vaporizer, while a significant fraction of solid particles bounced prior to vaporization/detection. The consistency of single particle signals indicated that the phase (and hence CE) of mixed component particles did not affect the AMS sensitivity to a particular chemical species once volatilization occurred. Particle phase might explain a significant fraction of the variable AMS CEs reported in the literature. For example, ambient particles that were liquid (e.g., composition dominated by ammonium nitrate or acidic sulfate) have been reported to be sampled with 100% CE. In contrast, most ambient particle measurements report CEs of < 100% (typically~ 50%).     

Aerosols Analysis by LIBS for Monitoring of Air Pollution by Industrial Sources

In the context of the air quality improvement, there is an increasing need to monitor gas and particle emissions originating from exhaust stacks (incinerators, foundries, etc.) for regulation enforcement purposes. Lots of pollutants are targeted; among them, heavy metals are mostly found in particulate forms. Hence, there is a need to promote the development of suitable on line analytical techniques. To that end, laser-induced breakdown spectroscopy (LIBS) appears to be a good technique. Indeed, it is quantitative, fast (<1 min), requires no sample preparation, and can be performed at remote distance. The instrumentation is compact and offers the possibility to be used for continuous and in-situ monitoring. Two different approaches have been tested by several authors to analyze aerosols by LIBS, by focusing the laser either on particles collected on a filter or directly into the aerosol. In this work, these two approaches, aiming at measuring the mass concentration of micrometer metallic particles in air, are investigated and compared. The experimental setup includes an aerosol source (an ultrasonic nebulizer producing a diluted aerosol of CuSO₄ particles); two sampling lines for particle sizes and, for reference concentration measurements, a line for direct LIBS analysis; and a fourth one devoted to filter sampling for subsequent LIBS measurements. Calibration curves were obtained with those two experimental approaches and the results are compared. In terms of sampling particles number, indirect analysis appears to be more efficient than direct analysis for our experimental conditions. Better detection limits were found with direct analysis when comparing the two approaches under similar sampling conditions (analysis time and sampling flow).     

Characterization of Multicomponent Aerosols by Raman Spectroscopy

In this work the feasibility of Raman spectroscopy, especially the detection limit of this technique for the chemical characterization of multicomponent aerosols, which appear in technical processes has been investigated. In such kind of aerosols high number concentrations (>10⁶ cm^?3) can be observed whereas the range of the pollutant loading varies from 10–1000 mg/m³. For these purposes different type of aerosols have been investigated. Aerosols in which the pollutant can be found in the dispersed phase as well as in the gas phase (aqueous solutions of NH₃ aerosols), those where the pollutant appears only in the dispersed phase (aqueous solutions containing SO₄ ^2?/ NO₃ ^? salts) and aerosols where there is no Raman shift between the signals of the gas and the dispersed phase (toluene/ dodecane aerosols). Furthermore aerosols generated by the reaction between NH₃ and HCl in nitrogen containing different amounts of vapor are also investigated.

The characterization of the aerosols with Raman spectroscopy with respect to their gas phase is without any difficulty, whereas the analysis in the dispersed phase is partially marginal and in majority of cases almost not possible.

Especially for the reaction aerosols rejection of elastically scattered light is the principle limitation in collecting Raman scattered light from particles in the Mie-scattering regime.     

Inactivation of Virus-Containing Aerosols by Ultraviolet Germicidal Irradiation

The increasing incidence of infectious diseases has prompted the application of Ultraviolet Germicidal Irradiation (UVGI) for the inactivation of viruses. This study evaluates UVGI effectiveness for airborne viruses in a laboratory test chamber by determining the effect of UV dosage, different nucleic acid type of virus (single-stranded RNA, ssRNA; single-stranded DNA, ssDNA; double-stranded RNA, dsRNA; and double-stranded DNA, dsDNA), and relative humidity on virus survival fraction after UVGI exposure.

For airborne viruses, the UVGI dose for 90% inactivation was 339–423 μW sec/cm² for ssRNA, 444–494 μW sec/cm² for ssDNA, 662–863 μW sec/cm² for dsRNA, and 910–1196 μW sec/cm² for dsDNA. For all four tested, the UVGI dose for 99% inactivation was 2 times higher than that for 90% inactivation. Airborne viruses with single-stranded nucleic acid (ssRNA and ssDNA) were more susceptible to UV inactivation than were those with double-stranded ones (dsRNA and dsDNA). For all tested viruses at the same inactivation, the UVGI dose at 85% RH was higher than that at 55% RH, possibly because water sorption onto a virus surface provides protection against UV-induced DNA or RNA damage at higher RH. In summary, UVGI was an effective method for inactivation of airborne virus.     

电熔炉顶插电极的应用与电气控制

主要介绍了顶插电极的使用、配电方式、电气控制方案和在电熔炉中的应用。     

HPLC测定吡喏克辛钠滴眼液中尼泊金酯的含量

目的:测定吡喏克辛钠滴眼液中尼泊金酯的含量。方法:高效液相色谱法,色谱柱:Alltech C18柱(4.6 mm×250 mm,5μm);流动相:乙腈∶水(70∶30);检测波长:254 nm。结果:用高效液相色谱法测定,尼泊金甲酯和丙酯的平均加样回收率分别为99.59%和99.68%,在样品中的平均含量分别为1.187×10-3 mol/L和4.216×10-4 mol/L。结论:建立了同时测定吡喏克辛钠滴眼液中对羟基苯甲酸甲酯、丙酯的高效液相色谱分析法,该方法操作简单,结果较好,能够广泛用于食品、药品、洗发液等的尼泊金酯含量的测定。     

Preparation of Blue Vanadium-Zircon Pigments by Aerosols Hydrolysis

A continuous procedure for the preparation of V-ZrSiO₄ powders based on the hydrolysis of liquid aerosols composed of a mixture of TEOS, zirconium propoxide, and VOCl₃ is reported. These powders consist of spherical amorphous particles, having a high degree of Si-Zr mixing and a homogeneous distribution of vanadium in the ceramic matrix. The raw composition (Zr/Si ratio and V content) was systematically varied in order to optimize the color of the final pigments. The color changes produced in the samples during heating are discussed in terms of the location of the vanadium species in the zircon matrix. In vanadium-zircon blue pigments, evidence of the substitution of Si by V⁺⁴ in tetrahedral sites forming a solid solution with the zircon matrix is observed by infrared spectroscopy.     

浅谈电光源玻璃

电光源玻璃是制造光源设备、电器元件的主要材料之一。由于电光源多使用铅玻璃,容易造成污染,其生产和使用过程中所带来的有害物质对环境的污染引起了人们的关注。文章针对玻璃的类型、化学成分与结构特点,论述了电光源用铅玻璃的产品结构特征,研究了电光源用铅玻璃的危害及其污染治理,阐述了解决电光源用铅玻璃对环境污染的治理对策,提出了电光源用环保玻璃的发展趋势。     

Automated Spore Measurements Using Microscopy,Image Analysis,and Peak Recognition of Near-Monodisperse Aerosols

Rapid detection of airborne fungal and bacterial spores would enable public agencies to respond quickly and appropriately to intentional releases of hazardous aerosols. Automated analysis of microscope images and automated detection of near-monodisperse peaks in aerosol size distribution data offer complementary approaches to traditional methods for the identification and counting of fungal and bacterial spores. First, spores of the fungus Scopulariopsis brevicaulis were aerosolized in a chamber and then collected with a slit impactor; later, digital microscope images were analyzed manually to determine spore cluster distributions. The images also were analyzed with ImageJ, a program that automatically outlined objects and measured Feret's diameter, area, perimeter, and circularity. These characteristics were used to identify spore clusters automatically using two data analysis methods. Second, a computer program was developed to discriminate near-monodisperse bioaerosol peaks from those for polydisperse ambient particulate matter (PM) and was successfully tested using simulated and real aerosol mixtures. The observed agreement between manual and automated spore counts and the ability to detect spore peaks suggest that it may be possible to develop a system to recognize intentional releases rapidly through examination of particle morphology and size distributions. The peak detection procedure is potentially the fastest technique when used with real-time instrument data, but assumes that intentional releases would consist of large numbers of uniformly sized particles in the respirable size range.

Copyright 2012 American Association for Aerosol Research     

Chemical Characterization of Flowing Polydisperse Aerosols by Raman Spectroscopy

We have applied Raman spectroscopy to the in-situ measurement of chemical composition of polydisperse flowing aerosols. Monodisperse and polydisperse aerosols in the size range 0.3 to 1.8 w m, composed of diethylsebacate (DES) and ammonium sulfate, were generated. The particles were irradiated with 514.5 nm laser light and Raman spectra were collected. The Raman intensities of DES at 2935 cm -1 and ammonium sulfate at 981 cm -1 , normalized by the nitrogen carrier gas Raman intensity at 2313 cm -1 , were approximately proportional to the aerosol mass loading over the particle size range studied. Calculations based on previous theoretical studies support this observation. The mass loading ranged from 0.17 to 12.8 g/m 3 for DES and 20 to 138 mg/m 3 for ammonium sulfate. The method was applied to mixing aerosol streams containing DES and ammonium sulfate in a turbulent jet. The Raman system, with a sensitive volume of 0.02 mm 3 , was used to measure radial and axial concentration profiles in the mixing region. The results compared well with turbulent mixing theory. The primary limitation for application of the method is the low signal to noise ratio.     

Journal Spherical Mullite Particles Prepared by Hydrolysis of Aerosols

Nonhollow spherical particles were prepared by hydrolysis of liquid aerosols consisting of mixtures of silicon methoxide and aluminum sec-butoxide. In order to obtain particles with mullite composition, some chloroform had to be added to the alkoxides mixture. TEM microanalyses carried out in single particles revealed a rather narrow distribution in composition around the mullite nominal value. The particles, as prepared, were amorphous. Their thermal evolution was studied by thermal analyses, X-ray diffraction, and infrared and ²⁷A1, ²⁹Si NMR spectroscopies. Crystallization of pseudo-tetragonal mullite was detected at 950°C, suggesting a high degree of Al-Si mixing in the original particles. At the same time, some silica segregation was also observed. Between 1200°-1400°C, the pseudo-tetragonal/ orthorhombic mullite transformation took place, accompanied by the incorporation of segregated silica into the originally formed mullite.     

Optical Properties of Organic-based Aerosols Produced by Burning Vegetation

The real and imaginary refractive indexes of organic-based nonvolatile aerosols produced by burning vegetation are reported for the infrared spectral region. The data were obtained by an iterative Kramers-Kronig analysis of the transmission spectra (2–25 μm) obtained from thin-film samples deposited on a KBr substrate immersed directly in the smoke plumes of small-scale test fires. The results include samples from fires fueled by lawn grass, alfalfa, mesquite, tumble-weed, pine needles, and mixed twigs, leaves, and weeds. The most significant characteristics of all spectra are as follows: (a) strong absorptions in the 3–5-μm region owing to condensed water and CH₃/CH₂ groups of aliphatic hydrocarbons; (b) characteristic peaks in the 6-, 8-, and 10-μm regions owing to skeletal modes of aromatic and terpenic groups; and (c) relatively little absorption in the 10–12-μm region. The imaginary refractive index of all samples is comparable (～ 0.10–0.30) in the 3–5- and 8–10-μm regions and is 3–10 times lower in the 10–12-μm region. In the 3–5-μm region, most of the absorption takes place in the interval between 3 and 4 μm as opposed to the 4–5-μm interval which shows significantly less absorption. It is also noteworthy that there is insignificant absorption in the 2.0–2.5-μm window region. Results are significantly different from values for elemental carbon which are known to be relatively wavelength independent in these spectral regions and of magnitude between ～ 0.50 and 1.0 for the imaginary index. Theoretical calculations, assuming particle sizes in the Rayleigh scattering regime, yields a mass extinction coefficient (m²/g) for the organic smokes on the order of ～ 0.20 for the 8–10-μm region and as high as 0.40 at 3 μm to near zero at 5 μm in the 3–5-μm window.