Electrical Agglomeration of Aerosol Particles in an Alternating Electric Field

A laboratory scale test system has been designed and constructed to study the electrical agglomeration of charged aerosol particles as a method to increase the fine particle collection efficiency of electrostatic precipitators. The system consists of test aerosol generator, aerosol charger, agglomerator chambers, and aerosol measurement equipment. Air atomizing nozzles and the TSI six-jet atomizer have been used as the test particle generators. The test particles have been charged by a corona discharge. Two types of agglomerator chambers have been investigated. In one agglomerator the gas flows between two parallel plates, across which the alternating high voltage is applied. The other agglomerator is a quadrupole structure with cylindrical electrodes positioned between the grounded plates. Particle concentration and size distribution measurements have been carried out downstream of the agglomerator with agglomerator voltage on and off. Particle concentrations and size distributions have been measured with differential mobility analyzer (DMA) and a Berner low pressure impactor. These measurements show that agglomeration causes about a 4%-8% decrease in the fine particle concentration when the total mass concentration is between 1 and 2 g/m³. There was no difference between the results measured with the parallel plate and the quadrupole agglomerator.     

Fatigue Crack Growth in Ferroelectric Ceramics Driven by Alternating Electric Fields

Electric-field-induced fatigue crack growth in ferroelectric ceramic PZT-5 with precracks was investigated. The experimental results showed that there were two distinct characteristics in the crack growth under electric loading. Under low electric loads, microcracks located ahead of the main crack emerged and grew and, as a result, impeded the growth of the main crack. On the other hand, under high electric loads, microcracks were absent, and the main crack was the only mode of fatigue cracking. The main crack grew macroscopically along the original path perpendicular to the electric field. Microscopically, the crack grew along the grain boundaries and grain breakaway was observed. The crack growth rate was nonlinearly related to the cyclic electric load. Similar to mechanical fatigue, there existed a crack growth threshold in the applied electric-field amplitude below which the crack ceased to grow. A steady crack growth occurred when the applied electric field exceeded this threshold. An empirical model for crack growth was obtained. Domain-switching effect and fracture-mechanics concepts were used to explain the observed crack closure and crack growth under electric loads.     

An Experimental Investigation of Agglomeration with One and Two Nozzle Atomisation

Water-droplet size and velocity measurements were taken throughout two different sprays produced by a single nozzle and two nozzles pointed towards each other. The aim of this investigation was to understand the manner in which the motion of the droplets in a spray leads to agglomeration of these droplets. It appears that the inertia of the droplets plays an important role in the redistribution of droplets throughout a spray. Larger droplets tend to concentrate at the outer portions of the spray, because they are able to maintain their radial momentum farther downstream of a nozzle, while the smaller droplets follow the airflow more closely and thus collect in the core of the spray. Agglomeration can result from both turbulent collisions and collisions due to the relative velocities of the droplets. The difference between the agglomeration rates in the sprays from a single nozzle and two-nozzles pointed towards each other was difficult to resolve in these experiments, although the results suggest that th     

An Investigation of Proteohormones by Alternating Current Polarography

The behavior of some proteohormones as mixtures of FSH and LH at different proportions and purity was studied by polarography. Proteins which contain groups of -SH and/or -S-S-, develop in an ammoniacal buffer of Co^II or Co^III salts a typical double wave, which is believed to be a catalytic wave of hydrogen evolution. It is called a Brdicka double wave. It depends on various parameters such as concentration of the protein, pH, buffer capacity, temperature, height of mercury current, etc. The influence of changing the various parameters on the height of the wave and on the potential of the maximum of the wave height was studied. Comparison was made among the various hormones and with the simple protein human albumin. The measurements were performed by direct current and alternating current polarography. An attempt is made to investigate the mechanisms of each of the two components of the double wave. Hormone preparations, containing different proportions of LH and FSH, could be characterized.     

家用电器用绝缘搪瓷釉研究

家用电器用绝缘搪瓷釉研究蒋伟忠（轻工业部玻璃搪瓷工业科学研究所２０００５２）ＡｎＩｎｖｅｓｔｉｇａｔｉｏｎｏｎＩｎｓｕｌａｔｉｏｎＥｎａｍｅｌｆｏｒＥｌｅｃｔｒｉｃＡｐｐｌｉａｎｃｅ￥ＪｉａｎｇＷｅｉｚｈｏｎｇ（ＴｈｅＧｌａｓｓａｎｄＥｎａｍｅｌＲｅ...     

Accelerated Hydrolysis of Aspirin Using Alternating Magnetic Fields

The major problem of current drug-based therapy is selectivity. As in other areas of science, a combined approach might improve the situation decisively. The idea is to use the pro-drug principle together with an alternating magnetic field as physical stimulus, which can be applied in a spatially and temporarily controlled manner. As a proof of principle, the neutral hydrolysis of aspirin in physiological phosphate buffer of pH 7.5 at 40 °C was chosen. The sensor and actuator system is a commercially available gold nanoparticle (NP) suspension which is approved for animal usage, stable in high concentrations and reproducibly available. Applying the alternating magnetic field of a conventional NMR magnet system accelerated the hydrolysis of aspirin in solution.     

Multichannel Flow Electrophoresis in an Alternating Electric Field

Abstract

Investigation on the mass transfer behavior of multichannel flow electrophoresis (MFE) has confirmed the existence of concentration polarization in the separation process, which is characterized by a reduction of the relative protein migration flux corresponding to an increase in the protein concentration in the feed. The mobility of bovine serum albumin (BSA) in a gel membrane, as interpreted from its elution curve, was about one-sixth of its mobility in solution as determined by high capillary electrophoresis. This indicates that accumulation of charged protein onto the membrane surface occurs in MFE. An alternating electric field was applied instead of the steady one in MFE. The negative part of the alternating electric field reduced the polarization layer periodically. The effectiveness of this method was demonstrated by an over 40% increase of BSA migration flux at pH 6.9 in an optimized alternating electric field. The separation outputs of BSA and hemoglobin bovine blood conducted in an optimized alternating electric field at pH 6.0 were about 26 and 32% higher than their respective outputs obtained in a steady electric field. Because of its proven efficiency for reducing concentration polarization and its ease of operation, the use of an alternating electric field is a promising application in other membrane separation processes.     

An Ion Generator for Neutralizing Concentrated Aerosols

An ion generator was developed to neutralize concentrated streams of large, highly charged particles in a low-velocity wind tunnel. The aerosol stream tested consisted of 30 mu m aluminum oxide particles (aerodynamic diameter 52 mu m) at a flow rate of 9.6 m³/h (160 L min) and a mass concentration of 43 g/m³. The average number of excess charges per particle was 240,000 (positive), which corresponds to a neutralizing current requirement of 0.11 mu A. Neutralization to < +/- 10,000 charges per particle was necessary to prevent electrostatic sampling artifacts. Neutralization with radioactive sources would have required an impractically large source. The ion generator, constructed from 21 and 32 mm PVC pipe, has 4 peripheral radial electrodes of 0.5 mm tungsten wire and a 2.0 mm diameter central electrode. The aerosol flowed through the ion generator along its axis. The ion generator was powered by an adjustable (0-8.5 kV) power supply. Performance of the ion generator was monitored with an isokinetic Faraday-cup sampler connected to a Keithley Model 6512 electrometer capable of 0.1 fA resolution. The sampler used a stainless steel 47 mm filter holder as the Faraday cup. The cup was insulated with Teflon inside a 90 mm diameter stainless steel enclosure with a 21 mm diameter inlet. This setup gave near real-time measure ment of the charge state of the aerosol in the wind tunnel. By adjusting the ion generator power supply, particle charge could be reduced to < 2% of its original charge. Ion generator output was sufficiently stable to maintain the particle charge within +/- 2% of the original charge over a 1 h period. These reduced charge levels are comparable to charge levels found on workplace aerosols.     

Use of Electric Image Forces for Collection of Aerosols by Arrays of Drops

The use of electric image forces for collection of uncharged aerosols by two- and three-dimensional arrays of charged drops is considered. Trajectories of aerosols are simulated using an algorithm for transformation of electric image forces and flow field from spherical coordinate systems of the drops to the central system, where the equation of motion is solved. Radius and efficiency of collection of aerosols, as a function of the number of rows of drops, are presented for different geometries and charge levels. The nature of the weak image force dictates the need to use a charge level closer to the Rayleigh limit and optimized array geometries. Inertial effects that enhance dispersive modes, of otherwise convergent trajectories, become significant for aerosols as small as 20 w m. In this case, multiple values of radius of collection and collection efficiency can be obtained for the same number of rows. Geometries with no shifts between rows of drops are shown to be inferior to those involving a larger shift. The former geometries require a substantially larger number of rows for a prescribed level of collection and may not facilitate complete collection. Systems of uncharged drops and charged aerosols behave similarly to those with charged drops and uncharged aerosols. Three-dimensional arrays can be more efficient than two-dimensional ones, provided that weakness planes, where aerosols show deep penetration, are eliminated by appropriate shifts of rows. A decrease of the drop size at a fixed volume fraction with the charge set at its Rayleigh limit enhances the collection efficiency. Finally, the random model of collection, using the exponential distribution, is recast in order to accommodate for the effect of the order of the array and the deterministic nature of the aerosol trajectories.     

Kinematic Coagulation of Charged Droplets in an Alternating Electric Field

An analytic-numerical model has been developed to study kinematic coagulation caused by the vibrational motion of charged particles in an alternating electric field. The primary aim of this study was to find out the reduction in the number concentration of fine particles of diameter 0.1 μm-1.0 μm caused by collisions with larger, supermicron particles. Three cases are considered: (1) unipolar charging, (2) fine particles are neutral, and (3) fine particles and large particles have opposite polarity. We find out that in cases 1 and 2 the rate of kinematic coagulation in negligible and in case 3 significant. The results are demonstrated with two sample calculations with total mass loadings of 2 and 20 g/m³. In the former, where the mass median diameter is 3.0 μm, we discover a 20%-50% reduction in number concentration of particles in the range 0.5–1.0 μm and less significant reduction in smaller particles. The latter (MMD = 6.0 μm) represents power plant conditions. In this case the reduction varies from 10% (0.1 μm) to 95% (1.0 μm).     

Evaluating the Mobility of Nanorods in Electric Fields

The mobility of a nonspherical particle is a function of both particle shape and orientation. In turn, the higher magnitude of electric field causes nonspherical particles to align more along the field direction, increasing their mobility or decreasing their mobility diameter. In previous works, Li et al. developed a general theory for the orientation-averaged mobility and the dynamic shape factor applicable to any axially symmetric particles in an electric field, and applied it to the specific cases of nanowires and doublets of spheres. In this work, the theory for a nanowire is compared with experimental results of gold nanorods with known shape determined by TEM images. We compare the experimental measured mobility sizes with the theoretical predicted mobility in the continuum, free molecular, and the transition regime. The mobility size shift trends in the electric fields based on our model, expressed both in the free molecular regime and in the transition regime, are in good agreement with the experimental results. For rods of dimension: width d_r = 17 nm and length L_r = 270 nm, where one length scale is smaller than the mean free path and one larger, the results clearly show that the flow regime of a slender rod is mostly controlled by the diameter of the rod (i.e., the smallest dimension). In this case, the free molecule transport properties best represented our nanorod. Combining both theory and experiment we show how, by evaluating the mobility as a function of applied electric field, we can extract both rod length and diameter.

Copyright 2013 American Association for Aerosol Research     

Investigation of Volatility Method for Measuring Aqueous Sulfuric Acid on Mixed Aerosols

The thermal discrimination or volatility technique is a widely used method exploiting differences in aerosol volatility to discriminate between particles of different chemical composition. In recent years numerous investigators applied this technique to determine the existence and the amount of sulfuric acid in the aerosol phase of aircraft contrails forming in the upper troposphere and lower stratosphere (UT/LS). Although the potential for systematic errors due to incomplete evaporation and recondensation of volatile material as well as internal wall losses was recognized by other investigators, we are not aware of any study on polydisperse aerosol (broad size distribution) incorporating these effects into the volatility technique. Here, a tandem differential mobility analyzer (TDMA) is employed to investigate the performance of a thermal discriminator designed at the University of Missouri-Rolla (UMR). Since sulfuric acid is of particular interest for atmospheric aerosol, this study focused on aqueous sulfuric acid (H 2 SO 4 /H 2 O) aerosol. For an operating temperature of 300°C and an aerosol residence time of more than 0.25 s, we found that complete evaporation of H 2 SO 4 /H 2 O aerosol occurred up to diameters of at least 1.9 w m, which is consistent with theoretical calculations. No evidence for recondensation was found for H 2 SO 4 /H 2 O particle surface area and mass concentrations typical for UT/LS background and aircraft plume conditions. Wall losses were measured and incorporated into a size-resolved version of the volatility method, allowing more accurate measurements of the volatile (H 2 SO 4 /H 2 O) volume fraction of polydisperse aerosol. The increased accuracy was demonstrated using well-characterized, mixed (partially volatile) H 2 SO 4 /H 2 O/NaCl aerosol.     

Hydrostatic Levitation of Particles in Electric and Magnetic Fields

Abstract

Nonhomogeneous magnetic and electric fields generate levitational forces in magnetic and dielectric liquids whereby particles are separated according to their specific gravity and magnetic and electric properties, respectively. The corresponding systems are called magnetohydrostatic separation and wet dielectric separation. These forces depend on the field intensity and gradient, and on properties of the liquid and the particles to be levitated. This paper deals with the potential application of electric fields as compared with that of the magnetic field. It is shown that unless special measures are taken, the electric field is inferior to such an extent that its application is not promising. In this context the influences of particle size and shape in both methods are discussed.     

Barium Sulphate Agglomeration in a Pipe – An Experimental Study and CFD Modeling

Agglomeration effects, observed during precipitation of barium sulphate in the unpremixed feed two‐dimensional tubular precipitator, are studied experimentally and interpreted theoretically. Effects of process parameters on precipitation–agglomeration phenomena are predicted using a CFD based model that describes micromixing (the multiple‐time‐scale turbulent mixer model is used) and precipitation (including nucleation, growth and agglomeration of crystals). Agglomeration rate is defined as a product of the collision frequency and the probability of agglomeration.     

An Experimental Investigation of Hydrogen Production from Biomass

In gaseous products of biomass steam gasification, there exist a lot of CO, CH4 and other hydrocarbons that can be converted to hydrogen through steam reforming reactions. There exists potential hydrogen production from the raw gas of biomass steam gasification. In the present work, the characteristics of hydrogen production from biomass steam gasification were investigated in a small-scale fluidized bed. In these experiments, the gasifying agent (air) was supplied into the reactor from the bottom of the reactor and the steam was added into the reactor above biomass feeding location. The effects of reaction temperature, steam to biomass ratio, equivalence ratio (ER) and biomass particle size on hydrogen yield and hydrogen yield potential were investigated. The experimental results showed that higher reactor temperature, proper ER, proper steam to biomass ratio and smaller biomass particle size will contribute to more hydrogen and potential hydrogen yield.     

Mass Transport from Single Droplets in Imposed Electric Fields

Abstract

The influence of electric charge phenomena on mass transfer in systems involving droplets in a continuous medium is of increasing importance. The enhanced transport behavior of droplets in imposed fields on mass transfer and the influence of naturally occurring charges on droplets, particularly in the atmosphere, are both subjects of current interest. The objective of this study is to elucidate the hydrodynamic and mass transfer effect of imposed fields on charged single droplets. Investigations of both static and pulsed electric fields are reported.

The experimental approach is based on the suspension of single droplets in a precisely machined expanding channel. A stationary, saturated water droplet is fluidized by the upflow of 2-ethylhexanol. This arrangement allows precise photographic monitoring of droplet size and shape as well as the hydrodynamics of both phases in the region of the interface.

Baseline continuous-phase mass transfer studies with internally circulating droplets corroborate earlier studies with the same system. The effect of the accumulation of unavoidable surfactant on droplet circulation and mass transport rate at long exposure times is reported. The imposition of a static electric field in the axial direction caused distortion of droplets into prolate spheroidal shape.

An electric field pulsed at a tuned frequency is observed to cause oscillation of droplets between prolate-and oblate-spheroidal shapes. In addition to frequency and field amplitude, the interfacial properties of the fluid system as well as viscosities and densities of the two phases influence the oscillation. The effect of the pulsation of the field on mass transfer to the continuous phase is reported. These data are compared with results for both nonoscillating mass transfer and theoretical models.     

磁场下硫酸浸出赤泥回收钛的研究

对贵州某氧化铝厂的赤泥进行了磁场下酸浸回收钛的研究,考察了不同磁场强度下硫酸浓度、液固比、温度对钛浸出率的影响。研究结果表明:磁场下钛浸出效果显著好于无磁场下浸出效果,在0.41 T磁场强度下,当硫酸浓度位5 mol/L,温度为90℃,浸取时间120 min,液固比3∶1的条件下,赤泥中钛的浸出率达85.15%,而无磁场条件下钛的浸出率只有81.5%。说明磁场对硫酸对赤泥中钛的浸出率具有促进作用。     

Effects of Electric Fields on Slow Crack Growth in Glass

Electrical de fields applied through electrodes on either side of a slow-running crack in soda-lime-silica glass resulted in a deviation of the crack plane and in delayed deceleration, arrest, and healing. In some cases crack closure occurred while still under load. Resumption of propagation resumed gradually upon removal of the field. It is suggested that the effects involve displacement of the dilated negatively charged zone at the crack tip, while healing is effected by reformation of bonds between the crack surfaces.