• 대한기계학회논문집B
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• 제21권11호
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• pp.1509-1517
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• 1997

Charged and uncharged particle motions and collection characteristics around a bipolar charged rectangular shape electret fiber are studied numerically. Particle inertia, fluid drag, Coulomb force and polarization force are considered to predict the particle motion around the electret fiber. The effects of particle sizes, flow velocities, number of charges and polarities are also systematically investigated. For small size particles, the single fiber collection efficiency is greatly dependent on the charge polarity and the number of charges on a particle. However, particles larger than 5.mu.m do not show charging effect on collection efficiencies in the flow velocity ranges from 1.5 cm/s to 150 cm/s when the maximum charges are within +5 to -10. The results show that a strong electric field gradient at the corner of the bipolar charged fiber plays a very important role on collecting particles regardless of its charge polarity because of the polarization force. It also shows that the most penetrating particle size for a single electret fiber decreases as the flow velocity increases and the number of charges of a particle decreases.

• 한국입자에어로졸학회지
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• 제10권1호
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• pp.27-31
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• 2014

A simple bimodal model has been developed to analyze charged particle coagulation by modifying previously suggested bimdal model for evolution of particle generation and growth. In the present model, two monodisperse modes are used and 40 charge nodes are assigned to each mode to account both change of the particle size and charge distribution. In addition, we also implemented the effect of electrostatic dispersion loss in the present model. Based on the developed model, we analyzed coagulation of asymmetric bipolar charged particles by computing evolutions of particle number concentration, geometric mean diameter of particles, charge asymmetric ratio and geometric standard deviation of particle size distribution for various initial charge asymmetric ratios. The number concentration of asymmetric bipolar charged particles decreases faster than that of neutral particles but that does not give faster growth of particles since the electrostatic dispersion loss overwhelms particle growth by coagulation.

• 대한기계학회논문집B
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• 제26권2호
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• pp.227-237
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• 2002

A numerical technique for simulating the aggregation of charged particles was presented with a Brownian dynamic simulation in the free molecular regime. The Langevin equation was used for tracking each particle making up an aggregate. A periodic boundary condition was used for calculation of the aggregation process in each cell with 500 primary particles of 16 nm in diameter. We considered the thermal force and the electrostatic force for the calculation of the particle motion. The electrostatic force on a particle in the simulation cell was considered as a sum of electrostatic forces from other particles in the original cell and its replicate cells. We assumed that the electric charges accumulated on an aggregate were located on its center of mass, and aggregates were only charged with pre-charged primary particles. The morphological shape of aggregates was described in terms of the fractal dimension. In the simulation, the fractal dimension for the uncharged aggregate was D$\_$f/ = 1.761. The fractal dimension changed slightly for the various amounts of bipolar charge. However, in case of unipolar charge, the fractal dimension decreased from 1.641 to 1.537 with the increase of the average number of charges on the particles from 0.2 to 0.3 in initial states. In the bipolar charge state, the average sizes of aggregates were larger than that of the uncharged state in the early and middle stages of aggregation process, but were almost the same as the case of the uncharged state in the final stage. On the other hand, in the unipolar charge state, the average size of aggregates and the dispersion of particle volume decreased with the increasing of the charge quantities.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1684-1689
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• 2003

Dielectric Barrier Discharges (DBD) in oxygen and air are well established for the production of large quantities of ozone and are more recently being applied to a wider range of after treatment processes for HAPs(Hazardous Air Pollutants). The potential use as a charger for particle collection are not well known. In this work, we measured charge distribution of nanometer or submicron sized particles passing through the dielectric barrier discharge reactor. The bipolar charge characteristics of particles passing DBD reactor were investigated. Fluorometric method using uranine particles and a fluorometer was employed to examine the bipolar charging characteristics of the charged particles by DBD reactor. Finally, the charge distributions of particles were determined from the electrical mobility classification using DMA.

• 대한기계학회논문집B
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• 제25권3호
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• pp.442-450
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• 2001

Experiments were carried out on agglomeration of bipolarly charged particles in an alternating current electric field. Laboratory-scale setup was built and experiments were conducted at atmospheric condition. DOS(Di-octyl Sebacate) particles with 100% purity were generated by an atomizer. The particles were branched into two, each of which passed through a wire-to-plate type charging section where a positive or a negative DC high voltage was applied and was charged positively or negatively. These bipolarly charged particles together passed through an agglomeration section where an $\pm$20kV AC power was applied between two plates. The resident time in the agglomeration section was adjusted as l sec. Particle sampling was made by a cascade impactor (MOUDI). The effect of agglomeration system on the reduction ratio of particles below l ㎛ was 42∼45%. Effect of AC frequency on the particle size distribution was found insignificant.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권10호
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• pp.465-470
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• 2005

In this paper. an experimental study, for method of increasing the efficiency of electrostatic precipitator for the collection of submicron-sized particles has been studied. All AC electric field was used to induce agglomeration of bipolory charged Particles. .4 bipolar AC-agglomeration system. consisted with a multineedle-mesh discharge system with a control grid, was proposed and investigated. Systematic experiments were carried out to investigate the agglomeration ratio of the AC-agglomeration system as a function of the different grid spacings and grid resistances for the submicron particles generated from liquid prorhane gas burning. The agglomeration ratios, which indicate the particle numbers before and after agglomeration of the test particles in number concentration base, were found to be 0.87, 1.80, 3.86, 9.50 and, 11.00 times for the particle sizes of 0.3. 0.5, 0.7, 1.0, and 2.0$\mu$m at applied voltage of 3.5kV, respectively which showed that the fine particle numbers were decreased while the larger particle numbers were increase greatly.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.71-76
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• 2001

An electret filter is composed of permanently charged electet fibers and is widely used in applications requiring high collection efficiency and low-pressure drop. In this work, the collection efficiency of the filter media used in manufacturing cabin air filters was investigated by using poly-disperse particles when submicron particles are loaded. Long-term experiments were conducted by applying different charging states, which are spray electrification and charge equilibrium by bipolar ionization. In order to investigate on the effect of particle loading in filter media, NaCl particles were generated from 0.1% and 1% solutions by an atomizer. In NaCl 0.1%, the collection efficiency of electret filter decreased and then did not change in equilibrium state. In the case of relative larger particles of NaCl 1%, collection efficiency for the equilibrium charged particles increases due to the particle loading on the filter fibers. Particles charged by spray electrification are small in collection efficiency after equilibrium state and increase of filter media's pressure drop was very low in comparison of the equilibrium charged particles.

• 대한기계학회논문집B
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• 제27권10호
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• pp.1498-1507
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• 2003

A SMPS(scanning mobility particle sizer) system measures the number size distribution of particles using electrical mobility detection technique. An aerosol charge neutralizer, which is a component of the SMPS, is a bipolar charger using a radioactive source to apply an equilibrium charge distribution to aerosols of unknown charge distribution. However, the performance of aerosol charge neutralizers is not well known, especially for highly charged particles. In this study, the effect of the particle charging characteristics of two aerosol charge neutralizers on the measurement using a SMPS system was experimentally investigated for highly charged polydisperse particles. One has radioactive source of $^{85}$ Kr (beta source, 2 mCi) and the other has $^{210}$ Po (alpha source, 0.5 mCi). The air flow rate passing through each aerosol charge neutralizer was changed from 0.3 to 3.0 L/min. The results show that the non-equilibrium character in particle charge distribution appears as the air flow rate increases although the particle number concentration is relatively low in the range of 1.5∼2x10$^{6}$ particles/㎤. The low neutralizing efficiency of the $^{85}$ Kr aerosol charge neutralizer for highly charged particles can cause to bring an artifact in the measurement using a SMPS system. However, the performance of the $^{210}$ Po aerosol charge neutralizer is insensitive to the air flow rate.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.605-611
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• 2001

A numerical technique for simulating the aggregation of charged particles was presented with a Brownian dynamic simulation in the free molecular regime. The Langevin equation was used for tracking each particle making up an aggregate. A periodic boundary condition was used for calculation of the aggregation process in each cell with 500 primary particles of 16 nm in diameter. We considered the thermal force and the electrostatic force for the calculation of the particle motion. The morphological shape of aggregates was described in terms of the fractal dimension. The fractal dimension for the uncharged aggregate was $D_{f}=1.761$. The fractal dimension changed slightly for the various amounts of bipolar charge. However, in case of unipolar charge, the fractal dimension decreased from 1.641 to 1.537 with the increase of the average number of charges on the particles from 0.2 to 0.3 in initial states.

• 대한기계학회논문집B
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• 제25권1호
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• pp.124-132
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• 2001

This paper reports on the charge distribution measurements of submicron particles for three different charging mechanisms, which are spray electrification, bipolar ionization and corona discharge process, respectively. The number of elementary charges per particle was investigated by classifying and counting of a discrete mobility class. Charge distribution measurements were performed with NaCl particles generated from a collision atomizer for 0.01, 0.1, 1% NaCl solutions. Experimental results show than charge level of atomized NaCl particles is high and decreases with increasing the dissolved ion concentration. The charge level of the atomized NaCl particles can be reduced to that o Boltzmann equilibrium conditions by the bipolar ionization(Po(sup)210 bipolar ionizer). The charge level on NaCl particles passing through the corona discharge reactor is much higher than those of atomized or bipolar ionized NaCl particles. The evaluation of these measurements results in charge distribution of the submicron particles.