• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.315-323
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• 2004

An electrical cascade impactor is a multi-stage impaction device to separate airborne particles into aerodynamic size classes using particle charging and electrical detection techniques. A Faraday cage and an aerosol charger, which are basic components of the electrical cascade impactor, were designed and evaluated in this study. The low-level current response of the Faraday cage was investigated with changing particle size and air flow rate by using sodium chloride (NaCl) particles. The response of the prototype Faraday cage was very similar to that of a commercial aerosol electrometer (TSI model 3068) within ${\pm}$5% for singly-charged particles. The response linearity of the prototype Faraday cage could be extended up to flow rate of 30 L/min. For the performance evaluation of the aerosol charger the monodisperse liquid dioctyl sebacate (DOS) particles, with diameters of 0.1∼0.8$\mu\textrm{m}$, were generated using spraying from an atomizer followed by evaporation-condensation process. Typical performance parameters of the aerosol charger such as P$.$n, wall loss, and elementary charges per particle were evaluated. The performance of the prototype aerosol charger was found to be close to that of the aerosol charger used in an electrical low pressure impactor (ELPI, Dekati).

• 연구논문집
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• s.34
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• pp.21-28
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• 2004

In this study, we report an investigation for the charging and collection of aerosol nanoparticles in an electrostatic precipitator (ESP) according to particle charging and diffusion effects. The competition between charging probability and diffusion effect determines the collection efficiency of nanoparticles in the ESP. In conclusion, collection efficiency continuously decreased with the reduction in the particle size. This indicates that poor partial charging effect of nanoparticles is more dominant than their diffusion effect in the ESP for the nanoparticles in the particle size range of 4-20 nm. Theoretical calculations using a unipolar diffusion charing theory were in good agreement with the experimental data for the nanoparticles less than 20 nm in diameter.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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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.

• Particle and aerosol research
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• v.13 no.4
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• pp.151-158
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• 2017

Electrostatic precipitator is widely used to remove particulate matters in indoor air and industrial flue gas due to low pressure drop and high collection efficiency. However, it has a low collection efficiency for the submicrometer sized particles. Electrospraying is a potential method to increase the particle charging efficiency, which results in increased collection efficiency. Although particle charging efficiency is highly dependent upon droplet size, the effective measuring method of the droplets is still uncertain. Tap water was electrosprayed in this study, and the images of electrosprayed droplets were taken with a high speed camera coupled with several visualization methods in order to measure the droplets size. The droplet size distribution was determined by an image processing with an image-J program. As a result, a droplet measured by a laser visualization, had a half size of that by a Xenon light visualization. In addition, the experimentally measured droplet sizes were a good agreement with the predicted values suggested by $Fern{\acute{a}}ndez$ de la Mora and Loscertales(1994).

• Air Cleaning Technology
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• v.17 no.4 s.67
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• pp.39-57
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• 2004

첨단산업으로 불리는 반도체, LCD, PDP, 유기EL(OLED) 등의 생산 공정은 고도의 청정상태를 요구하며, 때문에 이들의 생산공정 중 대부분이 클린룸 내에서 이루어진다. 클린룸 내에서의 주요공정은 크게 박막형성(Layering), 노광(Photo Lithography), 식각(Etching) 등 3가지 공정으로 나눌 수 있으며, 반도체 제조공정의 경우 특별히 도핑(Doping) 공정이 추가된다. 오염물질을 함유하는 클린룸 배기는 일반적으로 산, 알칼리, Toxic(PFCs, Flammable), VOC 등으로 분류하며, 각각의 배기는 각 배기특성에 맞는 오염제어 장치를 통해, 정화된 후, 대기로 방출된다. 산, 알칼리 배기는 일반적으로 최종 단계에서 중앙집중식 습식스크러버에 의해 흡수, 중화 처리되며, VOC의 경우 농축기(Concentrator) & 축열식 열 산화장치(RTO) 설비에 의해 연소 처리된다. 하지만 CVD공정으로부터의 배기가 주를 이루는 Toxic배기의 경우, 다량의 PFCs(과불소화합물) 가스를 함유하고 있는 이유로, 대부분 클린룸 내부에 P.O.U(Point of use) 처리장치가 설치되며, P.O.U에 의해 1차 처리된 후 최종적으로 중앙집중식 습식스크러버를 거쳐 대기로 방출된다. 알칼리배기의 주성분으로는 암모니아($NH_3$), HMDS (Hexa Methyl DiSilazane), TMAH (Tetra Methyl Ammonium Hydroxide), LGL, CD 등이며 흡수액에 황산(Sulfuric Acid)용액을 공급, 중화처리하고 있다. 탄소성분을 먹이로 하는 미생물의 번식에 의한 막힘 문제를 제외하고는 큰 문제가 없다. 하지만 Toxic배기 및 산배기의 경우 처리효율이, 가스흡수 이론에 의한 계산결과와 비교할 때, 매우 저조하게 나타나는 효율부족 현상을 겪고 있으며, 이는 잔여 PFCs 가스성분 및 반응에어로졸, 응축에어로졸 등의 영향으로 추정하고 있다. 최근 Toxic 배기의 경우, P.O.U 설비를 Burn & Wet type으로 변경하여, 배기 중 PFCs 및 반응에 에어로졸($SiO_2$)의 농도를 원천적으로 감소시키는 노력이 진행 중이다. 산배기의 경우, 산결로 현상에 의한, 응축에어로졸이 문제가 되고 있으나 내식열교환기(Anti-Corrosive Heat Exchanger), 하전액적스크러버 시스템(Charged Droplets Scrubber System), Wet ESP(Wet Electrostatic Procipitator) 등의 도입을 통해 문제해결을 위한 노력을 경주하고 있다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1489-1497
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• 2003

Aerosol charge neutralizers with various radioactive sources have been used 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. Measurements of highly charged particles are needed in air cleaning devices, e.g. electrostatic precipitator, bag filter with a pre-charger, and electrical cyclone. In this study, the particle charging characteristics of two different aerosol charge neutralizers were experimentally investigated for singly charged monodisperse particles and 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 0.2 to 2.5 L/min. The results show that the charge distribution of singly charged monodisperse particles passing through the $^{85}$ Kr aerosol charge neutralizer is well agreed with the Boltzmann equilibrium charge distribution at an air flow rate of 0.3 L/min, However, it deviates from the equilibrium charge distribution when the air flow rates are 0.6, 1,0, and 1,5 L/min, On the other hands, the effect of air flow rate is insignificant for the $^{210}$ Po aerosol charge neutralizer. The non-equilibrium character in charge distribution of highly charged polydisperse particles passing through the $^{85}$ Kr aerosol charge neutralizer greatly depends on the air flow rate, however it is insensitive to the air flow rate for the $^{210}$ Po aerosol charge neutralizer.

• Particle and aerosol research
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• v.12 no.3
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• pp.95-102
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• 2016

Controlling exposures to occupational hazards is important for protecting workers. Certified facepiece respirators are recommended when engineering controls do not adequately prevent exposures to airborne nanomaterials. The objective of this study is to carry out the experimental performance test to investigate the fractional efficiencies of the filter media for two grades of facepiece respirators. Experimental performance evaluations were carried out for the test NaCl particles and silver nanoparticles. For media of respirator filter, the penetration of NaCl particles was less than 5% and the most penetrating particle size occurred at about 40 nm. For silver nanoparticles, the most penetrating particle size was about 20nm with higher efficiency than those of NaCl particles. Charge characteristics of airborne nanoparticles is important because the media of respirator filter is made by the electret filter media.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.237-246
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• 1994

Experimental data are reported for charging and collection of NaCl aerosols in the 0.03- to $0.2{\mu}m$-geometric-mean-diameter range in 2-stage parallel-plate electrostatic precipitators. The NaCl aerosols are generated with geometric standard deviation of about 1.74 and particle generation rate of about 10^9 particles/see by the constant output atomizer and injected into the air flow in the clean wind-tunnel. The 2-stage parallel-plate electrostatic precipitator installed in the test section of the wind-tunnel is operated with a positive corona discharge. The NaCl aerosols in the channel flow are sampled and transported to the aerosol particle number concentration measurement system by using the isoaxial sampling and transport system constructed based on the Okazaki and Willeke design. The aerosol particle number concentration measurement system measures the size distribution of submicrometer aerosols by an electrical mobility detection technique. It is confirmed from comparing the measured collection efficiencies in this study and the predicted ones by our previous theoretical analysis that the predicted collection efficiencies agree well with the experimental ones. It is also found from the comparison that below about $0.02{\mu}m$ all particles are not charged and the uncharged particles are not collected, and consequently 2-stage parallel-plate electrostatic precipitators are not suitable for that particle size range.