• Title/Summary/Keyword: droplet charging

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Research on the Electrical Charging of a Water Droplet on the Electrode and Droplet Actuation Method using Electrical Charge (전극표면에서 액적의 충전현상과 이를 이용한 액적의 이동 방법에 관한 연구)

  • Jung, Yong-Mi;Oh, Hyung-Chang;Kang, In-Seok
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.666-669
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    • 2008
  • Droplet in miniaturized microfluidic systems have received much focused attention recently. In this work, electrical charging phenomenon of a conducting water droplet on the electrode under the dc electric field is studied and using this phenomenon droplet actuation method for microreactor applications is experimentally demonstrated. To find effects of key factors, the effects of electric field, medium viscosity, and droplet size are investigated. A scaling law of charging for the conducting droplet is derived from the experimental results. Unlike the case of a perfect conductor, the estimated amount of electrical charge ($Q_{est}$) of a water droplet is proportional to the 1.59 power of the droplet radius (R) and the 1.33 power of the electric field strength (E). (For a spherical perfect conductor, Q is proportional to R2 and E.) It is thought that the differences are mainly due to incomplete charging of a water droplet resulted from the combined effect of electrochemical reaction at electrode and the relatively low conductivity of water. Using this phenomenon, we demonstrate the transport of the charged droplet and fusion of two oppositely-charged droplets. When electric field is subjected sequentially on the electrode, the charged droplet is transported on the electrode. For the visualization of fusion of charged droplets, the precipitation reaction is used. When subjected to a DC voltage, two droplets charged are moving and merging toward each other due to the Coulombic force and chemical reaction is simultaneously occurred by coalescence of droplets. It may be due to the interchange effect of charge. It is shown that the droplet can be used for microreactor where transporting, merging etc. of reagents constitute unit operation.

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A Study on Droplet Charging of an High Voltage Spraying System (고전압 분사시스템의 액적 하전 특성연구)

  • Son, Seung-Woo;Yoo, Kyoung-Hoon;Kim, Yoon-Shin
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.893-898
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    • 2003
  • An experiment was conducted to characterize water droplet charging performance of an electrostatic spraying nozzle for an electrostatic wet scrubber. Charge-to-mass ratios, the nozzle currents divided by the mass flow rate of water were obtained with respect to the applied voltage to the ring-electrode for 2 different flow conditions. It was shown that the charge-to-mass ratio increased in proportion to the applied voltage and tended to saturate at a certain higher voltage.

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Charging of an Ionic Liquid Droplet in a Dielectric Medium (비전도성 매질 내 이온성 액체 액적의 충전 현상)

  • Im, Do Jin
    • Clean Technology
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    • v.20 no.4
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    • pp.354-358
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    • 2014
  • Ionic liquid (IL) is a salt presents in a liquid form at room temperature. Recently, it attracts huge attention due to its possibilities as a clean solvent, electrolyte, and catalyst. In the present work, the charging behavior of six different ILs were investigated using droplet contact charging phenomenon in a dielectric medium. Basically, the charging of an IL droplet can be explained by a perfect conductor theory. However, there were several different features depending on the species of ions of ILs, which requires rigorous molecular level modeling of charge transport through electrochemical reaction of IL. We hope the present results contribute to build up fundamental understanding of electrochemical charge transport of IL.

Pulsed Corona Charging Characteristics of Aqueous Pesticide Spray (펄스 코로나 농약산포장치의 분무대전 특성)

  • 문재덕;이운태;배창환;권남열
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.52 no.9
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    • pp.388-394
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    • 2003
  • Many toxic pesticides as aqueous-base sprays are dispensed for protection of food crops from pests into farm fields. When dispensed with conventional nozzles, a large portion of the spray is often lost by airborne drifts of droplets away and lack of deposition onto the plants due to rapid gravitational settling of droplets to the soil beneath. And target deposition efficiencies poorer than 20% are often encountered in agricultural pesticides. An electrostatic spraying technology offers a very favorable means to increasing pesticides droplets deposition onto biological surfaces of living crops. In this paper a corona type spray nozzle, utilizing a set of corona charging devices and a pulsed droplet-charging voltage applied, has been proposed and tested its potential experimentally. As a result, it exhibits a large current deposition of aqueous pesticide sprays on the sensing target, which, however, promise to be as one of the effective electrostatic spraying nozzle.

Liquid Atomization and Spray Characteristics in Electrostatic Spray of Twin Fluids (2유체 정전분무의 액체 미립화 및 분무 특성)

  • Kim, Jeong-Heon;Bae, Choong-Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.11
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    • pp.1552-1560
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    • 2001
  • This paper presents the experimental results of a study undertaken to develop an electrostatic spray system for a combustion application. The characteristics of the liquid atomization and the droplet dispersion in the electrostatic spray of twin fluids were investigated by the optical measurement techniques. The processes associated with the break-up of charged jets were also observed using the laser sheet visualization. The diameter and velocity of droplets were simultaneously measured using the phase Doppler measurement technique. The electrostatic atomization of the liquid fuel depended primarily on the charging voltage and the flow rate, but the dispersion of droplets depended significantly on the aerodynamic flow. Aerodynamic influences on the liquid atomization decreased with an increase of the charging voltage. Consequently, the liquid atomization and the droplet dispersion could be independently controlled using the electrostatic and aerodynamic mechanisms.

Characteristics of Unipolar Charging of the Submicron Particles by the Condensation-Evaporation Method (응축 증발법을 통한 서브마이크론 입자의 단극하전 특성)

  • Choi, Young-Joo;Kim, Sang-Soo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.2 s.245
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    • pp.186-192
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    • 2006
  • We applied a new charging system using the condensation and evaporation method to charge the submicron particles with a uniform charging performance. The monodispersed NaCl submicron particles were condensed by n-butanol vapor and grew up to micron droplets with a same size, regardless of their initial size. Those condensed droplets were charged in an indirect corona charger. The indirect corona charger consisted of the ion generation zone and the particle charging zone. In the ion generation zone, Ions were generated by corona discharge and some of them moved into the particle charging zone by a carrier gas and mixed with the condensed droplet. And finally, the charged and condensed droplets dried through an evaporator to shrink to their original size. The average charge and penetration rate of the particles before and after evaporation were measured by CPC and aerosol electrometer and compared with those of a conventional corona charger. The results showed that the average charge was $5\~7$ charges and the penetration rate was over $90\%$, regardless of the initial particle size.

Influence of AC Frequency on the Liquid Breakup in Electrohydrodynamic Atomization (전기수력학적 미립화에서 교류 주파수가 액적 분열에 미치는 영향)

  • Sung, K.A.;Lee, C.S.
    • Journal of ILASS-Korea
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    • v.9 no.2
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    • pp.41-49
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    • 2004
  • Liquid breakup under the variation of AC frequency has been studied experimentally in the electrohydrodynamic atomization. The effect of parameters such as charging voltage, flow rate, nozzle tip inner diameter and power frequency have been considered. This work was performed to investigate the experimental analysis for the effect of AC frequency on breakup process, the mapping of occurrence of disintegration region, and the relationship between the applied power and the droplet radius. The experimental results show that the increase of applied voltage in a certain frequency band leads to a reduction in the droplet size within the limits from 50Hz to 400Hz. The transition phenomena from dripping mode to spindle mode were observed under the band of sudden fall of droplet radius changing ratio, and the synchronous region were produced within the range of applied voltage from 5kV to 6kV.

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Size measurement of electrosprayed droplets using shadowgraph visualization method (Shadowgraph 가시화 기법을 활용한 정전분무액적의 크기 측정)

  • Oh, Min-Jeong;Kim, Sung-Hyun;Lee, Myong-Hwa
    • 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).

A Study on the Optimal Generation Conditions of Micro-Droplet in Electrostatic Spray Indirect Charging Method (정전 분무 간접 하전 방식에서 미세액적 최적 발생 조건에 관한 연구)

  • Jihee Lee;Sunghwan Kim;Haiyoung Jung
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.37 no.1
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    • pp.79-87
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    • 2024
  • This paper is a study on the optimal microdroplet generation conditions in indirect charging electrostatic spraying. Unlike the direct charging method, which applies power to the nozzle, the indirect charging method applies power to the discharge electrode between the nozzle and the collection electrode. Therefore, an electrically simplified system can be obtained by minimizing the insulation part a stable spray pattern can be obtained with a wide spray angle, and a stable spray pattern can be obtained with a wide spray angle. To conduct the study, an indirect charging type electrostatic spray visualization system was constructed and the static characteristics of the microdroplets were analyzed through image processing of the spray shape of the microdroplets. The total number of microdroplets and the number of microdroplets per power consumption are confirmed according to the changes in the distance between the discharge electrode and the collection electrode, the flow rate, and the applied voltage, which affect the generation of microdroplets, and using this, the optimal generation conditions are derived and the corresponding microdroplet size distribution was analyzed. As a result of the experiment, it was confirmed that the optimal generation condition was at a flow rate of 15 to 20 mL/min and a voltage of -22.5 to -25 kV in terms of the number of microdroplets, and at a flow rate of 15 to 20 mL/min and a voltage of -20 kV in terms of energy consumption efficiency.

Investigation of Spread-Splash Transition Criterion of an Electrically Charged Droplet (전기적으로 대전된 액적의 스프레드-스플래시 영역 간 천이조건에 대한 연구)

  • Ryu, Sung-Uk;Lee, Sang-Yong
    • Proceedings of the KSME Conference
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    • 2008.11b
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    • pp.2995-3000
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    • 2008
  • Understanding of the impinging behavior of an electrically charged spray is essential in determining appropriate operating conditions for electro-spraying of paints, surface coating materials and insecticides. In the present work, the wall impact behavior of an electrically charged drop has been investigated and compared with that of a neutral drop experimentally. The critical Sommerfeld number representing the spread-splash boundary for the charged drop impacting on the dielectric substrate turned out to be larger compared to that for the neutral drop with the same surface condition. The change of the transition boundary is due to the increase in the surface wettability of the drop on the substrate. However, with the electrically conducting substrates, the charging effect on the transition boundary appeared negligible. This is because the electric discharging time is much shorter than the time required for the flattened drop to reach its maximum extent.

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