• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2067-2072
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• 2007

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, as an initial step, the wall impact of an electrically charged droplet has been experimentally investigated. The charged drops were directed on the surface of a paraffin wax, and the impinging behavior was visualized and recorded using a CCD camera to identify the impingement regime. The spread-rebound boundary for the charged drop turned out to be smaller compared to that for an electrically neutral droplet under the same surface condition. The shift of the transition criterion is considered to be due to the discrepancy between the maximum spread ratio of the electrically charged droplet and that of the neutral droplet.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.19-20
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• 2003

Brownian-dynamics simulation on highly charged colloidal suspensions is performed by employing Tokuyama effective force recently proposed. The radial distribution function suggests that there exist three novel phases, a gas phase, a liquid droplet phase, and a face-centered cubic (FCC) crystal droplet phase, depending on the minimum values of that potential. The dynamics of droplet growth is also investigated both in liquid droplet phase and in crystal droplet phase. Thus, different types of characteristic growth stages are found.

• 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.

• Journal of the Korean Society of Visualization
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• v.13 no.1
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• pp.49-53
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• 2015

Recently, researches for droplet impact phenomena have been faced a new phase in the direction of studying the effect of complex external conditions (e.g. wettability, temperature, morphology, electric field, etc.) for depth understanding and precise controlling in various applications. Hence, here we investigated the electrified droplet impact phenomena, because there were few quantitative researches for electrified droplet impact when we considering many real applications such as electrospray, electrohydrodynamic (EHD) jet printing. To observe interaction effect of surface charge between substrate and droplet simultaneously, micro-droplets with various Reynolds number (Re) and Weber number (We) were dripped on super-hydrophobic surface with existence and nonexistence of electrical surface charge. It shows three kinds of impact behaviors, fully bouncing, partial bouncing, and splashing with different We. Also, charged droplet bounced higher on electrically charged surface than on non-charged surface. Additionally, transition regions of three impact behaviors were classified quantitatively with water hammer pressure value, which means instant pressure inside droplet at the impact moment.

• Journal of ILASS-Korea
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• v.11 no.2
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• pp.98-104
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• 2006

A charged droplet scrubber was introduced to remove visible smokes generated in many industrial facilities. Lab-scale and field tests were conducted in this study. The system consists of a corona discharger to effectively charge the fine particles, fellowed by an electrostatic chamber to promote coagulation between charged fine particles and oppositely charged droplets and a demister to remove resultant particles. Overall collection efficiency, 98.4% was obtained from a lab-scale test, when a high voltage was applied to an ionizer and a charged droplet scrubber. Field tests also show the high collection efficiencies, 93.5% with one stage and 99.4% with two stage system. This system can be used to increase the collection efficiency of the conventional air pollution control devices to satisfy the national emission standard.

• 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.

• Journal of the Korean Society of Combustion
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• v.21 no.2
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• pp.7-14
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• 2016

Evaporation and combustion characteristics of fuel droplet with carbon nanoparticle were investigated in a rapid compression machine(RCM). RCM is an experimental equipment to simulate one compression stroke of reciprocating engine. Nitrogen was charged into reaction chamber for evaporation experiment, while oxygen was charged for combustion experiment. N990 carbon black and n-heptane were used to synthesize the carbon nanofluids. Surfactant, span80, was used to make synthesis easier. The droplet pictures were taken using a high speed camera with 500 frames per second. Thermocouple, of which tip is $50{\mu}m$, was used not only to measure transient bulk temperature, but also to suspend the droplet. Reaction chamber temperature was calculated from pressure data. The evaporation rate of nanofluids was improved compared to pure fuel. The ignition delay was promoted due to the nanoparticle, but the burning rate was decreased.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2005.11a
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• pp.488-490
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• 2005

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.297-300
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• 2006

This article discusses about the droplet movement on the super-hydrophobic surface by the electro-wetting on dielectric and the effect of particles on the contact angle as well as the movement is investigated. The movement of droplet, driven by the principle of electro-wetting on dielectric, and the effect of particles are experimentally verified according to the driving voltage and different particles concentrations (fluorescent, charged particles). To increase the contact angle, the super-hydrophobic surface is fabricated and applied to the dielectric layer for the EWOD device. Then its performance is verified and discussed.

• Journal of Mechanical Science and Technology
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• v.20 no.3
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• pp.409-417
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• 2006

Polymer nanofibers can be generated by a electrospinning process. The process involves electrically charged jet of polymer solutions evolving from a droplet. The jet stretches in vertical direction due to the difference between charged particle and constant current located at the collector, while the Coulomb and viscoelastic forces start to contribute to radial and azimuthal (torsional) stretching. In this paper, the unstable dynamics of the liquid polymer jet is examined experimentally and theoretically. A complex viscoelastic rheological model has been adopted to analyze the behavior of a charged liquid jet. The model includes complex phenomena of stress relaxation of the liquid jet resulting from the competing force components. The experimental data of the jet paths captured by high-speed videocamera also confirm the similar behavior with the predictions.