• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.21-26
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• 2012

Hydrophobic characteristics of high temperature metal surface were investigated by high-speed visualization of water droplet impact. An aluminum plate was used as the sample plate and the initial diameter of a water droplet was 2 mm. Transient behavior of a single droplet impinging on the surface with and without heating was captured by using a high speed camera running at 4,000 frames per second. The Leidenfrost phenomenon was demonstrated for the case of $300^{\circ}C$ surface temperature, however there was no rebounding of droplet on the cold plate due to hydrophilic nature. The experimental results show that the shape evolution of a droplet impinging on the surface varies with the Weber number, i.e. the ratio of impact inertia to capillary force. The overall water-repellent characteristics of the heated surface was very similar to that of the super hydrophobic surfaces.

• Korean Journal of Materials Research
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• v.16 no.10
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• pp.633-638
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• 2006

Silica powders with spherical shape and narrow size distribution were prepared by large-scale ultrasonic spray pyrolysis applying the droplet classification apparatus. On the other hand, silica powders prepared by large-scale ultrasonic spray pyrolysis without droplet classification apparatus had broad size distribution. Droplet classification apparatus used in this paper applied the principles of cyclone and dispersion plate with small holes. The droplets formed from the ultrasonic spray generator applying the droplet classification apparatus had narrow size distribution. The droplets with fine and large sizes were eliminated by droplet classification apparatus. The optimum flow rate of the carrier gas and diameter of the hole of the dispersion plate were studied to reduce the size distribution of the silica powders prepared by large-scale ultrasonic spray pyrolysis. The size distribution of the silica powders prepared by large-scale ultrasonic spray pyrolysis at the optimum preparation conditions was 0.76.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.161-166
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• 2004

A study of argon droplet vaporization is conducted using molecular dynamics. Instead of using traditional method such as the Navier-Stokes equation. Molecular dynamics uses Lagrangian frame to describe molecular behavior in a system and uses only momentum and position data of all molecules in the system. So every property is not a hypothetical input but a statistical result calculated from the momentum and position data. This work performed a simulation of the first-order stability for phase transition of a three dementional submicron argon droplet within quiescent environment. Lennard-Jones 12-6 potential function is used as a intermolecular potential function. The molecular configuration is examined while an initially non-sperical droplet is changed into the spherical shape and droplet evaporates or condensates.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.3
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• pp.320-330
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• 1999

A numerical study was performed to investigate spray behavior and its interaction with air flow in a flame holding region of an oil burner(0.1MW) using the KIVA3 code. The numerical results in shape of the recirculating flow and size of the recirculation zone under different conditions were compared to those experimental results. The numerical results in fuel droplet trajectory show that a droplet under 30${\mu}m$ can follow the air flow but a droplet over 50${\mu}m$ penetrates the recirculation zone due to large momentum and a droplet of 30-50${\mu}m$ can follow the recirculating flow or pene-trates the recirculation zone.

• Proceedings of the Korean Society of Laser Processing Conference
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• 2001.11a
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• pp.43-47
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• 2001

This paper presents a study of the uniform metal droplet generation using laser. The theoretical model, based on the variational principle instead of solving the Wavier-Stokes equation with moving boundaries, is developed. Our model is considered the Young-Laplace equation and force equilibrium conditions. Surface tension coefficient is determined under the statical condition with induced differential equation by using experimental result. In case of dynamic vibration, metal droplet shape and critical detaching volume are predicted by recalculating of proposed model. The simulation result revealed that the developed model could reasonably describe the molten metal droplet behavior on vibration with metal wire.

• Journal of the Korean Society of Visualization
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• v.17 no.2
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• pp.83-89
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• 2019

In this study, we show the maximum cavity radius prediction model that a droplet impacts an inclined bath. Surface tensions, viscosities, inclination angles of a bottom substrate, droplet diameters, falling heights of the droplet are varied for the experiment. We experimentally observe that the cavity grows in hemispherical shape like the cavity formed in a deep bath although the depth of the bath is non-uniform due to an inclined bottom substrate. We derive two theoretical models to predict the experimental results of the fully developed cavity. Although each model has error, we observe that qualitatively theoretical model predicts the trend of experiment results well.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1742-1746
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• 2008

An EHD (Electro-Hydro-Dynamic) jet for electrostatic inkjet head shows advantages to print micro-size patterns using various inks because it can generate sub-micron droplets and can use highly viscous inks. Thus, many researchers in industrial fields are concerned about the EHD jet in these days. Since the basic principle of the EHD jet is to form a droplet from an apex of meniscus at the end of the nozzle, the ejection mechanism can be changed by the shape of the meniscus. The stable ejection of the droplet is greatly affected by the shape of the meniscus which is also influenced by surface characteristics of the nozzle, electric potential and ink properties. Experiments have been performed using the nozzles with hydrophilic and hydrophobic coatings in this study. The hydrophobic nozzle forms the stable droplets in wider range of the electric potential than the hydrophilic nozzle does.

• Korean Chemical Engineering Research
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• v.51 no.6
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• pp.760-765
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• 2013

Lysozyme crystallization was performed by using flow-focusing chip in droplet-based microfluidic system. Water-in-oil droplets were formed in the system and collected on petri-dish and cross type mold. Liquid-liquid reaction of lysozyme and sodium chloride occurred in the droplet and crystals were observed through microscope. Solution pH was varied as 4.8 and 7.2. Crystals of polyhedron and plate-like shape were obtained at pH 4.8, while needle structure crystals formed at pH 7.2. Lysozyme in single droplet for two pHs were crystallized with constant or decreased droplet size. However, crystals at pH 4.8 were only obtained in the droplet of which size was increased by the interaction between droplets. Droplet volume did not change at pH 7.2 and crystals formed in both droplets.

• Corrosion Science and Technology
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• v.19 no.6
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• pp.310-317
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• 2020

This study investigated the damage to the specimen due to liquid droplet impingement erosion corrosion, which improved the corrosion resistance and durability via hard anodization of 5083-H321 aluminum alloy, which is widely used for small ships and marine structures. The experiment combined liquid droplet impingement erosion and electrochemical equipment with the flow rates in natural seawater solution. Subsequently, Tafel extrapolation of polarization curves was performed to evaluate damage due to the liquid droplet impingement erosion corrosion. The damaged surface was observed using a 3D microscope and a scanning electron microscope. The degree of pitting damage was measured using the Image J program, and the surface hardness was measured using the micro-Vickers hardness tester. The corrosion current density, area, depth, and ratio of the damaged areas increased with the increase in flow rate. The grain size of the damaged area at a flow rate of 20 m s-1 showed fewer and minor differences in height, and a smooth curved shape. The hardness of the damaged surface tended to decrease with increase in flow rate.

• Journal of Ship and Ocean Technology
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• v.7 no.4
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• pp.32-40
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• 2003

Numerical simulation code is developed to study the formation of liquid drops from a nozzle into another quiescent liquid. The Navier-Stokes equations for two immiscible, incompressible, Newtonian fluids are solved on a fixed, staggered grid of cylindrical axisymmetric coordinates. Interfacial motion is captured using a Front-Tracking Method. The time variation of interfacial shape simulated by the code is in excellent agreement with experiments. Simulation results show that the viscosity ratio affects the size of the satellite drops.