• Journal of ILASS-Korea
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• v.9 no.1
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• pp.21-29
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• 2004

The flow characteristics of a swirl injector were investigated with the variation of the flow condition and geometric dimensions, such as orifice length for considering the viscous effect and tangential entry port area for considering the swirl intensity. The liquid film thickness strongly influencing on the formed drop size of the spray was measured using a new technique. The film thickness measurement technique proposed here, used the attenuation of fluorescence signal near the injector exit. The breakup length that is important for the flame location as well as the spray cone angle which influences on the ignition performance was measured using a backlit stroboscopic photography technique. From the experimental results, it is found that an increase in injection pressure decreased the film thickness and breakup length, and also enlarged the spray cone angle. A decrease in orifice length and tangential entry port area has a similar tendency of thinner film thickness, shorter breakup length and larger spray cone angle. In the present study, we proposed empirical models of the flow characteristics of the swirl injectors.

• International Journal of Fluid Machinery and Systems
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• v.9 no.1
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• pp.57-65
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• 2016

By high speed Liquid Droplet Impingement (LDI) on material, fluid systems are seriously damaged, therefore, it is important for the solution of the erosion problem of fluid systems to consider the effect of material in LDI. In this study, by using an in-house fluid/material two-way coupled method which considers reflection and transmission of pressure, stress and velocity on the fluid/material interface, high-speed LDI on wet/dry material surface is simulated. As a result, in the case of LDI on wet surface, maximum equivalent stress are less than those of dry surface due to damping effect of liquid film. Empirical formula of the damping effect function is formulated with the fluid factors of LDI, which are impingement velocity, droplet diameter and thickness of liquid film on material surface.

• Journal of ILASS-Korea
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• v.12 no.1
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• pp.1-10
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• 2007

The low frequency combustion instability phenomena generated by pressure drop oscillation such as propellant shake in feed line are studied. To generate the flowrate oscillation by the pressure pulsation up to 400Hz without flow discontinuities and cavitations, a hydrodynamic mechanical pulsator of rotating disk type was produced. Injection pressure conditions are 5, 7 and 9 bar and pressure fluctuation frequency conditions are 0, 4, 6 and 8 Hz. When the injection pressure was oscillated by a mechanical pulsator, the spray shape was pulsated regularly. During the pulsated state of the spray with a mechanical pulsator, the spray characteristics, such as spray angle and liquid film thickness in orifice exit, were measured and compared with those in steady state without a mechanical pulsator. Though the mean injection pressure was fixed in the steady and fluctuating state, there were some differences in all measured values, i.e. liquid film thickness and spray cone angle, between both states.

• Journal of Mechanical Science and Technology
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• v.16 no.11
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• pp.1477-1484
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• 2002

Various characteristics of a thin liquid film in its vapor-phase are investigated using the molecular dynamics technique. Local distributions of the temperature, density, normal and tangential pressure components, and stress are calculated for various film thicknesses and temperature levels. Distributions of local stresses change considerably with respect to film thicknesses, and interracial regions on both sides of the film start to overlap with each other as the film becomes thinner. Integration of the local stresses, i.e., the surface tension, however, does not vary much regardless of the interfacial overlap. The minimum thickness of a liquid film before rupturing is estimated with respect to the calculation domain sizes and is compared with a simple theoretical relation.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1998.05a
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• pp.3-3
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• 1998

The atmospheric corrosIOn properties of Zinc (Zn) under wet/dry transition of $H_20$ film were investigated in this study. The atmospheric corrosion of metal is usually occurred as a result of repetitious thickness transition (so called wet/dry transition) of liquid phase which is covering the metal surface. Corrosion potential and the polarization behaviour of Zn during liquid film thickness transition were measured by Kelvin probe method which IS using vibrating reference electrode without touching the liquid film. The oxidized states of Zn as a result of successive wet/dry transition were also investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the corrosion potential and the corrosIOn rate of Zn both are increasing during drying. However, the corrOSIon rate is decreasing again when the Zn surface is completely dried while the corrosion potential still remains high. This behaviour can be explained by the polarization behaviour change of Zn according to the $H_20$ film thickness change. The completely dried surface is consisted mostly with Zn and ZnO phases. After a number of cycles of wet/dry transition, however, the oxidized Zn phase of ${\varepsilon}-Zn(OH)_2$, which has rather voluminous and defected structure, were found.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.5
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• pp.459-467
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• 2005

The effect of anti freezing solution liquid film on the frost prevention is experimentally investigated. It is desirable that the antifreezing solution spreads widely on the heat exchanger surface forming thin liquid film to prevent frost nucleation and reduce the thermal resistance across the film. A porous layer coating technique is adopted to improve the wettedness of the anti freezing solution on a parallel plate heat exchanger. The antifreezing solution spreads widely on the heat exchanger surface with 100 $\mu$m thickness by the capillary force resulting from the porous structure. It is observed that the antifreezing solution liquid film prevents a parallel plate heat exchanger from frosting. The reductions of heat and mass transfer rate caused by thin liquid film are only $1\~2\%$ compared with those for non-liquid film surface.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.2
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• pp.188-196
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• 2003

Liquid-assisted cleaning technology utilizing a nanosecond laser pulse is effective for removing submicron particulates from a variety of solid substrates. In the technique, saturated vapor is condensed on a solid surface to form a thin liquid film and the film is evaporated explosively by laser heating. The present work studies the role of liquid-film evaporation in the cleaning process. First, optical interferometry is employed for in-situ monitoring the displacement of the laser-irradiated sample in the cleaning process. The experiments are performed for estimating the recoil force exerted on the target with and without liquid deposition. Secondly, time-resolved visualization and optical reflectance probing are also conducted for monitoring the phase-change kinetics and plume dynamics in vaporization of thin liquid layers. Discussions are made on the effect of liquid-film thickness and dynamics of plume and acoustic wave. The results confirm that cleaning force is generated when the bubble nuclei initially grow in the strongly superheated liquid.

• Journal of ILASS-Korea
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• v.14 no.3
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• pp.97-102
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• 2009

The spray characteristics of the high speed rotating fuel injection system were studied. The five variants of rotating fuel nozzle were used by spray test. The diameter of single column injection orifices are varied from 1 mm, 2 mm, 3 mm, 4 mm and 5 mm. We constructed high speed rotating test rig and measured droplet size by PDPA (Phase Doppler Particle Analyzer) system. Also spray was visualized by using high speed camera. In the test results, we could understand that length of liquid column from the injection orifice is mainly controlled by the rotational speeds. SMD is decreased with increasing injection orifice diameter and rotational speeds. Furthermore, from the comparison to the theoritical calculation, we confirmed that SMD is influenced by the liquid film thickness which is formed inner surface of injection orifice.

• Transactions on Electrical and Electronic Materials
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• v.7 no.6
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• pp.305-308
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• 2006

We have studied liquid crystal (LC) aligning capabilities for homeotropic alignment and the control of tilt angles on the $SiO_{x}$ thin film by electron beam evaporation method. A high tilt angle of about $86.5^{\circ}$ was obtained, and also the suitable tilt angle of the NLC on the $SiO_{x}$ thin film at $20{\sim}50\;nm$ thickness with e-beam evaporation can be achieved. The uniform LC alignment on the $SiO_{x}$ thin film surfaces with electron beam evaporation can be achieved. It is considerated that the LC alignment on the $SiO_{x}$ thin film by electron beam evaporation is attributed to elastic interaction between LC molecules and micro-grooves at the $SiO_{x}$ thin film surface created by evaporation.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1409-1411
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• 2006

A new rod-like liquid crystalline monomer having divinyl terminal groups was synthesized and polymerized by using thiol-ene UV polymerization technique. High quality thin film with good retardation value was prepared on a rubbed alignment layer without the inert gas purging. The retardation value of the resulting film was controlled by experimental conditions such as spin speed, concentration, and spin time. From the retardation value and thickness measurement, ${\bigtriangleup}n$ was calculated to be 0.169 for the resulting film having thickness of 815.1 nm.