• Title/Summary/Keyword: 스플래시

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Surface Wetting Effect on Spread-Splash Transition Criterion (표면 젖음성이 스프레드-스플래시 영역 간 천이 조건에 미치는 효과)

  • Ryu, S.U.;Lee, S.Y.
    • Journal of ILASS-Korea
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    • v.12 no.4
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    • pp.198-203
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    • 2007
  • In the present work, surface wetting effect on spread-splash regime and transition criterion of the water and ethanol droplets impacting an unheated dry wall has been experimentally investigated. The droplet was directed on a polished STS plate and a glass slide, and the impinging behavior was visualized and recorded using a CCD camera. Droplet diameter and velocity approaching the wall were measured as well. The critical Sommerfeld number representing the spread-splash boundary for the ethanol droplet impinging on the substrates turned out to be smaller compared to that for the water droplet impinging on the substrates with the surface roughness condition remained unchanged. The shift of the transition boundary is considered to be due to the effect of the surface wettability represented by static contact angle and surface tension of droplet.

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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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Numerical Study on the Effect of Anisotropic Turbulence Characteristics on the Droplet Behaviors for Impinging Sprays (충돌분무의 액적 거동에 미치는 비등방성 난류특성의 영향에 대한 수치해석 연구)

  • Ko G. H;Ryou H. S
    • Journal of computational fluids engineering
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    • v.8 no.4
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    • pp.6-15
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    • 2003
  • It is an aim of this study to perform extensive numerical study for analyzing the anisotropic turbulence effects on spatial and temporal behaviors of droplet for impinging sprays. The turbulence model of Durbin is used for comparisons with the k-ε model. The turbulence-induced dispersions of droplets are considered to describe the anisotropy of turbulence effectively and spray/wall interactions are simulated using the model of Lee and Ryou. Present study investigates the overall and the internal structures of impinging diesel sprays such as spray shapes, radius and height of wall sprays, Sauter mean diameter (SMD), local droplet velocity, and local gas velocity and compared the results with experimental data by two adopted turbulence models. When the anisotropy effect of turbulence is included, better predictions for both gas and droplet tangential velocities are obtained, compared to the k-ε model. It is concluded that anisotropic effect of turbulence should be considered for simulating impinging diesel sprays.

Numerical Study of Impinging Sprays Considering Anisotropic Characteristics of Turbulence (비등방성 난류특성을 고려한 분무의 벽면충돌 현상에 대한 수치해석 연구)

  • 고권현;유홍선;이성혁
    • Transactions of the Korean Society of Automotive Engineers
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    • v.11 no.3
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    • pp.77-84
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    • 2003
  • It is an aim of this study to perform extensive numerical study for analyzing the anisotropic turbulence effects on spatial and temporal behaviors of diesel sprays after wall impingement. The turbulence model of Durbin is used for comparisons with the $k-\varepsilon$ model. The turbulence-induced dispersions of droplets are considered to describe the anisotropy of turbulence effectively and the spray/wall interactions are simulated using the model of Lee and Ryou. The present study investigates the internal structures of impinging diesel sprays such as Sauter mean diameter (SMD), loca1 droplet velocities, and local gas velocities and also compares the results predicted by two turbulence models with the experimental data. The Durbin's model considering the anisotropy of turbulence predicts both gas and droplet tangential velocities better than the$k-\varepsilon$ model does. It is concluded that the anisotropy of turbulence should be considered in simulating impinging diesel sprays.

Numerical Study on the Effect of the Wall Curvature on the Behaviors of the Impinging Sprays (충돌분무의 거동에 미치는 벽면곡률의 영향에 대한 수치해석 연구)

  • 고권현;유홍선
    • Transactions of the Korean Society of Automotive Engineers
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    • v.12 no.3
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    • pp.59-65
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    • 2004
  • In this paper a numerical study was performed for the effect of the wall curvature on the behaviors of fuel sprays impinging on the concave Surface. Actually, in the real diesel engines, a piston head has a curved shape for the purpose of the controlling the movement of fuel droplets and the mixture formation. For past decades, although many experimental and numerical works had been performed on the spray/wall impingement phenomena, the curvature effect of impinged wall was rarely investigated. The wall curvature affects on the behaviors of the secondary droplets generated by impingement and the concave wall obstructs the droplets to advance from the impinging site to outward. In present study, the simulation code was validated for the flat surface case and three cases of the different curvature were calculated and compared with the flat surface case for several parameters, such as the spray radius, the spray height and the position of vortex center of gas phase. The simulation results showed that the radial advance of the wall spray and the vortex is decreased with increasing the curvature. It was concluded that the curvature of the impinged wall significantly affects the behaviors of both the gas-phase and the droplet-phase.

A Physical-based Particle Method for Small Scale Feature in Multi-phase Fluid Simulation (다상 유체 시뮬레이션에서 격자 크기 이하의 미세한 특징 표현을 위한 물리기반 입자 기법)

  • Lee, Ho-Young;Hong, Jeong-Mo;Kim, Chang-Hun
    • Journal of Korea Multimedia Society
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    • v.12 no.3
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    • pp.445-450
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    • 2009
  • This paper presents a multi-phase fluid simulation that realistically represents small scale details. We achieve this by creating escaped particles based on physical methods. Escaped particles are the remained particles after correcting levelset. Generation of escaped particles in this paper differs from previous works; this fluid simulation is extended by adding lift force and drag force to positive escaped particles. And negative escaped particles represent droplet or splash effect; when they are merged into the negative levelset value, they affect the nodes' velocity (two-way coupling). This simulation that uses positive and negative escaped particles deals with detailed fluid motions dynamically in small scale.

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A Study on Measures for Improving Obligatory Use of Digital Certificate for Eletronic Financial Transactions (전자금융거래시 공인인증서 의무사용 개선방안에 관한 연구)

  • Jeong, Gi Seog
    • Convergence Security Journal
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    • v.13 no.6
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    • pp.25-33
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    • 2013
  • Digital certificate must be used for electronic financial transactions in Korea. But because digital certificate is based ActiveX of Internet Explorer, it is difficult to use digital certificate in other web browsers. It interrupts a development of various authentication technology and a growth of related industry. Also digital certificate can be leaked because of being stored in harddisk or USB. The government eased obligatory use of digital certificate and opened doors to other authentication techniques. But any other authentication techniques are not used because they are not approved as alternative technology. The revised bills with digital certificate abolition as the main agenda have been submitted to the National Assembly. Whether the revised bills pass or not will be decided by a regular session of the National Assembly depending on the calculation and dynamics composition of related industry. In this paper, a controversy over obligatory use of digital certificate is examined and measures are found.

Growth Characteristics and Hydrocarbon Patterns of Flammable Liquid on a Vinyl Layer (비닐장판 위에서 연소된 인화성 액체의 성장 특성과 탄화 패턴)

  • Joe, Hi-Su;Choi, Chung-Seog
    • Fire Science and Engineering
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    • v.32 no.5
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    • pp.15-21
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    • 2018
  • This study examined the growth characteristics and carbonization pattern when a fire occurs due to a flammable liquid sprinkled on a vinyl floor. When acetone was sprinkled on a floor, the flame reached its peak in approximately 0.2 s after it was ignited. The lower part of the flame showed a laminar pattern while the upper part showed a turbulent pattern. The pattern showed a turbulent pattern and generated white smoke. The combustion completed floor surface showed carbonization of a dim pore pattern. In the case of benzene, an intense flame was formed in approximately 0.6 s after ignition. The flame length was measured to be approximately 50 mm. When the flame became weak, a significant amount of black smoke was generated due to incomplete combustion. The combustion completed floor surface showed carbonization of a pour pattern and splash pattern. In the case of alcohol, an intense flame was formed in approximately 1.1 s after ignition. In addition, the depth of carbonization was significant where the flammable liquid was collected and a trace of carbonization was observed at the boundary of the flow path of the flammable liquid.