• Title/Summary/Keyword: Droplet shape

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A Study on the Behavior of an Impacting Droplet on a Wall Having Obstacles (방해물이 존재하는 평판 위 충돌 액적 거동에 관한 연구)

  • Yang, W.J.;Kang, B. S.
    • Journal of ILASS-Korea
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    • v.17 no.1
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    • pp.27-34
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    • 2012
  • In this paper an experimental study is presented to investigate the effect of a step edge and a stationary droplet on the dynamic behavior of impacting droplet on a wall. The main parameters are the distance from the edge and the center-to-center distance between two droplets. Photographic images are presented to show coalescence dynamics, shape evolution and contact line movement. The emphasis is on presenting the spreading length of droplet for the step edge and two coalescing droplets along their original centers. It is clarified that the droplet exhibits much different dynamic behavior depending on the location of the step edge. The momentum of impacting droplet was better transferred to the stationary droplet as the center- to-center distance between two droplets was reduced, which results in more spreading of coalescing droplet.

Collision Behavior of Molten Metal Droplet by Laser Beam (레이저 빔에 의해 생성된 금속액적의 충돌거동)

  • 김용욱;양영수
    • Laser Solutions
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    • v.6 no.1
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    • pp.1-8
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    • 2003
  • A molten metal droplets are deposited onto solid substrate for solid freeform fabrication, Collision dynamic and substrate heat transfer associated with solidification determine the final shape of molten metal droplets. In this study, the experimental model, based on the variational condition with substrate temperature and falling height, was produced reliable optimal data of droplet pattern.

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An Experimental Study of Breakup of Impinging Droplets on a Hot Surface (표면 충돌 액적의 분열에 관한 실험적 연구)

  • Ko, Y.S.;Chung, S.H.
    • Transactions of the Korean Society of Automotive Engineers
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    • v.2 no.5
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    • pp.85-92
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    • 1994
  • Characteristics of breakup of a liquid droplet impinging on a hot surface has been investigated experimentally by using decane fuel. Factors influencing droplet breakup are surface temperature, impinging velocity, droplet diameter and incident angle. Droplets impinging on a hot surface begins to breakup at $220{\sim}235^{\circ}C$. This temperature varies with impinging Velocity, droplet diameter and incident angle. For wall temperature of $220{\sim}245^{\circ}C$ and above $270^{\circ}C$, breakup probability increases as impinging velocity increases showing S shape curve. For $245{\sim}265^{\circ}C$, a local minimum heat transfer rate occurs. In this temperature range, breakup probability shows nonmonotonous behavior as functions of impinging velocity. As droplet diameter decreases, impinging velocity required for droplet breakup increases. An optimum impinging angle for droplet breakup exists which are found to be about $75^{\circ}$.

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The Effects of Initial Droplet Shape and Number Density on Modeling of Non-evaporating Diesel Sprays (디젤분무의 모델에서 액적의 형상 및 수밀도의 영향에 관한 연구)

  • Won, Y.H.
    • Journal of ILASS-Korea
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    • v.7 no.2
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    • pp.22-30
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    • 2002
  • A number of droplet breakup models have been developed to predict the diesel spray. The capabilities of droplet deformation and breakup models such as TAB, ETAB, DDB and APTAB models are evaluated in modeling the non-evaporating diesel sprays injected into atmosphere. New methods are also suggested that take into account the non- spherical shape of droplets and the reduced drag force by the presence of neighbouring droplets. The KIVA calculations with standard ETAB, DDB, and APTAB models predict well the spray tip penetrations of the experiment, but overestimate the Sauter mean Diameter(SMD) of droplets. The calculation with non spherical droplets injected from the nozzle shows very similar results to the calculation with spherical droplets. The drag coefficient which is linearly increased with the time after start of injection during the breakup time gives the smaller SMD that agrees well with the experimental result.

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Characteristic Analysis of Electrowetting on Dielectric Layer (절연층에 따른 액적의 전기습윤 특성 분석)

  • Choi, Jin Ho;Kim, Gyu man
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.18 no.8
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    • pp.38-43
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    • 2019
  • Electrowetting on dielectric (EWOD) is a unique method of shape control of small-volume droplets in microfluidic biochips that relies on modification of surface wetting characteristics using electrical methods. In this study, the droplet shape control on various dielectric surfaces by the EWOD and the effect of droplets on the contact angle as well as the shape were investigated. The droplet used in the experiment was on a sample substrate with $5{\mu}l$ of de-ionized water (DIW) using a micropipette, and wettability was measured with a contact angle meter. This study is expected to be helpful for the development of various micro-total-analysis-systems (${\mu}TAS$) and microfluidic systems with MEMS technology.

Numerical Study of Droplet Motion in a Microchannel with defferent contact angles (접촉각에 따른 마이크로채널 내에서의 액적 거동에 대한 수치적 연구)

  • Choi, Ji-Young;Son, Gi-Hun
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.656-657
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    • 2008
  • The droplet dynamics in a hydrophilic/hydrophobic microchannel, which is applicable to a typical proton exchange membrane fuel cell (PEMFC), is studied numerically by solving the equations governing conservation of mass and momentum. The liquid-gas interface or droplet shape is determined by a level set method which is modified to treat contact angles. The matching conditions at the interface are accurately imposed by incorporating the ghost fluid approach based on a sharp-interface representation. The effects of contact angle, inlet flow velocity, droplet size and side wall on the droplet motion are investigated parametrically. Based on the numerical results, the droplet dynamics including the sliding and detachment of droplets is found to depend significantly on the contact angle. Also, a droplet removal process is demonstrated on the combination of hydrophilic and hydrophobic surfaces.

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A Study on the Behavior of a Droplet Impacting onto a Heated Surface (고온 벽면과 충돌하는 단일 액적의 거동에 관한 연구)

  • Kang, Bo-Seon;Lee, Dong-Hwan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.7
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    • pp.871-880
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    • 1999
  • In this paper an experimental study is presented of the problem of dynamic behavior of a water droplet impinging upon a heated surface. The experiments are mainly focused on the effects of impinging angle of a droplet and surface temperature on the impact dynamics of the droplet. It Is clarified that the droplet exhibits much different behavior depending on the normal momentum of an impinging droplet before impact. At surface temperature In the nucleate boiling regime. the disintegration of a droplet doesn't occur, whereas the deforming droplet adheres to the surface. The spreading and contraction of the liquid film is repeated a couple of times for the horizontal surface but the expanded droplet just slips without noticeable contraction for the inclined surfaces. In the film boiling regime, the impinging droplet spreads over the surface as a liquid film which is separated from the surface by produced vapor. Depending on the magnitude of the normal momentum of the droplet the disintegration into the several irregular shapes of liquid elements occurs for the horizontal and 30o-inclined surfaces, whereas the impinging droplet for the 60o-inclined surface doesn't break up and tends to recover the original spherical shape.

Molecular Dynamics Simulation of Droplet Vaporization (분자 동력학을 이용한 액적 기화 시뮬레이션)

  • Nam, Gun-Woo;Yoon, Woong-Sup
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.121-126
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    • 2003
  • A study of argon droplet vaporization is conducted using molecular dynamics, instead of using traditional methods 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 complete vaporization of a three dimensional 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-spherical droplet is changed into the spherical shape and droplet evaporates. And the droplet radius versus time is calculated with temperature and pressure profile.

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Modeling the Influence of Gas Pressure on Droplet Impact Using a Coupled Gas/liquid Boundary Element Method

  • Park, Hong-Bok;Yoon, Sam S.;Jepsen Richard A.;Heister Stephen D.
    • Journal of ILASS-Korea
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    • v.11 no.2
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    • pp.89-97
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    • 2006
  • An inviscid axisymmetric model capable of predicting droplet bouncing and the detailed pre-impact motion, influenced by the ambient pressure, has been developed using boundary element method (BEM). Because most droplet impact simulations of previous studies assumed that a droplet was already in contact with the impacting substrate at the simulation start, the previous simulations could not accurately describe the effect of the gas compressed between a failing droplet and the impacting substrate. To properly account for the surrounding gas effect, an effect is made to release a droplet from a certain height. High gas pressures are computationally observed in the region between the droplet and the impact surface at instances just prior to impact. The current simulation shows that the droplet retains its spherical shape when the surface tension energy is dominant over the dissipative energy. When increasing the Weber number, the droplet surface structure is highly deformed due to the appearance of the capillary waves and, consequently, a pyramidal surface structure is formed; this phenomenon was verified with our experiment. Parametric studies using our model include the pre-impact behavior which varies as a function of the Weber number and the surrounding gas pressure.

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Development of Measurement System for Contact Angle and Evaporation Characteristics of a Micro-droplet on a Substrate (미소 액적의 접촉각 및 건조 특성 측정 시스템 개발)

  • Kwon, Kye-Si;An, Seung-Hyun;Jang, Min Hyuck
    • Journal of the Korean Society for Precision Engineering
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    • v.30 no.4
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    • pp.414-420
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    • 2013
  • We developed inkjet based measurement system for micro-droplet behavior on a substrate. By using the inkjet dispenser, a droplet, which is as small as few pico-liter in volume, can be jetted and the amount can be controlled. After jetting, the droplet image on the substrate is acquired from side view camera. Then, droplet profile is extracted to measure droplet volume, contact angle and evaporation characteristics. Also top view image of the droplet is acquired for better understanding of droplet shape. The previous contact angle measurement method has limitations since it mainly measures the ratio of height and contact diameter of droplet on a substrate. Unlike previous measurement system, our proposed method has advantages because various behavior of droplet on substrate can be effectively analyzed by extracting the droplet profile.