• 대한기계학회논문집B
• /
• 제35권4호
• /
• pp.353-360
• /
• 2011

액적 충돌은 물방울 형성 및 분무 유동 등의 현상을 예측하는데 있어 매우 중요하다. 이러한 액적 충돌은 액적 속도, 충돌 파라미터, 액적 크기비에 영향을 받아, 충돌 후 거동 특성이 결정된다. 충돌 후 액적은 반사, 합일, 스트레칭 분리, 리플렉시브 분리와 같은 거동 특성을 갖는다. 본 연구에서는 레벨셋 방법을 사용하여 충돌 후 액적 거동 특성에 대한 이상유동 해석을 수행하였다. 정면충돌 현상에 대한 2차원 축대칭 해석으로부터 합일 및 리플렉시브 분리 현상을, 비중심충돌 현상에 대한 3차원 해석으로부터 합일, 리플렉시브 분리, 스트레칭 분리 현상을 예측할 수 있었다. 이러한 해석 결과는 기존 실험 및 이론적 연구 결과와 일치하는 결과를 보였다. 또한, 초기 액적의 부피비에 대한 수송 방정식을 사용하여 충돌하는 두 액적의 성분을 추적하였다. 이로부터 크기가 다른 두 액적의 정면충돌에 대한 액적 성분 추적을 통해 액적 거동 및 액적 성분에 대해 분석하였다.

• 한국분무공학회지
• /
• 제16권2호
• /
• pp.104-109
• /
• 2011

The present study investigated experimentally the spreading characteristics of a single liquid impinging on the inclined micro-textured aluminum (Al 6061) surfaces manufactured by using a micro computerized numerical control (${\mu}$-CNC) milling machine. The textured surfaces were composed of patterned micro-holes (diameter of $125\;{\mu}m$ and depth of $125\;{\mu}m$). In our experiment, the de-ionized (DI) water droplet of $4.3\;{\mu}l$ was impinged normally on the non-textured and textured surfaces at two different Weber numbers, and the droplet impinged on the inclined surfaces with different angles. A high speed camera was used to capture sequential digital images for measurement of the maximum spreading distance. It was found that for the textured surface, the measured apparent equilibrium contact angle (ECA) increased up to $105.8^{\circ}$, higher than the measured ECA of $87.6^{\circ}$ for the non-textured (bare) surface. In addition, it is conjectured that the spreading distance decreased because of a liquid penetration during droplet spreading through the holes, the increase in hydrophobicity, and viscous dissipation during impact process.

• 대한기계학회논문집B
• /
• 제36권6호
• /
• pp.609-617
• /
• 2012

충돌, 퍼짐 및 수축을 포함한 나노입자 혼합 액적의 거동에 대한 수치모사를 수행하였다. 기체-액체 상경계면은 벽면에서의 접촉각 이력현상을 포함한 레벨셋 방법을 이용하여 해석하였다. 액적 내부의 나노입자 분포를 해석하기 위하여 물질의 열확산을 반영한 농도 방정식을 해석에 포함하였다. 수치해석 결과로부터 나노 입자의 분포는 온도의 불균일 분포에 크게 영향을 받는 것을 확인하였다. 나노입자의 농도 집중도에 의한 표면 장력 및 접촉각변화 효과에 대한 연구를 수행하였다.

• Bulletin of the Korean Chemical Society
• /
• 제32권6호
• /
• pp.2027-2031
• /
• 2011

Molecular dynamics simulation is used to study the binary collisions of nanometer-sized droplets of argon in the presence of a surrounding gas. By systematically varying the droplet size, the impact parameter and the velocity of collision, the outcome of such collisions were examined and they can be classified into coalescence, separation and shattering. If one of the colliding droplets is half or less than the other in diameter, a shattering is not possible to occur. The threshold of impact parameter for a given separation was studied by adjusting the Weber number. Overall nanoscale droplets were more likely to coalesce than the macroscopic sized ones due to their high surface-to-volume ratio.

• 한국가시화정보학회지
• /
• 제11권3호
• /
• pp.12-16
• /
• 2013

The impact and spreading behaviors of silicon dioxide nanoparticle colloidal suspension droplets were quantitatively visualized using a high-speed imaging system. Millimeter-scale droplets were generated by a syringe pump and a needle. Droplets of different velocity were impacted on a non-porous solid surface. Images were consecutively recorded using a CMOS high-speed camera at 5000 fps (frames per second) for millimeter-scale droplets. Temporal variations of droplet diameter, velocity and maximum spreading diameters were evaluated from the sequential images captured for each experimental condition. Effects of Reynolds number, Weber number, and particle concentration were investigated experimentally.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회B
• /
• pp.2995-3000
• /
• 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.

• International Journal of Ocean System Engineering
• /
• 제1권1호
• /
• pp.28-31
• /
• 2011

An attempt was made to compute the free surface deformation due to the impact of a water droplet. The Cauchy Poisson, i.e. the initial value problem, was solved with the kinematic and dynamic free surface boundary conditions linearized. The zero order Hankel transformation and Laplace transform were applied to the related equations. The initial condition for the free surface profile was derived from a captured video image. The effect of the surface tension was not significant with the water mass used in this investigation. The computed and observed free surface deformations were compared.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집D
• /
• pp.214-219
• /
• 2001

In this study, numerical investigation has been performed on the spreading and solidification of a droplet impacting onto a solid substrate in the thermal spray process. The finite difference method with volume-of-fluid approach is used to analyze the free surface flow and the source-based enthalpy method is employed to model the latent heat release during the solidification. In this work, the numerical model is validated through the comparison of the present numerical result with experimental data available for the flat substrate.

• 한국주조공학회지
• /
• 제13권5호
• /
• pp.476-483
• /
• 1993

The influence of substrate materials on the degree of basal porosity during spray casting process has been investigated. Different conditions of droplet spreading on the substrate were induced by varying the substrate material. Flat sections of cast iron and aluminum have been spray deposited via spray casting process onto an aluminum substrate, a low carbon steel substrate, and an alumina based refractory substrate. Results for cast iron and aluminum sprayed onto the aluminum substrate showed significant improvements in the surface condition and degree of basal porosity with evidence of substrate deformation that round pits ranging from $5{\mu}m$ to $20{\mu}m$ in diameter are distributed on the surface of aluminum substrate. The lowest level of porosity was developed in alumina based refractory material. Several mechanisms for porosity formation were discussed with droplet impact pressure and droplet spreading. Adopting a spray cutting mechanism for removing the periphery of spray cone, porosity level was remarkably decreased.

• 한국정보통신학회논문지
• /
• 제15권8호
• /
• pp.1727-1734
• /
• 2011

본 논문에서는 잉크젯 프린터의 고품질 인쇄 및 인쇄 속도 향상을 위하여 헤드 노즐로부터 분사된 잉크 액적의 위치 제어 정밀도를 향상할 수 있는 방법을 제안한다. 샤프트를 따라 이동하고 있는 캐리지에 탑재된 잉크젯 프린터 헤드의 노즐로부터 분사 신호에 동기되어 분사된 액적의 운동 방정식을 수립하고 이로부터 액적이 용지에 도달하는 궤적을 모델링하여 탄착지점을 예측함으로써 분사 액적을 원하는 지점에 정확하게 탄착시키도록 액적 분사 신호의 타이밍을 제어하는 방법을 제안한다. 캐리지의 위치 신호와의 단순 동기에 기반을 둔 기존의 분사 제어 방법에 비해 본 논문에서 제안하는 방법은 이동하는 캐리지의 속도를 고려하여 분사 타이밍을 보상하므로 캐리지의 속도 변동에 대해서도 보다 정확한 위치 제어가 가능하여 고품질 인쇄를 구현할 수 있을 뿐만 아니라 방향 전환을 위한 가감속 구간에서도 프린팅을 가능하게 하므로 동일한 인쇄 영역에 대해서 캐리지의 이동 경로가 짧아져 인쇄 속도를 향상시킬 수 있다.