• 한국분무공학회지
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• 제13권4호
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• pp.187-192
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• 2008

In this study, the mechanisms of binary droplet collision were studied with diesel, ethanol and purified water. The droplet collisions of liquid droplet have been investigated for the same droplet diameter. In order to obtain the digital images of the droplet collision behavior, the experimental equipment was composed of the droplet generating system and the droplet visualization system. The droplets were produced by the vibrating orifice monodisperse generator. The visualization system consisted of a long distance microscope, a light source, and a high speed camera. The outcomes of binary droplet collision can be divided into four regimes, bouncing, coalescence, reflexive separation and stretching separation. The impact angle and the relative velocity of binary droplet are main parameters of collision phenomena, so the transition mechanism of droplet collision can be divided by the impact parameter.

• 한국분무공학회지
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• 제22권3호
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• pp.129-136
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• 2017

Effects of collision angle on heat transfer characteristics of a liquid droplet impinging on a heated wall above the Leidenfrost point temperature were experimentally investigated. The heated wall and droplet temperatures were $506^{\circ}C$ and $100^{\circ}C$, respectively, and the impact angle varied from $20^{\circ}$ to $90^{\circ}$ while the normal collision velocity was constant at 0.27 m/s. The droplet collision behaviors and the surface temperature distribution were measured using synchronized high-speed video and infrared cameras. The major physical parameters influencing upon droplet-wall collision heat transfer, such as residence time, wall heat flux, effective heat transfer area, heat transfer amount, were analyzed. It was found at the constant normal collision velocity that the residence time, wall heat flux and effective heat transfer area were hardly not changed, resulting in the almost constant heat transfer amount.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.559-564
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• 2008

A prediction of binary droplets collision is important in the formation of falling drops and the evolution of sprays. The droplet velocity, impact parameter and drop-size ratio have influence on the interaction of the droplets. By the effect of these parameter, the collision processes are generated with the complicated phenomena. The droplet collision can be classified into four interactions such as the bouncing, coalescence, reflexive separation and stretching separation. In this study, the two-phase flow of the droplet collision was simulated numerically by using the Level Set method. 2D axi-symmetric simulations on the head-on collisions in the coalescence and reflexive separation, and 3D simulation on the off-center collisions in the coalescence and stretching separation were performed. These numerical results showed good agreements with the experimental and analytical results. For tracking the identity of droplets after the collision, transport equation for the volume fraction of the each initial droplet were used. From this, the identities of droplets were analyzed on the collision of droplets having different size.

• 한국분무공학회지
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• 제21권2호
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• pp.78-87
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• 2016

This study experimentally investigated the effects of droplet temperature on the heat transfer characteristics during collision of a single droplet on a heated wall above the Leidenfrost temperature. Experiments were performed by varying temperature from 40 to $100^{\circ}C$ while the collision velocity and wall temperature were maintained constant at 0.7 m/s at $500^{\circ}C$, respectively. Evolution of temperature distribution at the droplet-wall interface as well as collision dynamics of the droplet were simultaneously recorded using synchronized high-speed video and infrared cameras. The local heat flux distribution at the collision surface was deduced using the measured temperature distribution data. Various physical parameters, including residence time, local heat flux distribution, heat transfer rate, heat transfer effectiveness and vapor film thickness, were measured from the visualization data. The results showed that increase in droplet temperature reduces the residence time and increases the vapor film thickness. This ultimately results in reduction in the total heat transfer by conduction through the vapor film during droplet-wall collision.

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

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1891-1896
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• 2004

The present article proposes a new droplet collision model including the stretching separation regime and the formation of satellite droplets. The new model consists of a several equations to calculate the post-collision characteristics of colliding droplets and satellite droplets. These equations are derived from the energy balance of droplets between before and after collision. For binary collision of water droplets, the new model shows good agreement with experimental data for the number of satellite droplets. Nevertheless, it is thought that, in order to guarantee the generality of the new model, the improvements should be performed to consider the effects of the bouncing and the reflexive separation, which is essential process in the collision of hydrocarbon droplets.

• 한국레이저가공학회지
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• 제6권1호
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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.

• 한국분무공학회지
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• 제11권2호
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• pp.75-80
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• 2006

The present article proposes a new droplet collision model including the stretching separation regime and the formation of satellite droplets. The new model consists of several equations to calculate the post-collision characteristics of colliding droplets and satellite droplets. These equations are derived from the energy balance of droplets between before and after collision. For binary collision of water droplets, the new model shows good agreement with experimental data far the number of satellite droplets.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.381-381
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• 2006

• Journal of Welding and Joining
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• 제18권4호
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• pp.55-63
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• 2000

This paper presents a study of the solder bumping process. The theoretical model, based on the variational principle instead of solving the Navier-Stokes equation with moving boundaries, was developed to considered the energy dissipation in semi-solid phase and the approximate solidification time of the molten metal droplet. The simulation results revealed that the developed model could reasonably describe the collision behavior of molten metal with solid surface. Simulations were made with variation of initial droplet temperature, substrate metal and initial substrate temerature.