• Journal of ILASS-Korea
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• v.13 no.4
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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.

• Journal of ILASS-Korea
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• v.22 no.3
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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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• 2008.03b
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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.

• Journal of ILASS-Korea
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• v.21 no.2
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.4
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• pp.353-360
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• 2011

The prediction of binary droplet collisions is important in the formation of falling drops and the evolution of sprays. The droplet velocity, impact parameter, and drop-size ratio influence the interaction between the droplets. The effect of these parameters results in complicated collision phenomena. Droplet collisions can be classified into four types of interactions: bouncing, coalescence, reflexive separation, and stretching separation. In the present study, the interfacial flow problem of the droplet collision was numerically simulated by using the level set method. 2D axisymmetric simulations on the head-on collisions and 3D simulation on the off-center collisions were performed. The numerical results of droplet behavior after the collision agreed well with the experimental and analytical results. The mixing of the mass of the initial droplets after the collision was also predicted by using different species index of colliding droplets.

• Proceedings of the KSME Conference
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• 2004.04a
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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.

• 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.

• Journal of ILASS-Korea
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• v.11 no.2
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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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• 2006.05a
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• pp.381-381
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• 2006

• Journal of Welding and Joining
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• v.18 no.4
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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.