• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.4
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• pp.71-78
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• 2005

The vaporization characteristics of a liquid heptane droplet in a supercritical nitrogen flow is numerically analyzed. The present model can account for real gas effects, liquid-phase internal circulation, variable thermodynamic properties and high-pressure effects. Time marching method with preconditioning scheme is employed to handle the low Mach number flows in dense heptane droplet region. Computations are made for the wide range of convective velocity and ambient pressure. Numerical results indicate that the droplet deformation becomes stronger by increasing the Reynolds number and it becomes relatively weak by increasing the pressure.

• Journal of ILASS-Korea
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• v.5 no.3
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• pp.37-44
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• 2000

High velocity, gas-assisted liquid drop trajectories were investigated under well-controlled experimental conditions at elevated gas densities and room temperature. A monodisperse stream of drops which are generated by a vibrating-orifice drop generator were injected into a transverse high velocity gas stream. The gas density and air jet velocity were adjusted independently to keep the Weber numbers constant. The Weber numbers studied were 72, 148, 270, 532. The range of experimental conditions included studied the three drop breakup regimes previously referred as bag, stretching/thinning and catastrophic breakup regimes. High-magnification photography and conventional spray field photographs were taken to study the microscopic breakup mechanisms and the drop trajectories in high velocity gas flow fields, respectively. The parent drop trajectories were affected by the gas density and the gas jet velocities and do not show similarity with respect to the either Weber or the Reynolds number, as expected.

• Journal of ILASS-Korea
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• v.9 no.4
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• pp.83-89
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• 2004

Vaporization characteristics of a liquid heptane droplet in high-pressure and temperature flow field are numerically studied. Variable thermodynamic and transport properties and high-pressure effects are taken into account in order to consider real gas effects. Droplet Vaporization in convective environments was investigated on the basis of droplet vaporization in quiescent and convective environment. In quiescent environments, droplet lifetime is directly proportional to pressure at the subcritical temperature range but it is inversely proportional to pressure at the supercritical temperature range. In convective environment, droplet deformation becomes stronger by increasing Reynolds number due to increase of velocity while droplet deformation is relatively weak at a higher pressure for the same Reynolds number cases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.4
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• pp.337-346
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• 2014

This study aimed to understand the mode characteristics of a droplet subject to periodic forced vibration and the detachment of a droplet placed on a plate surface. An surface was coated with Teflon to clearly observe the behavior of a droplet. The contact angle between the droplet and surface and the hysteresis were found to be approximately $115^{\circ}C$ and within $25^{\circ}C$, respectively. The coating process was performed in a clean room that had an environment with a low level of contaminants and impurities such as air dust, detergents, and particles. To predict the resonance frequency of a droplet, theoretical and experimental approaches were applied. Two high-speed cameras were configured to acquire side and top views and thus capture different characteristics of a droplet: the mode shape, the detachment, the separated secondary droplet, and the waggling motion. A comparison of the theoretical and experimental results shows no more than 18 discrepancies when predicting the resonance frequency. These differences seem to be caused by contact line friction, nonlinear wall adhesion, and the uncertainty of the experiment. For lower energy inputs, the contact line of the droplet was pinned and the oscillation pattern was axisymmetric. However, the contact line of the droplet was de-pinned as the oscillation became more vigorous with increased energy input. The size of each lobe at the resonance frequency is somewhat larger than that at the neighboring frequency. A droplet in mode 2, one of the primary mode frequencies, exhibits vertical periodic movement as well as detachment and secondary ejection from the main droplet.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.489-494
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• 2013

This study aims to understand the mode characteristics of a droplet under a periodic forced vibration. To predict the resonance frequency of a droplet, theoretical and experimental approaches were employed. A high-speed camera was used to capture the various deformation characteristics of a droplet-mode shape, detachment, separated secondary droplet, and skewed deformation. The comparison between the theoretical and the experimental approaches shows a ~10% discrepancy in the prediction of the resonance frequency, which appears to be caused by the effect of contact line friction, nonlinear wall adhesion, and experimental uncertainty. Owing to contact-line pinning and smaller amplitude, the droplet shape becomes symmetric and the size of each lobe at the resonance frequency exceeds that at the neighbor, which is out of resonance.

• Korean Chemical Engineering Research
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• v.56 no.5
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• pp.761-766
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• 2018

Droplet-based microfluidic device has led to transformational new approaches in various applications including materials synthesis and high-throughput screening. However, efforts are required to enhance the production rate to industrial scale because of low production rate in a single droplet generator. In here, we present a method for enhancing production rate of monodisperse droplets via parallelization of flow-focusing generators. For this, we fabricated a three-dimensional monolithic elastomer device (3D MED) that has the 3D channel structures in a single layer, using a double-sided imprinting method. We demonstrated that the production rate of monodisperse droplet is increased by controlling the flow rate of continuous and dispersed phases in 3D MED with 8 droplet generators. Thus, we anticipate that this microfluidic system will be used in wide area including microparticle synthesis and screening system via encapsulation of various materials and cells in monodisperse droplets.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.6-9
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• 2011

In this study, the two-phase incompressible flow in two-dimensional channel considering the effect of surface tension is simulated using an improved level-set method. Quadratic element is used for solving the continuity and Navier-Stokes equations to avoid using an additional pressure equation, and Crank-Nicholson scheme and linear element are used for solving the advection equation of the level set function. Direct approach method using geometric information is implemented instead of the hyperbolic-type partial differential equation for the reinitializing the level set function. The benchmark test case considers various arrays of defomable droplets under different flow conditions in straight channel. The deformation and migration of the droplets are computed and the results are compared very well with the existing studies.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.517-518
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• 2010

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.689-690
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• 2009

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.703-704
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• 2012