• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.362-364
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• 2010

Shock wave interaction with droplet-gas medium is investigated in this paper. In the present computation, the shock wave is initially started in a pure gas and reflected from the wedge to interact with the droplet-ridden gas flows. We used the compressible two-fluid two-phase model that is solved by the two-fluid version of the HLL scheme. The interfacial drag force and heat transfer were included to model the interaction between continuous and dispersed phases. The parametric effect of void fraction on the shock wave reflection in the two-phase media was investigated.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.109-114
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• 2010

Interface tracking of two phase is significant to analyze multi-phase phenomena. The VOF(Volume of Fluid) and level set are well known interface tracking method. However, they have limitations to solve compressible flow and incompressible flow at the same time. CIP(Cubic Interpolate Propagation) method is appropriate for considering compressible and incompressible flow at once by solving the governing equation which is divided up into advection and non-advection term. In this article, we analyze the droplet impingement according to various We number using improved CIP method which treats nonlinear term once more comparison with original CIP method. Furthermore, we compare spread radius after droplet impingement on the wall with the experimental data and original CIP original CIP method, and it reduces the mass conservation error which is generated in the numerical analysis comparison with original CIP method.

• 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.

• Journal of the Korean Society of Visualization
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• v.8 no.4
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• pp.43-47
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• 2010

We demonstrate the droplet bistability in a microchannel which has two symmetric necks that operate as capillary valves. It is shown that there are certain flow conditions, determined by droplet velocity and droplet size, to achieve bistability. Droplet bistabililty allows simple but precise control of droplet at a bifurcation channel. Therefore, by an appropriate channel design to induce droplet bistability, we can distribute droplets at a junction passively in the manner of perfect alternation and perfect switching in the choice of the outlets.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.10
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• pp.1025-1033
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• 2001

A scaling analysis is provided which predicts the sliding velocity of a liquid drop down an inclined surface. The analysis is based on the balance of the gravitational work rate that drives the drop sliding and the resistances by capillary and viscous forces. The capillary resistance is accounted for via the contact angle hysteresis, which is quantified by measuring the critical inclination causing the drop to start sliding. The sliding of the drop is governed by the rate of the viscous dissipation of the Stokes flow. The analysis result in its limit form for small contact angles is consistent with previous results. In the experiments to verify the analysis results, the measured sliding velocity of various liquid drops are shown to obey the predictions made in this study.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2658-2663
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• 2008

In the present study, we designed a microfluidic flatform that generates monodisperse droplets with diameters ranging from hundreds of nanometers to several micrometers. To generate fine droplets, T-junction and flow-focusing geometry are integrated into the microfluidic channel. Relatively large aqueous droplets are generated at the upstream T-junction and transported toward the flow-focusing geometry, where each droplet is broken up into the targeted size by the action of viscous stresses. Because the droplet prior to rupture blocks the straight channel that leads to the flow-focusing geometry, it moves very slowly by the pressure difference applied between the advancing and receding regions of the moving droplet. This configuration enables very low flow rate of inner fluid and higher flow rate ratio between inner and outer fluids at the flow-focusing region. It is shown that the present microfluidic device can generate droplets with diameters about 1 micrometer size and standard deviation less than 3%.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2568-2573
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• 2008

A drop impact on the liquid film/pool generates several phenomena such as the drop floating, bouncing, formation of vortex ring, jetting, bubble entrapment and splashing. These phenomena depend on the impact velocity, the drop size, the drop properties and the liquid film/pool thickness. These parameters can be summarized by four main dimensionless parameters; Weber number, Ohnesorge number, Froude number and non-dimensional film/pool thickness. In the present study, the phenomena of the splashing and bubble entrapment due to the drop impact on the liquid film/pool were numerically investigated by using a Level Set method for the sharp interface tracking of two distinct phases. After the drop impact, the splashing phenomena with the crown formation and spreading were predicted. Under the specific conditions, the bubble entrapment at the base of the collapsing cavity due to the drop impact was also observed. The numerical results were compared to the available experimental data showing good agreements.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.2
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• pp.103-110
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• 2011

A two-dimensional immiscible droplet deformation phenomena on moving wall in a channel has been investigated by using lattice Boltzmann method involving two-phase model. The dependence of the deformation of the droplet with different sizes on the contact angle and the velocity of bottom wall has studied. When the bottom wall starts to move, the deformation of the droplet occurs. For the largest bottom wall velocity, eventually, the deformation of the droplet is classified into the three patterns according to the contact angle.

• Clean Technology
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• v.25 no.1
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• pp.19-32
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• 2019

As regional air pollution gets worse by the sulfur oxides emitted from various types of vessels passing through the many countries, the International Maritime Organization establishes the emission control areas and regulates sulfur dioxide in those areas. In order to satisfy these regional regulations, the fuel selection method and the exhaust gas post-treatment device are applied to the ships. Due to the economic reasons, the post-treatment method of exhaust gas for reducing the amount of sulfur oxides discharged is mainly preferred. The scrubber which is dominantly used in the ships are the spray type system where the sprayed liquid drops used for capturing the soluble sulfur dioxides in the exhaust gas. The performance of the spray type system depends on the size distribution of the sprayed droplets. In order to evaluate this performance, we designed counterflow type scrubber and cyclone scrubber and evaluated the desulfurization efficiency and the amount of droplet evaporation according to the size of each droplet by using computational fluid dynamics. The Eulerian-Eulerian analysis method was used because the scrubber had a gas-liquid two-phase flow inside the scrubber. When the diameter of the droplet was $100{\mu}m$, $300{\mu}m$, $500{\mu}m$ and $700{\mu}m$. As a result, both of scrubbers showed high desulfurization efficiency and low evaporation amount at $500{\mu}m$ and $700{\mu}m$.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.2
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• pp.39-45
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• 2004

Experiments were performed in a two-phase swirling spray facility that has been described elsewhere. Measurements of spray transport and drop size distribution are analyzed over wide ranges of air to liquid mass flow ratios, utilizing four different internal mixing pneumatic nozzles. The spatial distributions of mean velocities. fluctuating velocities, and velocity-diameter correlation were quantitatively analyzed. Also, the exponential correlation curves were obtained with ALR along the spray centerline, which indicated an approximately identical formulation regardless of ALR. It indicated that the atomization characteristics were remarkably superior in the case of 30o of swirl angle with higher ALR. Among other things. nozzle configuration is one of the significant parameters affecting spray phenomena from an internal mixing nozzle. Turbulence intensities are increasingly degenerated with an increase of nozzle configuration, allowing a rapid increment of drop size distribution.