• Electrical & Electronic Materials
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• v.5 no.1
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• pp.81-88
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• 1992

본 연구는 고체-액체 계면에서 액체가 유동할때 발생되는 대전에 미치는 계면 활성제의 영향에 대하여 분석한 것이다. 유동전류는 유속의 증가에 따라 선형적으로 증가하고 유온의 증가에 따라 약 46[.deg.C] 이하에서는 증가하고 그 이상에서는 감소한다. 계면활성제의 종도가 증가함에 따라 유동전류는 감소하고 계면활성제의 한 분자내 산소 원자의 수가 많을수록 유동전류의 감소효과가 크게 됨을 제시할 수 있다. 계면활성제가 첨가된 절연유의 전도전류는 온도에 따라 무첨가보다 다소 큰 경향이 있으나 첨가량에는 현저한 차이가 없다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.7
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• pp.695-701
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• 2013

The suppression of a thermocapillary flow (Marangoni flow) by a nonionic surfactant is experimentally investigated for evaporating pure water droplets on hydrophobic substrates. The experiment shows that as the initial concentration of the surfactant increases, the velocity and lifetime of the flow monotonically decrease. The result confirms the no-slip boundary condition at a liquid-air interface, which is explained on the basis of the previous model regarding the effect of surfactants on the no-slip condition. Interestingly, at an initial concentration much less than a critical value, it is found that depinning of the contact line occurs during the early stage of evaporation, which is ascribed to a reduction in the contact angle hysteresis owing to the presence of the Marangoni flow.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.299-307
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• 1991

A unified correlation of the interfacial friction factor for air-water and steam-water flows in inclined rectangular channels has been developed. The correlation was expressed in the form of a power law of the liquid and the gas Reynolds number, and the liquid-to-gas viscosity ratio. In addition, a relation between the equivalent roughness and the intensity of wave height fluctuation of the interface has been investigated. A new dimensionless intensity of fluctuation including a liquid film Reynolds number is proposed. It has been shown that the dimensionless equivalent roughness, which is calculated from the Nikuradse equation, can be uniquely related to this dimensionless intensity of fluctuation for both air-water and steam-water flows.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.475-480
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• 1998

계면면적 밀도는 two-fluid 모델에서 각 상 간의 상호작용에 영향을 주는 중요한 인자로서 이상유동 현상의 해석을 위하여는 이의 적절한 모델링이 필요하다. 계면면적 밀도의 모델링은 크게 상관식에 의존하는 방법론과 수송 방정식을 사용한 이론적인 접근방식으로 개발되어왔다. 후자는 시간적, 공간적으로 변하고 있는 동적 유동조건에 대하여 계면면적 밀도를 효과적으로 예측할 수 있는 방법론으로서 flow regime의 의존성을 줄이거나 없앨 수 있는 장점을 가진다. 계면면적 수송 방정식은 유체입자의 수밀도에 대한 수송 방정식의 통계적인 모델로부터 유도되며 입자들의 상호작용 및 상변화와 관련된 생성항을 포함하고 있다. 본 연구에서는 계면면적 밀도 수송 방정식 및 그 구성 모델들에 대한 연구현황을 정리하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.599-606
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• 1988

Structures of interfacial waves in nearly-horizontal countercurrent stratified air-water flow have been measured by means of a needle contact method. Based upon a statistical analysis for the liquid film distribution, statistical properties of the waves such as mean film thickness, mean wave amplitude and rms value of the wave fluctuation have been calculated. The results show that the film distribution can be described by a Gaussian probability density function for the three-dimensional wave regime. It is also indicated that the mean film thick ness and the rms value of the wave fluctuation increase as gas and liquid flow rates are increased in countercurrent two-phase flow. The dimensionless intensity of the wave fluctuation may be regarded as a function of the Froude number and the dimensionless mean film thickness.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.20 no.1
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• pp.52-63
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• 1994

It was investigated that the effects of surfactant to cosurfactant ratio on the stability and rheological properties of o/w microemulsion. The stability of microemulsion was good in the surfactant to cosurfactant ratio 20/40 - 30/30. In the point of rheological properties, a yield stress meande the inner structure formation was detected and the area of hysteresis loop was increased with increasing of surfactant content of the ratio. The microemulsion prepared by the Microfluidizer was characterized by rheopetic.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.7
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• pp.549-555
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• 2015

A measurement technique of interfacial velocity in air-water separated flow by particle tracking velocimetry using an infrared camera (IR-PTV) was developed. As infrared light with wavelength in the range of 3-5 um could hardly penetrate water, IR-PTV can selectively visualize only the tracer particles existing in depths less than 20 um underneath the air-water interface. To validate the measurement accuracy of the IR-PTV technique, a measurement of the interfacial velocity of the air-water separated flow using Styrofoam particles floating in water was conducted. The interfacial velocity values obtained with the two different measurement techniques showed good agreement with errors less than 5%. It was found from the experimental results obtained using the developed technique that with increasing air velocity, the interfacial velocity proportionally increases, likely because of the increased interfacial stress.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.1
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• pp.116-122
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• 1988

Interfacial shear stresses have been determined for countercurrent stratified flow of air and water in a nearly-horizontal rectangular channel, based upon measurements of pressure drop, gas velocity profiles and mean film thickness. A dimensionless correlation for the interfacial friction factor has been developed as a function of the gas and liquid Reynolds numbers. Equivalent surface roughnesses for the interfacial friction factor have been calculated using the Nikuradse correlation and have been compared with the intensity of the wave height fluctuation on the interface. The results show that the interfacial shear stress is mainly affected by turbulent mixing near the interface due to the wave motion rather than by the roughened surface.

• Journal of the Korean Society for Marine Environment & Energy
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• v.2 no.2
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• pp.70-77
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• 1999

The disturbance of oil-water interface confined between tandem fences caused by a sequence of traveling vortices below the interface is investigated. The traveling vortices are assumed to be those detached from the tip of the fore fence. The potential flow is assumed and the density interface is replaced as a sheet of vortex. The shape of the interface is predicted by tracing a finite number of marker particles placed at the interface. The velocity of the marker particles is determined by the Biot-Savart integral along the vortex sheet plus the contribution from the traveling point vortices. The rate of change of vortex-sheet strength is predicted by using an evolution equation for vorticity. The calculated results obtained for various conditions demonstrate that the large amplitude of interfacial wave following the moving vortek can be generated by the vortices.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.114-122
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• 2015

In the high convective gas flow condition, irregular shaped water waves from which droplet entrainment occurs are generated under horizontally stratified two-phase flow condition. KAERI proposed a new mechanistic droplet entrainment model based on the momentum balance equation consisting of the shear stress, surface tension, and gravity forces. However, this model requires correlation or experimental data of several physical parameters related to the wave characteristics. In the present study, we tried to measure the physical parameters such as wave slope, wave hypotenuse length, wave velocity, wave frequency, and wavelength experimentally. For this, an experiment was conducted in the horizontal rectangular channel of which width, height, and length are, respectively, 40 mm, 50 mm, and 4.2 m. In the present test, the working fluids are chosen as air and water. The PIV technique was applied not only to obtain images for phase interface waves but also to measure the velocity field of the water flow. Additionally, we developed the parallel wire conductance probe for the confirmation of wave height from PIV image. Finally, we measured the physical parameters to be used in the validation of new droplet entrainment model.