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Behavior of Oil-Water Interface between Tandem Fences
강관형,이정묵,Kang Kwan Hyoung,Lee Choung Mook 한국해양환경·에너지학회 1999 한국해양환경·에너지학회지 Vol.2 No.2
와류에 의한 이중 유벽 사이에 가두어진 기름층과 물의 계면의 교란에 대하여 고찰하였다. 와류는 전부 유벽의 끝에서 발생되는 것으로 간주하였다. 유동장의 해석을 위하여 포텐셜 유동 가정하에 계면을 와 특이점 분포면(vortex sheet)으로 나타내었다. 계면의 형상은 계면에 유한개의 가상의 입자를 설정한 후 그 위치를 추적하여 추하였다. 입자의 속도는 와 분포면에 의해서 유발되는 속도를 Biot-Savart 적분을 통해 구하고 여기에 이동하는 점와류(point vortex)에서 유발되는 속도를 합하여 구하였다. 시간에 대한 와 분포면상의 와도의 변화는 계면에서의 와도 방정식을 해석하여 구하였다. 여러 조건하에서 계산된 결과를 바탕으로 상당한 파고의 계면파가 전부 유벽 하단에서 발생되는 와류에 의하여 생성될 수 있음을 입증하였다. 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.
전기습윤 현상에서의 선장력과 전기 이중층의 영향에 대한 해석
정상국,강관형,이정묵,강인석,Chung, Sang-Kug,Kang, Kwan-Hyoung,Lee, Choung-Mook,Kang, In-Seok 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.7
The Lippmann-Young equation has been widely used in electrowetting to predict the contact-angle change of a droplet on a insulating substrate with respect to the externally-applied electrical voltage. The Lippmann-Young equation is derived by assuming a droplet as a perfect conductor, so that the effect of the electrical double layer and the line tension are not taken into account. The validity of the assumption has never been checked before, systematically. In the present investigation, a modified Lippmann-Young equation is derived taking into account of the effect of the electrical double layer and the line tension. To assess their influence on contact-angle change in electrowetting, the electrostatic field around the three-phase contact line is analyzed by solving the Poisson-Boltzmann equation numerically. The validity of the numerical methods is verified by using the past theoretical results on the electrostatic field around a wedge-shaped geometry, which shows fairly good agreement. The results of the present investigation clearly indicate that the effect of the electrical double layer and the line tension is negligible for a millimeter-sized droplet. On the other hand, for a micron-sized droplet, the effect of the line tension can become a dominating factor which controls the contact-angle change in electrowetting.
증발 액적 내부 유동의 스케일링 관계 및 액적 표면 점착 조건의 영향
이희웅(Hee Woong Lee),강관형(Kwan Hyoung Kang),이정묵(Choung Mook Lee),이상준(Sang Joon Lee) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
We analyzed the Rayleigh-type natural convection inside an axisymmetric, two-element evaporating droplet numerically, and the numerical results are verified by experimental results obtained by PIV technique. We found experimentally that the boundary condition on the droplet surface is close to the no-slip condition, which is assumed to be due to the Marangoni effect. The effect of boundary condition on the flow and concentration distribution is discussed based on the numerical results. From the numerical results verified by the experimental results, it is found that the governing scaling factor for the flow field inside a naturally evaporating droplet is the Rayleigh number. It is also shown, as predicted before, that there exists a pseudosteady condition for the velocity field.