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Microscopic Spreading of Nonpolar Perfluoropolyalkylether Film
김민찬,이상백 濟州大學校 産業技術硏究所 2000 산업기술연구소논문집 Vol.11 No.2
The spreading mechanism of nonpolar perfluoropolyalkylehter (PFPE) on carbon surfaces is proposed. For the thin thin-film regime. adsorption-desorption is a main driving force for spreading, and the surface diffusion coefficients increase as the film thickness increases. Two dimensional van der Waals equation is employed to explain the dependency of surface diffusion coefficient on the film thickness. For the thick thin-film regime. the spreading characteristic is determined by the disjoining pressure gradient. The present theoretical analysis explain the dependence of surface diffusion coefficients on film thickness reasonably.
Onset of evaporation-driven gravitational instability in a saline solution
김민찬 한국화학공학회 2021 Korean Journal of Chemical Engineering Vol.38 No.1
The onset time of buoyancy-driven instability in a saline solution where evaporation proceeds through the solution-air interface is analyzed theoretically and numerically. Based on linear stability theory, new stability equations are derived and numerically solved. Also, nonlinear numerical simulations are conducted using FEM solver, COMSOL Multiphysics.® It is clearly shown that as the evaporation proceeds, the height of solution continuously decreases with time. Moreover, as the evaporation proceeds, concentrated saline solution near the evaporating surface induces gravitational instability. The critical time determined from the linear stability analysis explains the numerical simulation results reasonably. The present theoretical and numerical studies present that evaporation-driven instability is governed by the dimensionless evaporation rate, α, and the initial salt concentration, Ra. The present numerical simulations explain the previous experimental plume dynamics in the evaporation-driven instability systems quite well.
위암 환자의 복강경 위절제술 후 발생한 그물막 경색의 임상적 의의
김민찬,정갑중,오종영 대한위암학회 2010 Journal of gastric cancer Vol.10 No.1
목적: 조기위암 환자에서 널리 시행되고 있는 복강경 위절제술은 큰그물막을 부분 절제함으로 그물막 경색의 가능성을 가지고 있다. 이에 저자들은 위암 환자의 복강경위절제술 시행 후 발생한 그물막 경색의 임상적 고찰을시행하였다. 대상 및 방법: 2003년 4월부터 2007년 11월까지 동아대학교 의료원 외과에서 병리조직검사에서 T2 이하의 환자로복강경 위절제술이 시행된 390명의 환자를 대상으로 술 후복부 단층 촬영 사진을 이용하여 그물막 경색을 진단하였다. 위암 데이터 베이스와 환자들의 차트를 이용하여 그물막 경색의 빈도, 발생 위치와 크기 및 증상 여부를 조사하였으며 그물막 경색이 발생하지 않은 환자들의 임상 병리적 특징들과 비교하였다. 결과: 전체 390명 환자 중 그물막 경색은 9명에서 발생(2.3%)하였으며 평균 나이는 57.2세였고 9명 중 남자가 6명여자가 3명이었다. 발생 부위는 상복부 정중과 좌 상복부가 각각 3명이었다. 임상 증상은 배꼽 주위와 좌 상복부에비특이적인 복통이 각 1명에서 나타났으며 9명 모두 술 후복막 전이와 감별이 가능하였다. 그물막 경색군의 환자는비경색군에 비해 수술 전 높은 비만도를 나타내었고(P=0.0230) 위절제 범위에서 위전절제술이 많이 시행된 것으로나타났다(P=0.0011). 결론: 위암 환자의 복강경 위절제술 후 발생하는 그물막경색은 일차성 그물막 경색들과는 상이한 임상적 특징을가지며 복막 재발과는 복부 단층 촬영으로 구별될 수 있다. 향후 다기관 공동 연구를 통하여 보다 더 정확한 임상양상이 규명될 수 있을 것으로 기대된다.
Double diffusive effects on radial fingering in a porous medium or a Hele-Shaw cell
김민찬 한국화학공학회 2018 Korean Journal of Chemical Engineering Vol.35 No.2
Double diffusive effects on the growth of radial viscous fingering in a porous medium or a Hele-Shaw cell were analyzed theoretically. Under linear stability theory, the stability equations were derived in a self-similar domain. The stability equations were transformed using the normal mode analysis and solved analytically and numerically. Regardless of the diffusivity ratio, Le, the Péclet number, Pe, makes the system unstable, i.e., accelerates the growth of instabilities. The double diffusive effects on the growth of the instabilities were strongly dependent on the viscosity distribution. If the displaced phase has stable viscosity distribution, as Le increases, the system becomes unstable regardless of the magnitude of Pe. However, as Le increases, the growth of the instabilities is suppressed if the displaced phase has unstable viscosity distribution.
김민찬 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.1
The effect of a magnetic field on the early stages of Soret-driven convection of a nanoparticle suspension with large negative separation ratio χ confined within a Hele-Shaw cell, heated from above, was analyzed. Taking the Lorentz force into account, new stability equations were formulated in a similar (τ, ζ)-domain as well as in a global (τ, z)-domain by introducing the Hele-Shaw Rayleigh number based on the Soret flux (RsH) and the Hele-Shaw Hartmann number (HaH). With and without the quasi-steadiness assumptions, the resulting stability equations were solved analytically by expanding the disturbances as a series of orthogonal functions, and also the numerical shooting method was used. The critical time of the onset of convection and the corresponding wave number were obtained as a function of RsH and HaH. It was found that the magnetic field plays a critical role in the onset of convective instability. The onset time increases with increasing HaH and decreasing RsH. The linear stability limits are independent of the solution methods, if the trial functions for the disturbance quantities are properly chosen. Based on the results of the linear stability analysis, a non-linear analysis was conducted using direct numerical simulations. The non-linear analysis revealed that the convective motion can be apparent far after the linear stability limit.