• Journal of Mechanical Science and Technology
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• 제19권12호
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• pp.2263-2269
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• 2005

The ship wave phenomena in the restricted waterway were investigated by a numerical analysis. The Euler and continuity equations were employed for the present study. The boundary fitted and moving grid system was adopted to enhance the computational efficiency. The convective terms in the governing equations and the kinematic free surface boundary condition were solved by the Constrained Interpolated Profile (CIP) algorithm in order to solve accurately wave heights in far field as well as near field. The advantage of the CIP method was verified by the comparison of the computed results by the CIP and the Maker and Cell (MAC) method. The free surface flow simulation around Wigley hull was performed and compared with the experiment for the sake of the validation of the numerical method. The present numerical scheme was applied to the free surface simulation for various canal sections in order to understand the effect of the sectional shape of waterways on the ship waves. The wave heights on the side wall and the shape of the wave patterns with their characteristics of flow are discussed.

• 한국수소및신에너지학회논문집
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• 제22권6호
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• pp.749-758
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• 2011

The present work explores the performance and operation limit of electrodialysis cell for HI concentration in sulfur iodine thermochemical hydrogen production process, For this purpose, the electrodialysis cell was assembled with Nafion 117 as a PEM membrane and two activated carbon papers as the electrodes. HIx solution was prepared with composition of HI: $I_2$: $H_2O$ = 1: 0.5~2.5: 5.2 in molar ratio. The cell and its peripheral apparatus were placed in the specially designed convective oven in order to uniformly maintain the operation temperature. As operation temperature increased, the amount of water transport from anode to cathode increased, thus reducing HI molarity in catholyte. Meanwhile, the current efficiency was constant as about 90 %, irrespective of temperature change. The cell voltage increased with initial $I_2$ mole ratio as well as anolyte to catholyte mole ratio. Moreover the cell voltage overshot took place within 10 h cell operation, which is due to the $I_2$ precipitation inside the cell. From the analysis of $I_2$ mole ratio in the anolyte, it is noted that operation limit (in $I_2$ mole ratio) of the electrodialysis cell, arising from was measured to be 3.2, which is much lower than bulk solubility limit of 4.7.

• 한국결정성장학회지
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• 제33권3호
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• pp.110-115
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• 2023

브로민화 수은(I)(Hg₂Br₂) 물리적 증착법 공정에서 구성요소 B의 분압, P_B를 40 Torr에서 200 Torr로 증가시켰을 때 1개의 셀(unicell)이 결정성장영역에서 기체상 공간의 중심으로 이동함을 보여주고 있다. P_B = 40 Torr에서는 경계층 흐름이 지배적이고, P_B = 200 Torr에서는 코어영역흐름(core region)을 보이고 있다. 고려되는 물리적 증착법 공정에서 P_B = 40 Torr와 P_B = 200 Torr에서 1개(single)의 셀(cell) 형태로 3차원의 유동의 흐름과 x, y 직교 중심축에 대하여 비대칭 유동흐름을 나타내고 있다. 소스와 결정 영역 사이의 임계 온도차는 약 30 K입니다. Hg₂Br₂의 총 몰 플럭스는 임계값에 도달할 때까지 온도차에 따라 증가한다. 임계 총 몰 플럭스에서 총 몰 플럭스는 갑자기 감소한다.

• 환경생물
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• 제22권1호
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• pp.75-82
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• 2004

2000년부터 2002년까지 통영 바다목장 해역 5개 정점표층수와 저층수에서 종속영양세균의 개체수를 평판계수법으로 측정하여 종속영양세균군집의 계절별 변동추이를 비교 분석하고, 우점종을 선별하여 동정하였다. 7월과 8월의 하절기에 채수한 해수에는 봄 혹은 가을 및 겨울에 채수한 해수에 비하여 모든 정점에서 훨씬 더 많은 종속영양세균이 검출되었다. 저층수에 비하여 표층수에서 종속영양세균의 수가 더 많았으나 동절기(2001년 12월과 2002년 2월)에는 해수 온도가 낮으며 해수의 대류가 느려짐에 따라 부유물질이 저층에 축적되는 관계로 저층수의 종속영양세균의 수가 표층수의 경우 보다 오히려 더 많이 검출되었다 해수 내 종속영양세균의 수와 태풍의 빈도는 뚜렷한 상관관계를 보이지 않아 태풍의 빈도 이외에 태풍의 진로와 강도 및 태풍을 수반하는 집중 호우와 해수의 온도 변화가 종속영양세균의 수에 영향을 미치는 것으로 판단되었다. 통영 바다목장 해역의 종속영양세균의 우점종은 Pseudomonas fluorescens, Pseudomonas stutzeri, Acinetobucter lwoffii 및 Sphingomonas paucimobilis로 동정되었다.

• 대한기계학회논문집B
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• 제21권2호
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• pp.252-263
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• 1997

Steady-state two-dimensional natural convective heat transfer in horizontal cylindrical annuli was studied by solving the governing equations based on the primitive variables. Emphasis was put on the occurrence of the multiple solutions at a given set of parameter values, and on the determination of the bifurcation points at which those multiple solutions begin to branch out. The multicellular flow pattern from the results of melting process in an isothermally heated horizontal cylinder for high Rayleigh numbers, was used as initial guesses for the field variables. This was succeeded in new bifurcation point to tetracellular solutions for an identical set of parameter variables of previous works. The close examination of flow pattern transition around bifurcation point was also conducted. It was found that the mechanisms of flow transition are different depending on the critical Rayleigh number of bifurcation point.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 추계학술대회
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• pp.407-410
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• 2006

Selection of flow channel in the separation plate of PEMFC is very important parameter to improve its performance and reduce parasite loss. Flow patterns in the channel have great influence on the transport of hydrogen and all and water generated from electrochemical reaction in diffusion layer In this study, fluid flow in flow channel with parallel and interdigitated patterns are simulated three dimensionally on full flow domain including anode and cathode electrode together. The numerical results show that the fuel cell with interdigitated flow channel represents better performance than that with parallel flow channel due to its strong convective transport across the gas diffusion layer. But the pressure drop in parallel flow channel is much more than that in nterdigitated flow channel. The effect of temperature and stoichiometric number on performance can be calculated and analyzed as well.

• Nuclear Engineering and Technology
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• 제41권8호
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• pp.1045-1052
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• 2009

A calculation model is developed to predict the transient free surface flow on the containment floor following a loss-of-coolant accident (LOCA) of pressurized water reactors (PWR) for the use of debris transport evaluation. The model solves the two-dimensional Shallow Water Equation (SWE) using a finite volume method (FVM) with unstructured triangular meshes. The numerical scheme is based on a fully explicit predictor-corrector method to achieve a fast-running capability and numerical accuracy. The Harten-Lax-van Leer (HLL) scheme is used to reserve a shock-capturing capability in determining the convective flux term at the cell interface where the dry-to-wet changing proceeds. An experiment simulating a sudden break of a water reservoir with L-shape open channel is calculated for validation of the present model. It is shown that the present model agrees well with the experiment data, thus it can be justified for the free surface flow with accuracy. From the calculation of flow field over the simplified containment floor of APR1400, the important phenomena of free surface flow including propagations and interactions of waves generated by local water level distribution and reflection with a solid wall are found and the transient flow rates entering the Holdup Volume Tank (HVT) are obtained within a practical computational resource.

• 한국결정성장학회지
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• 제23권1호
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• pp.20-26
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• 2013

Special attention in the role of convection in vapor crystal growth has been paid since some single crystals under microgravity environments less than 1 $g_0$ exhibits a diffusive-convection mode and much uniformity in front of the crystal regions than a normal gravity acceleration of 1 $g_0$. The total molar fluxes show asymmetrical patterns in interfacial distribution, which indicates the occurrence of either one single or more than one convective cell. As the gravitational level decreases form 1 $g_0$ down to $1.0{\times}10^{-4}\;g_0$, the intensity of convection, indicative of the maximum molar fluxes, is reduced significantly for ${\Delta}T=30K$ and 90 K. The total molar fluxes decay first order exponentially with the partial pressure of component B, PB (Torr) for 20 Torr ${\leq}PB{\leq}$ 300 Torr, and two gravity accelerations of $g_y=1\;g_0$ and 0.1 $g_0$.

• 한국결정성장학회지
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• 제16권5호
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• pp.203-209
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• 2006

For $P_B=50,\;{\Delta}T=10K$, Ar=5, Pr=2.36, Le=0.015, Pe=1.26, Cv=1.11, the intensity of solutal convection (solutal Grashof number $Grs=3.44x10^4$) is greater than that of thermal convection (thermal Grashof number $Grt=1.81x10^3$) by one order of magnitude, which is based on the solutally buoyancy-driven convection due to the disparity in the molecular weights of the component A($Hg_2Cl_2$) and B(He). With increasing the partial pressure of component B from 10 up to 200 Torr, the rate is decreased exponentially. The convective transport decreases with lower g level and is changed to the diffusive mode at 0.1 $g_0$. In other words, for regions in which the g level is 0.1 $g_0$ or less, the diffusion-driven convection results in a parabolic velocity profile and a recirculating cell is not likely to occur. Therefore a gravitational acceleration level of less than 0.1 $g_0$ can be adequate to ensure purely diffusive transport.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.55-63
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• 1995

The flow field around a high-speed train including cross-wind effects has been simulated. This study solves 3-D unsteady incompressible Navier-Stokes equations in the inertial frame using the iterative time marching scheme. The governing equations are differenced with 1st-order accurate backward difference scheme for the time derivatives, 3th-order accurate QUICK scheme for the convective terms and 2nd-order accurate central difference scheme for the viscous terms. The Marker-and-Cell concept was applied to efficiently solve continuity equation, which is differenced with 2nd-order accurate central difference scheme. The 4th-order artificial damping is added to the continuity equation for numerical stability. A C-H type of elliptic grid system is generated around a high-speed train including ground. The Baldwin-Lomax turbulent model was implemented to simulate the turbulent flows. To validate the present procedure, the flow around a high speed train at constant yaw angle of $45^{\circ}\;and\;90^{\circ}$ has been simulated. The simulation shows 3-D vortex generation in the lee corner. The flow separation is also observed around the rear of the train. It has concluded that the results of present study properly agree with physical flow phenomena.