• 마이크로전자및패키징학회지
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• 제18권2호
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• pp.11-15
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• 2011

폴리머의 흡습문제를 해석하기 위해 흡습확산 지배방정식과 열전달 방정식을 고찰하였다. 두 방정식의 동일 한 형식의 편미분방정식이기 때문에 상사의 법칙을 적용하여 물체가 등온 하중조건을 받고 있을 때 단일 매질의 확산문 제를 상용유한요소코드에 의해 수치적으로 해석하였다. 여러 소재로 구성된 매체는 흡습질량이 접착면에서 불연속 특성 을 갖기 때문에 확산해석에 상사법칙을 직접적으로 적용할 수 없으나 흡습관련 소재 특성이 온도만의 함수인 소재로 구 성된 매체에서 흡습확산 문제는 접착면에서 연속성을 가지고 있는 압력비를 고려함으로써 해석하였다. 실리콘-비전도성 수지 접합체의 측정된 흡습 변화량은 접합면을 경계조건으로 하고 단일 매체에 대한 해석 결과와 매우 근접한 결과를 보였으나, 복합체로 해석한 결과는 흡습시간이 경과할수록 점점 큰 오차가 발생하였다.

• 한국수소및신에너지학회논문집
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• 제18권4호
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• pp.422-431
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• 2007

Polymer electrolyte membrane fuel cell(PEMFC) is very interesting power source due to high power density, simple construction and operation at low temperature. But it has problems such as high cost, improvement of performance and effect of temperature. These problems can be approached to be solved by using mathematical models which are useful tools for analysis and optimization of fuel cell performance and for heat and water management. In this paper, the present work is to develop an electrochemical model to examine the electrochemical process inside PEM fuel cell. A complete set of considerations of mass, momentum, species and charge is developed and solved numerically with proper account of electrochemical kinetics. When depth of gas channel becomes thinner, diffusion of reactant makes well into gas diffusion layer(GDL) and the performance increases. Although at low current region there is little voltage difference between experimental data of PEM fuel cell and numerical data. When the porosity size of gas diffusion layer for PEM fuel cell is bigger, oxygen diffusion occurs well and oxygen mass fraction appears high in catalyst layer.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.409-412
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• 2008

본 연구에서는 라텍스개질 콘크리트 내에서 보강철근의 부식개시시기를 평가하였다. 촉진시험은 LMC 배합의 확산계수와 시간의존적 확산계수를 결정하기 위하여 실시하였으며, 평균염화물확산계수를 평가하였다. 평균 염화물이온 확산계수로부터 보강철근의 깊이에서의 임계염화물량에 도달하는 시간을 계산하였다. 임계염화물량에 도달하는 시간을 통하여 부식개시시를 계산하였으며, 이를 통하여 보수시기를 계산하였다. 시험결과 LMC 내에서 염화물 이온확산, 보강철근의 부식개시시기는 라텍스첨가비 및 물-시멘트비에 의하여 영향을 받았다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.137-142
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• 2001

The effects of acoustic excitation with various frequencies for combustion air as well as fuel on the combustion emission and local NO concentration in diffusion flame were investigated experimentally. It was studied to investigate the effects of combination between four frequencies for the fuel and various frequencies for the combustion air. The better characteristic for NO emission was revealed by acoustic exciting with frequencies for the air and the fuel excited at 0Hz and 120Hz and the generation of CO was decreased at low frequency for fuel and the excited combustion air. The amount of combustion emission could be controlled by acoustic exciting of the combustion air. And when both fuel and air are excited by some frequencies, the diffusion flame was affected by frequency which excited fuel in the middle of the flame and by air-exciting frequency at both sides of the flame. The local NO in the flame was generated much less at the condition that fuel was excited by frequencies than the condition was not.

• 대한기계학회논문집B
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• 제21권11호
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• pp.1527-1537
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• 1997

Extinction characteristics and acoustic response of hydrogen-air diffusion flames at various pressures are numerically studied by employing counterflow diffusion flame as a model flamelet in turbulent flames in combustion chambers. The numerical results show that extinction strain rate increases linearly with pressure and then decreases, and increases again at high pressures. Thus, flames are classified into three pressure regimes. Such nonmonotonic behavior is caused by the change in chemical kinetic behavior as pressure rises. The investigation of acoustic-pressure response in each regime, for better understanding of combustion instability, shows different characteristics depending on pressure. At low pressures, pressure-rise causes the increase in flame temperature and chain branching/recombination reaction rates, resulting in increased heat release. Therefore, amplification in pressure oscillation is predicted. Similar phenomena are predicted at high pressures. At moderate pressures, weak amplification is predicted since flame temperature and chain branching reaction rate decreases as pressure rises. This acoustic response can be predicted properly only with detailed chemistry or proper reduced chemistry.

• 한국기계가공학회지
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• 제19권2호
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• pp.9-17
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• 2020

In this study, the surface changes of titanium alloy using laser surface treatment and the surface analysis using laser-induced plasma spectroscopy were carried out. The laser surface treatment induced changes in surface roughness and the diffusion of atmospheric elements. Excessive melting or less melting caused roughness changes, but when moderate levels of energy were applied, a smoother surface could be obtained than the initial surface. In the process, the diffusion of atmospheric elements took place. To analyze the diffusion of atmospheric elements with respect to surface morphology, the surfaces were re-shaped with grinding. In this experimental conditions, the effect of plasma formation by surface roughness was identified. Compensated plasma signals for the material properties were obtained and analysed by removing the background plasma signal.

• 터널과지하공간
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• 제8권3호
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• pp.194-199
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• 1998

본 연구는 석회석 노천채광장의 발파 분진이 주변을 통과하는 특고압 선로에 어느정도 비산 퇴적할 것인지, 어떤 문제를 일으킬 것인지를 평가하기 위한 연구였다. 발파 현장이 분진 발생량 및 입도분포는 그간의 연구 실적도 있고 계측도 가능하지만 얼마만큼의 분진이 어느 정도 거리까지 비산 퇴적할 것인지를 예측하기란 매우 어려운 일이다. 따라서 본 연구에서는 최근 개발한 바 있는 수치유체역학(CFD)을 이용한 3차원 유체거동 해석 프로그램(3D-Flow)을 이용하여 송전선로에 미치는 영향을 예측하는 시도를 하였다. 지형조건, 기상조건에 따른 시뮬레이션을 통하여 석회석 분진은 송전선로에 큰 영향을 미치지 않을 것으로 판단 되었다.

• 한국입자에어로졸학회지
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• 제8권1호
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• pp.29-35
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• 2012

The Faraday cup electrode of different size has been developed and evaluated to investigate the diffusion effect of particles by Brownian motion in a particle beam mass spectrometer(PBMS). Particles which focused and accelerated by aerodynamic lens are charged to saturation in an electron beam, and then deflected electrostatically into a Faraday cup detector for measurement of the particle current. The concentration of particles is converted from currents detected by Faraday cup. Measurements of particle current as a function of deflection voltage are combined with measured relationships between particle velocity and diameter, charge and diameter, and mass and diameter, to determine the particle size distribution. The particle currents were measured using 5, 10, 20, 40 mm sized Faraday cup that can be move to one direction by motion shaft. The current difference for each sizes as a function of position was compared to figure out diffusion effect during transport. Polystyrene latex(PSL) 100, 200 nm sized standard particles were used for evaluation. The measurement using 5 mm sized Faraday cup has the highest resolution in a diffusion distance and the smaller particles had widely diffused.

• Computers and Concrete
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• 제21권4호
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• pp.471-484
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• 2018

Refined analysis depicting mass transportation and physicochemical reaction and reasonable computing load with acceptable DOFs are the two major challenges of numerical simulation for concrete durability. Mesoscopic numerical simulation for chloride diffusion considering binder, aggregate and interfacial transition zone is unable to be expended to the full structure due to huge number of DOFs. In this paper, a multiscale approach of combining both mesoscopic model including full-graded aggregate and equivalent macroscopic model was introduced. An equivalent conversion of chloride content at the Interfacial Transition Layer (ITL) connecting both models was considered. Feasibility and relative error were discussed by analytical deduction and numerical simulation. Case study clearly showed that larger analysis model in multiscale model expanded the diffusion space of chloride ion and decreased chloride content in front of rebar. Difference for single-scale simulation and multiscale approach was observed. Finally, this paper addressed some worth-noting conclusions about the chloride distribution and rebar corrosion regarding the configuration of rebar placement, rebar diameter, concrete cover and exposure period.

• 한국자기공명학회논문지
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• 제20권2호
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• pp.61-65
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• 2016

Undesirable convective flow in an NMR tube inhibits the accurate measurement of diffusion coefficients by NMR spectroscopy. To minimize the convection effects, various methods have been suggested, and it has been known that the use of sample rotation can be useful. However, it has not been clearly examined that the convection suppressing effect of the sample rotation under the different spinning speeds. In this study, the relation between convective flow and the sample rotation was investigated using PGSE NMR diffusion experiments to reveal the feasibility for controlling the convective flow in an NMR tube by sample rotation itself. The viscosity effect was also examined using solvents with four different viscosities, acetone-$d_6$ chloroform-d, pyridine-$d_5$, and $D_2O$. The sample rotation showed apparent convection suppressing effects at all temperature range for the low viscosity solvents, acetone-$d_6$ and chloroform-d, even at the faster than 5 Hz spinning rate. The similar patterns were also observed for pyridine-$d_5$ and $D_2O$, which have higher viscosity. This effect was observed even at high temperatures where convective flow arises conspicuously.