• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.46-53
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• 2011

Water is continuously produced in polymer electrolyte membrane fuel cell (PEMFC), and is transported and exhausted through polymer electrolyte membrane (PEM), catalyst layer (CL), microporous layer (MPL), and gas diffusion layer (GDL). The low operation temperatures of PEMFC lead to the condensation of water, and the condensed water hinders the transport of reactants in porous layers (MPL and GDL). Thus, water flooding is currently one of hot issues that should be solved to achieve higher performance of PEMFC. This research aims to study liquid water transport in porous layers of PEMFC by using pore-network model, while the microscale pore structure and hydrophilic/hydrophobic surface properties of GDL and MPL were fully considered.

• 대한기계학회논문집B
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• 제36권6호
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• pp.579-582
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• 2012

연료전지 시스템에서 잔류 수분의 제거과정은 연료전지의 성능 및 수명 관리를 위해 중요한 과정이다. 효과적인 수분 제거과정의 설계를 위해서는 연료전지내의 수분 제거 특성에 대한 이해가 필수적이다. 이를 위해 본 연구에서는 연료전지의 다공성막인 가스확산층을 통한 수분증발량을 정상상태에서 측정하는 실험 기법을 개발하였다. 이 기법을 이용하여 연료전지의 잔류수분 제거 현상을 모사하는 실험장치를 개발하였다. 그리고 건조가스와 가스확산층의 변수가 수분에 미치는 영향을 실험적으로 측정하였다. 건조가스의 습도가 낮고, 유량이 높을수록 가스확산층을 통해 증발되는 수분량이 높았다. 또한 가스확산층의 두께가 얇을수록 수분 증발량이 높은 특성을 확인하였다.

• 한국실내디자인학회논문집
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• 제18권3호
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• pp.102-113
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• 2009

The SARS virus began to appear and spread in North America and Southeast Asia in the early 2000' s, infecting and harming many people. In the process of examining the causes for the virus, studies on the airborne SARS virus and the way it spread were carried out mainly in the medical field. In the field of architecture, studies were done on the diffusion of air pollutants in buildings using gases such as $CO_2$, $N_2O$, or $SF_6$, but research on virus diffusion was limited. There were also explanations of only the diffusion process without accurate information and discussion on virus characteristics. The aim of this study is to analyze the physical characteristics of airborne virus, consider the possibility of using coupled analysis model and tracer gas for analyzing virus diffusion in building space and, based on reports of how the infection spread in a hospital where SARS patients were discovered, analyze infection risk using tracer gas density and also diffusion patterns according to the location, shape, and volume of supply diffusers and exhaust grilles. This paper can provide standards and logical principles for evaluating various alternatives for making decisions on vertical or horizontal ward placement, air supply and exhaust installation and air volumes in medium or high story medical facilities.

• 연구논문집
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• 통권25호
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• pp.175-184
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• 1995

Mechanical properties of the gas nitrocarburized product depend on the surface compound layer and the diffusion zone formed. The compound layer improves the wear resistance, and the corrosion resistance. Though phase composition, pore layer and growth rate of the compound layer varies according to the treatment time, temperature and the kind of the steel substrate, they are strongly influenced by the environmental gas composition. In the current study, the growth behavior of the compound layer and diffusion zone of the carbon steel and the alloy steel upon nitrocarburizing treatment at $570^{\circ}C$, and the phase composition and the variation in the growth rate of the compound layer according to the variation of the gas environment which was the medium of the nitriding and carburizing reaction were investigated.

• 한국화재소방학회논문지
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• 제30권5호
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• pp.9-17
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• 2016

중규모 도로터널의 경우 제연설비 설치가 의무화 되어있지 않기 때문에 화재가 발생할 경우 이용객들이 많은 피해를 입을 수 있다. 따라서 본 연구에서는 연장 1,000 m 2차로 일방통행방식의 도로터널을 대상으로 3차원 수치해석, 정량적 위험도 평가를 통해 제연경계벽이 설치되지 않을 때와 설치간격이 100, 150, 200, 250 m일 때 화재에 의하여 발생되는 연기류 등이 시간에 따른 확산을 분석하였다. 그 결과 중규모 도로터널에 제연경계벽을 설치할 경우 설치하지 않은 경우보다 화재로부터 발생되는 고온의 공기와 독성가스의 확산이 지연되는 것을 확인할 수 있었다. 또한 수치해석 대상 중에서 제연경계벽의 설치간격이 100 m인 경우 화재로 인해 발생된 고온의 공기와 독성가스의 확산이 다른 경우보다 많이 지연되어 터널 이용객이 피난하는데 가장 적합한 것으로 나타났다.

• 한국막학회:학술대회논문집
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• 한국막학회 1997년도 추계 총회 및 학술발표회
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• pp.69-70
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• 1997

Polyimides and related polymers, when synthesized from aromatic monomers, have generally rigid chain structures resulting in a low gas permeability. The rigidity of polymer chains reduces the segmental motion of chains and works as a good barrier against gas transport. To overcome the limit of use as materials of gas separation membranes due to low gas permeability, block copolymers with the incorporation of flexible segments like siloxane linkage and ether linkage have been studied. These block copolymers have microphase-separated structures composed of microdomains of flexible poly(dimethylsiloxane) or polyether segments and of rigid polyimides segments. In case of rigid-flexible block copolymers, the characteristics of both phases for gas permeation are of great difference. The permeation of gas molecules occurs favorably through microdomains of flexible segments, whereas those of rigid segments hinder the permeation of gas molecules. Accordingly the increase of content of flexible segments in a rigid polymer matrix will increase the gas permeability of the membrane linearly. However, this prediction does not satisfy enough many experimental results and in particular the drastic increase of the permeability is observed in a certain volume fraction. It was proposed that the gas transport mechanism is dominated by diffusion rather than gas solubility in a certain content of flexible phase if solution-diffusion mechanism is adopted. However, the transition from solubility-dependent to diffusion-dependent cannot be explained by the understanding of mechanism itself. Therefore, we consider an effective chemical path which permeable phase can form in a microheterogenous medium, and percolation concept is introduced to describe the permeability transition at near threshold where for the first time a percolation path occurs. The volume fraction of both phases is defined as V$_{\alpha}$ and V$_{\beta}$ in block copolymers, and the volume of $\beta$ phase in the threshold forming geometrically a traversing channel is defined as V$_{\betac}$. The formation mechanism of shortest chemical channel is schematically depicted in Fig. 1.

• 대한기계학회논문집B
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• 제28권6호
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• pp.726-733
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• 2004

The growth of the critical size bubble by diffusion process in viscoelastic medium was treated by an integral method for the concentration boundary layer adjacent to the bubble wall. In this study, we obtained a set of the first order time dependent equations to obtain bubble radius and gas pressure inside the bubble simultaneously. The calculated final cell sizes depending on the initial saturation pressure are in close agreement with the observed ones. The governing equations developed in this study may be used in polymer processing of microcellular foams.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.174-179
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• 2004

The growth of the critical size bubble by diffusion process in viscoelastic medium was treated by an integral method for the concentration boundary layer adjacent to the bubble wall. In this study, we obtained a set of the first order time dependent equations to obtain bubble radius and gas pressure inside the bubble simultaneously. The calculated final cell sizes depending on the initial saturation pressure are in close agreement with the observed ones. The governing equations developed in this study may be used in polymer processing of microcellular foams.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1734-1737
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• 2015

Insulating characteristics of Cl₂-He mixture gases in gas discharges were analysed to evaluate ability of these gases for using in medium voltage and many industries. These are electron transport coefficients, which are the electron drift velocity, density-normalized longitudinal diffusion coefficient, and density-normalized effective ionization coefficient, in Cl₂-He mixtures. A two-term approximation of the Boltzmann equation was used to calculate the electron transport coefficients for the first time over a wide range of E/N (ratio of the electric field E to the neutral number density N). The limiting field strength values of E/N, (E/N)_lim, for these binary gas mixtures were also derived and compared with those of the pure SF₆ gas.

• 천문학회보
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• 제44권2호
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• pp.48.4-48.4
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• 2019

We studied the metal-distribution of isolated Milky-way mass galaxy using various hydrodynamic solvers and investigated the difference of the result between AMR and SPH codes. In particle-based codes, physical quantities like mass or metallicity defined in each particle are conserved unless being injected explicitly by the effect of the supernova, whereas in the Eulerian codes the diffusion is simply accomplished by hydro-equation. Therefore, without including explicit physics of diffusion on the SPH- codes, the metal mixing in the galaxy or CGM only can be accomplished by the direct motion of the particles, however, the standard-SPH codes depress the instability of the turbulent fluid mixing. In this work, we simulated under common initial conditions, common gas-physics like cooling-heating models, and star-formation feedback using ENZO(AMR) GIZMO and GADGET-2 codes. We additionally included a metal-diffusion algorithm on the SPH-codes, which follows the subgrid-turbulent mixing model investigated by Shen et al. (2010) and compared the effect of the metal-outflow on the halo region of the galaxy in different hydro-solvers. We also found that for the implementation of the diffusion scheme in the SPH-codes, the existence of a sufficient number of the gas-particles, which is the carrier of the metals, is necessary. So we tested a new initial condition for proper implementation of the diffusion scheme on the SPH simulations. By comparing the metal-contamination of the circumgalactic medium with different hydrodynamics models, we quantify the diffusion strength of AMR codes using diffusion parameterization of the SPH codes and also suggest the calibration solutions in the different behavior of codes in metal-outflow.