• 설비공학논문집
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• 제27권5호
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• pp.241-246
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• 2015

Cellular foamed insulation such as polyurethane foam ages and degrades the thermal conductivity. Aging of foam is a result from the diffusion of gases, initially consisting of $CO_2$ but eventually replaced by air from the environment. The variation of the cell gas content with time is primarily influenced by the increase of thermal conductivity of the cellular foam. The weight of foam also changes as the gas diffuses and exchanges. In this study, a weight measurement method has been proposed to evaluate the effective diffusion coefficients of $CO_2$ and Air, $D_{CO2}=7.08504E-11$ and $D_{air}=4.86086E-12$, respectively and are compared with the gas analysis method.

• 한국해양공학회지
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• 제32권4호
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• pp.261-271
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• 2018

In this study, a hydraulic model test, to which Particle Image Velocimetry (PIV) system applied, was used to determine the hydrodynamic characteristics of the advection-diffusion of saltwater according to bottom conditions (impermeable/permeability, diameter, and inclination) and the difference of the initial salt. Considering quantitative and qualitative results from the experiment, the characteristics of the density current were discussed. As an experimental result, the advection-diffusion mechanism of salinity was examined by the shape of saltwater wedge and the flow structure of density currents with various bottom conditions. The vertical salt concentration obtained from the experiment was used as quantitative data to calculate the diffusion coefficient that was used in the numerical model of the advection-diffusion of saltwater.

• 자원환경지질
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• 제53권1호
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• pp.11-21
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• 2020

본 연구는 대수층과 저투수층이 존재하는 단일시스템에서 trichloroethylene (TCE)과 tetrachloroethylene (PCE)의 거동에 대해 1차원 확산 해석해를 사용하여 저투수층의 농도 분포, 대수층과 저투수층의 경계면에서 확산 선속, 그리고 역확산에 의한 대수층의 오염 지속성을 모델링하였다. 모델링에 사용된 해석해는 이전 연구에서 많이 사용되었던 저투수층의 두께가 무한한 조건의 해석해와 본 연구에서 제시한 저투수층의 두께가 유한한 조건을 고려한 해석해를 모두 사용하였다. 제시된 해석해의 타당성을 평가하기 위해 저투수층의 두께가 무한한 조건의 해석해와 Yang et al.(2015)이 개발한 1차원 확산 해석해의 결과를 Nash-Sutcliffe 유효계수(NSE)로 비교하였다. 저투수층의 농도 분포, 확산 선속, 그리고 대수층의 오염 지속성 등 모든 결과에서 무한한 조건의 해석해를 이용하였을 때 과소평가되는 결과를 나타내었다. 그리고 본 연구에서 제시한 해석해의 결과와 Yang et al. (2015)이 개발한 해석해의 결과는 높은 일치성(NSE = 0.99)을 보였다. 본 연구에서 제시한 해석해를 실제 오염된 부지에 효율적으로 적용하기 위해 유효확산계수, 저투수층의 두께, 그리고 확산된 시간을 이용하여 확산 거리(Z_d)라는 용어를 소개하였다. 확산 거리가 0.7 보다 작은 경우 저투수층의 두께가 무한한 조건의 해석해를 사용할 수 있으며, 확산 거리가 0.7 보다 큰 경우 저투수층의 두께가 유한한 확산 해석해를 사용하여야 모델링의 신뢰성을 높일 수 있을 것으로 사료된다.

• Journal of the Korean Wood Science and Technology
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• 제31권3호
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• pp.24-29
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• 2003

This research was performed to investigate the diffusivity of borate rods in radiata pine (Pinus radiata D. Don) conditioned to 40 percent moisture content (MC). The deepest penetration of boron were observed in the longitudinal direction, followed by the radial and the tangential directions. The boron loading on the wood face adjacent to the borate rod tended to increase with diffusion time in all directions. To mathematically quantify boron diffusion, the diffusion coefficient of boron was determined using Boltzmann's transformation by assuming that it was a function of concentration only. The values of the longitudinal diffusion coefficients were between 1.3×10^-8 cm²/sec and 9.2×10^-8 cm²/sec. The radial diffusion coefficients were between 1.4×10^-8 cm²/sec and 9.5×10^-8 cm²/sec, and the tangential diffusion coefficients were between 5.2×10^-9 cm²/sec and 1.3×10^-8 cm²/sec. The differences of diffusion coefficients between the longitudinal direction and the radial direction were slight, although their concentration profiles were markedly different. This indicates that the amount of boron loading on the wood face adjacent the borate rod is one of the most important factor for boron penetration in wood with low MC.

• 한국세라믹학회지
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• 제18권2호
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• pp.79-82
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• 1981

SiC powder was heated in air over the temperature range of 1100-135$0^{\circ}C$. $\beta$-cristobalite was formed to cover the surfaces of SiC particles by the reaction: $SiC(s)+20_2(g)=SiO_2(s)+CO_2(g)$. It is assumed that the diffusion of oxygen ion through the formed surface layer of $\beta$-cristobalite controls the oxidation of the SiC particles. The diffusion coefficient of oxygen ion through the $\beta$-cristobalite layer was obtained as the following equation: $D=3.84{\times}10^{-17}$exp(-14.7/RT)

• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2017년도 추계학술발표회
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• pp.34-34
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• 2017

• Environmental Engineering Research
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• 제10권3호
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• pp.112-121
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• 2005

The effectiveness of quicklime-based stabilization/solidification (S/S) in immobilizing lead (Pb) was assessed by performing semi-dynamic leaching tests (ANS16.1). In order to simulate landfill leaching conditions, the ANS 16.1 test was modified by using 0.014 N acetic acid (pH = 3.25) instead of distilled water. Artificial soil samples as well as field soil samples contaminated with Pb were tested. The effectiveness of quicklime treatment was evaluated by determining diffusion coefficients ($D_e$) and leachability indices (LX). A model developed by de Groot and van der Sloat was used to elucidate the controlling Pb leaching mechanisms. Overall, upon quicklime treatment Pb leachability was significantly reduced in a]l of the samples tested. The mean LX values were higher than 9 for an artificial soil sample containing 30% kaolinite treated with 10% quicklime and for a field soil sample treated with 10% quicklime, which suggests that S/S treated soils can be considered acceptable for "controlled utilization". Moreover, quicklime treatment was more effective in artificially contaminated soil with high kaolinite content (30%), indicating the amount of clay plays an important role in the success of the treatment. The controlling Pb leaching mechanism was found to be diffusion, in all quicklime treated samples.

• Bulletin of the Korean Chemical Society
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• 제23권11호
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• pp.1595-1603
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• 2002

In this paper we have presented the results of diffusion behavior of model systems for eight liquid n-alkanes ($C_{12}$-$C_{44}$) in a canonical (NVT) ensemble at several temperatures using molecular dynamics simulations. For these n-alkanes of small chain length n, the chains are clearly <$R_{ee}^2$>/6<$R_g^2$>>1 and non-Gaussian. This result implies that the liquid n-alkanes over the whole temperatures considered are far away from the Rouse regime, though the ratio becomes close to the unity as n increases. Calculated self-diffusion constants $D_{self}$ are comparable with experimental results and the Arrhenius plot of self-diffusion constants versus inverse temperature shows a different temperature dependence of diffusion on the chain length. The global rotational motion of n-alkanes is examined by characterizing the orientation relaxation of the end-to-end vector and it is found that the ratio ${\tau}1/{\tau}2$ is less than 3, the value expected for a isotropically diffusive rotational process. The friction constants ${\xi}$of the whole molecules of n-alkanes are calculated directly from the force auto-correlation (FAC) functions and compared with the monomeric friction constants ${\xi}_D$ extracted from $D_{self}$. Both the friction constants give a correct qualitative trends: decrease with increasing temperature and increase with increasing chain length. The friction constant calculated from the FAC's decreases very slowly with increasing temperature, while the monomeric friction constant varies rapidly with temperature. By considering the orientation relaxation of local vectors and diffusion of each site, it is found that rotational and translational diffusions of the ends are faster than those of the center.

• 에너지공학
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• 제21권2호
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• pp.119-123
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• 2012

LNG 저장탱크는 해안에 인접한 해양 구조물로써 염해에 대해 취약성을 가지고 있음에도 불구하고 그 동안 염해에 대한 특별한 건전성관리 체계에 대한 연구는 이루어진 바가 없었다. 탱크의 설계보증 수명 약 25년이 도래하는 시점에서 대체 신규 LNG 탱크 건설로 막대한 비용 및 자원의 낭비를 막고 효율적인 LNG 저장탱크의 수명관계를 위해서 염해에 대한 기초적인 실험데이터는 필수적이다. 따라서 본 연구는 추후 연구 될 LNG 저장탱크 콘크리트 수명예측에 대한 기초적인 자료를 만들기 위해 수행하였으며, 북유럽에서 시행하는 NT Build 492 규격을 신설 탱크의 벽체 콘크리트에 적용하였다. 시험결과 다량의 플라이애시 효과로 재령 90일의 확산계수가 재령 28일의 확산계수의 46%의 값을 보였다. 시방서(배합표)에 의한 계산값과 재령 28일 및 재령 90일 시험값을 비교한 결과, 재령 90일 시험값이 재령 28일 시험값보다 계산값에 근사한 결과를 보임에 따라 90일에 시험을 실시하는 것이 LNG 저장탱크 염해확산계수의 신뢰성을 높일 수 있음을 확인하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 추계학술대회 논문집 학회본부
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• pp.168-171
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• 1988

The p-n homo junction diode of the III-V ternary alloy semiconductor $In_{1-x}Ga_xP$ : S grown by the temperature gradient solution (TGS) was fabricated by Zn-diffusion, and it's characteristics was investigated. The carrier concentration of $In_{1-x}Ga_xP$ doped with sulfur, 0.5 mol %, was $1{\times}10^{17}cm^{-3}$ and the mobility was varied with the composition. In the case that the diffusion time was constant as 30 minutes. The temperature dependence of diffusion coefficient was decreased from D= $4.2{\times}10^{-5}$ exp (-1.74/$k_{B}T$) to D= $2.5{\times}10^{-5}$ exp (-3.272/$k_{B}T$) with increasing of composition $\times$ from 0.43 to 0.98. The major peak of E.L spectrum was due to D-A pair recombination and the peak intensity was increased with the increasing of input current. And the E.L intensity was decreased with the increasing temperature, and shift to the long wavelength. The luminescence efficiencies measured at $5^{\circ}C$, atmosphere temperature, was decreased from $2.6{\times}10^{-4}$% to $9.49{\times}10^{-6}$ % with increasing of composition it from 0.39, direct transition region, to 0.98, indirect transition region.