• Journal of Advanced Marine Engineering and Technology
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• 제32권5호
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• pp.737-746
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• 2008

Numerical study is conducted to grasp preferential diffusion effects on flame characteristics in $H_2/CO$ syn-gas diffusion flames diluted with $CO_2$. The models of Sun et al. and David et al., which have been well known to be best-fitted for $H_2/CO$ synthetic mixture flames. are evaluated for $H_2/CO$ synthetic mixture flames diluted with $CO_2$. Comparison of flame structures with mixture-averaged species diffusion and suppression of the diffusivities of $H_2$ and H was made. The behaviors of maximum flame temperatures with those species diffusion models are not explained by scalar dissipation rate but by the nature of chemical kinetics. Importantly-contributing reaction steps to heat release rate are also compared for the three species diffusion models in $H_2/CO/CO_2$ flames with and without $CO_2$ dilution.

• Journal of the Korean Wood Science and Technology
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• 제36권6호
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• pp.1-12
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• 2008

주요 국산재의 여러 가지 응용물성을 지난 3년에 걸쳐 조사하였다. 전보(강 외 4인 2008, 변 외 5인 2008)에 이어 본보에서는 우리나라의 활엽수 주요 수종인 백합나무, 거제수나무, 오동나무를 재료로 사용하였다. 매년 동일한 장치와 실험조건으로 실험하였기 때문에 모든 수종에 대한 결과를 상호 비교 할 수 있었다. 수분흡착성 실험은 80메시 목분을 이용하였으며, 넓은 범위의 상대습도조건에 따른 평형 함수율과 흡착등온선을 구하였다. 열전도율과 열확산률은 열선열전도장치를, 전기의 부피저항률과 저 항은 고전기저항계를 이용하여 측정하였다. 정목재와 판목재의 열적 전기적 특성차이가 관찰되었는데 이는 해부학적 차이에 의한 것으로 보인다. 음향적 성질은 음향측정시스템을 사용하여 동적탄성률, 내부마찰을 측정하였다. 본 논문의 결과들은 목재구조물 설계, 휴대용 목재수분계 보정, 음향적 성질 등에 필요한 기본 자료를 제공한다.

• 공업화학
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• 제10권4호
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• pp.608-614
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• 1999

촉매 담체로 사용되는 알루미나와 실리카-알루미나에 흡착된 tetra-phenylprophine과 coronene이 아세톤의 주입에 의해 탈착되는 역확산 과정과, coronene이 tetra-phenylporphine 용액에 의한 역확산 과정을 조사하였다. 이상흡착용액 이론을 적용한 역확산 모델을 이용하여 역확산 과정을 해석하고 모사한 결과로부터 역확산 계수를 결정하였다. 과량의 아세톤 주입에 의한 탈착에서 tetra-phenylporphine과 coronene의 역확산 계수는 ${\sim}10^{-15}m^2/sec$ 범위로 얻어졌다. 흡착용액과 비슷한 농도를 갖는 tetra-phenylprophine 용액에 의한 역확산의 경우 탈착되는 coronene의 역확산 계수의 값도 ${\sim}10^{-15}m^2/sec$ 범위에 있으며, 세공내로 들어가는 tetra-phenylporphine의 확산 계수는 ${\sim}10^{-11}m^2/sec$ 이었다. 흡착제 밖으로 탈착되어 나오는 coronene의 역확산 계수는 아세톤이나 tetra-phenylporphine 용액의 주입에 의한 흡착-탈착의 경우 탈착제는 종류와 양에 관계없이 모두 비슷한 범위의 값을 보여 주었다. 역확산계수는 비어 있는 세공내로의 확산에 대한 유효확산계수에 비해 현저히 감소하였다. 이러한 현상은 역확산 과정에 나타나는 확산 흐름의 교차에 기인하는 것으로 설명되었다.

• 대한기계학회논문집B
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• 제21권9호
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• pp.1126-1138
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• 1997

An axisymmetric laminar jet diffusion flame has been numerically modelled. The present study employs the refined physical submodels to account for the detailed chemical kinetics and the variable transport properties. It is found that preferential diffusion resulting from variable transport properties significantly influences the hydrogen diffusion flame structure in terms of the spatial distribution for temperature, species concentration, thermal and mass diffusivity, Lewis number, and NO concentration. The preferential diffusion effects on the diffusion flame in the high-pressure environment are also discussed in detail.

• 한국막학회:학술대회논문집
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• 한국막학회 2004년도 Proceedings of the second conference of aseanian membrane society
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• pp.33-38
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• 2004

Molecular modeling of gas permeation through zeolite membranes with/without intercrystalline region was carried out. Molecular dynamics (MD) and Monte Carlo (MC) simulations were performed to estimate the diffusion coefficient and adsorption parameters respectively, and our proposed combined method of molecular simulation techniques with a permeation theory (CMP) was used to estimate gas permeability. The calculated permeability of gases (Ar, He, Ne, $N_2$, $0_2$, $CH_4$) at 301 K for the single crystal membrane model was about one order of magnitude larger than the experiential values, although the dependence on the molecular weight of the permeating species agreed with experiments. On the other hand, the estimated permeability using the diffusivity and adsorption parameters of the intercrystalline region model was in good agreement with the experiments. The consistency between experiments and the estimated values means the importance of considering the intercrystalline region and the validity of CMP method to predict the performance of zeolite membranes.

• 한국연소학회지
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• 제15권4호
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• pp.58-64
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• 2010

Spontaneous ignition tests of five different coals with non-iso-thermal and iso-thermal test method based on the standard test procedure of NF T20-036 were carried. These five coals included the 2 low rank coals and 3 bituminous coals. Test results showed that the ignition temperatures of all coals at the iso-thermal conditions were higher than that of non-isothermal condition, and those of low rank SM and BR coal in both nonisothermal and isothermal conditions were lower than bituminous AN and CN coals. The chemical species of coals such as oxygen and hematite also plays an important role in enhancing the ignition rate that the ignition temperature of SM coal was lowered. The heat accumulation tendency of five coals inside outdoor stack pile was monitored with emphasis on the change in the temperature of the coal depth in stack pile. In case of low rank BR coal, its temperature inside coal stack pile due to the rate of high heat accumulation and oxidation was $59^{\circ}C$ compared to $51^{\circ}C$ for other SW bituminous coal. And the heat accumulation rate inside coal stack piles was increased with increased the Cp value which it was defined as the specific heat of coal at constant pressure, whereas other factors such as thermal diffusivity and conductivity of coal relatively had less effect on heat accumulation.

• 한국대기환경학회지
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• 제27권6호
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• pp.791-804
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• 2011

Numerical simulations were carried out to investigate the impact of PBL (Planetary boundary layer) scheme implemented in WRF on the result of meteorological fields and CMAQ modeling. 25-day period, representing high ozone concentration, was selected for the simulations. The three WRF domains covered East Asia region, Korean Peninsula and Seoul metropolitan area. The sensitivity of WRF-CMAQ modeling to the various PBL schemes was assessed and quantified by comparing model output and against observation from the meteorological and the air quality monitoring network within the domain. The meteorological variables evaluated included temperature, wind speed and direction over surface sites and upper air sounding sites. The CMAQ variables included gaseous species $O_3$ and $NO_x$ over monitoring stations. Although difference of PBL schemes implemented in WRF, they did not appreciably affect the WRF and CMAQ performance. There are partially differences between non-local and local mixing scheme, but are not distinct differences for the results of weather and air quality. It is suggested that impact of parameterization of vertical eddy diffusivity scheme in CMAQ also need to be researched in the future study.

• 방사성폐기물학회지
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• 제18권4호
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• pp.421-437
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• 2020

This study provides an assessment on a proposed method for separation of cesium, strontium, and barium using electrochemical reduction at a liquid bismuth cathode in LiCl-KCl eutectic salt, investigated via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS). CV studies were performed at temperatures of 723-823 K and concentrations of the target species up to 4.0wt%. Redox reactions occurring during potential sweeps were observed. Concentration of BaCl2 in the salt did not seem to influence the diffusivity in the studied concentration range up to 4.0wt%. The presence of strontium in the system affected the redox reaction of lithium; however, there were no distinguishable redox peaks that could be measured. Impedance spectra obtained from EIS methods were used to calculate the exchange current densities of the electroactive active redox couple at the bismuth cathode. Results show the rate-controlling step in deposition to be the mass transport of Cs+ ions from the bulk salt to the cathode surface layer. Results from SEM-EDS suggest that Cs-Bi and Sr-Bi intermetallics from LiCl-KCl salt are not thermodynamically favorable.

• 환경위생공학
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• 제7권2호
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• pp.95-110
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• 1992

Much progress has been made in understanding the subcellular events of the human lung injuries after acute exposure to environmental air pollutants. Host of those events represent oxidative damages mediated by reactive oxygen species such as superoxide, hydrogen peroxide, and the hydroxy, free radical. Recently, nitric oxide (NO) was found to be endogenously produced by endothelial cells and cells of the reticulo-endothelial system as endothelialderived relaxation factor (EDRF) which is a vasoactive and neurotransmitter substance. Together with superoxide, NO can form another strong oxidant, peroxonitrite. The relative importance of exogenous sources of $N0/N0_2$ and endogenous production of NO by the EDRF producing enzymes in the oxidative stresses to the heman lung has to be elucidated. The exact events leading to chronic irreversible damage are still yet to be known. From chronic exposure to oxidant gases, progressive epithelial and interstitial damages develop. Type I epithelial cells become thicker and cover a smaller average alveolar surface area while thee II cells proliferate instead. Under acute damages, the extent of loss of the alveolar epithelial cell lining, especially type II cells appears to be a good predictor of the ensuing irreversible damage to alveolar compartment. Interstitial matrix undergo remodeling during chronic exposure with increased collagen fibers and interstitial fibroblasts. However, Inany of these changes can be reversed after cessation of exposure. Among chronic lung injuries, genetic damages and repair responses received particular attention in view of the known increased lung cancer risks from exposure to several air pollutants. Heavy metals from foundry emission, automobile traffics, and total suspended particulate, especially polycystic aromatic hydrocarbons have been positively linked with the development of lung cancer. Asbestos in another air pollutant with known risk of lung cancer and mesothelioma, but asbestos fibers are nonauthentic in most bioassays. Studies using the electron spin resonance spin trapping method show that the presence of iron in asbestos accelerates the production of the hydroxy, radical in vitro. Interactions of these reactive oxygen species with particular cellular components and disruption of cell defense mechanisms still await further studies to elucidate the carcinogenic potential of asbestos fibers of different size and chemical composition. The distribution of inhaled pollutants and the magnitude of their eventual effects on the respiratory tract are determined by pollutant-independent physical factors such as anatomy of the respiratory tract and level and pattern of breathing, as well as by pollutant-specific phyco-chemical factors such as the reactivity, solubility, and diffusivity of the foreign gas in mucus, blood and tissue. Many of these individual factors determining dose can be quantified in vitro. However, mathematical models based on these factors should be validated for its integrity by using data from intact human lungs.

• 한국산림과학회지
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• 제33권1호
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• pp.33-58
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• 1977

수피(樹皮)는 원목(原木) 체적(體積)의 10~20%를 차지하고 있으며 일반적(一般的)을 운반(運搬), 제거(除去), 처리(處理)에 따른 비용에 비(比)해 효용가치(効用價値)는 적다. 뿐만아니라 세계적(世界的)인 임산자원(林産資源)의 부족(不足)에 따른 전수체이용화(全樹體利用化)의 개념이 점고(漸高)되면서부터 수피(樹皮)의 이용(利用)에 관심(關心)을 가지게 되었다. 본연구(本硏究)는 수피(樹皮)에 대(對)한 연구(硏究)가 전무(全無)한 국내(國內)의 실적(實積)에 비추어 국내주요(國內主要) 수종(樹種) 수피(樹皮)는 소나무속(屬), 사시나무속(屬), 참나무속(屬)을 대상(對象)으로 수피(樹皮)의 물리기계적(物理機械的) 성질(性質)을 구명(究明)하고 수피(樹皮)의 가능(可能)한 이용(利用) 책을 위한 기본적 성질을 밝히고자 하였다. 본(本) 연구(硏究)에서 사용(使用)한 공시수피(共試樹皮)는 서울대학교(大學校) 농과대학(農科大學) 부속연습림(附屬演習林)과 임업시험장(林業試驗場) 중부지장(中部支場) 부근에서 벌채이용(伐採利用)이 적령기(適齡期)에 달(達)하고 포고직경(胞高直徑)이 동급(同級)인 건전하고 정상적(正常的)으로 생장(生長)하는 입목(立木)의 흉고직경 부위(部位)에서 수종별(樹種別) 20주(株)씩 $200cm^2$로 채취(採取)하였다. 물리적(物理的) 성질(性質)로는 수피(樹皮) 전건비중(全乾比重), 내피(內皮) 및 외피(外皮)의 생수피(生樹皮) 함수량(含水量), 섬유포화점(纖維飽和點), 수분이력곡선(水分履歷曲線), 전수축율(全收縮率), 흡수량(吸收量), 비열(比熱), 습윤열(濕潤熱), 열전도도(熱傳導道), 열확산(熱擴散), 시차열분석(示差熱分析) 및 발열량(發熱量)을 측정(測定) 연구(硏究)하였다. 다음 기계적(機械的) 성질(性質)로는 곡강도(曲强度)와 압축강도(壓縮强度)를 측정연구(測定硏究)하였으며 본(本) 연구(硏究)에서 얻은 결론(結論)은 다음과 같다. 1. 전건비중(全乾比重)은 같은 개체(個體) 내(內)에 있어서도 목질부(木質部)와 수피간(樹皮間)에 차이(差異)가 있을 뿐아니라 수피(樹皮)에 있어서도 내피(內皮)와 외피간(外皮間)의 차이(差異)가 있다. 2. 수피(樹皮)의 전건비중(全乾比重)이 목질부(木質部) 비중(比重)보다 높은 사실(事實)은 수피내(樹皮內)의 사부섬유(篩部纖維) 및 보강세포(保强細胞)가 많이 있다는 해부적(解剖的)인 구조적(構造的) 특징(特徵)에 기인(基因)한다. 3. 전건비중(全乾比重)에 있어서 잣나무를 제외하고는 내피비중(內皮比重)이 외피비중(外皮比重)보다 높았으며 이는 내피(內皮)보다 높은 수축율(收縮率)에 기인(基因)한다. 4. 수피내(樹皮內)의 해부적(解剖的) 구조(構造)에 있어서 사요소(篩要素)의 구성비율(構成比率)이 높을수록 함수율(含水率)은 높아지고 후막조직(厚膜組織)과 주피조직(周皮組織)이 많으면 많을수록 함수율(含水率)은 떨어진다. 5. 수피(樹皮)의 섬유포화점(纖維飽和點)을 습윤열측정(濕潤熱測定)에 의(依)하여 구(求)할 수 있는 가능성(可能性)을 제시(提示)하였으며 그 결과(結果) 소나무에서는 26~28%사이에 상수리나무에서는 24~28%사이에 있는 것으로 나타났으나 이에 대(對)한 것은 금후연구(今後硏究)에 의(依)하여 더 밝혀져야 할 것이다. 6. 수피(樹皮)의 수축율(收縮率)은 목질부(木質部)와는 달리 경단방향(經斷方向)에서 제일 높고 수축방향(樹縮方向)에서 제일 낮았으나 졸참나무와 굴참나무에서는 열외(列外)이었다. 7. 수피(樹皮)의 비열(比熱)은 목질부(木質部)와 같고 습윤열(濕潤熱)은 목질부(木質部)보다 다소 높았다. 열전도도(熱傳導度)는 목재(木材)보다 낮으며 전건수피비중(全乾樹皮比重)과 수증기비중(水蒸氣比重)을 알고 열전도도(熱傳導度)를 계산할 수 있는 다음과 같은 회귀방정식(回歸方程式)을 유도(誘導)하였고 이 방정식(方程式)에 의(依)하여 얻어진 열전도도(熱傳導度) 수치는$(0.8{\sim}1.6){\times}10^{-4}cal/cm{\cdot}sec{\cdot}deg$이었다. $$K=4.631+11.408{\rho}d+7.628{\rho}m$$ 8. 수피(樹皮)의 열확산(熱擴散)은 $(8.03{\sim}4.46){\times}10^{-4}cm^2/sec$이며 시차열분석(示差熱分析)의 결과(結果)에 의(依)하면 발열량(發熱量)은 발열반응(發熱反應)이 시작(始作)되기 전(前)까지는 목질부(木質部)가 높고 발열반응(發熱反應)이 시작(始作)되면서부터는 수피(樹皮)가 목질부(木質部)보다 상회(上廻)하였다. 9. 경단방향(經斷方向)의 수피곡강도(樹皮曲强度)는 수피비중(樹皮比重)에 비례(比例)하고 회귀식(回歸式)은 M=243.78x-12.02(F=31.41)이었고 압축강도(壓縮强度)는 목질부(木質部)와는 달리 경단방향(經斷方向)이 가장 높고, 경단방향(經斷方向), 수축방향순(樹軸方向順)으로 적어졌다.