• Title, Summary, Keyword: effective diffusion coefficients

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Calculation of Film Diffusion Coefficients and Surface Diffusion Coefficients of Volatile Organic Compounds Using Activated Carbon Adsorption Model and Small Column Test (활성탄 흡착모델과 칼럼실험을 통한 Volatile Organic Compounds의 막확산계수와 표면확산계수의 도출)

  • Lee, Byoung-Ho;Lee, Joon-Hee
    • Journal of Korean Society of Water and Wastewater
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    • v.13 no.1
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    • pp.72-80
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    • 1999
  • Separation of VOCs(Volatile Organic Compounds) in Water Using Activated Carbon is known to be effective. Activated Carbon has been and will be employed in many water treatment plants. Simplified plug flow homogeneous surface diffusion model(PFHSDM) has been used to predict adsorption of organic matter. Finite Element Method(FEM) was used to analyze the model. Out of water quality control substances, benzene, toluene and tetrachloroethylene were used in the small column test. Film diffusion coefficients and surface diffusion coefficients were obtained from the column test, and were compared with the modeling results. Mc Cune, Williamson, William and Kataoka model, were compared with film diffusion coefficients obtained in the test. McCune model was fitted best for those VOCs used in this experiment. Film diffusion coefficients of VOCs obtained were benzene 0.265 cm/min, toluene 0.348 cm/min and tetrachloroethylene 0.298 cm/min. Surface diffusion coefficients of VOCs obtained were benzene $6.36{\times}10^{-8}cm^2/min$, toluene $3.20{\times}10-8cm2/min$, and tetrachloruethylene $4.94{\times}10^{-8}cm^2/min$.

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Effective Diffusion Coefficient in the Porous Media (다공성 미디아에 있어서 유효확산계수)

  • Jeehyeong Khim
    • Journal of Korea Soil Environment Society
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    • v.1 no.2
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    • pp.83-90
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    • 1996
  • A diffusion process is often the main mechanism of soil gas/vapor movement in the vadose zone. The diffusion coefficients in the porous soil media are different from those in the free air phase by the reduction of available area for diffusion, tortuous diffusion path and variable cross section area along the diffusion path. To take account those effects of the diffusion process in the porous media, usually the terms of effective diffusion coefficient and tortuosity are have been used. However, as there are many differents definitions for the tortuosity, when the term of tortuosity is used, it is necessary to examine it throughly. Moreover, there are many different equations for the effective diffusion coefficient according to the investigators and the differences in the values of effective diffusion coefficients between the equations are not insignificant, the selection of the equation should be done with caution. In this paper, the different definitions of effective diffusion coefficient are examined and discussed. As well as definitions, the lots of availabe models for the diffusion coefficient in terms of porosities are compared. Also, the constrictiviy which explains the effect of cross sectional area change over the diffusion path was discussed.

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Convection Effects on PGSE-NMR Self-Diffusion Measurements at Low Temperature: Investigation into Sources of Induced Convective Flows

  • Chung, Kee-Choo;Yu, Hyo-Yeon;Ahn, Sang-Doo
    • Bulletin of the Korean Chemical Society
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    • v.32 no.6
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    • pp.1970-1974
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    • 2011
  • The effects of convection on the measurement of the diffusion coefficients of liquids by the pulsed gradient spin echo (PGSE) NMR method at low temperature are discussed. To examine the generation of convective flows, we used four different types of sample tubes in the diffusion measurements with temperature variation; a normal 5 mm NMR tube, a Shigemi tube, an ELISE type tube, and a capillary tube. Below room temperature, the calculated diffusion coefficients of chloroform in 5 mm o.d. type tubes increased with decreasing temperature, while those in the capillary tube decreased linearly. The convective flow was found to be significant even at low temperature and it seemed to be mainly induced by the transverse temperature gradient. It was also found that the capillary tube was most appropriate to measure the diffusion coefficients, since its small diameter is effective in suppressing the convective flows at both high and low temperatures.

Migration of calcium hydroxide compounds in construction waste soil

  • Shin, Eunchul;Kang, Jeongku
    • Advances in environmental research
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    • v.4 no.3
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    • pp.183-196
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    • 2015
  • Migration of leachate generated through embankment of construction waste soil (CWS) in low-lying areas was studied through physical and chemical analysis. A leachate solution containing soluble cations from CWS was found to have a pH above 9.0. To determine the distribution coefficients in the alkali solution, column and migration tests were conducted in the laboratory. The physical and chemical properties of CWS satisfied environmental soil criteria; however, the pH was high. The effective diffusion coefficients for CWS ions fell within the range of $0.725-3.3{\times}10^{-6}cm^2/s$. Properties of pore water and the amount of undissolved gas in pore water influenced advection-diffusion behavior. Contaminants migrating from CWS exhibited time-dependent concentration profiles and an advective component of transport. Thus, the transport equations for CWS contaminant concentrations satisfied the differential equations in accordance with Fick's 2nd law. Therefore, the migration of the contaminant plume when the landfilling CWS reaches water table can be predicted based on pH using the effective diffusion coefficient determined in a laboratory test.

Chloride Diffusion in Mortars - Effect of the Use of Limestone Sand Part I: Migration Test

  • Akrout, Khaoula;Ltifi, Mounir;Ouezdou, Mongi Ben
    • International Journal of Concrete Structures and Materials
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    • v.4 no.2
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    • pp.105-108
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    • 2010
  • In order to determine the effect of the use of limestone sand on chloride ion ingress in mortar, specimens were cast with two different sands: siliceous sand (used as reference) and limestone crushed sand (used for this study). To compare and assess the resistance of this mortar to chloride penetration, two different diffusions tests were employed: slow migration and rapid migration (AASHTO test). In this study, calculation of the effective diffusion coefficient is proposed using a model based on Nernst. Planck equation. The diffusion coefficients from each sample were compared. The results for all tests show that the diffusion coefficients for siliceous sand mortar are larger than those obtained with limestone sand. It appears also that the diffusion coefficient varies as a function of the W/C ratio.

Adsorption and Diffusion Characteristics of Benzene, Toluene, and Xylene Vapors on Activated Carbon and Zeolite 13X (활성탄과 제올라이트 13X에서 벤젠, 톨루엔 및 자일렌 증기의 흡착 및 확산 특성)

  • Jung, Min-Young;Suh, Sung-Sup
    • Korean Chemical Engineering Research
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    • v.57 no.3
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    • pp.358-367
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    • 2019
  • Adsorption equilibrium and intraparticle diffusion characteristics of benzene, toluene, and xylene vapors on activated carbon and zeolite 13X were investigated. Static adsorption experiments were carried out under the pressure range of 0.01~0.07 bar while changing the adsorption temperature to 293.15 K, 303.15 K, and 313.15 K, respectively. Adsorption equilibrium was analyzed by Langmuir, Freundlich and Toth models. The adsorption energy was 5.26~31.0 kJ/mol representing physical adsorption characteristics. The maximum adsorption capacity on activated carbon was the largest for benzene, and the smallest for xylene. Toluene was in between. In the case of zeolite 13X, the maximum adsorption capacity was the largest for xylene, and the smallest for benzene as opposed to activated carbon. The effective diffusion coefficients of gas adsorbate were measured to be about $10^{-5}{\sim}10^{-4}cm^2/s$, and increased with temperature. As the pressure increased, the effective diffusion coefficients were decreased. The dependence of effective diffusion coefficients on temperature and pressure was greater in zeolite 13X particles than in activated carbon. Therefore, it is necessary to express the diffusion coefficients as a function of pressure in order to predict the precise dynamic behavior of the adsorption process using zeolite 13X where the pressure fluctuation occurs abruptly.

Prediction of VOCs Emissions from Multi-layers Materials (복합자재에서의 VOCs 방출량 예측에 관한 연구)

  • Yoon, Chang-Hyun;Kwon, Kyung-Woo;Park, Jun-Seok
    • Proceedings of the SAREK Conference
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    • pp.9-14
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    • 2005
  • The purpose of this study is to predict VOCs emission rates from multi-layers materials, which are composed of single-layer materials having various VOCs emission rates, by using effective diffusion coefficients of the single-layer materials. The study was consisted of two parts; the one is the prediction of VOCs emission rates from multi-layer materials through numerical methods. The other is the measurement of VOCs emissions rates of wall composite and floor composite in Mock-up rooms for comparing the prediction and the experiments' values. The results of the study show that the short-term VOCs emission rates of multi-layers materials can be predicted from the effective diffusion coefficients of single materials in odor accuracy.

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A Study on Chloride ion Diffusion in Cracked Concrete (균열이 발생한 콘크리트에서의 염화물 이온 확산에 관한 연구)

  • 배상운;박상순;변근주;송하원
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.677-682
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    • 2001
  • In this study, a method to evaluate diffusion coefficient of chloride ion in cracked concrete is proposed. For cracked concrete having either anisotropic or isotropic crack network, each crack of saturated concrete is considered as a V shape crack, and an effective diffusion coefficient is expressed with diffusion coefficients of cracked part and noncracked part and a so-called crack spacing factor. A comparison with experimental results shows that the diffusion coefficient for cracked concrete is accurately predicted by the effective diffusion coefficient. Prediction results also show that the cracks in concrete markedly change the diffusion properties and accelerate penetration of drifting species. The method in this paper can be effectively used to consider the effect of cracks on concrete diffusion coefficient of cracked concrete.

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A Modified Enskog-Like Equation of Self-Diffusion Coefficients for Penetrable-Sphere Model Fluids

  • Suh, Soong-Hyuck;Liu, Hong-Lai
    • Bulletin of the Korean Chemical Society
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    • v.32 no.4
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    • pp.1336-1340
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    • 2011
  • Molecular dynamics simulations have been performed to investigate the transport properties of self-diffusion coefficients in the penetrable-sphere model system. The resulting simulation data for the product of the packing fraction and the self-diffusion coefficient exhibit a transition from an increasing function of density in lower repulsive systems, where the soft-type collisions are dominant, to a decreasing function in higher repulsive systems, where most particle collisions are the hard-type reflections due to the low-penetrability effects. A modified Enskog-like equation implemented by the effective packing fraction with the mean-field energy correction is also proposed, and this heuristic approximation yields a reasonably good result even in systems of high densities and high repulsive energy barriers.

Advective-diffusive Characteristics of Waste Landfill Liner to Inorganic Chemicals (매립지 차수재의 무기화합물에 대한 이류-확산 특성)

  • 장연수;류정훈;류정훈
    • Journal of the Korean Geotechnical Society
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    • v.20 no.3
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    • pp.5-11
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    • 2004
  • Characteristics of advective-diffusive transport of inorganic chemicals in clayey soils as well as in two hardened barrier materials of silica and lime are analyzed from the laboratory column test and compared with those of pure diffusive column test. The results show that the average dispersion coefficients of three materials are $4.39\times l0^{-10}\textrm{m}^2 /s,\; 1.98\times l0^{-10}\textrm{m}^2 /s,\; 1.99\times l0^{-10}\textrm{m}^2 /s$, respectively, and the value of clay is higher than that of hardened barrier materials. There was no significant difference between the dispersion coefficients of advective-diffusive column tests and the effective diffusion coefficients from the pure diffusive column tests, if advective velocity was lower than l0$^{-7}$$m^2$/s. The range of dispersion coefficients of advective-diffusive column tests was narrower than that of diffusion coefficients of pure diffusion tests.