• Title/Summary/Keyword: water diffusivity

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A Kinetic Study on the Phosphorus Adsorption by Physical Properties of Activated Carbon (활성탄 물성에 따른 인 흡착의 동력학적 연구)

  • Seo, Jeongbeom;Kang, Joonwon
    • Journal of Korean Society on Water Environment
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    • v.26 no.3
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    • pp.491-496
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    • 2010
  • This study aimed to obtain equilibrium concentration on adsorption removal of phosphorus by activated carbon, to express the adsorption characteristics following Freundlich isotherm and also, based on the value obtained, to investigate the relationship between physical properties of activated carbon and dynamics of phosphorus removal by obtaining rate constant and effective pore diffusivity. The results summarized from this study are as follows. Phosphorus adsorption equilibrium reaching time of powdered activated carbon was reduced as the dosage of activated carbon increases, while granular activated carbon despite increased dosage did not have influence on adsorption equilibrium reaching times of phosphorus as well, taking more than 10 hours. It was also noted that powdered activated carbon showed better adsorption ability than granular activated carbon. The value of constant (f) of Freundlich isotherm of powered activated carbon on phosphorus was 4.26 which is bigger than those of granular activated carbon. The adsorption rate constant on phosphorus of powered activated carbon with low effective diameter and iodine number was highest as $8.888hr^{-1}$ and the effective pore diffusivity ($D_e$) was lowest as $2.45{\times}10^{-5}cm^2/hr$, and the value of phosphorus adsorption rate constant of granular activated carbon was $0.174{\sim}0.372hr^{-1}$, It was revealed that, with the same amount of dosage, the adsorptive power of activated carbon with lower effective diameter was better and its rate constant was also high.

Effects of Overburden Pressure and Clay Content on Water Retention Characteristics of Unsaturated Weathered Soils (상재하중과 점토함유량이 불포화 풍화토의 함수특성에 미치는 영향)

  • Park, Seong-Wan;Park, Jai-Young;Tae, Doo-Hyung;Sim, Young-Jong
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.30 no.1C
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    • pp.53-63
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    • 2010
  • Since the water retention curve is considered as a major parameter to evaluate the unsaturated ground or soils, overburden pressure and clay content on soils underneath ground surface have not been considered for estimating water retention characteristics. Therefore, a need exists that the effect of overburden pressure and clay content on water retention characteristics was assessed in typical weathered soils found in Korea. Soil-Water Characteristic Curve and the unsaturated hydraulic conductivity were estimated using water retention characteristics under the condition of different overburden pressure, clay content, and de-saturation path. Then, these effects are evaluated with the results of SWCC tests from the laboratory. In addition to that, the unsaturated moisture capacity and diffusivity of each case is discussed.

Time Evolution of Material Parameters in Durability Design of Marin Concrete (해양콘크리트의 내구성 설계를 위한 재료 매개변수의 시간단계별 해석)

  • Yoon, In-Seok;Kim, Young-Geun
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.04a
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    • pp.1077-1080
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    • 2008
  • Material parameters such as surface chloride content, water permeability coefficient, chloride diffusivity and critical chloride content are a substantial key parameter for understanding the durability performance of concrete and its micro-structural densification. Over the past few decades, a considerable number of studies on the durability design for marine concrete structures have been carried out. However, the results are different to each other. In order to establish a consistent durability design system of concrete, it is a precondition to define material parameters, which affect deterioration of concrete due to chloride penetration. Such parameters are surface chloride content, chloride diffusivity, and critical chloride content. Usually these parameters are assumed as temporary constant values or obtained from the experimental results for short term. However, it is necessary to define these parameters reasonably, because these significantly influence the calculation of service life of concrete. In this paper, it is introduced to define material parameters of concrete for chloride diffusion, such as surface chloride content $[Cl]_s$, water permeability coefficient K, chloride diffusivity $D_{Cl}$, critical chloride content $[Cl]_{cr}$. These are expressed as time function considering hydration evolution of hardened cement paste. The definition of the material parameters is a prerequisite to simulate chloride penetration into concrete as time elapsed.

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Molecular-dynamic simulation on the equilibrium and dynamical properties of fluids in a nano-channel

  • Hoang, H.;Kang, S.;Suh, Y.K.
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03a
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    • pp.208-214
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    • 2008
  • The equilibrium molecular-dynamic simulations have been performed to estimate the properties of the three kinds of fluids (the Lennard-Jones fluid, water and aqueous sodium-chloride solution) confined between two plates that are separated by 1.086 nm; included in the equilibrium properties are the density distribution and the static structure, and the diffusivity in the dynamic property. Three kinds of fluids considered in this study are. The water molecules are modeled by using the SPC/E model and the ions by the charged Lennard-Jones particle model. To treat the water molecules, we combined the quaternion coordinates with Euler angles. We also proposed a plausible algorithm to assign the initial position and direction of molecules. The influence of polarization of water molecules as well as the presence of ions in the solution on the properties will be addressed in this study. In addition, we performed the non-equilibrium molecular-dynamic simulation to compute the flow velocity for the case with the gravitational force acting on molecules.

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Molecular-dynamic simulation on the equilibrium and dynamical properties of fluids in a nano-channel

  • Hoang, H.;Kang, S.;Suh, Y.K.
    • 한국전산유체공학회:학술대회논문집
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    • 2008.10a
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    • pp.208-214
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    • 2008
  • The equilibrium molecular-dynamic simulations have been performed to estimate the properties of the three kinds of fluids (the Lennard-Jones fluid, water and aqueous sodium-chloride solution) confined between two plates that are separated by 1.086 nm; included in the equilibrium properties are the density distribution and the static structure, and the diffusivity in the dynamic property. Three kinds of fluids considered in this study are. The water molecules are modeled by using the SPC/E model and the ions by the charged Lennard-Jones particle model. To treat the water molecules, we combined the quaternion coordinates with Euler angles. We also proposed a plausible algorithm to assign the initial position and direction of molecules. The influence of polarization of water molecules as well as the presence of ions in the solution on the properties will be addressed in this study. In addition, we performed the non-equilibrium molecular-dynamic simulation to compute the flow velocity for the case with the gravitational force acting on molecules.

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Studies on Dosage Form Design of Anticancer Drug: Release of 5-Fluorouracil from Silicone Devices Containing Water Soluble Additives (항암제(然癌劑) 제형(劑形) 개발(開發)에 관(關)한 연구(硏究) : Silicone Rubber-수용성(水溶性) 첨가제(添加劑)의 Device에서 5-Fluorouracil의 용출(溶出))

  • Kim, Sung-Ho;Choi, Jun-Shik;Back, Chae-Sun;Yu, Young-Jong;Lee, Chi-Young
    • Journal of Pharmaceutical Investigation
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    • v.16 no.1
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    • pp.1-7
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    • 1986
  • The influences of sodium chloride, polyethylene glycol 4000 and 20000 on 5-fluorouracil release from disk type silicone polymer devices were examined in isotonic phosphate buffer. These water soluble cosolvent and sodium chloride caused devices to swell in aqueous media. Sodium chloride exerted the greatest influence on drug release. The addition of water soluble cosolvent or sodium chloride to silicone polymeric devices permitted controlled release of 5-fluorouracil, presumably due to the change of the physical microstructure of silicone network, and the solubility and diffusivity of 5-fluorouracil. It seemed that the water soluble drug was released through the hydrophilic pores or pathways formed in the device by the incorporation of a water soluble cosolvent or sodium chloride.

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Numerical Simulations of the Moisture Movement in Unsaturated Bentonite Under a Thermal Gradient

  • Park, J.W.;K. Chang;Kim, C.L.
    • Nuclear Engineering and Technology
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    • v.33 no.1
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    • pp.62-72
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    • 2001
  • The one-dimensional finite element program was developed to analyze the coupled behavior of heat, moisture, and air transfer in unsaturated porous media. By using this program, the simulation results were compared with those from the laboratory infiltration tests under isothermal condition and temperature gradient condition, respectively. The discrepancy of water uptake was found in the upper region of a bentonite sample under isothermal condition between numerical simulation and laboratory experiment. This indicated that air pressure was built up in the bentonite sample which could retard the infiltration velocity of liquid. In order to consider the swelling phenomena of compacted bentonite which cause the discrepancy of the distribution of water content and temperature, swelling and shrinkage factors were incorporated into the finite element formulation. It was found that these factors could be effective to represent the moisture diffusivity and unsaturated hydraulic conductivity due to volume change of bentonite sample.

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Aquacell Foaming Process On PMMA (Aquacell Process를 이용한 PMMA의 발포)

  • Lee, Hyun-Joo;Cha, Sung-Woon;Yoon, Jae-Dong
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.9
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    • pp.18-24
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    • 1999
  • Microcellular foaming is being researched as a method of maintaining and improving the mechanical characteristics of plastics as well as saving the material costs. This can not only improve the mechanical properties including impact strength of plastic by producing cells with the size of few ${\mu}$m diameters within the plastic, but also can save the material cost of plastic products with the general volumetric expansion of 2 to 10 times. But quite a long time is required for the gas to be absorbed in the plastic. Therefore consistent research should be done to reduce the saturation time of gas into the plastic and this paper provides the method of water microcellular foaming process as one of the methods using the high diffusivity of water. In addition, we can improve impact property of foamed plastic by using this method.

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Analysis of Hydraulic Gradient at Coastal Aquifers in Eastern Part of Jeju Island (제주도 동부지역 해안대수층의 조석에 의한 수리경사 변화 연구)

  • Kim, Kue-Young;Shim, Byoung-Ohan;Park, Ki-Hwa;Kim, Tae-Hee;Seong, Hyeon-Jeong;Park, Yun-Seok;Koh, Gi-Won;Woo, Nam-Chil
    • Economic and Environmental Geology
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    • v.38 no.1
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    • pp.79-89
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    • 2005
  • Groundwater level changes in coastal aquifers occur due to oceanic tides, where the properties of oceanic tides can be applied to estimate hyadraulic parameters. Hydraulic parameters of coastal aquifers located in eastern part of Jeju island were estimated using the tidal response technique. Groundwater level data from a saltwater intrusion monitoring well system was used which showed tidal effects from 3 to 5 km. The hydraulic gradient was assessed by utilizing the filtering method from 71 consecutive hourly water-level observations. Calculated hydraulic diffusivity ranged from 2.94${\times}10^7m^2d^{-1}$ to 4.36${\times}10^7m^2d^{-1}$ . The hydraulic gradient of the coastal aquifer area was found to be ~$10^{-4}$, whereas the gradient of the area between wells Handong-1 and 2 was found to be ~$10^{-6}$, which is very low comparatively. Analysis of groundwater monitoring data showed that groundwater levels are periodically higher near coastal areas compared to that of inner land areas due to oceanic tide influences. When assessing groundwater flow direction in coastal aquifers it is important to consider tidal fluctuation.

Development of Molecular Dynamics Model for Water Electrolysis Ionomer (수전해용 이오노머 분자동역학 모델 개발)

  • Kang, Hoseong;Park, Chi Hoon;Lee, Chang Hyun
    • Membrane Journal
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    • v.30 no.6
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    • pp.433-442
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    • 2020
  • In this study, in order to build a molecular dynamics simulation model of ionomer for water electrolysis, an ionomer model that reflects the characteristics of a water electrolysis system in which excess water molecules exist was compared to an ionomer built according to the conventional simulation method of the fuel cells membrane. The final ionomer MD models have a strong phase separation and water channel that is one of the important characteristics of the perfluorinated ionomer, and are stable and water-insoluble under excessive water and high temperature conditions. In the ionomer MD models built in this study, the excess water molecules decrease an ion conductivity due to the dilution of ions, but increase a hydrogen diffusivity. Therefore, it is necessary to design the molecular structure of ionomers for water electrolysis in experimental studies as well as molecular dynamics studies according to the characteristics of the water electrolysis system reported in this study.