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Now showing items 1 - 16 of 3389

  • Evaluation of membrane-based desalting processes for RO brine treatment

    Lee, Songbok   Kim, Youngjin   Kim, Albert S.   Hong, Seungkwan  

    Membrane-based desalting processes including reverse osmosis (RO), forward osmosis (FO), and membrane distillation (MD) were systematically evaluated for concentrating RO brine. Basic characteristics of membrane processes were first examined. Commercial polyamide RO exhibited higher water and lower salt permeability coefficients than cellulose FO membrane. However, salt rejection by FO seemed to be higher than RO primarily due to the hindrance of reverse draw solute flux. The water flux of MD comparable to RO was obtained when temperature gradient was more than 20-30 degrees C. The applicability of RO, FO, and MD was further tested with real brine obtained from full-scale RO plant processing brackish water. Results demonstrated that water flux was not significantly reduced in MD, while severe flux decline was observed in both RO and FO at high recovery. To elucidate major causes of different flux behaviors, the fouled membrane surfaces were analyzed by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. Foulant analysis suggested that CaCO3 scaling occurred particularly at high water recovery, which was in good agreement with water quality simulation. CaCO3 scaling, however, had only small impact on flux behavior in MD. From these findings, MD could be suggested as the best option for concentrating industrial RO brine if low-grade heat (below 50-70 degrees C) is available.
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  • Microhydrodynamics Simulation of Single-collector Granular Filtration

    Kim, Albert S.   Kang, Seok-Tae  

    Granular filtration phenomenon is fundamentally investigated using dissipative hydrodynamics with a large collector grain and a non-Brownian sphere. Effects of interparticle forces balanced with hydrodynamic interactions are studied for particle trajectory analysis. In addition to conventional deposition of fine particles on collector surfaces (mostly near front hemispheres), the hydrodynamic trapping of rotating fine particles on the back hemisphere surface is fundamentally investigated using the exact solution of two-body hydrodynamics.
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  • Microhydrodynamics Simulation of Single-collector Granular Filtration

    Kim, Albert S.   Kang, Seok-Tae  

    Granular filtration phenomenon is fundamentally investigated using dissipative hydrodynamics with a large collector grain and a non-Brownian sphere. Effects of interparticle forces balanced with hydrodynamic interactions are studied for particle trajectory analysis. In addition to conventional deposition of fine particles on collector surfaces (mostly near front hemispheres), the hydrodynamic trapping of rotating fine particles on the back hemisphere surface is fundamentally investigated using the exact solution of two-body hydrodynamics.
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  • Impact of surface porosity on water flux and structural parameter in forward osmosis

    Lee, Woonghee   Kang, Peter K.   Kim, Albert S.   Lee, Seockheon  

    Improving water flux is a crucial objective of research in forward osmosis (FO) technology. A structural parameter is the property of the support layer of the membrane that determines the internal concentration polarization, which is determined by the bulk porosity, tortuosity, and thickness of the support layer. Surface porosity, i.e., porosity at the interface between the active and support layers, has recently been recognized as another critical factor in determining the water flux behavior and the structural parameter. In this study, the relative importance of the surface porosity, bulk porosity, and pore geometry of the support layer on water flux behavior is investigated using a recently developed pore-scale CFD simulator. To this end, various straight-like pore geometries with different combinations of surface and bulk porosities are studied. An increase in bulk porosity reduces internal concentration polarization, thereby increasing effective osmotic pressure. However, for the same magnitude of increase, an increase in surface porosity leads to a significantly larger increase in water flux. We show that water flux is most sensitive to surface porosity, and inconsistency in the structural parameter can be resolved by introducing surface porosity into the FO modeling framework.
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  • Self-adjusting,combined diffusion in direct contact and vacuum membrane distillation

    Kim, Albert S.   Lee, Ho-Saeng   Moon, Deok-Soo   Kim, Hyeon-Ju  

    Coupled effects of two representative mass transfer phenomena in membrane distillation, i.e., Brownian and Knudsen diffusion, are investigated using molecular kinetics and statistical mechanics. Diffusive mass transfer along the membrane pore is analogously solved using the conventional theory of effusion phenomena, having both pressure and temperature gradients as driving forces. We quantitatively found that the molecular mean speed slightly increases in the presence of a temperature gradient, and the curvature effects of hollow fiber membranes are small if the inner radius is larger than the membrane thickness. In vacuum membrane distillation and direct contact membrane distillation, discarding the smaller of the Brownian or Knudsen diffusion may cause noticeable error in predicting the production rate of freshwater. When both the diffusion mechanisms are present, their coupling hinders the migration of the water vapor through pore spaces. Vapor molecules seem to take routes that minimize the diffusive coupling.
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  • Self-adjusting, combined diffusion in direct contact and vacuum membrane distillation

    Kim, Albert S.   Lee, Ho-Saeng   Moon, Deok-Soo   Kim, Hyeon-Ju  

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  • 3-D Monte Carlo simulation of particle deposition on a permeable surface

    Li, Yanling   Vu, Nam   Kim, Albert S.  

    Monte Carlo simulations are performed to investigate deposition phenomena of sticky particles that undergo diffusive, convective, and gravitational influences on a highly permeable surface. Deposited structures are studied in 3-D space using a Pelcet number as the key parameter. Fractal dimensions of the particle trajectory and deposit structure indicate that a transition from diffusion-limited to convection (and gravitation)-limited transport occurs at the Peclet number of Pe = 10(-0.84) = 0.146. Analysis of the lateral density shows three distinct regions of deposit structures (defined in this study): founding, grown, and progressing regions. A penetration depth is defined to explain the relationship between particle transport and the evolution of deposit structures. (C) 2009 Elsevier B.V. All rights reserved.
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  • Performance analysis of forward osmosis processes from the integral equation theory

    Kim, Albert S.   Kim, Sung Woo  

    We solved the Ornstein-Zernike integral equation to investigate non-linear behavior of osmotic pressure of solutions containing high concentrations of inorganic salts. Net interactions between molecules are assumed to be Lennard-Jones (LJ) potential, and various force fields were used to determine the potential parameters. Relationship between the LJ parameters and permeate flux are discussed, and relative significance of the osmotic pressure and diffusion coefficient on water flux in forward osmosis was investigated.
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  • Hydraulic permeability of polydispersed cake layers: an analytic approach

    Kim, Albert S.   Ng, Aileen N. L.  

    An analytic method is introduced to calculate hydraulic permeability of porous media composed of polydispersed spheres with log-normal and normal (Gaussian) distributions of particle sizes. From the comparison of the permeability for the two particle-size distributions, it was observed that a medium with normally distributed particle sizes consistently has a lower permeability than a medium with log-normally distributed particle sizes. This phenomenon is due to the larger number of smaller particles in the normal distribution, which results in greater cake resistance. The specific resistance of the cake layer is computed by taking the inverse of the permeability.
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  • Irreversible Chemical Potential and Shear-Induced Diffusion in Crossflow Filtration

    Kim, Albert S.   Liu, Yuewei  

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  • Origin of structural parameter inconsistency in forward osmosis models:A pore-scale CFD study

    Kang, Peter K.   Lee, Woonghee   Lee, Seockheon   Kim, Albert S.  

    Structural parameter is a representative quantity of a porous medium, often used to explain mass transfer rate in membrane processes. Intrinsic structural.parameter is defined using characteristic constants of a porous medium, and effective structural parameter is indirectly obtained by analyzing measured fluxes, especially in osmosis driven processes. Although the two parameters are fundamentally equivalent, recent experimental studies show noticeable discrepancies between them. To resolve the inconsistency, we hypothesize that the fraction of effective membrane surface area should include interfacial porosity between the active layer and the porous substrate. To test our hypothesis, we develop a new pore-scale CFD (computational fluid dynamics) solver for both mass and momentum transfer in transient forward osmosis phenomena. Two pre-existing solvers of OpenFOAM, an open-source computational fluid dynamics software package, are combined to seamlessly link the coupled transport phenomena across the active layer, the support layer, and the crossflow zone. We defined a new structural parameter using the simulated flux and the interfacial porosity, first addressed in this study, and obtained an excellent agreement between our CFD results and published experimental data in the literature.
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  • Analysis of full-scale membrane filtration processes using econophysics and econometrics

    Guo, Ying   Shi, Yong   Moncur, Jame E. T.   Lee, Yong Taek   Kim, Kyoung Wan   Kim, Albert S.  

    In this paper, econophysics and econometric approaches were employed to investigate statistical and dynamic properties of membrane performance, respectively, using filtration data provided by Woongjin Chemical Co., Ltd., Korea. For the econophysics approach, the filtration index tree was built to comprehensively visualize the closeness between filtration variables, analogous to the hierarchical index tree for the dynamics of stock prices. The logarithmic changes of the filtration variables follow the normal distribution, which implies that the filtration variables themselves are governed by the log-normal distribution due to periodic cleaning and/or seasonal variations. In the econometrics approach, the autoregressive model verified the periodicity of the pressure profile due to cleaning events and natural environmental changes. As developed in this study, the semi-loglinear and autocorrelation models captured pressure growth rates of 1.4% and 0.3 kg/cm(2) per week, respectively. Combined and complementary roles of econophysics and econometrics provided new methodological insights to statistically analyze and further forecast membrane filtration performance in terms of the pressure growth rate in the constant flux operation. (C) 2010 Elsevier B.V. All rights reserved.
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  • Hydrodynamics of an ideal aggregate with quadratically increasing permeability

    Kim, Albert S.   Yuan, Rong  

    In this study, we consider the ideal aggregate with quadratically increasing permeability κ
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  • Aggregate formation and collision efficiency in differential settling

    Kim, Albert S.   Stolzenbach, Keith D.  

    A new method of application of Stokesian dynamics, which can efficiently simulate movements of up to 500 particles with interparticle interactions in reasonable computational times, has been developed for the purpose of investigating particle–cluster aggregation in aqueous systems. The method is applied to monodisperse non-Brownian spherical particles aggregating in differential settling, while repulsive colloidal interaction is presumed to be negligible, so that a minimum separation distance can represent the attractive van der Waals force. The final aggregates formed by this algorithm, composed of 300 primary particles, have a common fractal dimension of 2.0. The computed collision efficiency, defined as the product of a global and a capture efficiency, is about 5.77×10−3. This value is significantly larger than the collision efficiency of primary particles colliding with an impermeable solid sphere of the same size as the aggregate, illustrating the important interplay between the permeability and the formation of aggregates.
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  • Performance control on adsorption desalination using initial time lag (ITL) of individual beds

    Kim, Albert S.   Lee, Ho-Saeng   Moon, Deok-Soo   Kim, Hyeon-Ju  

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  • Cake Structure in Dead-End Membrane Filtration: Monte Carlo Simulations

    Kim, Albert S.   Hoek, Eric M. V.  

    A statistical mechanical approach for predicting the long-term gradual flux decline due to colloid-cake formation in dead-end membrane filtration is presented. Monte Carlo simulations of cake layers composed of interacting colloidal particles are performed to predict volume fractions and corresponding radial distribution functions. The total osmotic pressure in the cake layer is extracted from interparticle interactions and the radial distribution function. The extracted osmotic pressure predictions are in good agreement with applied pressure, verifying the accuracy of the simulation method. The simulation method is then used to investigate the effect of particle size, ionic strength, zeta potential, and applied pressure on the cake structure, which is represented by the volume fraction and the radial distribution function. Finally, the influence of these effects on permeate flux decline during the dead-end membrane filtration of interacting colloidal particles is predicted and qualitatively compared to previously published experimental data.
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