Albert S. Kim

Influence of Crossflow Membrane Filter Geometry and Shear Rate on Colloidal Fouling in Reverse Osmosis and Nanofiltration Separations

A laboratory-scale crossflow membrane filtration apparatus was designed to investigate the relative influence of filter geometry and shear rate on colloidal fouling of reverse osmosis (RO) and nanofiltration (NF) membranes. An expression that allows clarification of the mechanisms of flux decline due to colloidal fouling in RO and NF separations was derived by combining the solution-diffusion model, film-theory, and a modified cake filtration model. With this new fouling model, the interplay between the salt concentration polarization layer and a growing colloid deposit layer may be quantified. The hydraulic pressure drop across a colloid deposit layer was shown to be negligible compared to cake-enhanced osmotic pressure. The difference in flux decline observed in filters with different channel heights resulted from different cake layer thickness, and thus, different cake-enhanced osmotic pressure. A moderate reduction in the initial concentration polarization and cake-enhanced osmotic pressure was obtain...

Cake structure in dead-end membrane filtration: Monte Carlo simulations

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 layer...

Fundamental mechanisms of three-component combined fouling with experimental verification.

The present article describes a novel fundamental theory for investigating combined fouling by colloids (STXL), macromolecules, and solute ions (NaCl). Three macromolecules were used for the combined fouling study, bovine serum albumin (BSA), alginate, and dextran. The presented theory unifies singlet, doublet, and triplet fouling phenomena, including cake-enhanced osmotic pressure and binary colloidal fouling models, giving rise to the combined flux equation for three-component fouling assuming a completely mixed fouling layer. The predicted combined flux was compared to two equivalent fluxes calculated from individual foulant contributions. The strong form of the equivalent flux, known as the additive flux, was based on a linear superposition of flux decline due to individual foulants. The weak form of equivalent flux assumed stratification of individual foulant layers and hence a linear superposition of the individual fouling resistance. A comparison of experimental data and theoretical calculations revealed that the weak form of equivalent flux and the combined flux that was predicted by the novel theory provided the upper and lower limits, respectively, of the observed permeate flux. Furthermore, the model simulation results suggested a structural compression of the BSA gel layer, whereas such a compression did not occur in cases of alginate and dextran. The gel concentrations of alginate and dextran in the combined fouling layer seemed to be less than those in the macromolecular gel layer.

Pervaporation of butanol/water mixtures using siloxane polymer/ceramic composite membranes

Abstract In this study, siloxane polymers were coated on a prepared alumina ceramic support layer (γ-Al2O3/α-Al2O3). A layer of rubbery polydimethylsiloxane (PDMS) was deposited on the γ-Al2O3 surface and a secondary coating of phenyltrimethoxysilane (PhTMS) was added to enhance membrane hydrophobicity. The role of the double ceramic support layers was discussed, using simple analytic calculations. PDMS/ceramic and PhTMS/PDMS/ceramic composite membranes were used to separate butanol from a butanol/water mixture using pervaporation. Eff ects of the secondary PhTMS coating were investigated with respect to butanol concentration, temperature, and fl ow rate of feed solution. The PhTMS/PDMS/ceramic composite membrane showed promising potential to improve butanol recovery from the fermentation broth but the trade-off is total flux reduction.

Development of Web-Based Engineering Numerical Software (WENS) Using MATLAB: Applications to Linear Algebra

In this article, we present Web‐based Engineering Numerical Software (WENS) developed using MATLAB and its Web Server Toolbox (WST) in order to provide basic solution tools in linear algebra, including eigenvalue problems, which are extensively used in engineering applications and education.

Knudsen Diffusion Through Cylindrical Tubes of Varying Radii: Theory and Monte Carlo Simulations

In this study, Knudsen diffusion of low-pressure gases of infinite mean free path through various tubes is studied using the integral equation theory (IET), standard diffusion theory, and Monte Carlo (MC) simulations. We investigated the transmission probabilities (TPs) of linearly diverging–converging, sinusoidally bulging, and periodic tubes as compared with TPs of conventional straight cylinders. An exact analytic solution for the TP through the straight cylindrical tube was developed using the standard diffusion theory with a linear concentration approximation. IET for the TPs through the diverging–converging and bulging tubes were developed. MC simulation techniques were applied to calculate TPs through all the tube types azimuthal symmetry of which was held with tube radius changing only along the axial coordinate (z). The linearly diverging–converging and sinusoidally bulging tubes provide noticeably higher TPs than those of the equivalent straight tubes. Periodic tubes show that if the tube length scaled by the equivalent diameter is of an order of or greater than the periodicity coefficient (equal to the number of peaks on the tube wall), then the TP of the periodic tube is larger than that of the equivalent straight tube.

Evaluation of membrane-based desalting processes for RO brine treatment

AbstractMembrane-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°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...

Perspective of membrane distillation applied to ocean thermal energy conversion

Authors investigated the potential application of vacuum membrane distillation (VMD) to the conventional ocean thermal energy conversion (OTEC). Open, closed, and hybrid cycles of OTEC are reviewed, and strategies to enhance performance of open cycle (OC) using VMD are discussed. The advantages of using VMD modular sets include reducing system sizes and enhancing power production rates. Our rough estimation indicates that VMD uses only about 10 per cent of the system volume required by OC-OTEC. Tasks to actualize the promising VMD technology are discussed for the next generation OC-OTEC.

Performance analysis of forward osmosis processes from the integral equation theory

Abstract 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.

Simulation of colloidal fouling by coupling a dynamically updating velocity profile and electric field interactions with Force Bias Monte Carlo methods for membrane filtration.

Pressure-driven flow through a channel with membrane walls is modeled for high particulate volume fractions of 10%. Particle transport is influenced by Brownian diffusion, shear-induced diffusion, and convection due to the axial crossflow. The particles are also subject to electrostatic double layer repulsion and van der Waals attraction, from both particle-particle and particle-membrane interactions. Force Bias Monte Carlo (FBMC) simulations predict the deposition of the particles onto the membranes, where both hydrodynamics and the change in particle potentials determine the probability that a proposed move is accepted. The particle volume fraction is used to determine an apparent local viscosity observed by the continuum flow. As particles migrate, the crossflow velocity field evolves in quasi-steady fashion with each time instance appearing fully developed in the downstream direction. Particles subject to combined hydrodynamic and electric effects (electrostatic double layer repulsion and van der Waals attraction) reach a more stable steady-state as compared to systems with only hydrodynamic effects considered. As expected, at higher crossflow Reynolds numbers more particles remain in the crossflow free stream.