Home About us Contact
|
Home About us Contact | ||
|
|
||
Mass Transport Model (mass + transport_model)
Selected AbstractsSimulations of IEF in microchannel with variable cross-sectional areaELECTROPHORESIS, Issue 5 2009Yin Chou Abstract This study develops a 1-D mass transport model to describe the electrophoresis transport behavior within a microchannel with a variable cross-sectional area. Utilizing three different numerical schemes, simulations are performed to investigate the IEF of proteins in ampholyte-based pH gradients within both a planar microchannel and a contraction,expansion microchannel, respectively. The simulation results obtained using the modified 1-D mass transport model and the finite-volume method (FVM) for the IEF separation of a single protein sample in a ten-ampholyte-based pH gradient within a planar microchannel are consistent with those presented by Shim et al. [Electrophoresis 2007, 28, 572,586] using a 2-D FVM scheme. In addition, the Courant,Friedrichs,Lewy number insensitive conservation element and solution element (CNI-CESE) method is found to be both more robust and more computationally efficient than the conventional CESE scheme when modeling IEF phenomena within a contraction,expansion microchannel. In modeling the IEF separation of four sample ampholytes in a 20-ampholtye-based pH gradient within a contraction,expansion microchannel, the results obtained using the CNI-CESE scheme are in good agreement with those published in literature. Moreover, the simulations can be performed significantly faster with the new 1-D model and the CNI-CESE scheme. Finally, the results obtained using the modified 1-D mass transport model and the CNI-CESE scheme demonstrate that the concentration of the focused test sample and the resolution of the pH gradient within the microchannel increase as the number of ampholytes used to accomplish the IEF separation process is increased. [source] Hydrologic and geochemical controls on soluble benzene migration in sedimentary basinsGEOFLUIDS (ELECTRONIC), Issue 2 2005Y. ZHANG Abstract The effects of groundwater flow and biodegradation on the long-distance migration of petroleum-derived benzene in oil-bearing sedimentary basins are evaluated. Using an idealized basin representation, a coupled groundwater flow and heat transfer model computes the hydraulic head, stream function, and temperature in the basin. A coupled mass transport model simulates water washing of benzene from an oil reservoir and its miscible, advective/dispersive transport by groundwater. Benzene mass transfer at the oil,water contact is computed assuming equilibrium partitioning. A first-order rate constant is used to represent aqueous benzene biodegradation. A sensitivity study is used to evaluate the effect of the variation in aquifer/geochemical parameters and oil reservoir location on benzene transport. Our results indicate that in a basin with active hydrodynamics, miscible benzene transport is dominated by advection. Diffusion may dominate within the cap rock when its permeability is less than 10,19 m2. Miscible benzene transport can form surface anomalies, sometimes adjacent to oil fields. Biodegradation controls the distance of transport down-gradient from a reservoir. We conclude that benzene detected in exploration wells may indicate an oil reservoir that lies hydraulically up-gradient. Geochemical sampling of hydrocarbons from springs and exploration wells can be useful only when the oil reservoir is located within about 20 km. Benzene soil gas anomalies may form due to regional hydrodynamics rather than separate phase migration. Diffusion alone cannot explain the elevated benzene concentration observed in carrier beds several km away from oil fields. [source] Sorption of copper by a highly mineralized peat in batch and packed-bed systemsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2010Marta Izquierdo Abstract BACKGROUND: The performance of peat for copper sorption was investigated in batch and fixed-bed experiments. The effect of pH was evaluated in batch experiments and the experimental data were fitted to an equilibrium model including pH dependence. Hydrodynamic axial dispersion was estimated by tracing experiments using LiCl as a tracer. Six fixed-bed experiments were carried out at copper concentrations between 1 and 60 mg dm,3 and the adsorption isotherm in dynamic mode was obtained. A mass transport model including convection,dispersion and sorption processes was applied for breakthrough curve modelling. RESULTS: Maximum uptake capacities in batch mode were 22.0, 36.4, and 43.7 mg g,1 for pH values of 4.0, 5.0, and 6.0, respectively. Uptake capacities in continuous flow systems varied from 36.5 to 43.4 mg g,1 for copper concentrations between 1 and 60 mg dm,3. Dynamic and batch isotherms showed different shapes but a similar maximum uptake capacity. Sorbent regeneration was successfully performed with HCl. A potential relationship between dispersion coefficient and velocity was obtained with dispersion coefficients between 5.00 × 10,8 and 2.95 × 10,6 m2 s,1 for water velocities ranging between 0.56 × 10,4 and 5.03 × 10,4 m s,1. The mass transport model predicted both the breakpoints and the shape of the breakthrough curves. CONCLUSIONS: High retention capacities indicate that peat can be used as an effective sorbent for the treatment of wastewater containing copper ions. Copyright © 2009 Society of Chemical Industry [source] Multicomponent mass transport model for the sorption of metal ions on bone charAICHE JOURNAL, Issue 9 2004Danny C. K. Ko Abstract The sorption of binary mixtures of copper/cadmium and copper/zinc ions onto bone char was studied in fixed beds. The effects of solution flow rate, initial dye concentration, and bone char particle size range were investigated. A mass transport model based on film-surface diffusion and the IAS model for the equilibrium relationship was used to develop theoretical fixed-bed breakthrough curves. The model incorporates the Sips isotherm for the first time in fixed-bed predictions, since this isotherm gives an excellent correlation of the experimental equilibrium data. The model was used to determine the optimum surface diffusivities as 7.37 × 10,10 and 2.73 × 10,9 cm2/s for copper and cadmium in the Cu/Cd system; and 1.61 × 10,9 and 2.43 × 10,9 cm2/s for copper and zinc in the Cu/Zn system. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2130,2141, 2004 [source] Performance assessment of hanging funnel-and-gate structures designed by reverse particle tracking for capturing polluted groundwaterREMEDIATION, Issue 3 2007Paul F. Hudak The objective of this study was to evaluate the capability of partially penetrating (hanging) funnel-and-gate structures, designed using reverse flow trajectories, for capturing plumes of contaminated groundwater. Linear capture structures, comprised of two slurry cutoff walls on either side of a permeable gate, were positioned perpendicular to regional groundwater flow in a hypothetical unconfined aquifer. A four-step approach was used for each of two simulated settings: (1) a numerical mass transport model generated a contaminant plume originating from a source area; (2) a particle-tracking model projected groundwater flow paths upstream from a treatment gate; (3) the structure was widened and deepened until bounding path lines contained the plume; and (4) mass transport simulation tested the ability of the structure to capture the plume. Results of this study suggest that designing funnel-and-gate structures using reverse particle tracking may result in too small a structure to capture a contaminant plume. This practice generally ignores effects of hydrodynamic dispersion, which may enlarge plumes such that contaminants move beneath or around a capture structure. This bypassing effect may be considerable even for low values of dispersivity. Particle-tracking approaches may also underestimate the amount of time required to reduce contaminant concentrations to acceptable levels. © 2007 Wiley Periodicals, Inc. [source] | |||||||||||||