bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and characterization of oriented MFI membranes prepared by secondary growth
Authors: Lovallo Mark C. , Gouzinis Anastasios , Tsapatsis Michael
Published: April 2004

MFI membranes were prepared as free‐standing and supported films on porous alumina disks and nonporous substrates. They were synthesized using secondary growth of precursor layers. For self‐supported films the first step was to prepare an alumina–silicalite composite film, while for supported films the substrate was first coated with layers of the nanocrystalline silicalite particles. During the following hydrothermal treatment, silicalite particles acting as seed crystals form a dense film, which consists of 0.5–100‐μm‐thick columnar, intergrown, preferentially oriented grains. The crystal orientation of the MFI films was examined using X‐ray diffraction pole‐figure texture analysis. The crystals were preferentially oriented with both sinusoidal and straight channel networks along directions nearly parallel to the membrane surface. The degree of orientation increased with increasing membrane thickness. Single gas permeances through thin, oriented membranes were measured. Apparent actiuation energies for permeation were 16, 24, 30, 22 and 26 kj/mol for H2, N2, O2, CH4, and CO2, respectively. Ideal selectivities for H2/N2, CO2/CH4, and O2/N2 were as high as 30, 10, and 3.5, respectively. Binary permeation measurements for the gas pairs CO2/CH4, O2/N2, and CO2/N2 revealed trends similar to those of single gas permeation and the properties are attributed to the membrane microstructure.
Theory of batchwise centrifugal casting
Authors: Maarten Biesheuvel P. , Nijmeijer Arian , Verweij Henk
Published: April 2004

In batchwise centrifugal casting a cylindrical mold is filled with suspension and rotated rapidly around its axis. This results in the movement of the particulate phase toward the cylinder wall and the formation of a tubular cast. Theory is presented for particle transport in the suspension phase and subsequent cast growth using concepts from the related fields of centrifugal sedimentation and centrifugal separation. Most attention is given to the situation of complete mold filling, which allows for several distinct simplifications. Analytical expressions for suspension concentration and cast growth are presented for the case of unhindered settling. Numerical simulations are made for hindered settling. The outcome shows a good agreement with experiments in which homogeneous porous ceramic membrane supports are made from a submicronsized α‐alumina powder.
Random motility of swimming bacteria in restricted geometries
Authors: Biondi Sherri A. , Quinn John A. , Goldfine Howard
Published: April 2004

The effects of restricted geometries on the swimming behavior of Escherichia coli were examined. Videomicroscopy and image analysis techniques were used to measure single‐cell motility parameters (cell velocity, tumbling probability, and turn angle) in microfabricated 2‐D channels ranging from 2 to 20 μm in height. Macroscopic motility coefficients were calculated from the single‐cell data and compared to literature values. These observations indicate that single‐cell parameters remain nearly constant in confined spaces in which channel heights approach the size of the bacterium. The nearly constant swimming behavior of individual cells in confined geometries indicates that the macroscopic motility coefficient describing population behavior will be greater than the unrestricted value by a factor proportional to the dimensionality of the system.
Influence of transport and reaction on wormhole formation in porous media
Authors: Fredd Christopher N. , Fogler H. Scott
Published: April 2004

The transport and reaction of fluids in porous media results in unique pore growth and channel evolution as the media are dissolved. This often leads to the formation of highly conductive flow channels, commonly referred to as wormholes. The objective of this work is to predict the influence of transport and reaction on the structure of the wormhole channels. An experimental and theoretical investigation of a variety of fluid systems, including strong acids, weak acids, and chelating agents, provides a wide range of conditions for studying wormhole formation. A generalized description of the dissolution phenomenon is introduced, and a common dependence on the Damköhler number is demonstrated. The Damköhler number is shown to dictate the type of wormhole structure formed by systems with various degrees of transport and reaction limitations. An optimum Damköhler number for channel formation is observed at a value of approximately 0.29 for all of the fluid systems investigated. The stochastic nature of the dissolution phenomenon is described using network models. Results from a 2‐D network model and a 3‐D physically representative network model agree qualitatively with experimental results and substantiate the existence of an optimum Damköhler number.
Mechanisms by which pulsatile flow affects cross‐flow microfiltration
Authors: Li Hong‐yu , Bertram Christopher D. , Wiley Dianne E.
Published: April 2004

The effect of pulsatile flow on particle deposition during cross‐flow microfiltration was studied to establish the degree to which backflushing and shear‐rate changes induced during pulsation alter cake formation. The minimum transmembrane pressure and maximum absolute cross‐flow velocity derivative were chosen to quantify the backflushing and shear effects, respectively. Experiments were conducted for pulsatile flows with four distinct types of transmembrane pressure and flow‐rate waveforms. In the absence of backflushing the cake resistance was reduced at high values of shear rate, but not significantly affected at low values compared with steady flow. Tests at constant shear rate demonstrated that the cake resistance was reduced when backflushing was imposed on the system. In tests with two transmembrane pressure waveforms, cake deposition was almost completely eliminated by instantaneous backflushing. Although both backflushing and shear‐rate changes reduce cake deposition in microfiltration, backflushing achieved the greatest reductions.
Hydrogen purification from refinery fuel gas by pressure swing adsorption
Authors: Malek A. , Farooq S.
Published: April 2004

Hydrogen purification and recovery from various process streams constitutes the largest commercial use of pressure swing adsorption (PSA) technology. This study investigates the performance of a six‐bed, dual‐sorbent PSA operation for hydrogen purification from the refinery fuel gas. Major impurities are methane, ethane, propane and butane, and comprise 30–40% of the feed. The dual‐sorbent PSA bed consists of an initial layer of silica gel adsorbent for trapping heavier hydrocarbons and a subsequent layer of activated carbon for removing lighter hydrocarbons. A numerical simulation model of the H2‐PSA process developed with all the essential features of the actual operation shows that butane is more strongly adsorbed on activated carbon than silica gel, and, hence, is less easily desorbed from the former using simple pressure reduction in the PSA cycle. Therefore, the initial layer serves to prevent butane from degrading the adsorptive capacity provided by activated carbon for other lighter hydrocarbons. The simulation model agrees well with the experimental results from a laboratory unit as well as with available H2 ‐PSA plant data from a refinery. The results also indicate the importance of heat effects in this process. Extensive parametric studies, which show effects of feed velocity and cycle time on the variation of product recovery and purity obtainable from the industrial unit, provide a valuable guide for its proper operation.
Robust optimization framework for process parameter and tolerance design
Authors: Bernardo Fernando P. , Saraiva Pedro M.
Published: April 2004

This article introduces a framework for including different uncertainties at the chemical plant design stage. Through an integrated robust optimization approach and problem formulation, equipment, operating, control, and quality costs are simultaneously taken into account, leading to system, parameter, and tolerance design. Rather than using single pointwise solutions in the decision space, operating windows leading to overall best performance are identified and defined. Such windows and their width allow us to point out control needs and goals at a very early stage of plant design. Two small‐scale case studies (for a CSTR and a batch distillation column) provide enough evidence to support the practicality of the optimization framework: the robust solutions found are different and much better than the corresponding solutions obtained with the fully deterministic optimization paradigms.
Numerical analysis of kinetic rate constants derived from stochastic computer simulation
Authors: Wu Peiru , McGuffin Victoria L.
Published: April 2004

A numerical approach has been developed to determine the individual rate constants (kf − s and ks − f), as well as the equilibrium constant from the ratio of the rate constants (kf − s/ks − f), by using stochastic simulation. This approach is illustrated for simulations of the absorption (partition) process between homogeneous fluid and surface phases under diffusion‐limited conditions. A pair of regression methods is derived from the chemical system with the initial distribution of molecules entirely in either the fluid or surface phase. These two methods are complementary in determining the rate constants for distribution coefficients that are lower or higher than unity, respectively. A standard exponential (two‐parameter) regression equation is compared with a biexponential (four‐parameter) equation, which provides for inherent correction of numerical error. The effects of the number of molecules, as well as the time increment and range, are examined in detail. This provides guidance to optimize the computational parameters of the simulation. The proposed approach has been successfully applied for distribution coefficients ranging from 0.01 to 100.0, yielding individual rate constants kf − s and ks − f with ± 0.84% and ± 0.57% average relative standard deviation, and the ratio of the rate constants with ± 1.04% average relative standard deviation and ± 1.14% average relative error.
Modeling and optimization of a model IV fluidized catalytic cracking unit
Authors: Ellis Robert C. , Li Xuan , Riggs James B.
Published: April 2004

The problem of on‐line optimization of a model IV fluidized catalytic cracking (FCC) unit is analyzed. The “process” was modeled by combining a model IV FCC unit dynamic simulator (McFarlane et al, 1993; Khandalekar, 1993) with a ten‐lump yield model (Jacob et al, 1976; Arbel et al., 1995) for the reactor section. The steady‐state optimization model consisted of macroscopic steady‐state models of the regenerator and reactor, a simplified reactor yield model, and models of the various process constraints. The steady‐state optimization problem was solved using successive quadratic programming software (NPSOL, Gill et al., 1986) and the optimum process set points were implemented on the process simulator using a nonlinear constraint controller (Kandalekar and Riggs, 1995). The relative performance of constraint control, off‐line optimization, and on‐line optimization is compared for different feed characteristics and product pricing structures.
Tuning alkylation reactions with temperature in near‐critical water
Authors: Chandler Karen , Liotta Charles L. , Eckert Charles A. , Schiraldi David
Published: April 2004

Quantitative kinetics for the alkylation reactions of phenol and p‐cresol with tert‐butyl alcohol in near‐critical water as a function of temperature are reported. The reaction products of the alkylation reactions were ortho‐ and para‐substituted phenols, which are used extensively as antioxidants in numerous polymer systems. A new experimental reaction apparatus was designed, constructed, and successfully operated to allow pressure control and sampling of the reaction systems, which provided rate constants in the temperature range 250–300°C. Additionally, activation energies and heats of formation were calculated from the temperature dependence of the rate constants, and ortho‐substitution was found to be exothermic whereas para‐substitution was found to be endothermic. These results demonstrate that product distribution of the alkylation reactions could be tuned with temperature to produce specific products.
Horizontal drying fronts during solvent evaporation from latex films
Authors: Routh Alexander F. , Russel William B.
Published: April 2004

Latex films cast on a substrate often dry nonuniformly, with a drying front separating fluid domains from solidified regions passing across the film. For initial film thicknesses that are smaller than the characteristic horizontal distance, the analysis predicts surface‐tension‐driven horizontal flow. In a limit that ensures vertical homogeneity it is shown how a front of close‐packed particles forms and propagates. Imposing a maximum for the capillary pressure causes a solvent front to recede into the film. This recession is minimal, but can markedly affect the propagation of the particle front. An overall mass balance offers a solution for infinite capillary pressure, thereby illustrating the mechanism for propagation of the front. The positions of the fronts are predicted for both infinite and finite domains as a function of the maximum capillary pressure. Selective or nonuniform evaporation produces final film profiles, while the evaporating regions are still visible. After predictions over different size areas are made, the smallest area is compared with experiment.
Optimal design and operation of heat exchangers under milk fouling
Authors: Georgiadis Michael C. , Rotstein Guillermo E. , Macchietto Sandro
Published: April 2004

This article presents a procedure for the simultaneous optimization of the design and operation of heat exchangers under milk fouling. This scheme is based on a highly accurate dynamic model described by integral, partial differential, and algebraic equations. Design and operating parameters determined by the dynamic optimization include the length and diameter of the exchanger, the control policy, and the timing of the key operating steps. An economic objective function is used to account for the important factors related to milk heat treatment, and many operating constraints are imposed. Three heat exchanger configurations are considered to study the effect of fouling on the optimal plant design. Optimization indicates that the cost factor due to the interruption of production is dominant, while an increase in energy consumption due to fouling is not very important. The constant wall temperature configuration proved to be the most economical. The economic impact of different control structures was also explored.
Microbial enhancement of TCE and 1,2‐DCA solute flux in UF‐membrane bioreactors
Authors: Inguva Subbalaxmi , Boensch Melissa , Shreve Gina S.
Published: April 2004

An ultrafiltration membrane process was used to remove and biograde chlorinated aliphatic hydrocarbons trichloroethylene (TCE) and 1,2‐dichloroethane (1,2‐DCA) from dilute aqueous streams. The effect of microbial biodegradative activity on TCE and 1,2‐DCA solute flux in a polypropylene membrane was examined using microbial strains Pseudomonas cepacia PR131 for the biodegradation of TCE and Xanthobacter autotrophicus GJ10 for the biodegradation of 1,2‐DCA. Initial experiments were conducted in diaphragm cells in the absence of microorganisms to determine the diffusion coefficient of 1,2‐DCA and TCE in the polypropylene ultrafiltration (UF) membranes. The diffusivities were 4.7 × 10−8 cm2/s for 1,2‐DCA and 1.41 × 10−7 cm2/s for TCE. Subsequent experiments were conducted with microorganisms on the permeate side to examine the effect of microbial degradation of 1,2‐DCA and TCE on the solute flux across the UF membrane. Experiments were conducted sequentially in batch and flow diaphragm cells and then in a hollow‐fiber UF module to systematically examine the effect of microbial activity on the solute flux in each configuration and the ability of mathematical models to predict the microbial enhancement of solute flux. Microbial biodegradation of TCE and 1,2‐DCA significantly enhanced the solute flux, and experimental results were correlated with steady‐ and nonsteady‐state solute component balance models for the flow and batch diaphragm cells, respectively. Model and experimental results agree well. Implications for using membrane bioreactors to treat CAH contaminated groundwater and industrial effluents are discussed, as well as a method for examining the effect of biological reaction on membrane transport processes.
Computational analysis of slot coating on a tensioned web
Authors: Feng James Q.
Published: April 2004

When a web (thin substrate with considerable flexibility) travels through a coating applicator in free span between the two supporting rollers, the gap between web and coating applicator is determined primarily by the hydrodynamic stresses in the coating flow and externally applied tension on the web. The elastohydrodynamic interaction between the tensioned‐web deformation and the viscous liquid flow in the coating bead has not been extensively studied, in spite of its practical importance. A tensioned‐web wrapped around a slot coater was analyzed here by finite‐element computations. The externally applied tension on the web typically is much greater than the force due to hydrodynamic stresses. Hence, tension in the web is assumed to be constant in the process direction tangential to the web surface. By neglecting the bending and twisting moments as in the approximation of membrane theory, the shape of the flexible web is determined by a normal stress balance equation, quite similar to that of the free surface of coating flow with a constant surface tension. In this work, elastohydrodynamic effects in tensioned‐web slot coating are examined with respect to variations of the liquid feeding rate and externally applied web tension, web wrap angle, and other variables.
Electrolytic membrane recovery of bromine from waste hydrogen bromide streams
Authors: Wauters Cary N. , Winnick Jack
Published: April 2004

A novel electrochemical process was developed for the recovery of bromine from waste gas‐phase hydrogen bromide streams. It uses a molten‐salt‐saturated membrane to electrolytically decompose hydrogen bromide into its molecular constituents, which are separated into a hydrogen‐enriched waste stream and a pure bromine product stream. Single‐cell studies were carried out in a configuration consisting of two cell housings (vitreous carbon), two gas‐diffusion electrodes (reticulated vitreous carbon or graphite felt), and a molten salt [(Li0.575K0.133Cs0.292)Br] saturated membrane (zirconia). Single‐cell results at 300°C, based on process stream concentrations ranging from 25 to 75% hydrogen bromide at 50 to 300 mL/min, demonstrated current densities exceeding 1 A/cm2 and removals as high as 95%. Water and acetone (as a light organic contaminant) addition to the process feed, as well as exposure to thermal cycling, showed no deleterious effects on cell performance. Preliminary economics indicate this to be a viable process.
Fractional crystallization by gas antisolvent technique: Theory and experiments
Authors: Bertucco Alberto , Lora Michele , Kikic Ireneo
Published: April 2004

The efficacy of CO2 us an antisolvent was studied experimentally for the precipitation of naphthalene and phenanthrene from their solutions in toluene at 298 and 310 K. Phenanthrene was salted out of solution at every condition investigated, whereas naphthalene was never segregated as a solid phase. These behaviors are explained by a model representing the composition of the phases and supersaturation of the solution as functions of pressure. Based on results from ternary systems, experiments were performed with the quaternary system CO2‐toluene‐naphthakne‐phenanthrene: starting from an equimolar solution of the two solids in toluene, phenanthrene with a purity higher than 98.5% can be collected in the precipitation cell, while naphthalene with about 13% of phenanthrene is recovered from the liquid phase after expansion. The simulation of the process was able to account for the experimental evidence. Although the solutes used do not have a practical application, a general method is outlined to exploit the possibility of using the supercritical antisolvent technique for separation.
Role of porosity in filtration: XIII. Behavior of highly compactible cakes
Authors: Tiller Frank M. , Kwon Jae Hyun
Published: April 2004

Compatibility of cakes and sediments is a key factor in the behavior of thickeners, filters, centrifuges and belt presses. Stress applied to cakes decreases porosity and increases resistance to flow. Empirical models presented here represent solidosity (volume fraction of solids) εs, specific resistance α and permeability K as functions of effective pressure ps that are essential to developing mathematical models of thickening, filtration, and centrifugation. As suspensions are flocculated, the resulting aggregates become increasingly fragile and more compactible. Cake behavior undergoes substantial change, until it reaches a point at which increasing pressure unexpectedly no longer affects either % cake solids or filtrate volume vs. time. Traditional formulas for filtrate volume vs. time and average values of α, K, and εs were modified for highly compactible materials. The average value of α is proportional to the pressure drop across the cake and the average permeability is inversely proportional to Δpc.
Electrochemical membrane separation of H2S from reducing gas streams
Authors: Robinson Jeffrey S. , Smith D. Scott , Winnick Jack
Published: April 2004

An improved electrochemical membrane was tested with simulated coal gas having concentrations from 25 to 4,500 ppm H2S. The process produces elemental hydrogen that enriches the process gas stream at the cathode and elemental sulfur vapor that emerges from the anode. Removal efficiencies average up to 90% at any inlet level; current efficiencies are near 100% at the high inlet concentrations, decreasing significantly at lower H2S levels as the competing reduction of H2O becomes more favored. Molten carbonate fuel cell (MCFC) materials can be used exclusively at the MCFC operating temperature of 650°C, with the low concentrations of H2S, including the NiO cathode. At concentrations higher than about 60 ppm the operating temperature must be lowered approximately 50°C to avoid melting of the sulfided nickel cathode.
Effect of kinetics and mass transfer on design of extractive reaction processes
Authors: Samant Ketan D. , Ng Ka M.
Published: April 2004

A generic model is derived for studying the effects of chemical kinetics and mass transfer on extractive reaction processes. Activity‐based models are used to describe non‐ideal liquid‐liquid phase equilibrium and reaction kinetics. Maxwell‐Stefan formulation and the film model are used to describe multicomponent mass transfer. The effects of kinetics and mass transfer are described in terms of Damköhler number matrices for reaction and for mass transfer, respectively. The elements of these matrices measure the rates of reactions and mass transfer relative to product removal. These effects are demonstrated using examples of systems with inherent phase separation and systems with solvent‐induced phase separation. The results show that it may not always be beneficial to operate extractive reaction processes near the equilibrium thermodynamic limit. Damköhler numbers have to be chosen carefully to obtain the desired performance. The use of the model in evaluating performance trade‐offs and in making judicious choices about reactor attributes is demonstrated.
State‐space nonlinear process modeling: Identification and universality
Authors: Sentoni Guillermo B. , Biegler Lorenz T. , Guiver John B. , Zhao Hong
Published: April 2004

A practical approach was used to identify nonlinear models from available data. Knowing the true dynamics of a process allows implementation of a better and more efficient control scheme. Since this knowledge is not always available, a valid alternative to obtain a model is to identify the system. For that purpose, the DABNet (Decoupled A‐B Net) structure was used that is composed of a decoupled linear dynamic system followed by a nonlinear static map. The linear dynamic system was initially spanned by a set of discrete Laguerre systems and then cascaded with a single hidden layer Perceptron. A model reduction technique (linear balancing) used on the hidden nodes of the neural network as part of the identification process makes it possible not only to identify the main time constants, but reduce the dimensionality of the Perceptron input. It was proven that the DABNet structure can approximate every nonlinear, causal, discrete time invariant, multiple‐input single‐output system with fading memory. The final model consists of a linear state‐space system whose states, decoupled by input, are mapped by a neural network. Results concerning the application of the methodology to the approximation of a CSTR and a polymer process are presented.
Synthesis of processing system around a crystallizer
Authors: Chang Wen‐Chi , Ng Ka M.
Published: April 2004

A systematic procedure is developed to synthesize the processing system upstream and downstream of a crystallizer. In a step‐by‐step manner, the procedure guides the user to generate alternative flow sheets for treating a given crystallizer effluent. It consists of five steps. The required unit operations are determined by comparing the product specifications (production rate, product purity, and others) with the crystallizer effluent characteristics (occlusions, inclusions, crystal size, and others). Secondly, the destinations of the reaction solvent, mother liquor, wash liquid, recrystallization solvent, and drowning‐out solvent are assigned. Third, the solvent recovery system is considered to recover the solvents and unconverted reactants and to remove the impurity from the system. Fourth, alternatives for enhancing process performance are identified. Finally, short‐cut models are used to screen process alternatives. Rules and heuristics are provided for each step, and examples for illustrating this procedure are presented.
Conversion of methane to higher hydrocarbons in AC nonequilibrium plasmas
Authors: Thanyachotpaiboon K. , Chavadej S. , Caldwell T. A. , Lobban L. L. , Mallinson R. G.
Published: April 2004

The effects of plasma chemistry on the conversion of methane were studied using a dielectric barrier discharge reactor at ambient temperatures. A dielectric barrier discharge reactor generates a nonequilibrium plasma when a sufficiently high voltage is applied across the reactor's electrodes. Methane molecules are activated at this temperature and coupled to form C2 hydrocarbons, higher hydrocarbons, and hydrogen. The study on the effect of voltage, residence time and third bodies on methane conversion and product selectivity shows that methane conversion initially increases with increasing voltage and residence time above the breakdown voltage, and product selectivities are essentially independent of the voltage. Production of hydrogen during the reaction limits olefin production. Methane conversion also increases when helium and ethane are in the feed stream. Helium and ethane both appear to be more easily activated than methane and enhance methane activation and conversion.
Analysis of microwave sintering of ceramics
Authors: Chatterjee Anindita , Basak Tanmay , Ayappa K. G.
Published: April 2004

The microwave heating of ceramic materials has been analyzed by solving the equations for grain growth and porosity (Svoboda and Riedel, 1992) during the late stages of sintering, coupled with the heat conduction equation and electric field equations for 1‐D slabs. Microwave power absorption and heating profiles have been calculated for A12O3 and SiC in the absence of sintering, and calculations have been carried out to study the effect of increasing dielectric loss ofAl2O3 as a function of temperature. A comparison of the densification and grain growth for A12O3 during microwave and conventional sintering indicates that within the framework of the present model, there is no difference between the two heating modes during the late stages of sintering.
Effect of nucleatipn profile on particle‐size distribution
Authors: Sathyagal A. N. , McCormick A. V.
Published: April 2004

Nucleation transients are important features in the reactive generation of monodisperse colloids from solution. Many previous theoretical investigations, both analytical and numerical, have addressed the roles of colloid aggregation or of direct growth from solution. Few have addressed the role of nucleation transients on the size distribution. The population balance model was used to study the effect of nucleation transients on an aggregating colloidal dispersion. (To simplify the problem, growth was neglected.) The focus was on whether, under the action of aggregation alone, extended and divided nucleation periods in some cases can lead to a very narrow particle‐size distribution. Our results support previous treatments (Look et al, 1990; Bogush and Zukoski, 1991b) suggesting this is the case. Our general approach also offers additional insights, such as strategies to manipulate the nucleation transients to independently tune the average particle size and the variance of the distribution.
Surface‐tension prediction for liquid mixtures
Authors: Escobedo Joel , Mansoori G. Ali
Published: April 2004

Escobedo and Mansoori (1996) recently proposed a new expression, originally derived from statistical mechanics, for the surface‐tension prediction of pure fluids. The theory presented here is extended to matures of organic liquids based on the conformal solution theory of mixtures. Using the proposed equation, surface tensions of 55 binary mixtures are predicted within an overall 0.50 AAD%, which is better than other available prediction methods. The 55 binary mixtures are predicted within an overall 2.10 AAD% with a corresponding‐states version of the theory. The expressions proposed in this work are general since they have been applied to a variety of binary mixtures, and the results obtained agree well with the experimental data. The proposed model is directly applicable to multicomponent liquid mixtures.
Entrainment of air by a solid surface plunging into a non‐newtonian liquid
Authors: Cohu Olivier , Benkreira Hadj
Published: April 2004

An experimental investigation of the effect of fluid rheology on air entrainment in plunging tape experiments (dip coating) was carried out. The critical velocity at which the dynamic wetting line breaks up, allowing air to entrain into the liquid, was measured for a range of viscoelastic polymer solutions in glycerin/water mixtures. Variations of the critical velocities with various solutions were found to be unexpectedly small in comparison with the large viscosity variations. The results suggest that dynamic wetting failure and subsequent air entrainment are governed by nonhydrodynamic phenomena occurring at the molecular scale at the wetting line. It was also found that fluid elasticity gives rise to flow instabilities that may lead to a different, hydrodynamic mechanism of air entrainment.
Incompressive cake filtration: Mechanism, parameters, and modeling
Authors: Civan Faruk
Published: April 2004

Improved models developed verify interpretation and prediction of incompressible filter cake thickness, filtrate volume, and rate data for linear and radial filtration cases at static and dynamic conditions. Based on the methods for determining model parameters from experimental filtration data, three sets of experimental data were analyzed, which demonstrate the diagnostic and predictive capabilities of the model. These models provide insight into the mechanism of incompressible cake filtration and offer practical means of interpreting experimental data, estimating the model parameters and simulating the linear and radial filtration processes.
Two‐dimensional model for proton exchange membrane fuel cells
Authors: Gurau Vladimir , Liu Hongtan , Kakaç Sadik
Published: April 2004

A 2‐D mathematical model for the entire sandwich of a proton‐exchange membrane fuel cell including the gas channels was developed. The self‐consistent model for porous media was used for the equations describing transport phenomena in the membrane, catalyst layers, and gas diffusers, while standard equations of Navier‐Stokes, energy transport, continuity, and species concentrations are solved in the gas channels. A special handling of the transport equations enabled us to use the same numerical method in the unified domain consisting of the gas channels, gas diffusers, catalyst layers and membrane. It also eliminated the need to prescribe arbitrary or approximate boundary conditions at the interfaces between different parts of the fuel cell sandwich. By solving transport equations, as well as the equations for electrochemical reactions and current density with the membrane phase potential, polarization curves under various operating conditions were obtained. Modeling results compare very well with experimental results from the literature. Oxygen and water vapor mole fraction distributions in the coupled cathode gas channel‐gas diffuser were studied for various operating current densities. Liquid water velocity distributions in the membrane and influences of various parameters on the cell performance were also obtained.
Equilibrium theory for simulated moving bed adsorption processes
Authors: Chiang Anthony S. T.
Published: April 2004

The steady‐state operation of a simulated moving bed (8MB) process can be modeled by that of an equivalence true countercurrent (TCC) adsorption unit. An equilibrium theory based on the TCC unit is very useful for the selection of a proper condition to operate an 8MB process. The exact analysis of such an equilibrium model, however, has been limited to systems following a constant selectivity stoichiometric isotherm, which is not frequently observed. In this article, the equilibrium theory was extended to a multi‐component system that follows a constant selectivity nonstoichiometric isotherm. An exact solution is presented for the complete separation regions on the parameter space. The analysis is further applied to cases where only partial separation can be achieved.
Recursive data‐based prediction and control of batch product quality
Authors: Russell S. A. , Kesavan P. , Lee J. H. , Ogunnaike B. A.
Published: April 2004

In typical batch and semibatch processes, process/feedstock disturbances occur frequently and on‐line measurements of product quality variables are not available. As a result, most batch processes have not been able to achieve tight quality control. Empirical, data‐driven approaches are very attractive for dealing with this problem because of the difficulties associated with developing accurate process models from first principles. An approach for recursive on‐line quality prediction was developed around data‐based model structures. Techniques designed to incorporate the predictive models into on‐line monitoring and control of batch product quality were also examined. The proposed control approach can be viewed as shrinking‐horizon model‐predictive control based on empirical models. The effectiveness of the proposed prediction and control methods are illustrated by using an industrially relevant simulated polymerization example.
Novel monolithic stirred reactor
Authors: Albers Rolf K. Edvinsson , Houterman Marco J. J. , Vergunst Theo , Grolman Eric , Moulijn Jacob A.
Published: April 2004

A novel reactor configuration in which blocks of monoliths are arranged in a stirrer‐like configuration was studied. A substantial liquid flow rate can be realized through the monolith blades at relatively low power input, owing to the high permeability of the monolithic structure. The inside of the monolithic channels can be coated with a thin layer of either a conventional catalyst or a biocatalyst, thereby eliminating many of the problems associated with using a suspended catalyst. The basic relationship among stirrer speed, geometry, liquid viscosity, and the resulting torque and flow through the blades were studied. Furthermore, the fast decomposition of a dilute, aqueous hydrogen peroxide solution was used to characterize the rate of external mass transfer.
A new technique for predicting the shape of solution‐grown organic crystals
Authors: Winn Daniel , Doherty Michael F.
Published: April 2004

A method for predicting the shape of solution‐grown organic crystals is presented. The shapes depend on properties of their internal crystal structure, as well as on the processing environment. The model developed here can account for the effects of solvent and may be extended to account for the influence of certain types of additives. This method may be used as a first approach for including crystal shape in the overall design and optimization of organic solids‐processes. The technique has been used successfully to predict the shape of adipic acid grown from water, biphenyl from toluene, and ibuprofen from polar and nonpolar solvents.
Search for a model polymer blend
Authors: Balsara N. P. , Lefebvre A. A. , Lee J. H. , Lin C. C. , Hammouda B.
Published: April 2004

The thermodynamics of binary and multicomponent mixtures comprising polymethyl‐butylene, polyethylbutylene, andpolymethylbutylene‐block‐polyethylbutylene was studied by small‐angle neutron scattering. The Flory‐Higgins interactions parameter, deduced from these measurements, was independent of blend composition, as well as molecular weight and molecular architecture of the components, over the accessible temperature (27–201°C) and pressure (0.01–0.86 kbar) range. At temperatures above 130°C, the interaction parameter becomes independent of pressure. These findings are compared with previous experimental studies on the thermodynamics of polymer blends. To our knowledge, this level of agreement with the Flory‐Huggins theory has not been seen in any other polymer blend.
Interparticle potential and sedimentation of monodisperse colloid system
Authors: Wang H. , Wen C. S.
Published: April 2004

The effect of interpartide potential on the sedimentation of a colloid system has not been solved completely. A key problem is how to deal with the interpartide potential in stable systems. Based on previous works, an interpartide potential function for a stable system that cuts off the potential interaction at the position of the potential barrier (the position where interpartide potential is equal to 15 kT) is presented. Adopting this potential function, the sedimentation coefficients of monodisperse systems containing potential interacting particles are calculated, and the theoretical results are compared with those given by experiments. The potential function for the adopted stable system is more useful and reasonable than previous ones.
Estimating maximum removal efficiency in Venturi scrubbers
Authors: Ananthanarayanan N. V. , Viswanathan Shekar
Published: April 2004

A simplified 2‐D model to predict liquid flux distribution and collection efficiency in a Venturi scrubber was tested successfully with experimental data from pilot‐ and industrial‐scale units. Establishing nonuniformity of flux distribution is the key to estimating collection efficiencies accurately. Liquid jet penetration and liquid injection velocity are critical in defining flux distribution for the entire range of conditions simulated. Increase in gas velocity makes flux distribution more uniform and enhances collection efficiencies. This effect becomes insignificant beyond a gas velocity as finer droplets get accelerated quickly to the throat gas velocity giving the collector very little interaction time. Increase or decrease in the liquid to gas (L/G) ratio beyond an optimum value made flux distribution more nonuniform and decreases collection efficiencies. Design parameters of the Venturi scrubber (aspect ratio and nozzle diameter) have an optimum that offers the most uniform flux distribution and the maximum collection efficiency. A new dimensionless group, the Venturi number, derived from the jet penetration correlation, could define both nonuniformity influx distribution and collection efficiency for changes in the L/G ratio, aspect ratio, nozzle diameter, and number of nozzles. Simulation results indicate that a maximum efficiency exists for the Venturi number between 1.0 and 1.5 × 10−3. The useful length of the scrubber throat could be determined from the L/G ratio defined by the Venturi number concept and appropriate throat gas velocity.
Recent contributions of statistical mechanics in chemical engineering
Authors: Deem Michael W.
Published: April 2004

Some of the recent advances that have been made by chemical engineers in the field of statistical mechanics, as well as some of the new products and processes that have resulted from these advances, are reviewed. New approaches to molecular dynamics, Monte Carlo, quantum mechanics, master equations, hierarchical methods, liquid state theory, and field theory are discussed. Applications and commercial results in the microelectronics, biotechnology, pharmaceutical, and chemical process industries are highlighted.
Adsorption of ethyl benzene on activated carbon from supercritical CO2
Authors: Harikrishnan R. , Srinivasan M. P. , Ching C. B.
Published: April 2004

Our work involves experimental and simulation studies of the adsorption breakthrough and equilibria of ethyl benzene (a pollutant commonly encountered in industrial waste streams) on activated carbon in the presence of supercritical carbon dioxide. Frontal and single breakthrough saturations were analyzed for a range of operating conditions of pressure (100–130 bar) and temperature (313–338 K). The equilibrium data correlated well with the Langmuir isotherm. The adsorption process was successfully modeled by a three‐parameter model with comparable fitting parameters for the two types of breakthrough curves.
Standing wave design of nonlinear SMB systems for fructose purification
Authors: Mallmann T. , Burris B. D. , Ma Z. , Wang N. H. L.
Published: April 2004

Design equations were derived from standing wave analysis for continuous moving bed (CMB) and simulated moving bed (SMB) systems with nonlinear isotherms. Simple wave solutions and hodograph plots from batch elution experiments can be used to derive the optimal operation conditions for SMB systems without mass‐transfer effects. The design equations are tested with results from computer simulations and experimental data from two pilot‐scale SMB units for the separation of fructose from glucose. Batch equilibrium tests of single component and binary solutions are used to estimate adsorption isotherm parameters. Overall mass‐transfer and axial dispersion coefficients are estimated from eight sets of pulse, frontal and elution data at different concentrations and flow rates. The isotherm and mass‐transfer parameters are used in the standing wave analysis to determine the zone flow rates and switching times for the two SMB units. Experimental column profiles, product purities, and product concentrations agree closely with simulation results. This method gives robust operation conditions for SMB systems with nonlinear isotherms, and optimal cycle time and zone flow rates for nonlinear systems without mass‐transfer effects can be determined from the standing wave analysis.
Leak detection in liquefied gas pipelines by artificial neural networks
Authors: Belsito Salvatore , Lombardi Paolo , Andreussi Paolo , Banerjee Sanjoy
Published: April 2004

A leak detection system for pipelines was developed by using artificial neural networks (ANN) for leak sizing and location and by processing the field data. This system can detect and locate leaks down to 1% of flow rates in pipelines carrying hazardous materials in about 100 s. A reference pipeline was considered for practical implementation of the package. The ability of the package to withstand spurious alarms in the event of operational transients was tested. The compressibility effect, due to “packing” of the liquid in the pipeline, causes many such spurious alarms. Adequate preprocessing of the data was performed by using a computer code in conjunction with the ANN to compensate for the operational variations and to prevent spurious alarms. The package detects leaks as small as 1% of the inlet flow rate and correctly predicts the leaking segment of pipeline with a probability of success that is greater than 50% for the smallest leak. In all cases, the timely response of the system was seen as a major advantage.
Direct sonication system suitable for medium‐scale sonochemical reactors
Authors: Dahlem Olivier , Demaiffe Vincent , Halloin Véronique , Reisse Jacques
Published: April 2004

A radially vibrating horn is studied as a possible system for scaling up sonochemical reactors. The anisotropic behavior of this horn was demonstrated, as were strong correlations among the acoustic field, the acoustic streaming, and the sonochemical reactivity. A comparison with the classic laboratory horn exhibits the benefits of the larger emitting surface of the radially vibrating horn for homogeneous reactions, but not for polymer degradation reactions or for heterogeneous liquid–liquid reactions. The experimental techniques used proved to be very useful in characterizing the sonochemical reactors.
Filtration of liquid aerosols on wettable fibrous filters
Authors: Agranovski Igor E. , Braddock Roger D.
Published: April 2004

Liquid aerosols produced in many manufacturing and refining processes need to be filtered from the exhaust streams. Where wettable fibers are used in the filters, the aerosol liquid collects on the fibers. Observation shows that thin films develop on the fibers, and the liquid drains down the fibers under the action of gravity. A model is developed for the flow of liquid in these films, and careful experimentation confirms the nature and importance of the flow pattern. The resultant overall efficiencies of the filter are also calculated from a theoretical analysis and compared with the results of experimentation using counting techniques. The theoretical and experimental results agree excellently for the range of aerosol sizes that are detectable by laser diffraction and cascade impactor techniques.
Filtration of liquid aerosols on nonwettable fibrous filters
Authors: Agranovski Igor E. , Braddock Roger D.
Published: April 2004

Chemical, manufacturing and refining processes often generate toxic liquid by products that are emitted as liquid aerosols in the waste stream. Wettable and nonwettable fibers can be used to filter these exhaust streams. The behavior of liquid aerosols and droplets on nonwettable fibers is studied by observation, measurement, and theory. Droplets form on the fibers, grow by accretion from the aerosol, oscillate, and then fall under the action of gravity. Observation and theory indicate that these developing droplets influence air and aerosol flow strongly in the filter. These droplets are akin to the dendritic structures formed by solid aerosol particles within filters, but the shapes are modified by surface tension. The total efficiency of the filter is influenced by these droplets, and the total filter efficiencies are estimated using theoretical methods. The results from both approaches agree excellently in the particle‐size range as measured using particle‐counting techniques.