bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion in heterogeneous media: Application to immobilized cell systems
Authors: Riley Mark R. , Muzzio Fernando J. , Buettner Helen M. , Reyes Sebastian C. 
Published: June 2004

AbstractTransport of small molecules in heterogeneous materials can be an important factor in many engineering and biological applications. This study focuses on the diffusion of cellular nutrients in an immobilized cell system. A Monte Carlo simulation technique is used to describe the diffusion of small molecules in a variety of simulated cellular structures. Diffusivity predictions are in close agreement with experimental values as well as with theoretical bounds reported in the literature. It is revealed that effective diffusivities are highly dependent on the diffusivities of the species in the various phases and on the volume fraction of cells. The spatial arrangement of the cells, however, has no apparent effect on the predicted diffusivity for the range of conditions investigated.
Effectiveness of calcium magnesium acetate as dual SO2 ‐NOx emission Control Agent
Authors: Steciak Judith , Levendis Yiannis A. , Wise Donald L. 
Published: June 2004

AbstractCalcium magnesium acetate (CMA) is an effective dual SO2‐NOx emission control agent. Laboratory‐scale experiments with dry injected particles at a Ca/S molar ratio of 2 [or (Ca + Mg)/S ratio of 6] resulted in SO2 and NOx removal efficiencies of over 90% at gas temperatures of 950 – 1,250°C in atmospheres containing 12% CO2, 3% oxygen, 2,000 ppm SO2, and 1,000 ppm NOx during a 1‐s residence time in an isothermal cavity followed by injection of after‐fire air. During the experiments, SO2 reacted with the porous, thin‐walled CaO, CaCO3 and MgO cenospheres, formed when CMA calcined, while NOx was reduced by hydrocarbon radicals from the organic acetate decomposition. While Ca was the dominant contributor to SO2 reduction by CMA in the isothermal furnace zone, Mg also contributed to SO2 reduction. At gas temperatures ≤ 950°C, Mg reacted directly with SO2 in the isothermal furnace zone and was the dominant SO2 remover in the post‐furnace quenching zone while indirectly SO2 at higher isothermal zone temperatures by precluding pore‐mouth plugging when CaSO4 formed. Interactions among hydrocarbons, SO2, and NOx are important but not fully understood.
Effect of liquid surface tension on small hole distillation sieve tray pressure drop
Authors: Biddulph Michael W. , Thomas Christopher P. 
Published: June 2004

AbstractExperimental work on a 229‐mm‐dia. air/liquid distillation simulator shows that the surface tension of a given liquid can affect the total tray pressure drop, which normally consists of the sum of dry tray pressure drop, clear liquid head, and residual pressure drop. Both the dry tray pressure drop and clear liquid head values establish correlations in the literature for their prediction. The residual pressure drop, however, has been regarded as a constant value. This is not the case and the residual pressure drop is a dynamic variable. Three different surface‐tension liquids (water, benzyl alcohol, and n‐Propanol) are used to isolate this effect. Results presented correlate the residual pressure drop in terms of the gas F‐factor, the clear liquid head, and the traditional residual head loss definition.
Optimization and modeling of the crystallization process in a cascade with backmixing
Authors: Jansens Pieter J. , Bruinsma Odolphus S. L. , van Rosmalen Gerda M. 
Published: June 2004

AbstractCascades of crystallizers are applied in many industrial processes. The optimization of the filterability of crystals produced in such a cascade is dealt with, since a good filterability is often one of the main product specifications. An integral model description of the crystallization process is developed that allows for the prediction of the crystal size distribution and the filterability in each stage of the cascade, and experiments are performed to support this model. The integral model can be used as a predictive tool in future filterability optimization studies.
Simplified local density model for adsorption over large pressure ranges
Authors: Rangarajan Bharath , Lira Carl T. , Subramanian Ramkumar 
Published: June 2004

AbstractA mean‐field model is developed that superimposes the fluid‐solid potential on a fluid equation of state to predict adsorption on a flat wall from vapor, liquid, and supercritical phases. A van der Waals‐type equation of state is used to represent the fluid phase, and is simplified with a local density approximation for calculating the configurational energy of the inhomogeneous fluid. The simplified local density approximation makes the model tractable for routine calculations over wide pressure ranges. The model is capable of prediction of Type II and III subcritical isotherms for adsorption on a flat wall, and shows the characteristic cusplike behavior and crossovers seen experimentally near the fluid critical point.
Equal area rule and algorithm for determining phase compositions
Authors: Eubank Philip T. , Hall Kenneth R. 
Published: June 2004

AbstractThe Maxwell equal area rule is a basic construct for determining saturated phase volumes from equations of state. The fundamental idea is that for a pure substance a horizontal line drawn through the trace of an isotherm, which equalizes the van der Waals loops area above and below the line, intersects the isotherm at the saturated volumes.Another basic construct exists for determining the phase compositions in a binary mixture by establishing the tangent line to the total Gibbs energy curve plotted against composition. We demonstrate that finding the tangent also reduces to an equal area construction for the derivative of the total Gibbs energy plotted against composition. An efficient algorithm suggested effects such equal area determinations. The trial‐and‐error procedure normally converges in one to three steps to the correct solution given any resonable starting guess. Implementation using modern calculators with graphics capabilities is simple and straightforward.
Analysis of zero‐reference‐pressure EoS/GE models
Authors: Kalospiros Nikolaos S. , Tzouvaras Nikolaos , Coutsikos Philippos , Tassios Dimitrios P. 
Published: June 2004

AbstractAn analysis of EoS/GE models, which are based on matching the EoS‐derived expression for the excess Gibbs free energy GE with that from a GE model at zero pressure, is presented, with the focus on the most successful and widely used of these models, MHV2 and PSRK. It shows why zero‐reference‐pressure models do not reproduce exactly the GE models at zero pressure and the ensuing implications on the prediction of asymmetric systems. The development of EoS/GE models that reproduce exactly the GE model is discussed. However, such reproducibility at zero pressure is impossible for systems containing components with reduced temperatures higher than about 0.9. Therefore, extrapolation schemes that allow treatment of such systems are examined.
Editor's note on special section
Authors: Tirrell Matthew 
Published: June 2004

AbstractThe collection of articles in this special topical section were prepared based on presentations made at the 1993 Annual Meeting of AIChE. Theme of the session was the applications of molecular thermodynamics to problems of protein structures, solution properties, transport propertties, separations, and other issues important to chemical engineers in the biotechnology, biomedical, pharmaceutical and food industries. These articles were submitted to and survived the regular Journal reviewing procedure; they were grouped to highlight this important area with a concentration of articles similar to the special section we published last year on new imaging techniques. Further background on this subject is given in the following remarks bu Bramie Lenhoff and Mike Paulaitis.
Development and validation of a simple antigen–antibody model
Authors: Busch N. A. , Chiew Y. C. , Yarmush M. L. , Wertheim M. S. 
Published: June 2004

AbstractA theoretical model for investigating physical phenomena underlying immune complex formation was developed, based on the statistical mechanical theory of associating fluids that identifies each molecule as a hard sphere with a nested point charge and vector dipole. The interaction between binding molecules (epitope–paratope binding) is represented as a cone truncated by two concentric spheres in which the potential energy is a modified square well with respect to particle separation and a square well with respect to mutual molecular orientation. Equilibrium binding results predicted by the model show good agreement with results obtained experimentally for a model system containing a single antigen and a single monoclonal antibody [bovine serum albumin (BSA) – anti‐BSA antibody]. Moreover, values obtained for the system isothermal compressibility and the second virial coefficient by both the model and light scattering experiments also show good agreement with one another.
Two‐phase flow in the vicinity of an elongated bubble in a fluidized bed
Authors: Levy Yeshayahou , Dorfman Yuri 
Published: June 2004

AbstractFluid and solid dynamics inside and outside a stable elongated gas bubble in operating conditions corresponding to those of the channeling regime in a fluidized bed are described. It considers the prolate ellipsoid of revolution as a model of the bubble. The results of the analytical model show a significant increase of the fluid velocity inside the bubble with the growth of its relative height. The maximum values of the fluid velocities exist along the vertical axis of the bubble. For the limiting case of a spherical bubble, the fluid and gas performance, such as the existence of a surface of penetration outside the bubble boundaries and circulation zone inside the bubble, are in good agreement with the existing theory.
Role of porosity in filtration: XII. Filtration with sedimentation
Authors: Tiller Frank M. , Hsyung N. B. , Cong D. Z. 
Published: June 2004

AbstractFiltration on horizontal surfaces facing upward is accompanied by sedimentation. Material balances that are based solely on the volume of filtrate and neglect sedimentation flux lead to an understatement of the solids deposited in the cake and potentially large errors in calculated values of the average specific resistance αav. In a gravitational sedimentation experiment with kaolin, the value of αav neglecting sedimentation was 3.75 times greater than the value including the effect of sedimentation. In addition to errors due to neglect of sedimentation, CATSCAN studies show that the slurry concentration above the cake increases with time, contrary to usual assumptions. In a manner similar to batch sedimentation in a closed cylinder, characteristics of constant composition arose from the cake surface. Approximate predictions based on a combination of traditional sedimentation and filtration theory were in accord with the CATSCAN data. Existing filtration theory must be substantially modified to account for the effect of sedimentation.
Simultaneous concentration and purification through gradient deformation chromatography
Authors: Velayudhan Ajoy , Hendrickson Richard L. , Ladisch Michael R. 
Published: June 2004

AbstractMobile‐phase additives, commonly used to modulate absorbate retention in gradient elution chromatography, are usually assumed to be either linearly retained or unretained. Previous theoretical work from our laboratory has shown that these modulators, such as salts in ion‐exchange and hydrophobic interaction chromatography and organic modifiers in reversed‐phase chromatography, can absorb nonlinearly, giving rise to gradient deformation. Consequently, adsorbate peaks that elute in the vicinity of the head of the deformed gradient may exhibit unusual shapes, form shoulders, and/or be concentrated. These effects for a reversed‐phase sorbent with aqueous acetonitrile (ACN) as the modulator are verified experimentally. Gradient deformation is demonstrated experimentally and agrees with simulations based on ACN isotherm parameters that are independently determined from batch equilibrium studies using the layer model. Unusual adsorbate peak shapes were found experimentally for single‐component injections of phenylalanine, similar to those calculated by the simulations. A binary mixture of tryptophan and phenylalanine is used to demonstrate simultaneous concentration and separation, again in agreement with simulations. The possibility of gradient deformation in ion‐exchange and hydrophobic interaction chromatography is discussed.
New discretization procedure for the breakage equation
Authors: Hill Priscilla J. , Ng Ka M. 
Published: June 2004

AbstractA new discretization method, applicable for both batch and continuous systems, is developed for the breakage equation. The problem of intrainterval interactions due to discretization is accounted for by matching the zeroth and first moments of the continuous population balance equation with the corresponding moments of the discretized equation, thereby guaranteeing conservation of mass and total number of particles. Without loss of generality, the use of this method is demonstrated with a power law form of the specific rate of breakage, and with both theoretical and empirical breakage functions. The systematic method requires minimum computational efforts by allowing the user to choose either geometric size intervals with any geometric ratio or equal‐size intervals for the particle size range. Simulation results show that the new method significantly improves predictions of the particle size distribution over the discretization method currently in use.
Reducing data dimensionality through optimizing neural network inputs
Authors: Tan Shufeng , Mayrovouniotis Michael L. 
Published: June 2004

AbstractA neural network method for reducing data dimensionality based on the concept of input training, in which each input pattern is not fixed but adjusted along with internal network parameters to reproduce its corresponding output pattern, is presented. With input adjustment, a property configured network can be trained to reproduce a given data set with minimum distortion; the trained network inputs provide reduced data.A three‐layer network with input training can perform all functions of a flue‐layer autoassociative network, essentially capturing nonlinear correlations among data. In addition, simultaneous training of a network and its inputs is shown to be significantly more efficient in reducing data dimensionality than training an autoassociative network The concept of input training is closely related to principal component analysis (PCA) and the principal curve method, which is a nonlinear extension of PCA.
Modifications to model IV fluid catalytic cracking units to improve dynamic performance
Authors: Huq Iftikhar , Moran Manfred , Sorensen Ronald C. 
Published: June 2004

AbstractModel IV fluid catalytic cracking units (FCCUs) differ from other cracking units in that model IV FCCUs do not have slide valves in the catalyst circulation lines to enable direct control of catalyst circulation rate through the unit. Reducing fluctuations in catalyst circulation rate is found to significantly improve closed‐loop performance of the FCCU. Some design and operational modifications that can be made to model IV FCCUs to improve closed‐loop performance at the regulatory level based on this insight are modeled and compared. Closed‐loop performance of a model IV FCCU operated with the weir and standpipe always flooded is examined. The achievable performance is significantly better thah that of the standard model IV FCCU. The closed‐loop performance of the model IV FCCU modified to incorporate slide valves in the catalyst circulation lines is also examined. The performance of the FCCU with slide valves is better than the performance achievable by the FCCU with the weir flooded. It is found that model IV FCCUs are ill‐conditioned owing to the use of the weir and standpipe arrangement in the regenerator section. Both the operational and design modifications studied reduce plant ill‐conditioning appreciably.
Three‐dimensionai temperature and current distribution in a battery module
Authors: Verbrugge Mark W. 
Published: June 2004

AbstractA method for treating three‐dimensional current and temperature distributions in large‐scale battety modules is described. Simulations are presented for a module consisting of cells formed with a lithium metal anode, a polymer electrolyte, and a vanadium oxide cathode. The calculations illustrate the nonlinear dependence of power output on system temperature, which for the investigated lithium‐polymer battery module is determined primarily by the influence of temperature on the electrochemical reaction rates and ionic conductivity. An appendix is devoted to the estimation of physicochemical parameters, some of which are not available from the current literature, but are nonetheless important model inputs.
Origin of disturbances in cocurrent gas‐liquid packed bed flows
Authors: Krieg D. A. , Helwick J. A. , Dillon P. O. , McCready M. J. 
Published: June 2004

AbstractVisual, video, pressure, and conductance techniques were used to study time‐varying disturbances in cocurrent flow in packed beds with vertical and horizontal columns. It is found that the trickle‐pulse transition, as defined in previous studies, corresponds to conditions where traveling disturbances finaly become measurable, not the conditions at which infinitesimal disturbances begin to grow. Observations demonstrate that even if the liquid and gas are uniformly distributed initially, segregated, vertical flowing regions with higher or lower than average liquid holdup form after a short distance. Horizontal packed bed experiments, designed to study how regions of differing liquid holdup interact, indicate that the first type of disturbance is infiltration of gas into the liquid region. A simple model suggests that infiltration occurs if the pressure drop exceeds a value necessary to push gas through liquid‐filled pores. Once infiltration is significant enough to form a third “bubbly” phase, traveling wave instabilities form and grow into pulses if sufficient column length is available. A three‐layer Kelving‐Helmholtz stability model is used to interpret the growth of disturbances in horizontal flows. Video obeservations of small‐scale events in the bed failed to detect significant correlations between different regions. Thus it should be possible to describe flow behaviour in these systems with volum‐averaged equations, as long as the presence of segregated regions is considered. Column diameter or thickness significantly affects the frequency of disturbances.
Evaporative cooling of air in impinging streams
Authors: Yao B. , Berman Y. , Tamir A. 
Published: June 2004

AbstractAn experience study was conducted on evaporative cooling of air in an impinging‐stream reactor, in which two droplets gas streams flow in opposite directions and meet in the impingement zone. The air was cooler by evaporation of water droplets. Volumetric heat‐transfer coefficients hv determined enabled us to evaluate the performance of the cooler. Maximum values of hv varied from 4 to 14 kW/m3 K. The effectiveness of impinging streams was evaluated by placing a partition in the implingement zone, which prevented interaction between the streams. A numerical modeling of the droplets' behavior in an impingin‐stream reactor was also performed on the basis of heat and momentum equations. Effects of initial droplets' size and velosity as well as atomization and coalescence on the enhancement by impinging streans have been investigated. Correlation equations are also discussed. The experimental and numerical resluts helped understant the fundamentals mechanisms of an impinging‐stream reactor with a gs‐droplet suspension and furthet verify the effectiveness of the method of impinging streams.
Global optimization for the phase stability problem
Authors: McDonald Conor M. , Floudas Christodoulos A. 
Published: June 2004

AbstractThe Gibbs tangent plane criterion has become important in determining the quality of obtained solutions to the phase and chemical equilibrium problem. The ability to determine if a postulated solution is thermodynamically stable with respect to perturbations in any or all of the phases is very useful in the search for the true equilibrium solution. Previous approaches have focused on finding stationary points of the tangent plane distance function. Obtaining all stationary points, however, cannot be guaranteed due to the complex and nonlinear nature of the models used to predict equilibrium. Simpler formulations for the stability problem are presented for special problems where nonideal liquid phases can be adequately modeled using the NRTL and UNIQUAC activity coefficient equations. It shows how the global minimum of the tangent plane distance function can be obtained for these problems. A global optimization approach is advantageous because a nonnegative solution can be asserted to be the globally stable equilibrium one, unlike available local algorithms. For the NRTL equation, the GOP algorithm of Floudas and Visweswaran (1990, 1993) is used to guarantee obtaining ϵ ‐global convergence to the global minimum. For the UNIQUAC equation, a branch and bound algonthm based on that of Falk and Soland (1969) is used to guarantee convergence to the global solution. Computational results demonstrate the efficiency of both global optimization algorithms in solving various challenging problems.
Avoiding the use of critical constants in cubic equations of state
Authors: Soave Giorgio S. , Bertucco Alberto , Sponchiado Michele 
Published: June 2004

AbstractA new way to define the two parameters a, b of the Redlich‐Kwong equation of state without using the critical constants is introduced. First, the “shifted” covolume (b ‐ c) of the Peneloux modification of the equation of state is estimated by group contributions (for a wide range of compounds); from it and one vapor pressure‐liquid density pair, the covolume b is then determined. The attractive parameter a is derived, at any temperature, from the covolume and the compound vapor pressure. The proposed method makes it possible to treat substances whose critical constants are not known (heavy or thermally unstable compounds) by using one density value and the vapor pressure curve. Examples are given of vapor‐liquid equilibrium calculations.
Transdermal delivery of peptide and protein drugs: An overview
Authors: Amsden B. G. , Goosen M. F. A. 
Published: June 2004

AbstractRecently, a large number of new and potentially potent peptide and protein drugs have been developed. Their systemic delivery is difficult because they are rapidly cleared from the bloodstream, are of large molecular size, are vulnerable to proteolytic attack and tend to undergo aggregation, adsorption and denaturation. Controlled release strategies have many advantages over the current delivery method of injection or intervenous infusion. Controlled release allows for prolonged delivery while maintaining the drug concentration within therapeutic limits. It also improves and increases patient compliance by removing the discomfort of repeated applications. The transdermal route of delivery is particularly attractive because it avoids peptide and protein degradation via the gastrointestinal tract and the hepatic first‐pass effect, and delivery can be interrupted by simply removing the device. Its primary problem is that the skin is an excellent barrier to large, hydrophilic, polar compounds. Recent work in the area of transdermal peptide and protein drug delivery is overviewed, including strategies such as prodrugs, chemical enhancement, iontophoresis, electroporation, and ultrasound, with focus on mass‐transport mechanisms of different systems. Of the strategies studied, iontophoretic delivery appears the most promising. It is clear, however that more work remains to be done before transdermalpeptide and protein delivery devices come to market. Chemical engineers can contribute significantly to further research in this exciting area.