bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solvation thermodynamics of gas solubility at sub‐ and near‐critical conditions
Authors: Chialvo Ariel A. , Kalyuzhnyi Yu V. , Cummings Peter T. 
Published: June 2004

AbstractThe recently developed formalism for describing the solute‐induced effect in dilute near‐critical mixtures is extended to fluids composed of anisotropic molecules through the statistical mechanical interpretation of the derivative (∂P/∂x2) whose critical value is the Krichevskii parameter.Rigorous expressions for Henry's constant and the solute distribution factor along the orthobaric curve are derived in terms of the volumetric and entropic solute‐induced local effects, and the quasi‐linear behavior of their orthobaric density dependence away from the solvent's critical point is rationalized.The formalism is illustrated with integral equation calculations of the orthobaric density dependence of several solvation thermodynamic quantities for an infinitely dilute volatile solute in near‐critical solutions of hard‐sphere Yukawa fluids.
Importance of macromixing in batch cooling crystallization
Authors: Bohlin Martin , Rasmuson Åke C. 
Published: June 2004

AbstractThe importance of spatial variations of the conditions in industrial‐scale, agitated, batch cooling crystallizers is investigated by computer simulations. A three‐compartment model is developed considering primary and magma density‐dependent secondary nucleation. An increasing crystallizer size is described by an increasing suspension turnover time. It is shown that accumulation of larger crystals in the bottom region, localized supersaturation generation and variations in the secondary nucleation rate due to varying local mixing intensity will, under normal conditions, exert a low and often negligible influence on the product‐size distribution of an industrial unit. In a batch process, the product‐size distribution is governed mainly by the conditions early in the process. During this period the supersaturation half‐life is much longer than the suspension turnover time, and the influence of local variations becomes weak.
Reverse micellar mass‐transfer processes: Spray column extraction of lysozyme
Authors: Lye Gary J. , Asenjo Juan A. , Pyle D. Leo 
Published: June 2004

AbstractProtein partitioning kinetics was measured for the semibatch extraction of lysozyme in a laboratory‐scale, liquid–liquid spray column. The organic, isooctane phase contained reverse micelles formed from the anionic surfactant, sodium di‐2‐ethylhexyl sulfosuccinate. For the extraction of protein from aqueous to reverse micellar phases, experiments were performed over a range of dispersed‐phase flow rates for cases of the organic‐ or aqueous‐phase dispersion. The influence of aqueous‐phase pH and ionic strength, which influence electrostatic interactions between protein and reverse micelles, was also investigated. Results were interpreted in terms of a two‐film model of mass transfer. The nature of the dispersed pahse could significantly influence the partitioning kinetics, while study of the droplet hydrodynamics suggested that stagnant drops were formed regardless of which phase was dispersed. Literature correlations for describing the droplet‐formation process and droplet hydrodynamics predicted measured values satisfactorily. Attempts wer also made to predict overall mass‐transfer coefficients based on existing correlations describing mass transfer during droplet formation, free rise (or fall), and coalescene. Predicted values of KL were 2–10 times greater than measured values, probably because of large concentrations of surfactant used to formulate the reverse micelle phases. This approach did, however, provide detailed information on the quantity of protein transferred during the successive processes of droplet formation, free rise (or fall) and coalescence.
Wavy‐to‐slug flow transition in slightly inclined gas–liquid pipe flow
Authors: Grolman Eric , Commandeur Niels C. J. , de Baat Eduard C. , Fortuin Jan M. H. 
Published: June 2004

AbstractA process‐engineering model is presented for the stratified‐wavy‐to‐intermittent (SW–I) flow‐pattern transition in slightly inclined gas–liquid pipe flow. The main parameter for predicting (in) stability of wavy flow in inclined pipes is the average liquid holdup, which was found to reach a maximum, critical value at flow‐pattern transition. Observed values of the critical liquid holdup vary between 0.07 and 0.42, depending on pipe diameter, angle of inclination and transport properties of the gas–liquid system. Measurements were performed in transparent glass pipes of 26‐ and 51‐mm dia., at ten angles of inclination (0.1° ≤ β ≤ 6.0°), using air/water and air/tetradecane (n‐C14H30) systems at atmospheric pressure. Flow‐pattern maps are presented for selected angles of inclination, showing excellent agreement between predicted and observed flow‐pattern boundaries.
Prediction of sedimentation and consolidation of fine tails
Authors: Eckert William F. , Masliyah Jacob H. , Gray Murray R. , Fedorak Phillip M. 
Published: June 2004

AbstractSedimentation and consolidation of suspensions of fine particles were analyzed by integrating experimental measurement of properties in a centrifuge with a comprehensive numerical model. The yield stress and settling velocity for tailings from tar sands extraction were determined experimentally as a function of the volume fraction of solids. The evaluated state functions were used to simulate batch settling and consolidation, and the results compare well with long‐term settling tube tests. This approach is very attractive where gravity sedimentation may take many years, and it allows prediction of the rate of clear water production, total time for sedimentation and consolidation, and the maximum concentration of solids.Scaling of the sedimentation between centrifuge and field conditions is discussed. Conversion of permeability‐void ratio relationships from geotechnical experiments to state functions of hindered settling velocity is demonstrated, allowing the use of data derived from a variety of experimental techniques.
Model for secondary nucleation in a suspension crystallizer
Authors: Meadhra Ruairí Ó. , Kramer Herman J. M. , Van Rosmalen Gerda M. 
Published: June 2004

AbstractA model that makes it possible to evaluate the secondary nucleation rate in a pilot‐scale industrial crystallizer is presented. It relates the secondary nucleation rate directly to the volume rate of attrition of large parent crystals. Two other terms are included in the equality, one that expresses the distribution formed by the attrition fragments, and the other that expresses a survival efficiency accounting for the percentage of attrition fragments that grow out after the attrition step. The model is further tested on a 970‐L draft‐tube‐baffled evaporative crystallizer with ammonium sulfate as the model material used for crystallization and having an on‐line crystal size‐distribution measuring device.
Generalized modular representation framework for process synthesis
Authors: Papalexandri Katerina P. , Pistikopoulos Efstratios N. 
Published: June 2004

AbstractA generalized modeling framework for process synthesis alternatives is proposed, based on fundamental mass/heat‐transfer principles. A multipurpose mass/heat‐transfer module is introduced as the building block of the framework, whereas basic block‐superstructure rules (such as splitting, mixing, and bypassing) are used to develop a systematic representation of process units and process structures, conventional or not. Process synthesis procedures are explored within this modeling framework, where synthesis alternatives are not postulated as process unit networks, but explored simultaneously without predefining synthesis schemes, as combinations of mass/heat‐exchange stream matches. The representation potential of this framework is illustrated with examples from unit operations, whereas synthesis example problems are presented to show the broad range of process alternatives that can be modeled, identified, and optimized.
Spatiotemporal patterns in catalytic reactors
Authors: Sheintuch Moshe , Shvartsman Stanislav 
Published: June 2004

AbstractThe study of spatial structures in heterogeneous reactors is a challenging academic topic, revealing patterns that differ from those known to exist in reaction‐diffusion systems exposed to uniform conditions, as well as a practical problem that should affect design and operation procedures of commercial reactors like the catalytic convertor. Experimental observations and mathematical models of spatiotemporal patterns in high‐pressure catalytic reactors are reviewed. Patterns in high‐pressure reactors, in which thermal effects provide the positive feedback, as well as the long‐range communication, usually emerge due to global interaction. Patterns are classified comprehensively by considering reactors of increasing degree of complexity: a wire or ribbon exposed to uniform conditions, a globally coupled catalyst in a mixed reactor or in a control loop, and a fixed bed in which interaction by convection occurs only in one direction. Catalytic wires are not expected to exhibit sustained patterns in the absence of global interaction. Global interactions by external control or gas‐phase coupling are shown experimentally and analytically to induce a rich plethora of patterns. Complex motions were simulated to occur due to the interaction of convection, conduction and reaction in a fixed‐bed; only a few of these patterns were experimentally observed. Directions for future research are suggested.
Reactor of vapor‐phase graft polymerization of reactive monomer onto porous hollow fiber
Authors: Uezu Kazuya , Saito Kyoichi , Sugo Takanobu , Aramaki Satoru 
Published: June 2004

AbstractA novel reactor for the modification of a porous hollow‐fiber membrane up to 1 m in length is presented. The polyethylene hollow fiber irradiated with an electron beam was exposed to the vapor of an epoxy‐group‐containing vinyl monomer (glycidyl methacrylate) in a cylindrical reactor rotated at 1 rpm. Construction of the hollow fibers resulted in a diffusion‐controlled reaction system, which led to the nonuniformity of degree of grafting (dg), whereas the shuffling of the hollow fibers by rotating the cylindrical reactor provided a higher reactivity (dg = 110% for 100 min at 300 K) and uniformity (standard deviation = 4.5%) of dg.
Laboratory batch reactor method for kinetic study of chemical vapor deposition
Authors: McConica Carol M. , Bell David A. , Baker Kevin L. , Moss Devin 
Published: June 2004

AbstractA lab‐scale nonflowing reactor was built to study chemical vapor deposition reactions. Mass spectrometry is used to follow reaction pathways and to determine instantaneous reaction rates throughout film growth. In each experiment, the kinetic rate dependence on concentration for a wide range of concentrations is observed as reactants convert to products. This method of obtaining kinetic data is efficient in terms of sample loading, gas usage, and time, since over 200 instantaneous rate/composition pairs can be determined from one 30‐min deposition. Because the rate is determined from gas‐mass balance, rather than film‐thickness measurements, an unlimited number of rate studies can be made on one sample. As a test case, the SiH4 reduction of WF6, used to deposit tungsten during integrated‐circuit production, was investigated in the 0.64‐L nonflowing laboratory reactor. Gas compositions were measured 2 mm from the growing surface, throughout time, with a mass spectrometer equipped with a capillary sampling tube. Tungsten was deposited on the 95°C surface, and SiHF3 was the primary silicon fluoride reaction product for most tested conditions. A multiple‐regression analysis of 1,975 instantaneous composition/rate pairs gives orders of 1.22 in silane, 0.27 in hydrogen, and −2.17 in WF6. The ratio of SiF4 to SiHF3 stays low and constant until the gas becomes silane‐rich. The evolution of the instantaneous rate over time implies that a minimal level of thermal activation of the reactive gases is necessary for the deposition to be surface‐rate‐limited. Preliminary heat‐transfer models of the wire substrate imply that heat transfer to the gas phase is in the Knudsen regime.
Demulsification of water/oil/solid emulsions by hollow‐fiber membranes
Authors: Tirmizi Neena Pradhan , Raghuraman Bhavani , Wiencek John 
Published: June 2004

AbstractThe demulsification techniques investigated use preferential surface wetting to allow separation of oil and water phases in ultrafiltration and microfiltration membranes. A hydrophobic membrane allows the permeation of an oil phase at almost zero pressure and retains the water phase, even though the molecular weight of the water molecule (18) is much smaller than that of the oil molecule (198 for tetradecane, used in this study). Hydrophobic membranes having pore sizes from 0.02 to 0.2 μm were tested for demulsification of water‐in‐oil emulsions and water/oil/solid mixtures. The dispersed (aqueous)‐phase drop sizes ranged from 1 to 5 μm. High separation rates, as well as good permeate quality, were obtained with microfiltration membranes. Water content of permeating oil was 32–830 ppm depending on operating conditions and interfacial properties. For emulsions with high surfactant content, simultaneous operation of a hydrophobic and hydrophilic membrane, or simultaneous membrane separation with electric demulsification was more efficient in obtaining complete phase separation.
Variable target mass‐exchange network synthesis through linear programming
Authors: Gupta Ashish , Manousiouthakis Vasilios 
Published: June 2004

AbstractA mass‐exchange network (MEN) synthesis problem is considered with streams whose target compositions are allowed to vary between upper and lower bounds. The design task is to determine the minimum mass separating agent (utility) cost needed for the transfer of a single component from the rich to the lean streams. The mathematical formulation of this synthesis problem leads to a mixed integer nonlinear program. In this work, we propose a novel formulation of the problem that leads to a linear program. Stream decomposition is employed in attaining this novel linear programming formulation and rigorous proofs are presented which establish that the two formulations have the same solution. The linear programming formulation reduces the complexity of the considered MEN synthesis problem, thus making feasible its solution even for large‐scale problems. Two examples, illustrating the procedure, are presented. Both demonstrate that significant utility cost savings can be achieved over the fixed composition MEN synthesis problem.
NMR Imaging of nonaqueous‐phase liquid dissolution in a porous medium
Authors: Baldwin Christopher A. , Gladden Lynn F. 
Published: June 2004

AbstractIt is demonstrated how NMR imaging can be used noninvasively to quantify the volume of nonaqueous phase liquid (NAPL) present in an otherwise water‐saturated porous medium. Data were recorded during the operation of a pump and treat (PT) remediation scheme on a bed of water‐saturated sand contained within a vertical column. The model contaminant used was n‐hexanol, and three different aqueous flow rates were employed. These data were then critically compared with the predictions of three models currently used to describe the dissolution of NAPL during a PT scheme: the linear mass‐transfer model, the pore‐diffusion model, and the shrinking‐core model. The pore‐diffusion model gave best agreement with the experimental data. However, none of the models predicted the observed dependence of mass transfer on Darcy velocity.
Mixed monolayers of acylglycerols on sugar aqueous solutions
Authors: de la Fuente Feria Julia , Patino Juan M. Rodríaguez 
Published: June 2004

AbstractStructural Characteristics of mono‐ and distearin mixed monolayers spread on aqueous solutions containing sugar (glucose or sucrose) at 0.5 mol/L were studied as a function of temperature and interfacial and subphase compositions. The compression isotherms were obtained using an automated Langmuir‐type film balance over a temperature range of 10 to 40°C. The results show an expansion in the structure of the mixed monolayer with sugar in subphase. Nonideal mixing of the component at interface was observed with positive deviation from the additivity rule. This fact is indicative of the presence of repulsive interactions between the two lipids on sugar aqueous solutions. The mixed monolayers with a monostearin molar fraction less than 0.8 are stable from a thermodynamic point of view. Mixed monolayer stability depends on monolayer composition, temperature, and surface pressure with different order of magnitude.
Spectral analysis of microtubule assembly dynamics
Authors: Odde David J. , Buettner Helen M. , Cassimeris Lynne 
Published: June 2004

AbstractMicrotubules are linear polymers of the cytoskeleton that serve to organize the cytoplasm of eukaryotic cells. Understanding how microtubule polymers self‐assemble is important in biotechnology, including the development of novel cancer therapies and proper guidance of regenerating neurons. The assembly of microtubules occurs by a unique process whereby an individual microtubule undergoes abrupt and apparently stochastic switching between alternating steady states of growth and shrinkage, a phenomenon known as microtubule dynamic instability. To characterize these oscillations spectral (frequency‐domain) analysis, commonly used in engineering for system identification, was applied. Power spectra of the individual microtubule‐length life histories revealed oscillations within growth phases, directly reflecting acceleration and deceleration in the growth process. These fluctuations were not accounted for by the standard two‐state model commonly used in the analysis of microtubule assembly, despite the inclusion of simulated measurement error in the model. Thus, the spectral analysis of microtubule assembly permitted characterization of assembly process dynamics independent of particular assembly models, and as such represents a powerful analytical framework within which to study microtubule dynamic instability and assess its function in vivo.
Model for ER chaperone dynamics and secretory protein interactions
Authors: Robinson Anne Skaja , Lauffenburger Douglas A. 
Published: June 2004

AbstractExpression of proteins in eucaryotic systems is often the only way to ensure the correct folding and processing necessary for protein function. Heterologous proteins, however, are commonly retained in the secretory pathway, so that secreted product yield is low despite a high level of transcription. A major limiting step in protein secretion is protein folding in the lumen of the endoplasmic reticulum. This process is assisted by accessory macromolecules resident in this compartment, including chaperones such as the hsp70 homologue binding protein (BiP). Although induction of foreign proteins in yeast initially elicits a transient increase in local chaperone concentration, long‐term protein expression lowers both chaperone and secreted product. A mechanistic model that can account for the experimentally observed role of BiP in secretion and the effects of BiP overexpression on the secretory pathway is described here. The model predicts that equimolar synthesis of chaperone and foreign protein should optimize protein secretion.
Meniscus control by string in roll coating experiment
Authors: Decré M. , Gailly E. , Buchlin J.‐M. 
Published: June 2004

AbstractThe ribbing instability hinders the roll coating process, as it produces wavy coating films. The technique studied here prevents ribbing, whereby a string is placed parallel to the rolls, in contact with the unstable meniscus. In this experiment, the fluid is a Newtonian oil. A free‐surface visualization technique allows measurement of the interface profile where the string interacts with the forming films. The ribbing can be eliminated under conditions at least 20 times its natural onset. The influence of the string position on the mass transfer is then examined. Measurements show that the streamwise position of the string controls the total flow rate of the process, while its transverse position accurately controls the relative thicknesses applied on each roll. The string proves to be both an efficient concept to eliminate ribbing, and a reliable way of fixing the coating film thickness, without resorting to traditional gap width and roller speeds selection.
Effectiveness factors for continuous mixtures
Authors: McCoy Benjamin J. 
Published: June 2004

AbstractCatalyst effectiveness factors provide a quantitative estimate of diffusion resistance for chemical reactions in porous particles. The objective of this research is to develop an approach to calculate liquid‐phase, porous‐particle effectiveness factors, which are based on spherical reactant molecules and cylindrical pores that both have size distributions. Reactants larger than a given pore are excluded from the pore. A first‐order reaction occurs when reactant molecules diffuse into pores that hinder their movement due to steric interactions with the pore wall. The reactant size distribution is described by rectangular or gamma distributions, and the pore‐size distribution is modeled by continuous rectangular or discrete fractal distributions. Effectiveness factors are defined and evaluated for (a) one‐size reactants in one‐size pores, (b) all reactants in one‐size pores, (c) one‐size reactants in all pores, and (d) all reactants in all pores. Most of the discussion deals with equal‐length pores, but the effect of a distribution of pore lengths is also considered.
Vapor–liquid equilibrium of formaldehyde mixtures: New data and model revision
Authors: Albert M. , Hahnenstein I. , Hasse H. , Maurer G. 
Published: June 2004

AbstractA physicochemical model for vapor–liquid equilibria and enthalpies in formaldehyde‐containing mixtures is revised and extended using recently published NMR spectroscopic data on chemical equilibria in aqueous and methanolic formaldehyde solutions as well as new vapor–liquid equilibrium data for the system formaldehyde–water at temperatures up to 413 K (pressures up to 450 kPa), which were taken in this work with a new apparatus. Furthermore, the model is revised so that it can be extended straight‐forwardly to explicitly account for reaction kinetic effects based on results from other recent NMR spectroscopic studies. The model is tested over the entire temperature range (293–413 K), where reliable experimental data on vapor–liquid equilibria are available, and against calorimetric data. Typical relative deviations between experimental data and the correlation are about 5% for vapor–liquid partition coefficients and 2% for the pressure. Deviations between calculated and measured enthalpies of vaporization are generally below 2%.
Finite‐element analysis of Taylor flow
Authors: Edvinsson Rolf K. , Irandoust Said 
Published: June 2004

AbstractA finite‐element analysis of Taylor flow in a cylindrical capillary was performed using a commercial FEM program (FIDAP) to solve the fundamental fluid dynamics equations together with the capillary forces at the gas–liquid interface. A moving‐surface formulation was used to calculate the bubble shape. The thickness of the liquid film surrounding the gas bubble, the degree of mixing in the liquid phase, and the slip velocity between the two phases were calculated. These parameters influence the performance of monolith reactors operating in the Taylor flow regime. On comparison with experimental results it was found that the FEM calculation generally predicts a thinner liquid film, which can possibly be explained in terms of a peripheral variation in surface tension. Moreover, the wavelength of the wiggles predicted in the liquid film near the tail end of the bubble was compared to those arising from a simplified mathematical analysis available in the literature. Good agreement was found for Ca < 0.005, while for higher Ca the FEM predicts significantly shorter wavelengths, indicating that the lubrication theory is not valid here.