bluuebunny/crossref_metadata_2025_split huggingface dataset:
Representation of high‐dimensional solid‐liquid phase diagrams of ionic systems
Authors: Samant Ketan D. , Ng Ka M. 
Published: April 2004

AbstractA generic framework is presented for representation of the solid‐liquid phase behavior of multicomponent ionic systems with and without compound formation. Isothermal isobaric phase behavior is represented in form of digraphs. The invariant points in the composition space are identified as vertices of the digraph. These vertices are connected by edges identified from the adjacency matrix, which is constructed by using a set of generic rules based on Gibbs phase rule. These edges form the boundaries of high‐dimensional saturation varieties, which are identified from the saturation variety matrix. For graphical representation, the number of independent coordinates is calculated and a suitable set of coordinates is developed. Projections are used to view high‐dimensional phase diagrams in their entirety and to simplify the analysis of the phase behavior. Potential applications of this framework include facilitation of experimental development and computer‐aided design of crystallization‐based separation processes.
Gypsum nucleation into sodium chloride solutions
Authors: Prisciandaro Marina , Lancia Amedeo , Musmarra Dino 
Published: April 2004

AbstractThe nucleation of gypsum into a NaCl solution was studied within a supersaturation range of 2–4 at 25–70°C. The experiments were carried out using a lab‐scale apparatus consisting of a batch crystallizer with the related measurement devices. Signals of scattered and transmitted light coming from a He–Ne laser source were analyzed to measure the induction period, that is, the time delay necessary for homogeneous nucleation to take place. Comparison of the experimental results with those previously obtained in the absence of added NaCl in solution showed that NaCl strongly affects gypsum precipitation. They were compared in terms of the activation energy and the interfacial tension between crystals and the surrounding aqueous solution.
Reactions in multiindexed continuous mixtures: Catalytic cracking of petroleum fractions
Authors: Peixoto F. C. , de Medeiros J. L. 
Published: April 2004

AbstractThe classic breakage problem is a population‐balance problem using first‐order kinetics and product distribution rules over a multidimensional continuum, mathematically expressed as linear integrodifferential equations for the multiindexed frequency distribution functions of entities. To model the catalytic cracking of petroleum fractions, population‐balance equations are solved through Galerkin formalism. It focuses on a simplified version of such equations, which was solved analytically through the method of characteristics. Kinetic and stoichiometric parameters were statistically estimated for both models from a set of pseudoexperimental data generated using available traditional lumped models. For this purpose, an arbitrary structural description for a continuous representation of the species also had to be developed.
Hydrogen bonding with aromatic rings
Authors: Brinkley Ray L. , Gupta Ram B. 
Published: April 2004

AbstractThermodynamic effects of hydrogen bonding are important in determining the phase behavior in polar fluids. While efforts to understand “strong” donor and “strong” acceptor combinations (H‐bonds involving a formation energy more negative than −20 kJ/mol such as alkanol‐alkanol H‐bonding have been substantial, weak H‐bonds involving double bonds or aromatic rings as proton acceptors) have largely been ignored. Using FTIR spectroscopy H‐bonding between alcohol donor and aromatic ring‐containing acceptor molecules was studied including l‐hexanol and cyclohexanol at low concentrations where self‐association is negligible (strong donors). H‐bonding “weak” acceptors studied include toluene and m‐xylene. Clear spectroscopic evidence existed for the formation of H‐bonds between the alcohol and aromatic molecules, which are much weaker than conventional “strong donor”–“strong acceptor” H‐bonds. Using quantitative FTIR measurements, the percentage of H‐bonded alcohol molecules over a range of aromatic concentrations was determined. Ab initio calculations also showed that alcohol–aromatic H‐bonds are much weaker than alcohol–alcohol H‐bonds. This H‐bonding, though weak, will contribute significantly to the chemical potential of the molecules.
Comparison of Hg0 capture efficiencies of three in situ generated sorbents
Authors: Lee Tai Gyu , Biswas Pratim , Hedrick Elizabeth 
Published: April 2004

AbstractThree different sorbent materials (Ti‐, Si‐, and Ca‐based) were compared for their mercury (Hg0) capture efficiencies in an entrained flow reactor. Agglomerated particles with a high specific surface area were generated in situ by injecting gas‐phase sorbent precursors into a high‐temperature furnace reactor. Titania particles in the presence of UV irradiation were most effective at mercury capture (>98%). In situ generated CaO particles had a capture efficiency of 33% (without any UV irradiation), while SiO2 was completely ineffective at Hg0 capture. The efficiency of elemental Hg capture of both CaO and TiO2 particles decreased with increasing SO2 concentration. The increase in the feed rate of the Ti sorbent resulted in the recovery of the higher Hg0 capture efficiency due to the availability of more active sites. The in situ generated titania sorbents were also effective at Hg0 capture (>87%) at elevated temperatures (160°C).
Estimating polymer/solvent diffusion coefficient by optimization procedure
Authors: Doumenc Frédéric , Guerrier Béatrice 
Published: April 2004

AbstractSolvent diffusion in polymer solutions is one of the main parameters that determine the drying kinetics of polymer films, especially in the concentrated domain. As is well known for polymer/solvent solutions, solvent diffusion coefficients decrease by several orders of magnitude when the solvent concentration decreases. Direct measurements of these coefficients are complex and time‐consuming, and most often dedicated to well‐characterized “model” systems. In this study, another approach is developed that is based on simple gravimetric experiments coupled with the modelization of the drying kinetics and an optimization iterative procedure. The sensitivity of the method to various errors (measurement errors and uncertainties on a priori known parameters) is thoroughly investigated. The method accurately estimates diffusion coefficients on a large concentration domain, provided a suitable experimental strategy is used.
An engineering approach to an unsolved problem in multicomponent diffusion
Authors: Nauman E. Bruce , Savoca Joseph 
Published: April 2004

AbstractBoth practical and conceptual problems arise in standard theories of multicomponent diffusion. They include the sometimes arbitrary and even artificial selection of one component as the solvent, the lack of explicit dependence on the properties of the solvent, and the difficulty in formulating compositionally dependent diffusion coefficients that satisfy material‐balance constraints. Two alternative approaches based on tracer diffusion coefficients for various components are physically reasonable and overcome these difficulties. Both approaches predict cross‐diffusion, that is, diffusion of component A as a result of a gradient in component B. Either approach can be used in systems where component diffusivities differ greatly in magnitude and where the number of chemical species is large, as in polymerizations.
Gas–solid fluidization in a centrifugal field
Authors: Qian Gui‐Hua , Bágyi István , Burdick Ian W. , Pfeffer Robert , Shaw Henry , Stevens John G. 
Published: April 2004

AbstractThe nature of fluidization and the behavior of particles in a centrifugal field are discussed. Powders are classified into four groups (A, B, C, and D) following Geldart based on their fluidization behavior. A simple general model, agreeing with conventional fluidized beds and usable for variable “g,” is proposed to determine the transition boundary between group A and C particles. The general model for conventional fluidized beds by Foscolo and Gibiloro was used to determine the boundary between group A and B particles, and the semiempirical equation of Molerus for the boundary between group B and D particles in a centrifugal field. Theoretical analysis showed that group A particles can shift to group B, and group C particles can shift to group A under a centrifugal force. Therefore, certain group C particles can be fluidized in rotating fluidized beds. For very high “g,” however, such particles shift to group D and cannot be fluidized. Experiments in a horizontal rotating fluidized bed under different “g” forces to check the theoretical analysis confirmed that Geldart group C particles (7 μm alumina), which cannot be fluidized in a conventional fluidized bed, can fluidize in a rotating fluidized bed operating at a sufficiently high rotating speed to shift them into group A or B. Similarly, in a series of experiments in a rotating fluidized bed, group A particles behaved as group B.
Suppression of gas separation membrane plasticization by homogeneous polymer blending
Authors: Bos A. , Pünt I. , Strathmann H. , Wessling M. 
Published: April 2004

AbstractPlasticization is a phenomenon frequently encountered in the application of glassy polymeric materials for solution–diffusion membranes. Conventional methods for stabilizing the membrane are either annealing or cross‐linking, which hardly influence the selectivity of the membrane, but decrease the permeability. For single‐gas experiments, the literature shows that plasticization can be stabilized by blending a polymer with high plasticization tendencies with one that is hardly affected by the sorbed molecules. Most permeation experiments are carried out with pure CO2, but little is known about the transport properties determined from mixed gas experiments. Stabilization of plasticization in mixed‐gas experiments for polymer blends of the polyimide Matrimid and polysulfone is reported, as well as transport properties of a new homogeneous polymer blend based on Matrimid and the copolyimide P84. Experimental results show that the material is stabilized against carbon dioxide plasticization and selectivity for a carbon dioxide/methane mixture significantly improves.
Contributions to electrostatic interactions on protein transport in membrane systems
Authors: Burns Douglas B. , Zydney Andrew L. 
Published: April 2004

AbstractSeveral recent studies have demonstrated the importance of electrostatic interactions on the transport of charged proteins through porous membranes. The objective of this study is to compare predictions of available hydrodynamic and partitioning models with experimental data for the sieving coefficient of ovotransferrin through both positively and negatively charged membranes over a range of solution conditions. Model calculations were performed with all parameters evaluated from independent experimental measurements. The membrane pore‐size distribution was determined from dextran sieving data, and the membrane surface charge was evaluated from streaming potential measurements. The model properly predicts the complex effects of solution pH and ionic strength on protein transmission in the presence of both attractive and repulsive electrical interactions. Model simulations were performed to highlight the key contributions to protein transport.
Concentration polarization in stirred ultrafiltration cells
Authors: Johnston Scott T. , Smith Kenneth A. , Deen William M. 
Published: April 2004

AbstractLaminar boundary‐layer theory was used to quantify concentration polarization in ultrafiltration systems in which the membrane forms the base of a stirred, cylindrical container. The flow was approximated as a rigid‐body rotation above a stationary surface (Bödewadt flow), with a filtration velocity dependent on the osmotic pressure of the retained solute, and therefore varying with radial position on the surface. Because the analysis was limited to moderate solute concentrations and filtrate velocities, physical properties were assumed to be constant. The axisymmetric convective‐diffusion problem was solved by a finite difference method. Boundary‐layer results were compared with predictions based on the common assumption of a uniform stagnant film and with a hybrid approach of applying locally the stagnant‐film relationships but allowing the film thickness to vary with position. In general, both of the approximate models underestimated polarization effects, with the hybrid approach yielding smaller errors. In one set of simulations on the osmotic reduction in filtration rate caused by a completely retained solute, predicted errors in filtration rates with the models were moderate, with a maximum discrepancy of 21% (for the stagnant‐film model). In the second set of simulations concerning polarization effects on apparent sieving coefficients for permeable solutes, the error in the predicted ratio of true‐to‐observed sieving coefficient was as much as 78% with the stagnant‐film approach, while with the hybrid model it was no more than 15%. Thus, the stagnant‐film approach was much less satisfactory for inferring sieving coefficients than for predicting mean filtrate velocities. The predictive capability of the boundary‐layer model was tested using previous filtration data for bovine serum albumin in two ultrafiltration cells. The agreement was excellent, provided that an appropriate value was selected for the angular velocity of the bulk fluid.
Dean vortex stability using magnetic resonance flow imaging and numerical analysis
Authors: Mallubhotla Hanuman , Belfort Georges , Edelstein William A. , Early Thomas A. 
Published: April 2004

AbstractMagnetic resonance flow imaging using flow encoding with spin warp imaging was used in three dimensions to measure velocity profiles and the dynamic behavior of centrifugally‐induced (Dean) vortices in curved tube flow. Experimental measurements were compared with numerical simulations obtained from the solution of Navier‐Stokes and continuity equations using a commercial finite‐element package. Effects of flow rate and geometry, and the ratio of the tube radius to that of curvature on the stability of Dean vortices were studied. Twisting and bifurcation of vortices increased with increasing flow rate and radius ratio. A six‐vortex pattern was measured experimentally and predicted numerically. Additional wall shear rates, due to Dean vortices, were estimated from velocity measurements in the cross‐sectional plane. A phase diagram was constructed to establish conditions for the existence of two, four or six vortices as a function of flow rate and curvature. Experimental observations were compared with numerical results obtained from three types of finite‐element grids. The full‐tube grid without symmetry planes was most predictive for vortex bifurcation, while the pseudo‐cylindrical full‐tube grid with a plane of symmetry gave best results for shear rates. Results from the numerical analysis agreed qualitatively well with the MRI measurements.
Mixed‐gas adsorption
Authors: Siperstein Flor R. , Myers Alan L. 
Published: April 2004

AbstractThe prediction of multicomponent adsorption equilibria from single‐component data is one of the most challenging and important problems in adsorption. The chief obstacle to progress is a scarcity of accurate and consistent experimental data over a wide range of temperature and loading for testing theories. Several binaries and one ternary system on two types of zeolites (silicalite and faujasite) were studied in a combination calorimeter‐volumetric apparatus. Activity coefficients and excess functions for enthalpy, free energy, and entropy were extracted from the binary data using a three‐constant equation to represent nonidealities. The successful correlation of binary excess functions with pure‐component properties for type I isotherms on zeolites is a first step toward predicting multicomponent adsorption from single‐gas adsorption and a major advancement over the theory of ideal adsorbed solutions.
Microkinetic models and dynamic Monte Carlo simulations of nonuniform catalytic systems
Authors: Dooling David J. , Broadbelt Linda J. 
Published: April 2004

AbstractThe combined insight gained from laboratory and computational experiments has historically provided detailed information about the complex interactions present in many heterogeneous catalytic systems. Although this information has been effectively used to interpret and explain experimental observations, it unfortunately has not, in general, been incorporated into kinetic models of the reacting systems. In particular, catalytic nonuniformity is one such phenomenon which is often ignored when kinetic models are constructed despite there being much experimental and computational evidence indicating its presence. Catalytic nonuniformity has been therefore incorporated into both microkinetic models and dynamic Monte Carlo simulations of catalytic reacting systems, and the performance and applicability of each solution method has been investigated for several model systems exhibiting different causes of nonuniform behavior.
Thermodynamic modeling of binary and ternary adsorption on silica gel
Authors: Steffan Dirk G. , Akgerman Aydin 
Published: April 2004

AbstractQualitative and quantitative characterization and prediction of multicomponent adsorption equilibria are essential for design of environmental remediation processes such as soil vapor extraction, bioventing, and thermal desorption. Single component, binary‐ and ternary‐mixture isotherms on silica gel were measured by the frontal analysis chromatography technique. Binary organic mixtures were composed of environmentally relevant VOCs, hexane/benzene (nonpolar/nonpolar), and hexane/trichloroethylene (nonpolar/slightly‐polar). Water binaries were water with hexane, benzene, or trichloethylene. Organic mixtures exhibited enhanced adsorption, where the adsorbed amount for each component was increased due to the second component. Water/hexane and water/benzene mixtures showed noncompetitive adsorption, where water adsorbed onto polar sites and n‐hexane or benzene adsorbed onto nonpolar sites. Competition for polar adsorption sites was observed for the trichloroethylene adsorption in water. Adsorption data of n‐hexane/benzene/water showed that n‐hexane and water were independently adsorbing onto different adsorption sites. Furthermore, n‐hexane and benzene with water showed the same adsorption behavior as without water. For the mixture of n‐hexane/trichloroethylene/water, only the amount of water adsorbed was reduced compared to the pure species adsorption of water. The adsorption equilibria of n‐hexane and trichloroethylene were not influenced in comparison to their pure species isotherms. Mixture isotherms were modeled with IAST, MSAM, and RAST. The nonideal adsorbed phase was characterized using activity coefficients.
Separating solvation from molecular diffusion in polymers
Authors: Elabd Yossef A. , Barbari Timothy A. 
Published: April 2004

AbstractThe diffusion of methyl ethyl ketone (MEK) in two vinyl alcohol/vinyl butyral (VA/VBu) copolymers (11‐ and 19‐wt. % VA) was studied at low vapor activities using Fourier transform infrared‐attenuated total reflectance (FTIR‐ATR) spectroscopy. MEK has the ability to interact through hydrogen bonding to sites in the polymer and was chosen to study the effect of penetrant–polymer solvation on molecular diffusion. The assumption of local equilibrium was verified by examining the time‐evolved concentrations of hydrogen‐bound and free MEK determined from the carbonyl (C = O) stretching bands. A mathematical model that accounted explicitly for solvation during the diffusion process was developed. Solvation hindered the diffusion of MEK in the VA/VBu copolymer by factors of 2.0 (11‐wt. % VA) and 2.6 (19‐wt. % VA). After separating solvation from diffusion, true diffusion coefficients of MEK were compared to those of methylene chloride (CH2 Cl2 ), a noninteracting penetrant of similar size to MEK. Within experimental error, true diffusion coefficients for MEK were the same as those for CH2 C12 over the concentration range studied.
CFD modeling of gas‐fluidized beds with a bimodal particle mixture
Authors: van Wachem B. G. M. , Schouten J. C. , van den Bleek C. M. , Krishna R. , Sinclair J. L. 
Published: April 2004

AbstractA computational fluid dynamics model was developed for gas‐solid fluidized beds containing a mixture of two particle species. To calculate stresses of the solid phase, the kinetic theory of granular flow was extended to consider a binary mixture of smooth, nearly elastic, spheres. The developed model was simulated to demonstrate key features of binary mixture fluidization. Bed expansion with a binary mixture of different size particles, but with identical densities, was much higher than that of a system consisting of mono‐sized particles of the same mean size as the bimodal mixture. Minimum fluidization velocity for the binary particle system was significantly lowered. The mixing behavior of the binary mixture of particles, characterized by the mixing index, increased with increasing superficial gas velocity. For a binary mixture of particles of larger size with lower density and smaller size with higher density, larger, lighter particles segregated to the top of the fluid bed, while smaller, heavier particles segregated to the bottom. With increasing fluidization velocity, this segregation pattern reversed and “inversion” occurred. The drag and gravity force difference between small, heavy particles and large, light particles was dominant at low gas velocities. With an increase in gas velocity, however, the gradients in granular temperature and pressure became dominant terms in the equations for the relative force and thus velocity between two different particle species.
Stochastic modeling of particle coating
Authors: Alonso M. , Alguacil F. J. 
Published: April 2004

AbstractDry coating of powders, in forming a layer, consists of fine particles of one component onto the surface of coarser particles of another component. In the process, fine particles are transferred among colliding coarse particles (carriers) until a steady‐state distribution of fines on the carriers surface is attained. A stochastic model was developed for the kinetics of fines transfer based on a birth‐death population balance including theoretically‐derived one‐step transition probabilities. First, the population balance equation is solved under steady‐state conditions leading to the result that, at equilibrium, the number of fines per carrier follows a Bernoulli distribution. Based on the obtained equilibrium distribution, an approximate transient solution proposed agrees fairly well with the numerical solution of the birth‐death equation. Model predictions were compared qualitatively with earlier experimental results.
Flow pattern transition in a large jetting fluidized bed with double nozzles
Authors: Guo Qingjie , Tang Zhi , Yue Guangxi , Liu Zhenyu , Zhang Jiyu 
Published: April 2004

AbstractAn experimental study was conducted in a 500 mm ID, 8,000 mm high jetting fluidized bed with double vertical nozzles using frame‐by‐frame analysis of experimental videos. Three different flow patterns (separated jets, flow transition, and jet coalescence), with the two jets always coalesce within the penetration depth, were first observed in the jetting fluidized bed. Radial profiles in the fluidized bed were measured with a PC‐4 optical fiber probe. Effects of jet gas velocity and nozzle distance on the radial and axial voidage distribution were studied. The bed hydrodynamic behavior was characterized using a deterministic chaotic theory to analyze effects of jet gas velocity, static bed height, and nozzle distance on the correlation dimension, which increased with increasing jet gas velocity and static bed height.