bluuebunny/crossref_metadata_2025_split huggingface dataset:
Particle dynamics and heat transfer under plasma conditions
Authors: Vardelle M. , Vardelle A. , Fauchais P. , Boulos M. I. 
Published: June 2004

AbstractA study was carried out of the momentum and the heat transfer to fine alumina particles injected into a DC plasma jet. Measurements are reported of particle number flux distribution, particle velocity, and inflight particle surface temperature under different operating conditions. The results show that the particle trajectories and associated particle flux distribution depends to a large extent on the particle injection velocity. The maximum particle velocity and surface temperature are noted, however, to remain close to the centerline of the jet, independent of the particle injection conditions. The maximum surface temperature reached by the particles increases with increasing plasma power and the use of an Ar/H2 plasma gas (17 vol. % H2) compared to that for a pure argon plasma.The particle velocity data are in good agreement with the predictions of a two‐dimensional mathermatical model used for the calculation of the particle trajectories and temperature history. The model predictions, however, agreed only in trend with the measured particle surface temperatures. Deviations between the two could still be observed at large distances from the point of injection of the powder. The computed particle number flux distributions were narrower than the measured profiles, which can be attributed to the fact that the model did not include, at this stage, turbulent particle diffusion effects.
On‐line optimizing control of a packed‐bed immobilized‐cell reactor
Authors: Hamer John W. , Richenberg Carl B. 
Published: June 2004

AbstractOn‐line optimizing control has been used to find and track the economically optimal operating conditions of a packed‐bed reactor. The continuous reactor under study converts the ammonium salt of fumaric acid to aspartic acid using whole cells immobilizing in K‐carrageenan beads. The on‐line optimizing control was performed using a leastsquares recursive estimation algorithm with a variable forgetting factor to estimate the parameters in a linear discrete‐time model. A Newton optimization procedure used these parameters to calculate the direction and distance to the optimal conditions. Features found to enhance the speed and stability of the algorithm included the use of a variable forgetting factor algorithm, both low‐ and high‐pass filtering of the data, outlier rejection, and linearizing input‐outupt transformations.
Galvanic interactions on periodically regular heterogeneous surfaces
Authors: Morris Rael , Smyrl William 
Published: June 2004

AbstractA heterogeneous electrode surface has been modeled using a regular distribution of circular anodes in a surrounding coplanar cathodic matrix. In the absence of mass transport effects, galvanic currents and potentials have been calculated using finite‐element analysis, with nonlinear electrode kinetics. For a fixed ratio of anodic to cathodic areas on a heterogeneous surface, calculated galvanic currents increase linearly with the active perimeter between cathodic and anodic regions. Furthermore, the current is independent of the shapes and distributions of anodic regions in a surrounding cathodic plane provided that the ratio of overall anodic area to active perimeter is conserved. Thus, due to its longer active perimeter, a surface represented by a large number of tiny anodic islands dispersed in a cathodic sea will exhibit much greater galvanic currents than an equivalent surface represented by a small number of large anodic continents.
Global phase behavior of mixtures of short and long n‐alkanes
Authors: Peters C. J. , De Arons J. Swaan , Sengers J. M. H. Levelt , Gallagher J. S. 
Published: June 2004

AbstractThe perturbed‐hard‐chain model of Beret, Donohue, and Prausnitz, in the simplified version of Kim et al., is compared with recent VLE data on mixtures of ethane and n‐alkanes with carbon numbers from 16 to 24. By using and extrapolating the linear relations between the three adjustable model parameters and the carbon number, as given by Kim et al., we find that the experimental isothermal bubble curves are well represented up to the critical pressure without the use of any adjustable parameters. Experimental Henry constants for ethane in eicosane are well predicted at all temperatures. We find this global model more accurate than the Soave‐Redlich‐Kwong equation, even if the latter is fitted isotherm‐by‐isotherm to individual mixtures with temperature‐dependent mixing parameters.
Fixed‐bed adsorption of gases: Effect of velocity variations on transition types
Authors: LeVan M. Douglas , Costa Carlos A. , Rodrigues Alirio E. , Bossy Alain , Tondeur Daniel 
Published: June 2004

AbstractIn fixed‐bed adsorption or desorption of gases, velocity variations accompany changes in gas composition, and these variations affect the transition types (spreading waves or shocks). A general criterion is developed for determining the transition type for isothermal monovariant systems (one adsorbable component in inert gas or two adsorbable components with no inert gas). Several examples are given to illustrate the determination of transition types for simple waves, contact discontinuities, shocks, and combined waves.
Robust nonlinear state feedback under structured uncertainty
Authors: Kravaris Costas , Palanki Srinivas 
Published: June 2004

AbstractThis work follows the global input/output linearization approach for the design of control systems for nonlinear plants of Kravaris and Chung. A robust nonlinear state feedback is proposed for uncertainties considered as a class of bounded perturbations to the state model. A Liapunov‐based approach is used to guarantee uniform ultimate boundedness.
Representation of the solubility behavior of amino acids in water
Authors: Nass Kathryn K. 
Published: June 2004

AbstractExpressions suitable for the description of the behavior of small biological zwitterions in aqueous systems are developed. The validity and usefulness of the expressions are tested by correlating data for the activity coefficients of several amino acids in water. Development of rational expressions for the solid‐liquid equilibria (SLE) of amino acids, in terms of the heat of solution at infinite dilution, is also presented. The solubility data of phenylalanine, tyrosine and diiodotyrosine as a function of pH are successfully correlated using the approach developed here. In addition, simultaneous correlation of the pH and temperature dependence of solubility data for diodotyrosine in water gives very good representation. The expressions described here should prove useful for the design and optimization of separation processes, such as crystallization, with minimal experimental information.
Nonlinear dynamic matrix control for high‐purity distillation columns
Authors: Georgiou Apostolos , Georgakis Christos , Luyben William L. 
Published: June 2004

AbstractThe performance of Dynamic Matrix Control (DMC) for different product purity distillation columns is studied and compared with a conventional multiloop proportional‐integral control structure (LV). The load‐rejection capability (regulatory response) of DMC becomes worse than that of the conventional structure as product purity increases. Large load disturbances take the highly nonlinear system away from the nominal linear model, adversely affecting the performance of DMC. The LV structure is less sensitive to process nonlinearities. However, simple nonlinear output transformations suggested by the fundamental design equations of the process give models that are quite insensitive to nonlinearities of the process. This results in a nonlinear version of DMC that has better performance than the standard DMC and it is much simpler than the gain and time constant scheduling DMC or adaptive DMC. The complexity of DMC when it is applied on systems with very large time constants is also addressed. Suggestions to overcome this problem are proposed.
Origin of roll waves in horizontal gas‐liquid flows
Authors: Bruno Kenneth , McCready M. J. 
Published: June 2004

AbstractThe mechanism of formation of roll waves on a horizontal liquid layer sheared by a gas flow is examined. Measurements of the wave amplitude spectrum show that, for liquid film Reynolds numbers greater than about 100, roll waves evolve from disturbances that initially have wave‐lengths much longer than the film thickness and which grow slowly with distance. Predictions of linear stability analysis are shown to agree well with the observation of these instabilities and not the visual transition to roll waves as was suggested in earlier studies. For very thin films, the data do not give conclusive proof of the origin of roll waves, but it is speculated that these are actually solitary waves which have begun to break.
Heat capacity and heat of dissociation of methane hydrates
Authors: Rueff Roger M. , Dendy Sloan E. , Yesavage Victor F. 
Published: June 2004

AbstractThe objective of this study was to determine the heat capacity and heat of dissociation of methane hydrates. A technique has been devised which circumvents the two major problems encountered in measuring gas hydrate heat capacity: the need to impose a mechanical pressure during the measurement and the need to have an absolutely pure hydrate sample. The technique was shown to be successful utilizing high‐pressure, constant‐volume cells in a differential scanning calorimeter.
A linear chemical‐physical theory model for liquid metal solution thermodynamics
Authors: Howell Wayne J. , Lira Carl T. , Eckert Charles A. 
Published: June 2004

AbstractThe simplified chemical‐physical theory (SCPT) for compound‐forming liquid metal solutions is improved by a reduction in the number of modeling parameters using an adaptation of the group contribution approach. A group contribution technique is applied to linearize the Gibbs energy (and enthalpy) of formation of intermetallic compounds. As a result, the activities or Gibbs energies of many binary liquid alloy systems are represented successfully with only a single parameter for the chemical interactions and another for the physical interactions. Similarly, the enthalpies of mixing are modeled well using only the temperature derivatives of these two parameters.
Application of thin films to porous mineral oxides using two‐dimensional solvents
Authors: Wu Jengyue , Harwell Jeffrey H. , O'Rear Edgar A. , Christian Sherril D. 
Published: June 2004

AbstractThin polymeric films have been applied to the surface of a porous material in a novel process. Nitrogen sorption, a conventional tool for measuring surface areas and pore size distributions, can be employed for determining the thickness of such films through a comparison of the pore size distribution curves before and after film formation. The thickness of a polystyrene film on a porous alumina powder is determined and compared with the theoretical thickness for styrene polymerized inside a two‐dimensional solvent, which consists of a partial bilayer of sodium dodecyl sulfate physically adsorbed from an aqueous solution onto the powder. Film thicknesses ranged from 1.8 to 0.4 nm while BET surface area decreased from 94.7 to 57.8 m2/g. The powder surface changes from hydrophilic to hydrophobic while retaining the basic pore structure.
Monte Carlo simulation of supported metal catalyst sintering and redispersion
Authors: Glen Campbell W. , Lynch David T. , Wanke Sieghard E. 
Published: June 2004

AbstractMonte Carlo simulations of sintering and redispersion of supported metal catalysts, based on an atomic migration mechanism, are presented. The support surface was modeled as a square grid with metal atoms located at various grid points. Interaction energies between metal atoms, and between metal atoms and support sites were specified. The probability of movement of each metal atom during one time increment (iteration) was calculated from the interaction energies. The effects of interaction energies, metal loading and initial distribution of the metal were examined. The model predictions are in good qualitative agreement with experimental observations. The model predicts “apparent” movement, splitting and coalescence of entire metal particles; these experimentally observed phenomena have usually been cited as evidence that sintering occurs by a particle migration mechanism.
Optimal production of secreted protein in fed‐batch reactors
Authors: Park Seujeung , Fred Ramirez W. 
Published: June 2004

AbstractThe optimal control policy for the maximization of the secreted heterologous protein in a fed‐batch bioreactor was obtained using SEY2102 as a model host yeast and SUC2‐s2 as a model secretory protein. A dynamic model for host cell growth, gene expression, and the secretion of expressed polypeptides was formulated. The optimal system trajectory contains multiple singular arcs that are distinct from one another. Optimal control requires transitions between these singular arcs. Optimal transitions between multiple singular arcs with bounded controls are uniquely located in observance with the Minimum Principle of Pontryagin. An iterative numerical search strategy for determining the optimal control showed successful convergence properties.
Molecular thermodynamics of aqueous two‐phase systems for bioseparations
Authors: King Robert S. , Blanch Harvey W. , Prausnitz John M. 
Published: June 2004

AbstractAqueous polymer‐polymer two‐phase systems provide a powerful method for separating biomolecules by extraction. When a complex mixture of biomolecules (e.g., a fermentation broth or a solution of lysed cells) is added to such a system, biomolecules partition uniquely between the two phases, achieving separation.A thermodynamic framework is presented for optimizing extraction performance in biological separations. First, a molecular‐thermodynamic model, based on the osmotic virial equation, is proposed to describe phase equilibria for dilute aqueous mixtures containing polymers and protein. Second, experimental phase‐equilibrium data (protein partition coefficients) are reported for a number of model proteins including albumin, lysozyme, and α‐chymotrypsin. To interpret and correlate the experimental data, Low‐Angle Laser‐Light Scattering (LALLS) measurements were made to determine osmotic second virial coefficients for aqueous mixtures containing polymers, proteins, salts (KCl, KH2PO4 and K2SO4 at concentrations of 50 and 100 mM) and several combinations of polymer‐polymer and polymer‐protein pairs. Combined with electrochemical measurements (differences in potential between the two phases and protein net charge), these data provide parameters for the model to calculate the desired phase equilibria. A comparison of calculated and experimental results indicates that the virial‐equation model provides good prediction of binodals and a reliable basis for estimating infinite‐dilution protein partition coefficients for biotechnical process design.
Rule‐based mineral sequences in geochemical flow processes
Authors: Novak Craig F. , Schechter Robert S. , Lake Larry W. 
Published: June 2004

AbstractThe infiltration of an aqueous solution into a permeable medium generally results in the dissolution of some of the minerals initially present and the possible precipitation of others. When the infiltration velocities are small, as is the case for many natural processes, conditions of local equilibrium apply and the dissolution and precipitation processes exhibit a wave‐type behavior reminiscent of chromatogrphic fronts. Zones of constant composition (state) will be separated by narrow regions within which the aqueous and solid phase concentrations exhibit sharp changes. Because of this wave‐like structure, an algebraic solution of the coupled material balance equations exists, but in a form that involves a trial and error solution procedure which has heretofore discouraged its application. This paper describes the essence of a scheme which uses a combination of graph theory and heuristics to minimize trials and thereby render the algebraic solution practical. The scheme offers an alternative to time‐sequencing solutions (e.g., finite difference) of the set of partial differential equations.
Conversion distribution in diffusion‐governed chlorination of poly(vinyl chloride)
Authors: Wachi Shun , Morikawa Hisashi , Inoue Hakuai 
Published: June 2004

AbstractConversion distribution in particles of chlorinated poly(vinyl chloride) (CPVC) is conceptually described based on balance equations involving mass transfer and chemical reaction. In the physical sorption of chlorine in poly(vinyl chloride) (PVC) as measured by the constant volume cell method, equilibrium concentration and diffusion rate obeyed Henry's law and Fick's law. The rate process of photo chlorination of PVC, which was investigated by the gravimetric method, could be well predicted by theoretical calculation of chlorine diffusion in PVC accompanying the infinitely fast chemical reaction. In a free grain of PVC synthesized by suspension polymerization, the chlorination rate was governed by the polymer‐phase diffusion within agglomerates of coalesced primary particles.To produce homogeneously chlorinated PVC, a periodic photo‐irradiation method was theoretically proposed and experimentally demonstrated. The effect of the periodic operation on the thermal property of CPVC was evaluated by DSC.
A discretized population balance for nucleation, growth, and aggregation
Authors: Hounslow M. J. , Ryall R. L. , Marshall V. R. 
Published: June 2004

AbstractThe population balance for batch aggregation of particulate suspensions is recast in a form that may be solved simply and accurately. The transformed equation is deduced with the introduction of only one additional parameter, which is found to be a constant for all cases. The transformed equation is tested by comparison with some analytical solutions with which it is found to be in excellent agreement. In particular, the equation is shown to predict correctly the rate of change of total particle number and volume. Compatible descriptions of linear growth and nucleation are developed with similar success.The method is then applied to modeling the in vitro growth and aggregation of kidney stones (calcium oxalate monohydrate crystals). It is found that these phenomena are well described by McCabe's ΔL law, a size‐independent coalescence kernel, and first‐order kinetics. Simulated particle size distributions and their moments are in excellent agreement with the experimental results.
Onset of pulsing in two‐phase cocurrent downflow through a packed bed
Authors: Grosser K. , Carbonell R. G. , Sundaresan S. 
Published: June 2004

AbstractIn cocurrent downflow of a gas and a liquid through a packed column, a transition from trickling flow to pulsing flow is observed as one increases the flow rates. A simple macroscopic model for the two‐phase flow is analyzed to examine whether this regime transition should be viewed as the loss of stability of a steady state or the loss of existence of any solution for the steady‐state equations of motion. The former appears to be a more reasonable interpretation and an explicit algebraic criterion for the onset of pulsing is presented.
Number of passage distribution functions with application to dispersive mixing
Authors: Tadmor Zehev 
Published: June 2004

AbstractNumber of passage distribution (NPD) functions in batch and continuous recirculating systems are presented, and their application to dispersive mixing of plastics and rubber is discussed. Dispersive mixing requires a process of repeated ruptures of the dispersed phase. This is accomplished by repeated passages in special regions of the system where stress levels above a given threshhold value are imposed on the liquid. The application of NPD functions to certain batch and continuous mixers and compounders is discussed.
Modeling chromate ion‐exchange processes
Authors: Sengupta Arup K. , Lim Lois 
Published: June 2004

AbstractIn spite of chromate's very high selectivity at acidic pH, fixed‐bed chromate‐exchange processes always suffer from severe gradual breakthroughs of chromate during column runs. Earlier, Sengupta and Clifford confirmed that such a gradual breakthrough is an equilibrium phenomenon and provided the underlying ion‐exchange mechanism. An algorithm, developed with the aid of the governing chromate ion‐exchange mechanism, is presented here to predict the salient properties of chromate‐exchange processes in a multicomponent system. The model predicts the gradual chromate breakthroughs during column runs fairly accurately and also accounts for other unusual characteristics of chromate ion exchange. Average separation factor models, often used for designing fixed‐bed ion‐exchange processes, are unable to predict the gradual breakthrough characteristics of a preferred component such as chromate.
Comparative SO2 reactivity of CaO derived from CaCo3 and Ca(OH)2
Authors: Bruce Kevin R. , Gullett Brian K. , Beach Laura O. 
Published: June 2004

AbstractExperimental data on sulfation rates of CaO particles derived from CaCO3 are compared to those derived from Ca(OH)2 using a product layer diffusion control model differing only in the shape of the CaO grain. Both the model and the experimental data indicate slightly higher reactivity for the Ca(OH)2‐derived oxide due to the observed difference in grain shape. This effect is considered as a contributor to the greater performance of Ca(OH)2 in pilot‐scale SO2 removal studies.
The theory of precipitation/dissolution waves
Authors: Helfferich Friedrich G. 
Published: June 2004

AbstractThe concepts of coherence and composition paths, originally developed for multicomponent chromatography, are used to establish a simple theory of transport in systems with precipitation and dissolution in the course of multicomponent, single‐phase flow in permeable media. Composition route construction in phase diagrams in combination with distance‐time diagrams yields concentration profiles without recourse to trial‐and‐error procedurs. Detailed results are given for systems with three ions A, B, and X and up to two precipitates AX and BX. The extension to systems with additional, nonprecipitating species is described. The new approach confirms most conclusions of Bryant's earlier theory, removes assumptions stipulated in the latter, and is simpler to handle.
Methane steam reforming, methanation and water‐gas shift: I. Intrinsic kinetics
Authors: Xu Jianguo , Froment Gilbert F. 
Published: June 2004

AbstractIntrinsic rate equations were derived for the steam reforming of methane, accompanied by water‐gas shift on a Ni/MgAl2O4 catalyst. A large number of detailed reaction mechanisms were considered. Thermodynamic analysis helped in reducing the number of possible mechanisms. Twenty one sets of three rate equations were retained and subjected to model discrimination and parameter estimation. The parameter estimates in the best model are statistically significant and thermodynamically consistent.
Flow in driven cavities with a free surface
Authors: Canedo Eduardo L. , Denson Costel D. 
Published: June 2004

AbstractA study of the flow of viscous liquids contained in an open cavity driven by a moving wall has been undertaken as a first step toward understanding interphase heat and mass transport in polymer processing equipment where rolling pools of liquid are generated. Solutions to the equations of motion for creeping flow in cavities of different aspect ratios were obtained using a finite‐differences technique for circumstances when the wall moves in the same direction as the gravitational field.Experimental studies of the flow patterns in cavities of various aspect ratios were found to be in good agreement with the creeping flow predictions for cavity Reynolds numbers Re < 50 and aspect ratios a < 1. The structure of the flow in this geometry was found to be similar to that in closed cavities of the same shape. The position and strength of the principal vortex were observed to be nearly independent of the existence of a free surface, and the gas‐liquid interface was found to significantly stabilize the rotational motion in shallow cavities.