bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamics of highly dilute solutions and the quest for ultrapurity
Authors: Sciamanna S. F. , Prausnitz J. M. 
Published: June 2004

AbstractSince very high purity is sometimes required for health‐related (and other) products, it is useful to reexamine the common thermodynamic relations that describe the chemical potential of a solute at very high dilution. Because Stirling's approximation is not valid for small numbers, the usual thermodynamic relations must be reformulated for small systems, i.e., for a solute in a small bubble or drop. A simplistic analysis indicates that in a small bubble or drop, the chemical potential of a solute goes to a finite value as the mole fraction of solute goes to zero, in contrast to the conventional result, where that chemical potential goes to negative infinity. This simplistic analysis has profound implications for separation science; it implies that (in theory) ultrapurity may be attained by conventional diffusional methods. While serious objections can be raised to invalidate the simplistic analysis, it may nevertheless be useful for chemical engineers to consider separation methods using highly dispersed systems.
A multivariable nonlinear self‐tuning controller
Authors: Agarwal Mukul , Seborg D. E. 
Published: June 2004

AbstractA new self‐tuning controller (STC) has been developed for a general class of nonlinear multiinput, multioutput process models. These models can include arbitrary, known nonlinear functions of the old inputs and outputs as well as the products of these functions and any powers of the most recent inputs. A very general control algorithm has been proposed that allows different numbers of inputs and outputs, different time delays for each input‐output pair, and a performance index that can include different penalties on the outputs and on the incremental changes in the outputs. Simulation results are presented for two‐point composition control of a pilot‐scale distillation column. The results demonstrate that the new nonlinear STC performs significantly better than conventional STC's based on linear models.
Generalized likelihood ratio method for gross error identification
Authors: Narasimhan S. , Mah R. S. H. 
Published: June 2004

AbstractA new method for detecting, identifying, and estimating gross errors in steady state processes is described in this paper. The generalized likelihood ratio method is based on the likelihood ratio statistical test and provides a general framework for identifying any type of gross error that can be modeled. The procedure is illustrated with gross errors caused by measurement biases and leaks. One significant advantage of the method is that the identification of gross errors is not confounded by departure from steady state conditions, which may now be accounted for by “leaks”. Also proposed is a new strategy for identifying multiple gross errors using serial compensation of gross errors, which may be applied to all types of gross errors including leaks and biases and which requires less computing time than the existing strategies.
Kinetics of the sodium carbonate–sulfur dioxide reaction
Authors: Kimura Shoichi , Smith J. M. 
Published: June 2004

AbstractThe Kinetics of the SO2‐Na2CO3 reaction were studied at 353 to 413 K and atmospheric pressure with thermal gravimetric analysis data. Since the reaction is very fast, special precautions were taken to operate at conditions such that transport effects did not influence results. The data indicated that Na2SO3 was formed by two paths: direct reaction, and adsorption of SO2 followed by conversion of adsorbed SO2 to adsorbed CO2 and finally desorption to final product. Rate constants were evaluated for each step in the proposed mechanism. Product distribution predicted from the rate constants agreed well with the distribution calculated from the experimental data at temperatures from 353 to 413 K. At 413 K the results suggested a change in mechanism.
Effect of film size on drainage of foam and emulsion films
Authors: Malhotra A. K. , Wasan D. T. 
Published: June 2004

AbstractAll available theoretical analyses for the drainage of thin plane‐parallel liquid films, such as those existing between two approaching liquid droplets or bubbles in the coalescence process, predict essentially the same dependence of rate of thinning of the intervening film on its size as is described by the Reynolds equation—that is, drainage time increases with the square of the film radius. Recently, we have reported experimental data for both foam and emulsion films which showed that the measured drainage times increase with about a 0.8 power of the film radius, a value much smaller than the theoretically predicted value of 2.0. Here we present a hydrodynamic analysis to predict the experimentally observed effect of film size on the kinetics of thinning of emulsion and foam films. We extend the applicability of the Reynolds model by accounting for the flow in the Plateau borders as well as the London‐van der Waals forces in the thin film phase. Our theoretical predictions are in good agreement with the experimental data on the dependence of drainage time of both foam and emulsion films on their radii.
Effect of solids on oxygen transfer in agitated three‐phase systems
Authors: Mills D. B. , Bar Raphael , Kirwan D. J. 
Published: June 2004

AbstractA dynamic response method was used to measure the volumetric mass transfer coefficient for oxygen in a mechanically agitated vessel containing an aqueous suspension of 66 μm glass beads. At constant stirring speed and superficial gas velocity the volumetric gas transfer coefficient kLa was found to decrease with solids loading. A generalized equation correlated the results in terms of the volume concentration of the solids, the total power input per slurry volume, and the superficial gas velocity.
Compressed fluid technology: Application to RIE‐developed resists
Authors: Ziger D. H. , Wolf T. M. , Taylor G. N. 
Published: June 2004

AbstractA novel plasma‐developed resist lithographic process is described that uses compressed CO2 to extract nonvolatile siloxane molecules from host organic polymers. The process is capable of at least 0.75 μm resolution with an X‐ray sensitive guest siloxane‐host polymer system. A processing window was investigated and defined to eliminate or minimize film damage during compressed fluid extraction. Polymer deformation was usually avoided by using supercritical CO2 rather than liquid CO2, provided that film thicknesses were ≤1 μm. Increased solute concentrations in the host polymer also adversely affected the quality of extracted films. An in situ capacitance process monitoring scheme was developed which indicated that film damage, when observed, was primarily caused by explosive decompression of the solvent from the host polymer.
STICT model for surface thermodynamics of liquid metal solutions
Authors: Howell W. J. , Eckert C. A. 
Published: June 2004

AbstractA new model, called STICT for surface thermodynamics using ideal chemical theory, is developed for the surface tension of liquid metal alloys. It uses the Guggenheim approach to relate surface phase properties to those in the bulk. For strongly solvated metal mixtures, ideal chemical theory is used to characterize bulk properties. The STICT model fits experimental data well for the seven systems for which sufficient data exist. Moreover, calculations of bulk and surface true compositions give some guidance to the tailoring of the surface properties of alloys for various applications.
Diffusion in pore networks: Effective medium theory and smooth field approximation
Authors: Burganos V. N. , Sotirchos S. V. 
Published: June 2004

AbstractThe problem of diffusion in pore networks of a certain class is considered, and a procedure for estimating effective diffusivities is formulated. The effective‐medium theory is used to obtain an effective conductance for the network, which is then used to determine the effective diffusivity starting from first physical principles and utilizing the observation that a network of pores of uniform conductance satisfies the smooth field approximation. Comparison of the estimated intraparticle diffusivities with those obtained from the exact solution of the transport equation for large networks reveals high accuracy and reliability of the method. Results for a number of pore networks show that the smooth field assumption should not be employed arbitrarily since it always predicts higher effective diffusion coefficients than the exact ones, by more than one order of magnitude in some cases.
Crystallization kinetics of potassium chloride from brine and scale‐up criterion
Authors: Qian Ru‐Ying , Chen Zu‐De , Ni He‐Gen , Fan Zhang‐Zhang , Cai Fu‐Di 
Published: June 2004

AbstractA systematic study of potassium chloride crystallization shows that constant tip speed, TIPS, is the agitation criterion for scale‐up. Three hydrodynamic regions are identified by a group MT TIPS3. Thus, a new generalized kinetic equation is proposed: B° = KGi(MT TIPS)j.The values of the power index j are 0.7 and 1.2 for low and high ranges of MT TIPS3, respectively. At even higher MT TIPS3, j scatters due to the breakage of crystals. The power index i is independent of hydrodynamic conditions and depends only on the crystallization temperature, e.g., it is 2.8 at 313.2 K.
A generalized bubble diameter correlation for gas‐solid fluidized beds
Authors: Horio Masayuki , Nonaka Akira 
Published: June 2004

AbstractA new bubble diameter correlation is derived to predict bubbling characteristics of fluidized beds of varieties of powders. The present model is founded on the postulate that the steady bubble size, which is often called the maximum stable diameter, observed in a bed of Geldart group A powder is formed as a result of an equilibrium of successive coalescence and splitting. For the cases of group B powders the present correlation automatically converges to the conventional correlation of Mori and Wen (1975), whose predictions are close to those of Rowe (1976) and Darton et al. (1977). For group A powders the present correlation is validated by comparison with experimental data in the literature. Based on this correlation a theoretical explanation is presented for the fact that the maximum bubble diameters observed were up to 50 to 100 times as large as those from the stable bubble theory of Harrison et al. (1961).
Design of set point regulators for processes involving time delay
Authors: Sanathanan C. K. , Quinn S. B. 
Published: June 2004

AbstractAn efficient frequency domain methodology for the design of set point regulators for high‐order process models involving relatively large pure time delay is presented. The unique advantage of the methodology is that it enables the designer to rapidly visualize the structure of the required controller as soon as the time and frequency domain specifications are stipulated for the closed‐loop system. Optimizing the parameters of an appropriate structure improves the robustness of the controller. The method does not require order reduction of the original model, and time delay is handled directly. Also, only output feedback is utilized.
General conditions of collinearity at the phase boundaries of fluid mixtures
Authors: Eubank P. T. , Barrufet M. A. 
Published: June 2004

AbstractThe general collinearity conditions at phase boundaries for mixtures are proved by thermodynamic identities for density and for entropy as functions of temperature, pressure, and composition. In the case of density/temperature/pressure/composition collinearity is always found at the cricondentherm or any temperature extremum, whereas for entropy/temperature/pressure/composition collinearity is always found at the cricondenbar or any pressure extremum. Qualitative phase diagrams for a typical binary system are presented in accordance with the derived inequalities. Whether a particular slope, involving the above variables, from the homogeneous side of the phase boundary is greater or less than that from the heterogeneous side depends on location on the phase boundary with respect to cricondentherm, critical point, and cricondenbar.
Heat transfer from a circulating fluidized bed to membrane waterwall surfaces
Authors: Wu R. L. , Lim C. J. , Chaouki Jamal , Grace J. R. 
Published: June 2004

AbstractAverage and local heat transfer coefficients were measured for transfer from circulating fluidized beds of sand particles (mean size 188 and 356 μm) to two water‐cooled membrane wall surfaces located on one face of a 152 mm square by 7.3 m tall column. The measurements cover a range of superficial gas velocities from about 4 to 7 m/s, suspension densities from about 8 to 130 kg/m3, suspension temperatures from 150 to 400°C, and secondary‐to‐primary air ratios of 0 to 1.5. Heat transfer coefficients, averaged over a 1.53 m length of the membrane waterwall surfaces, depend strongly on suspension density, but show almost no separate dependence on gas velocity, bed temperature, or secondary‐to‐primary air ratio for the conditions studied. For the surface nearest the top of the unit, the coefficient decreases with distance measured downward from the top, suggesting that particles travel downward along the surface. As a result, averaged coefficients are lower and the influence of particle size is less than for previously reported circulating fluidized bed heat transfer measurements where miniature heat transfer surfaces were employed.
Use of a finite‐element method to interpret rheological effects in blade coating
Authors: Sullivan Tim , Middleman Stanley , Keunings Roland 
Published: June 2004

AbstractData and finite‐element simulations are presented for the blade coating of a series of Newtonian and non‐Newtonian fluids. Numerical simulations for purely viscous fluids show good agreement with coating thickness data for Newtonian and relatively inelastic non‐Newtonian liquids, including geometries for which lubrication theory is inaccurate. These simulations account for the shape of the free surface, with surface tension included, and incorporate realistic inflow and outflow boundary conditions. By comparing pressure distributions generated with the finite‐element technique to those calculated using lubrication theory, it is shown that the simple lubrication theory analysis suffers from inadequate inflow and outflow boundary conditions. Comparison of these simulations with new experimental results for three well‐characterized viscoelastic liquids, having nearly identical steady shear viscosities but different normal stress behavior, confirms speculations of earlier work with respect to the effect fluid rheology has on coating thickness.
Modeling of free‐radical polymerization of styrene by bifunctional initiators
Authors: Choi K. Y. , Lei G. D. 
Published: June 2004

AbstractA detailed kinetic model for the bulk styrene polymerization initiated by symmetrical diperoxyester bifunctional initiators is presented. When chain termination occurs via a combination termination mechanism, six distinct polymeric species are identified in accordance with the nature of the polymer end units. It is shown that the unequal thermal decomposition characteristics of the peroxides of the bifunctional initiator system lead to the formation of polymers having considerably higher molecular weight than those obtained by the monofunctional intiator systems. It has also been found that high monomer conversion, high molecular weight, and narrow molecular weight distribution can be obtained simultaneously by using the bifunctional initiators at high reaction temperatures. This is due to the reinitiation and propagation of inactive polymers carrying undecomposed peroxides. The molecular‐weight‐increasing effect of the bifunctional initiator is more pronounced at high reaction temperatures. The new possibilities of increasing the monomer conversion and controlling the polymer molecular weight properties more effectively through the use of bifunctional initiators are discussed.
Computer generation of reaction schemes and rate equations for thermal cracking
Authors: Hillewaert L. P. , Dierickx J. L. , Froment G. F. 
Published: June 2004

AbstractReaction schemes for the thermal cracking of paraffins, naphthenes, olefins, and aromatics, and the associated rate equations, are generated by an algorithm based upon Boolean relation matrices. In order to reduce calculation times for the heavier components, a self‐learning system is introduced. This self‐learning system avoids repetition of identical calculations by recognizing intermediate species, for which the reaction schemes have already been generated. The software includes routines for standardizing the representation of the species, an information retrieval system, and libraries containing the necessary information for recognition of the species and the reaction schemes for these species.
Narrowing diagnostic focus using functional decomposition
Authors: Finch F. E. , Kramer M. A. 
Published: June 2004

AbstractThe problem of diagnosing faults in chemical plants can be efficiently addressed by a hierarchical procedure involving successive narrowing of the space in which the fault search is conducted. A technique is presented for narrowing diagnostic focus useful in the first stages of a diagnostic search. Based on a decomposition of the process according to function, the technique assesses the functionality of process systems based on measurements of controlled and manipulated variables. A procedure for identification of possibly faulty systems and units from the system states is outlined. Detailed diagnosis, not treated in this paper, would be applied after candidate systems or units are located. An example is presented using a hypothetical chemical reaction process.
Pore evolution and channel formation during flow and reaction in porous media
Authors: Hoefner M. L. , Fogler H. S. 
Published: June 2004

AbstractA theoretical and experimental study on the dissolution of porous media by flowing acid has been carried out. Dissolution of the media results in an evolution of the pore geometry and the formation of random flow channels. The goal is to predict the range of conditions under which channels will form, and the effects of various parameters on the structure of the channels and on their rate of propagation through the media. A random network model is used to describe the behavior of the stochastic, rootlike channels that form during flow and dissolution in carbonate rock and in other systems. The structure of the flow channels that form as a result of acid attack are characterized and studied using a Wood's metal casting technique. A comparison of model results shows that the rates of channel formation and growth are intimately related to the developing structure of the channels (size of branches and degree of branching), which in turn is controlled by factors such as the fluid velocity and the rate of reaction. Depending on the experimental conditions, the channels range from a single conduit with a minimum of branching to a highly branched, spongy network of channels. The dependence of permeability increase and channel branchedness on injection rates and acid diffusion rates is described by the Damkohler number for flow and reaction.
Micellar‐enhanced ultrafiltration of chromate anion from aqueous streams
Authors: Christian S. D. , Bhat S. N. , Tucker E. E. , Scamehorn J. F. , El‐Sayed D. A. 
Published: June 2004

AbstractMicellar‐enhanced ultrafiltration can be used to remove multivalent anions or cations from aqueous streams. In the removal of chromate ions (CrO), the cationic surfactant hexadecylpyridinium chloride is added to the solution, and the chromate ions preferentially adsorb at the surface of the highly charged surfactant micelles. The solution is processed by ultrafiltration, using a membrane with pore sizes small enough to block the passage of the micelles and adsorbed ions. The permeate solution has a chromate concentration less than 0.1% that in the original stream. A new equilibrium model, combining the simple two‐phase polyelectrolyte theory of Oosawa with thermodynamic activity, material‐balance, and charge‐balance equations, successfully correlates ultrafiltration and equilibrium dialysis results for chromate solutions.
Flooding, holdup, and drop size measurements in a multistage column extractor
Authors: Kirou V. I. , Tavlarides L. L. , Bonnet J. C. , Tsouris C. 
Published: June 2004

AbstractThe hydrodynamics of a pilot plant multistage mixer column extractor was studied for the toluene/water physically equilibrated system. The effects of rotational speed, and continuous and dispersed phase flow rates were investigated under a variety of operating conditions. Dispersed phase axial holdup profiles, determined by a noninvasive ultrasonic method, showed a strong nonuniformity. Depending on the operating conditons, holdup profiles can change from a concave shape to a sigmoidal form with a maximum in the bottom of the column. Sauter mean diameter and drop size distribution profiles are strongly affected by rotational speed. Significant, but weaker, are the effects of continuous and dispersed phase flow rates. Continuous monitoring of the holdup profile in the proximity of flooding leads to the formulation of proper criteria for the prediction of flooding. These criteria are appropriate for models allowing for axial variation of the holdup along the contactor.
Stability and tensile strength of liquids exhibiting density maxima
Authors: Debenedetti P. G. , D'Antonio M. C. 
Published: June 2004

AbstractIf a given liquid exhibits a density maximum anywhere in its phase diagram, thermodynamic consistency dictates that such a point cannot be isolated: a density maxima locus must necessarily exist. For a fluid that does not also exhibit density minima, the pressure‐temperature projection of such a locus is negatively sloped, and can only end at a stability limit. There exist two thermodynamically consistent ways in which such an intersection can occur, and they correspond, respectively, to the highest and lowest possible temperatures at which a liquid can exhibit a negative coefficient of thermal expansion. These theoretical predictions are confirmed by experimental observations. The existence of density anomalies anywhere in a liquid's phase diagram is shown to have a profound influence in determining the shape of such a fluid's stability boundary.
Recycle continuous‐flow electrophoresis: Zero‐diffusion theory
Authors: Gobie William A. , Ivory Cornelius F. 
Published: June 2004

AbstractRecycle continuous‐flow electrophoresis (RCFE) is a modification of Hannig's thin‐film CFE device in which eluant is continuously recycled to the chamber inlet. Shifting the recycled eluent laterally a specific distance prior to reinjection enables the RCFE to separate any two solutes to arbitrary purity. This paper studies solute transport in an idealized RCFE in the absence of diffusion. The model is solved analytically by means of a two‐sided Laplace transform. Three distinct types of solute distribution are found, and guidelines for construction and operation of an RCFE are derived.
Recursive identification of gross errors in linear data reconciliation
Authors: Crowe Cameron M. 
Published: June 2004

AbstractIn the reconciliation of measurements of flows and concentrations so that they conform to conservation laws and other constraints, any gross errors in the measurements must be identified in order that they can be either corrected or deleted.A new method is derived for the recursive prediction of the changes in the objective function, and of the statistical tests for the measurements, which would result from the deletion of suspect measurements. Inverses of large matrices are not required and the reconciliation can also be easily calculated for any set of deletions. It is shown that the decrease in the objective function caused by deletion of a single measurement equals the square of the corresponding maximum power measurement statistic, calculated prior to that deletion. An algorithm for the detection of suspect sets of gross errors, whose deletion leads to acceptable values of all statistical tests and process flow rates, is proposed and illustrated.