bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamics of hydrogen‐bonded molecules: The associated perturbed anisotropic chain theory
Authors: Ikonomou G. D. , Donohue M. D. 
Published: June 2004

AbstractThe perturbed anisotropic chain theory (PACT) developed by Vimalchand and Donohue has been generalized to treat pure fluids that associate through hydrogen bonding, as well as mixtures of one associating component and several diluents. Using an approach similar to that of Heidemann and Prausnitz, a closed‐form equation of state has been derived. It is applicable to simple as well as complex molecules at both gas and liquidlike densities and takes into account dipole and/or quadrupole moments. Molecular parameters were obtained by fitting the equation to experimental liquid density and vapor pressure data.
Turbulent flow in stirred tanks. Part II: A two‐scale model of turbulence
Authors: Placek Jiří , Tavlarides L. L. , Smith G. W. , Fořt Ivan 
Published: June 2004

AbstractThe two‐scale turbulence concept is recommended for modeling the turbulence in a baffled vessel equipped with a Rushton‐type turbine impeller. A three‐equation isotropic turbulence model is proposed that employs the balance equations for: the kinetic energy of the large scale vortices; the kinetic energy of the inertial subrange eddies; and the dissipation rate of the small‐scale turbulence. The energy transfer rate from the large‐scale vortices is prescribed algebraically. Flow patterns are modeled by solving the transport equations for vorticity, stream function, and tangential momentum. The Reynolds stresses are modeled by means of the effective viscosity, based on the three‐equation model of turbulence. The calculated profiles of the mean velocity at the tank wall agree with experimental data obtained in the same system by means of a Pitot tube.
Molecular thermodynamics for fluids at low and high densities. Part II: Phase equilibria for mixtures containing components with large differences in molecular size or potential energy
Authors: Cotterman R. L. , Prausnitz J. M. 
Published: June 2004

AbstractThe molecular‐thermodynamic correlation presented in Part I for pure fluids is extended to mixtures; this extension is particularly useful for mixtures of components with large differences in molecular size or potential energy. The novel feature of this correlation is a separation of the high‐density and low‐density contributions to the residual Helmholtz energy; this separation allows use of separate mixing rules for each density regime, guided by theoretically defined boundary conditions. Such flexibility is necessary to represent phase equilibria in highly asymmetric fluid mixtures such as water‐hydrocarbon systems. Phase equilibria are correlated for a variety of binary and multicomponent mixtures, including a petroleum reservoir fluid containing carbon dioxide and including a mixture of hydrogen and coal‐derived liquids.
Numerical analysis of jet‐stirred reactors with turbulent flows and homogeneous reactions
Authors: Liu Chih‐Hsiung , Barkelew C. H. 
Published: June 2004

AbstractA computer program designed to model the turbulent reacting flow in jet‐stirred reactors has been developed. In solving the single‐phase flow field, a two‐equation turbulence closure was used to predict the turbulent eddy viscosity variation in the reactor. The model was used to predict the performance of a real reactor. The predicted results compared favorably with measurements in the field. It was found that the key to the reactor performance is the strength of the recirculating eddy caused by the jet entrainment.
Kinetics of hydrogen absorption in a stirred metal hydride slurry
Authors: Tung Yuanki , Grohse E. W. , Hill F. B. 
Published: June 2004

AbstractIsothermal, isobaric measurements were made of the rate of hydrogen absorption by a slurry of LaNi5 powder suspended in n‐undecane in a baffled stirred reactor. The data were interpreted using a model emobodying three resistances in series: a gas‐liquid mass transfer resistance, a liquid‐solid mass transfer resistance, and an “overall reaction resistance.”At the highest agitator speeds employed, 2,000 rpm, conversions of LaNi5 to hydride of 90% or better were obtained within one minute or less, thereby confirming the potential of the metal hydride slurry concept for commercial applications.
Designing hollow‐fiber contactors
Authors: Yang Ming‐Chien , Cussler E. L. 
Published: June 2004

AbstractHollow‐fiber contactors can provide fast mass transfer without flooding or loading. They are a promising alternative to packed towers for gas treating, and to centrifugal extractors for liquid‐liquid extraction. Hollow‐fiber contractors can be designed effectively using the mass transfer correlations reported in this paper. The correlations, based on aqueous deaeration and carbon dioxide absorption, are similar to earlier heat and mass transfer correlations, but can be complicated by diffusion across the fiber wall and by alterations in fiber geometry.
Diffusion and mass transfer in supercritical fluids
Authors: Debenedetti P. G. , Reid R. C. 
Published: June 2004

AbstractThe different behavior of fluid density and viscosity in going from the dilute gas to the dense fluid state gives rise to kinematic viscosities which, in the near supercritical region, are lower than for liquid metals. As a consequence, the relative importance of natural convection (as measured by the ratio of buyoant to inertial forces) is two orders of magnitude higher in a supercritical fluid (at constant Reynolds number) than in normal liquids.Binary diffusion coefficients of nonvolatile solutes in supercritical fluids were measured with a technique that involved laminar flow and diffusion in a rectangular channel. The solution to this hydrodynamic problem is presented. By varying the inclination of the solute source plane with respect to the horizontal position, apparent diffusion coefficients were measured that were up to six times higher than the “true” coefficients.Experimental binary diffusion coefficients, including published literature data, were analyzed in the light of hydrodynamic (Stokes‐Einstein) theory. The analysis suggests that under the high‐density, low‐viscosity conditions that characterize supercritical fluids, hydrodynamic behavior at the molecular level is approached, and can be used as a basis for data extrapolation.
Internal model control of coupled distillation columns
Authors: Levien K. L. , Morari Manfred 
Published: June 2004

AbstractAn experimental evaluation of methods to analyze process resilience based on internal model control (IMC) has been performed. A pilot plant consisting of two coupled distillation columns was instrumented for control studies using an LSI 11/23 microcomputer. Two alternative sets of inputs were chosen and the two full 7 (all outputs) × 4 (all inputs) transfer matrix models of the pilot plant were identified. From these models, a large number of potential 3 × 3 control structures were first screened for different levels of achievable control performance using the newly developed tools for resilience analysis. Without the need for simulation and with minimal computational effort these new techniques allow prediction of the effect of nonminimum phase characteristics, input constraints, and model uncertainty on achievable closed‐loop performance. The resilience analysis results were found to be in agreement with qualitative physical intuition. To more fully investigate the usefulness and precision of the resilience analysis, three control structures for maintaining three product compositions from a distillation system were studied experimentally. The design and performance of IMC for this complex system is demonstrated and compared with single‐loop PID controllers combined with a dynamic decoupler.
Chaos during the electrodissolution of iron
Authors: Diem C. B. , Hudson J. L. 
Published: June 2004

AbstractExperiments were carried out on the electrodissolution of iron from a disk electrode rotating at 900 rpm in 1 M H2SO4. Current was measured as a function of applied potential. Potentiostatic current oscillations, all of which were chaotic, occurred over a range of applied potential. The characteristics of these chaotic oscillations were studied with the aid of state space plots and Poincaré sections, and with the calculation of ν, the correlation dimension; the latter quantity varied smoothly between 2.4 and 6.0 throughout the range of applied potential studied. The attractor for which ν = 2.4 can be represented by a three‐dimensional state space plot.
Steady state phenol degradation in a draft‐tube, gas‐liquid‐solid fluidized‐bed bioreactor
Authors: Tang Wen‐Tzung , Fan Liang‐Shih 
Published: June 2004

AbstractExperiments on phenol biodegradation by a mixed culture in a draft‐tube, three‐phase fluidized‐bed biofilm reactor (DTFBR) at the steady state were performed. The characteristics of biofilms developed in the DTFBR were identified. A steady state biofilm model was proposed that considers the simultaneous diffusion and reaction of oxygen and phenol within the biofilm and the external mass transfer resistance between the biofilm and the completely mixed bulk liquid phase. The proposed model assumes a double‐substrate limiting mechanism for microbial growth kinetics, and Haldane and Monod type expressions were used to characterize the dependence of microbial specific growth rate on phenol and oxygen, respectively. The experimental results were used to test the validity of the proposed model.
Kinetics of dissolution of alumina in acidic solution
Authors: Franke M. D. , Ernst W. R. , Myerson A. S. 
Published: June 2004

AbstractThe dissolution kinetics of alumina in aqueous solution was studied in batch and continuous systems. Data were correlated by the kinetic equation C(t) = 1 − exp(−ktα). The parameter k was a function of temperature and acid concentration, while the parameter α remained constant.The temperature variation of k was accurately represented by an Arrhenius‐type equation with a temperature coefficient, 18,200 kJ/kmol. The data obtained in batch experiments were free of mass transport and mixing effects. Adsorption‐desorption equilibrium of hydrogen ion at the alumina surface was observed. The results supported postulated reactions reported in the literature for alumina dissolution. The basic features of the mechanism include hydration of the aluminum oxide surface, hydrogen ion adsorption followed by reaction to form a positively charged surface species [Al(OH)2+], formation of stable surface species [AlOOH and (Al(OH)2)2 SO4], and desorption of products.
Wall and interfacial shear stress in stratified flow in a horizontal pipe
Authors: Kowalski J. E. 
Published: June 2004

AbstractExperimental values are presented for the wall and interfacial shear stresses in stratified gas‐liquid flow in a pipe. The wall and Reynolds shear stresses were measured using a hot‐film anemometry technique. The interfacial shear stress was determined using two methods: from a momentum balance, using the wall shear stresses and void fraction measurements, and from an extrapolation of the Reynolds shear profile at the gas‐liquid interface. The predicted interfacial shear stress data were approximated by the formula relating the interfacial friction factor with the void fraction and gas and liquid Reynolds numbers, and were compared with other reported data.
Mathematical modeling of pulsing flow in large trickle beds
Authors: Sundaresan S. 
Published: June 2004

AbstractA crossflow model for pulsing flow in a trickle bed of large cross section is presented. The trickle bed is idealized as being made up of pulses and the trickling flow region surrounding these pulses. Assuming the macroscopic gas flow around the pulses to be irrotational and the pulses to contain only liquid, the model equations are derived. An analysis of the model and comparison with the experimental results of Christensen (1986) reveals that the irrotational flow model underestimates the pulse velocity for realistic pulse shapes. This can be attributed to the underestimation by the model of the drag exerted by the trickling region on the pulses. By dropping the irrotational flow assumption and viewing the model as semiempirical, a single parameter characterizing the magnitude of this drag is estimated from the pulse velocity data. When this estimated value for this parameter is employed, the model predicts the average pressure gradient data reasonably well.
Ternary gas mixture separation in two‐membrane permeators
Authors: Sengupta A. , Sirkar K. K. 
Published: June 2004

AbstractSingle‐stage separation of ternary gas mixtures of He, CO2, and N2 in a hollow‐fiber permeator that simultaneously houses two different types of membranes, cellulose acetate and silicone rubber, was investigated. The two membranes have reverse selectivities with respect to He and CO2. Such a two‐membrane permeator separates the feed into three streams, two permeates and one reject, each stream being enriched in a different component. The species permeabilities through each membrane were measured independently, and these values were utilized in a simulation that incorporates the fiber lumen pressure drops, the elastic deformation of the silicone capillaries, and the asymmetric structure of the CA membrane. Simulation results are compared with experimental data. Effects of flow pattern, relative permeation areas of the two membranes, permeate pressure ratios, feed composition, and membrane selectivities are studied. Advantages of the two‐membrane scheme over the conventional permeators with only one kind of membrane are discussed.
Dissolution and reprecipitation in model systems of porous hydroxyapatite
Authors: Kim Jeung Lark , Cussler E. L. 
Published: June 2004

AbstractStudies of the attack of gel‐stabilized suspensions of hydroxyapatite show dissolution at the boundary of the solid region and reprecipitation within this region. The results are apparently consistent with a theory which assumes that porous solid dissolution is diffusion‐controlled but constrained by nonlinear solubility products.
Toward a molecular equation of state for real materials
Authors: Fleming P. D. , Brugman R. J. 
Published: June 2004

AbstractAn equation of state based on molecular interaction concepts has been developed. This equation contains three parameters corresponding to a square‐well potential characterized by a molecular radius, a well depth, and a well width. It is obtained by perturbation theory with a hard sphere reference system and, with appropriate choice of parameters, yields good agreement with experimental PVT properties of 12 nonaqueous substances. The agreement is in all cases for superior to that obtained with the usual implementation of the Peng‐Robinson equation, and is better for most cases than that obtained by optimizing the parameters in the Peng‐Robinson equation.For water, neither the reported equation nor the Peng‐Robinson equation is in agreement with experiments. To obtain acceptable agreement, it is necessary to employ an equation that treats the particular geometry of attractive interactions characteristic of water. The Fleming‐Gibbs lattice equation of state for water does give reasonable agreement with PVT properties.
Theory and measurement of hydrate dissociation
Authors: Ullerich J. W. , Selim M. S. , Sloan E. D. 
Published: June 2004

AbstractExperimental data on the rate of dissociation of methane hydrates are presented. The data were obtained from hydrate mass loss measurements using an electrobalance. A resistance heater with a known heat flux was used in the dissociation experiments. A mathematical model describing the dissociation process is also presented. The model, based upon first principles, assumes that the water formed during dissociation is blown away by the methane gas produced so that the dissociation process may be regarded as a moving‐boundary ablation problem. Agreement between the model and the data is within 10%.
The isothermal flash problem: New methods for phase split calculations
Authors: Ammar M. N. , Renon H. 
Published: June 2004

AbstractVarious numerical approaches have been adopted to solve the single‐stage isothermal flash problem. These approaches result in two classes of methods. The first includes equation‐solving methods that try to solve a nonlinear equation system; the second is based on a minimization of the total Gibbs free energy. Most of these methods may fail to find a solution or may lead to erroneous solutions near critical conditions when an equation of state is applied to both the vapor and liquid phases.New methods for solving the problem are proposed. Combining the simplicity in structure of the conventional successive‐substitution method and the efficiency of some unconstrained minimization algorithms, they all ensure convergence to local minima of the Gibbs free energy. The new methods are compared from the standpoints of computer storage and calculational effort requirements. The performance of these methods is tested on four multicomponent systems taken from literature, and a comparison is made with other published methods.
Droplet dynamics in vertical gas‐liquid annular flow
Authors: Lopes J. C. B. , Dukler A. E. 
Published: June 2004

AbstractData for the two‐dimensional velocity and size of entrained drops carried by the gas core during upward annular gas liquid flow are presented. The measurements of velocity and size were made simultaneously using a new experimental technique. Information on the variation of the drop velocity with flow rates, radial position in the core, and drop size are presented and analyzed. Droplet velocity is shown to increase with size, counter to intuitive expectation. This is explained in terms of highly modified drag‐Reynolds number relationships caused by the high turbulence level in the core.
A rule‐based approach to fault diagnosis using the signed directed graph
Authors: Kramer M. A. , Palowitch B. L. 
Published: June 2004

AbstractFault diagnosis is the problem of determining the root causes of process upsets. This paper presents a very efficient method of identifying the possible causes of process disturbances using the signed directed graph (digraph) representation of process interactions. The analysis is based on forming logical statements (rules) derived from the process digraph; these are evaluated using on‐line data to yield the diagnosis. Evaluation of rule antecedents is more efficient than the previous algorithmic approach of Shiozaki et al. In the rule‐based approach, the diagnostic criteria are represented explicitly, not hidden by a complex algorithmic procedure. This allows the diagnostic rules to be tailored to reflect the best available knowledge of plant behavior. The rules generated by this technique can be integrated with other rules on plant operations using an expert systems framework.
Intraparticle diffusion coefficients in packed columns: Measurement by arrested‐flow gas chromatography
Authors: Park In‐Soo , Smith J. M. , McCoy B. J. 
Published: June 2004

AbstractArrested‐flow chromatography was used to determine intraparticle diffusivities of large‐pore particles packed in columns. Particle and column tortuosity factors were determined for helium tracer in nitrogen carrier gas at 40°C and atmospheric pressure. Semiempirical modifications of Maxwell's, Burger's, Jeffrey's, and Rayleigh's relations for the composite diffusivity of spherical particles in a stationary medium are proposed for the effective composite diffusion coefficient for a packed bed of porous particles. The equations, modified to represent accurately the extraparticle void diffusion based on measurements for beds of nonporous particles, are used to evaluate intraparticle diffusivities from experimental data obtained by arrested‐flow chromatography.
Total and radiative heat transfer to an immersed surface in a gas‐fluidized bed
Authors: Mathur Ajay , Saxena S. C. 
Published: June 2004

AbstractA high‐temperature heat transfer probe capable of measuring both the total and radiative heat transfer coefficients between an immersed surface and the bed has been designed, fabricated, and tested. Measurements of these coefficients in beds of 559 and 751 μm sand particles at temperatures up to 1,175 K have been made using this probe. A thermal analysis of the probe is developed in order to ensure a reliable interpretation of the measured quantities. The dependence of the total and radiative heat transfer coefficients on such parameters as bed temperature, fluidizing air velocity, and mean bed particle size are investigated. The various models proposed to describe high‐temperature heat transfer are evaluated from this perspective. The models capable of best simulating the heat transfer process with relative ease of computation are identified and evaluated using data generated in the study.
Chemically reactive generalized Taylor dispersion phenomena
Authors: Shapiro Michael , Brenner Howard 
Published: June 2004

AbstractGeneralized Taylor dispersion theory for nonreactive solutes (Brenner 1980a; 1982) undergoing convection and diffusion is extended to include irreversible first‐order volumetric and surface chemical reactions possessing position‐dependent reactivity coefficients at the microscale. For sufficiently long times the equivalent chemical kinetic description of the rate of solute depletion at the macroscale is shown to manifest itself as a single constant reactivity coefficient K̄* characterizing an apparent first‐order irreversible volumetric reaction. Subtraction of this gross solute depletion rate from the original microscale transport equation permits the resulting Taylor dispersionlike problem to be resolved by a solution scheme closely paralleling that for the comparable nonreactive case. This allows a straightforward determination of the mean global solute velocity vector Ū* and dispersivity dyadic D̄* appearing in the macroscale convection‐diffusion‐reaction equation describing the local‐space averaged mean transport process. By way of example, these three coefficients are explicitly calculated for reacting and diffusing solute particles sedimenting from a solvent flow occurring between two parallel plates onto the reactive surface of one of these plates.
Reaction kinetics and reactor modeling of the plasma etching of silicon
Authors: Stenger H. G. , Caram H. S. , Sullivan C. F. , Russo W. M. 
Published: June 2004

AbstractA model including the effects of diffusion and convection can be used to predict the etch rate of crystalline silicon in a plasma discharge of nitrogen trifluoride. The case of a radial flow reactor with crystalline silicon wafers located at discrete positions can be solved using a finite‐element solution to a boundary value problem. Such a model is useful to predict the effects of pressure, flow rate of etchant gas, percent silicon exposed, and wafer position on both inter‐and intrawafer etch rates. It was found from modeling that greater uniformity in etch rate is achieved by lowering the pressure and percent exposure of silicon, and to a lesser degree the volumetric flow rate.
Mineral sequences in precipitation/dissolution waves
Authors: Bryant S. L. , Schechter R. S. , Lake L. W. 
Published: June 2004

AbstractA theory for flow through permeable media with equilibrium precipitation/dissolution interactions is rigorously established. The general solution in terms of waves, which represent the propagation of concentration changes is developed, and the detailed structure of a precipitation/dissolution wave in the presence of dissipation (diffusion and dispersion) is derived; this structure plays a vital role in the general solution. The solution is based on Riemann invariants and thus exhibits certain similarities to wave solutions of related problems in gas dynamics and chromatography. However, a discontinuity peculiar to the precipitation/dissolution problem prevents unification of these similar solutions into a single, more general theory.