bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrodynamics of electroluidization: Separation of pyrites from coal
Authors: Shih Y. T. , Gidaspow Dimitri , Wasan Darsh 
Published: June 2004

AbstractDry, electrostatic separation is a potentially efficient method of removing pyrites from coal. However, progress in the past was hampered by a lack of a quantitative analysis of the process. To help us design better separation equipment, we have developed a hydrodynamic model of separation of pyrites from coal in a batch electrofluidized bed. The simulations were done on a Cray‐2 computer. The input variables include the surface charge of the particles and the solids stress, which were measured.Realistic shapes and sizes of bubbles were computed with and without an applied electric field for a two‐dimensional bed with a central jet. The bubble sizes and the rising velocities were smaller with an applied field, consistent with observations. Computed electrophoretic mobilities in the fluidized bed will be useful for a better design of continuous beds.
Mass transfer in nitric acid absorption
Authors: Miller D. N. 
Published: June 2004

AbstractThe mechanism and rate limitations in aqueous nitrogen oxides absorption are reviewed and data available on chemical kinetics for performance predictions are discussed. Application of a rate relationship to characterize interphase mass transfer for the primary reactant N2O4 is shown, with mass transfer coefficients derived from plant‐scale data. Correlations for these coefficients as functions of acid strength and temperature for both bubble cap and sieve plate designs are presented.
A vapor pressure equation from extended asymptotic behavior
Authors: Iglesias‐silva G. A. , Holste J. C. , Eubank P. T. , Marsh K. N. , Hall K. R. 
Published: June 2004

AbstractThe vapor pressure equation proposed here possesses several interesting features and does an excellent job representing data. The currently accepted theoretical behavior in the regions of the triple point and the critical point are intrinsic features of the expression. The equation is valid over the entire range from the triple point to the critical point and yet possesses only three adjustable constants. Results are presented for a small but chemically diverse set of compounds. This work represents an extension of the Churchill‐Usagi correlation technique from heat transfer and fluid mechanics to thermodynamics.
Effect of interfacial viscosities upon displacement in sinusoidal capillaries
Authors: Giordano R. M. , Slattery J. C. 
Published: June 2004

AbstractThis quantitative analysis shows the relative effects of interfacial tension, interfacial viscosities, and wetting during displacement in a capillary whose radius is a sinusoidal function of axial position. The effect of the interfacial viscosities is to increase the resistance to displacement regardless of the wetting condition. The result are consistent with a previous qualitative analysis and with a previous quantitative analysis for displacement in capillaries whose radii are independent of axial position.In screening surfactant systems for potential use in tertiary oil recovery, it is recommended that the interfacial tension be minimized first, since it determines whether oil displacement will occur, and that the interfacial viscosities be minimized second, since they influence the rate of oil displacement.
Transport of particulate suspensions in porous media: Model formulation
Authors: Sharma M. M. , Yortsos Y. C. 
Published: June 2004

AbstractA mathematical model is formulated for the general class of problems that involve the transport of stable particulate suspensions in porous media. The porous medium is represented by a network of pore bodies (sites) and pore throats (bonds). Population balances for the species responsible for particle retention and permeability reduction are written in terms of the various mechanisms of particle capture and reentrainment. Rates of capture and release are evaluated using appropriate physical models. We specifically concentrate on mass transfer limited processes. The effective‐medium theory is suitably formulated to determine the fluid flow distribution in the network and to calculate the permeability. The network representation of the porous medium together with the population balances and the rates of deposition and release provide a consistent model that finds application in filtration and fines migration processes.
Pore distribution changes of calcium‐based sorbents reacting with sulfur dioxide
Authors: Gullett B. K. , Bruce K. R. 
Published: June 2004

AbstractChanges in the pore structure of calcium oxide sorbents derived from calcium carbonate (c‐CaO) and calcium hydroxide (h‐CaO) reacting with sulfur dioxide are determined. Results show that the pore shape of c‐CaO approximates a cylinder while that of h‐CaO appears to be slit‐ or platelike. The pore volume of c‐CaO is located in much smaller pores than that of h‐CaO when compared on the basis of an equivalent pore shape model. The effect of sintering was to reduce surface area through coalescence of smaller pores, while only minor effects were observed upon pore volume and conversion from calcium oxide to calcium sulfate. Both sorbents expand to allow greater reaction than is possible given the initial porosity and formation of a larger volume product. The h‐CaO reacts to higher levels of conversion than the c‐CaO because the pore shape of the h‐CaO allows for greater particle expansion and, therefore, reaction beyond the limits of the initial porosity.
Pool boiling from a surface with a porous layer
Authors: Lu S. M. , Chang R. H. 
Published: June 2004

AbstractBoiling heat transfer from a porous layer sintered on a horizontal heater surface and heated from the base was analyzed for laminar to turbulent regions. The effects of the thickness of the porous layer, particle diameter, porosity, pore size distribution, and the properties of fluids on boiling heat transfer were analyzed. Reynolds number, parameter ψ, and a dimensionless heat flux were related to each other. Most experimental data used in this work fall in the region where the vapor Reynolds number is less than 100; very few data exceeded far beyond 1,000.For thick porous beds, the thickness no longer affects the heat transfer. For thin porous beds, heat transfer is affected by the thickness of the porous layer. The prediction equations of various investigators for dryout heat flux were put into dimensionless forms and the differences that exist among the equations are explained.
Interpretation of the sulfation rate of CaO, MgO, and ZnO with SO2 and SO3
Authors: Kocaefe Duygu , Karman Deniz , Steward F. R. 
Published: June 2004

AbstractPublished models for gas‐solid reactions have been used with certain modifications to interpret sulfation data for CaO, MgO, and ZnO with SO2 and SO3. None of the models evaluated gave an adequate interpretation for high solid conversions, which were found to exceed 90% in some cases. Such high conversions are inconsistent with the current models, and a new mechanism must be postulated to explain the reaction after the solid product theoretically fills the initial pores of the particle. An important factor in successfully interpreting the experimental data is the distributed nature of the pore sizes within the solid particle.
Parametric sensitivity in fixed‐bed reactors: Inter‐ and intraparticle resistance
Authors: Morbidelli Massimo , Varma Arvind 
Published: June 2004

AbstractThe role of inter‐ and intraparticle transport resistances in the sensitivity behavior of a fixed‐bed catalytic reactor is fully elucidated. The parametric sensitivity regions obtained using a heterogeneous one‐dimensional plug flow model are reported for various values of the involved dimensionless parameters. Comparisons with previous sensitivity criteria and with experimental data are also presented.
Finite‐element steady state simulation of multiphase distillation
Authors: Swartz C. L. E. , Stewart W. E. 
Published: June 2004

AbstractA finite‐element method is given for efficient simulation of multiphase distillation systems. Breakpoints are adaptively located to coincide with phase discontinuities. Thermodynamic criteria for the states at these discontinuities are included in the equation system. The adjustable breakpoint locations are calculated simultaneously with the other system variables by global Newton iteration. Worked examples demonstrate the accuracy and efficiency of the method.
Mass transfer and solubility in autocatalytic oxidation of cyclohexane
Authors: Suresh A. K. , Sridhar T. , Potter O. E. 
Published: June 2004

AbstractMass transfer coefficients for the solution, without reaction, of oxygen in cyclohexane over a wide range of temperature and pressure have been measured in a flat interface reactor (FIR) and a gas sparged stirred‐tank reactor (STR). Solubilities have also been measured and it is suggested that a modified Henry's law coefficient of 1.09 × 10−2 kmol/m3 · bar can be regarded as constant over the temperature range 293–435 K. The physical mass transfer coefficient in the STR shows very little variation over this temperature range and a value of 3.5 × 10−4 m/s can be assumed for 423–435 K. However, coefficients in the FIR increase with agitation rate as expected. The difference is ascribed to interference by neighboring bubbles in the transfer process, when diffusivities are high, and also to the lowering of surface tension at high temperatures. A model proposed by Gal‐Or and Resnick is reviewed in its application to the present system.
Autocatalytic oxidation of cyclohexane—modeling reaction kinetics
Authors: Suresh A. K. , Sridhar T. , Potter O. E. 
Published: June 2004

AbstractLiquid phase oxidation of hydrocarbons is a major source of organic chemicals. This paper concerns itself with the oxidation of cyclohexane. The process is one in which gas absorption is accompanied by chemical reaction, but little information has been reported. A major factor has been safety considerations, the Flixborough explosion being a constant reminder. In this paper attention is given to the kinetics and to the interaction of kinetics and mass transfer, showing that in this autocatalytic system the dissolved oxygen level rises to saturation and falls as the rate of reaction increases. Initially zero order in oxygen, the reaction becomes first order at low oxygen levels. Oscillations and enhancement due to reaction within the boundary layer are noted. A kinetic model is developed based on simplification of the accepted free radical scheme and it is reasonably successful in accounting for the results reported. Experiments at temperatures up to 170°C and 70 bar using uncatalyzed reaction are reported from three different reactors: a homogenous batch reactor, a flat interface reactor, and a sparged agitated bubbling reactor.
Autocatalytic oxidation of cyclohexane—mass transfer and chemical reaction
Authors: Suresh A. K. , Sridhar T. , Potter O. E. 
Published: June 2004

AbstractIn an industrial gas‐liquid reactor both mass transfer and kinetics have, in principle, a role to play. This paper describes studies on the oxidation of cyclohexane in two‐phase, gas‐liquid reactors. Regimes of absorption have been clarified by measurements of dissolved oxygen concentrations. The behavior is found to be complex, arising from the fact that the reaction is autocatalytic, and zero order in oxygen over almost the entire absorption range. As reaction velocity increases, due to the autocatalytic kinetics, enhanced physical mass transfer rates arise. Bubble swarms have properties that prevent the simple application of mass transfer and enhancement from flat‐surface systems. A theory is developed here that accounts qualitatively for the enhancement found in bubble swarms in the present case. The theory is also shown to predict quantitatively the appropriate physical mass transfer coefficients.
Simulation of injection mold filling of viscoelastic polymer with fountain flow
Authors: Kamal M. R. , Goyal S. K. , Chu E. 
Published: June 2004

AbstractViscoelasticity, nonisothermality, and fountain flow influence the microstructure development during injection mold filling of polymer melts and, therefore, the ultimate properties of a molded article. A comprehensive two‐dimensional mathematical model is developed to evaluate the effects of these factors on the structure of the flow field. Special consideration is given to the shape of the flow front, which is crucial in determining the structure of flow in the fountain region. The effects of slip and crystallization are also considered and their influence on model predictions are analyzed. Simulations using the no‐slip and slip boundary conditions show that a slip boundary condition is necessary to alleviate the singularities in the flow structure. The results also indicate that the predicted stress profiles are significantly influenced by the viscoelasticity of the polymer melt. Furthermore, the nonisothermality and subsequent deposition of a solid layer next to the mold walls considerably alter the moldability parameters and the flow field.
Reaction kinetics in oxygen bleaching
Authors: Hsu C. L. , Hsieh J. S. 
Published: June 2004

AbstractThe oxygen bleaching of wood pulp takes place in a heterogeneous system involving oxygen (gas), water (liquid), and fiber (solid). Inconsistent effects of process variables (reaction temperature, alkali concentration, and oxygen pressure) on the overall oxygen delignification rate of wood pulp in various reacting systems have been reported in the literature.An apparent intrinsic reaction rate model, excluding the interphase mass transfer effects, has been developed based on oxygen bleaching experiments in an agitated and ultralow‐consistency (solids content) reactor. The apparent intrinsic reaction rate model shows a faster delignification rate than those reported in the literature. The degree of inadequate delignification observed in the literature data is likely to be caused by insufficient mass transfer of bleaching chemicals to fibers.
Compression zone effect in batch sedimentation
Authors: Font R. 
Published: June 2004

AbstractTheories of batch sedimentation, taking into account the compression zone effect, are reinterpreted and modified. According to the discussion presented and the experimental results shown, characteristics—which are the loci of points representative of layers with the same settling rate and the same solids concentration in the settling zone—rise tangentially to the sediment curve on a height vs. time plot. Mathematical expressions that relate the solids concentration to the variations of the pulp‐supernatant interface height and of the sediment height are presented. In addition, the model presented is proposed for use when it is not possible to measure the sediment height. A procedure for calculating the concentration at the top of the sediment is also indicated.Calcium carbonate suspensions in water were selected for testing the equations deduced. The relation between the continuous thickener unit area and the underflow solids concentration was obtained from the batch tests, and is compared with that calculated by the graphic methods of Talmadge and Fitch, and Fitch.
Temperature‐programmed desorption: Multisite and subsurface diffusion models
Authors: Leary K. J. , Michaels J. N. , Stacy A. M. 
Published: June 2004

AbstractTwo models are presented that can simulate two peaks in a temperature‐programmed desorption (TPD) spectrum from a high surface area catalyst at atmospheric pressure: a multisite model and a subsurface diffusion model. The multisite model assumes that the two peaks arise from two distinct adsorption sites on the catalyst surface with different activation energies for desorption. The subsurface diffusion model assumes that the high‐temperature peak is produced by adsorbate that diffuses into the subsurface region of the catalyst during heating, and then back to the surface when it becomes depleted by the desorption process. It is shown that one can distinguish between the two models experimentally by measuring the effect of carrier gas flow rate and heating rate on the TPD spectrum.
A novel hollow‐fiber reactor with reversible immobilization of lactase
Authors: Jones C. K. S. , Yang R. Y. K. , White E. T. 
Published: June 2004

AbstractExperimental and theoretical studies on a backflush hollow‐fiber enzymatic reactor (HFER) were conducted in this work for a lactose/lactase system. An A. niger lactase was chosen, from the four lactases tested, for reversible immobilization in the sponge layers of the fibers. An enzyme loading procedure was developed that allowed reliable and reproducible operation of the hollow‐fiber reactor and produced industrially significant conversions without apparent change in the activity or stability of the lactase used. This reversible immobilization scheme also permitted easy replacement of the enzyme used. The performance of the backflush HFER was investigated and a large number of data concerning its operation were obtained and interpreted. Momentum and mass transports in such a HFER were analyzed, and mathematical models that took the experimental findings into consideration were also developed and solved analytically and/or numerically. Predictions from the computer model developed in this work were found to be in excellent agreement with the experimental data collected, suggesting the possibility of a priori design of a process‐scale backflush HFER. With minor modifications, the models developed are expected to be applicable to hollow‐fiber reactors with a wide selection of immobilized cells, organelles, and other enzymes.
Adsorption of gas mixtures: Effect of energetic heterogeneity
Authors: Valenzuela D. P. , Myers A. L. , Talu O. , Zwiebel I. 
Published: June 2004

AbstractThe ideal adsorbed solution (IAS) theory of adsorption of gas mixtures is extended to the case of energetic heterogeneity. A heterogeneous ideal adsorbed solution (HIAS) behaves ideally on a particular site, but energetic heterogeneity causes a segregation in the composition of the adsorbed phase. Equilibrium properties are obtained by integrating over a multivariate energy distribution based upon perfect positive correlation of site energies. The fact that predictions from HIAS are always an improvement over IAS indicates that heterogeneity is a factor that must be considered in theories of mixed‐gas adsorption. Errors in HIAS predictions may be caused by steric exclusion of the larger molecules from micropores accessible to smaller molecules.
Coating flows in a nip region and various critical phenomena
Authors: Adachi K. , Tamura T. , Nakamura R. 
Published: June 2004

AbstractWhen thin films of liquid are produced by roll coaters it is commonly observed that the liquid film is not uniform but shows either regular or irregular patterns resulting from hydrodynamic origins. The appearance of the liquid film has been considered to be governed by the flow geometry and dynamics in a nip region between two adjacent solid planes.Experimental work was done to observe the flow geometries in the nip region and patterns of liquid film by using a roll‐stationary, transparent flat plate system. Two fundamental mechanisms for rib disappearance in practical high‐speed coatings were recognized. It was also found that the constant rib interval for infinite capillary number depends not only upon the minimum gap size but also upon the physical properties of the liquid. Experimental data are presented in dimensionless form for meniscus position, rib interval, constant rib interval, and for the critical or transient conditions of rib formation, rib disappearance, unstead ribbing, and centrifugal splash.Comparison of present results for the speed ratio U2/U1 = 0 with previous results for U2/U1 = 1 shows the significance of the speed ratio to the meniscus position and the rib interval.
A theory of design reliability using probability and fuzzy sets
Authors: Kubic William L. , Stein Fred P. 
Published: June 2004

AbstractAll process designs are subject to uncertainties which make it impossible to state with complete certainty that a design will work. This study presents a measure of design confidence which considers the nature of the uncertainty and the operability of the process as a whole. This measure, called design reliability, quantifies the likelihood that a design will work. Detailed analyses are presented for three special cases: designs subject to random uncertainties, designs subject to fuzzy uncertainties, and designs subject to both random and fuzzy uncertainties. Practical procedures for estimating design reliability in these special cases are also presented.
Dispersion of viscous liquids by turbulent flow in a static mixer
Authors: Berkman Paul D. , Calabrese Richard V. 
Published: June 2004

AbstractDrops are stabilized in agitated liquid‐liquid systems by both surface and internal viscous forces. The dispersion of an inviscid liquid into a turbulent continuous phase in static mixers has been studied but the effect of dispersed phase viscosity is not well understood. Systematic experiments have been conducted in a Kenics mixer by photographically examining dilute suspensions of viscous oils in water to determine how viscosity and conditions of agitation affect equilibrium mean drop size and size distribution. A semiempirical theory is developed which correlates the mean size data and collapses to the well‐known Weber number result in the inviscid limit. A correlation for drop size distribution in terms of cumulative volume frequency is developed by normalization with the Sauter mean diameter D32. Measurements at the mixer entrance indicate that the method of introduction of the dispersed phase should be considered when evaluating mixer performance.
The molecular basis of temperature effects in supercritical extraction
Authors: Debenedetti P. G. , Kumar S. K. 
Published: June 2004

AbstractThe behavior of solute partial molar enthalpies in dilute supercritical mixtures gives rise to the well‐known phenomenon of retrograde solubility (equilibrium solubility decreasing with increasing temperature at constant pressure). A mechanistic interpretation of this phenomenon in terms of the formation of large clusters of solvent molecules around solute molecules is consistent with experimentally observed retrograde behavior. Cluster formation occurs as a consequence of the unbounded increase in the solvent's compressibility arbitrarily close to the latter's critical point. At infinite dilution, the solute's partial molar volume and enthalpy grow linearly with cluster size. This means that the negative divergence of these quantities is simply a macroscopic manifestation of a “condensation” in which an increasing number of solvent molecules cluster around solute molecules. Arbitrarily close to the solvent's critical point, scaling relationships show that the decay of both solvent‐solvent and solute‐solvent correlation functions exhibits the same radial dependence. This functionality is thus solute‐independent, and is determined exclusively by the proximity to the solvent's critical point. The locus along which thermal effects associated with cluster formation are maximized is arbitrarliy close to the solvent's critical isochore as the latter's critical point is approached.