bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimization of multiple‐fraction batch distillation by nonlinear programming
Authors: Farhat S. , Czernicki M. , Pibouleau L. , Domenech S. 
Published: June 2004

AbstractBatch distillation processes are very attractive for the recent development of the chemical industry: multipurpose, flexible plants and fine chemistry. For many separations of high‐added value products, even a modest change in operating conditions has a significant economic impact—there is an important challenge for optimizing such processes.Short‐cut and dynamic models are the two classical approaches to the simulation of batch distillation columns. For problems without holdup, an intermediate procedure based on a decoupling method is validated.For a multifraction separation problem with fixed final time, the reflux policies for each period and the period switching times constitute the set of decision variables. For predefined reflux policies, we apply an engineering approach to the solution of a such constrained variational problem, based on its transformation into a nonlinear programming problem. In this computer‐implementable algorithm, the gain in distillate for the optimal linear or exponential reflux policies is significant (about 10%) compared with the optimal constant reflux policy.
Heat transfer under multiple slot jets impinging on a permeable moving surface
Authors: Polat S. , Douglas W. J. M. 
Published: June 2004

AbstractLocal and average heat transfer were measured for a system of multiple jets impinging on a moving permeable surface at which there may be throughflow. Multiple jets were confined by a hood, as is required industrially for thermal efficiency. Exhaust ports located symmetrically between the jet nozzles eliminated crossflow, otherwise a strongly detrimental effect. Impingement surface motion decreases average heat transfer, by 17% at industrially relevant values of the surface motion parameter,Mvs. Enhancement of impingement heat flux by throughflow is linearly additive. Expressed as ΔSt, this enhancement depends only on the throughflow parameter,Mus, with ΔSt/Mus= 0.17. For typical operating conditions, withdrawal as throughflow of only 10% of the jet flow increases mean Nusselt number by over 50%. Industrial design modeling for the potential process of combined impingement and throughflow drying of wet webs such as paper is demonstrated.
Hydrodynamics of particulate motion in sinusoidal pores via a singularity method
Authors: Nitsche Ludwig C. , Brenner Howard 
Published: June 2004

AbstractAxisymmetric motions of suspended spheres and dumbbells through sinusoidally corrugated capillaries are considered as an illustrative model of particulate or macromolecular transport in porous media. Numerical simulations are carried out using a least‐squares singularity method, which is well suited to simulating creeping flows in the complicated, time‐evolving geometries associated with particle motion through nonrectilinear pores. The numerical method is applied to a representative closure problem, whose solution yields effective transport coefficients describing particulate flow in porous media. With reference to polymer‐induced mobility control in enhanced oil recovery, a hydrodynamic mechanism of mobility reduction is studied using a rigid dumbbell polymer model.
Bubble coalescence and break‐up in air‐sparged bubble columns
Authors: Prince Michael J. , Blanch Harvey W. 
Published: June 2004

AbstractA Phenomenological model is proposed for the rates of bubble coalescence and bubble break‐up in turbulent gas‐liquid dispersions. Bubble coalescence is modeled by considering bubble collisions due to turbulence, buoyancy, and laminar shear, and by analysis of the coalescence efficiency of collisions. Bubble break‐up is analyzed in terms of bubble interactions with turbulent eddies. A method for the measurement of coalescence and break‐up events in turbulent systems is described and used to test the validity of the proposed model. The measurement technique relies on the mixing of tracer gases within bubbles upon coalescence, in conjunction with Monte‐Carlo simulations of coalescence events. Both distilled water and salt solutions are examined. Favorable agreement is found between the model and the individual coalescence and breakage rates, as well as with data obtained for the average bubble size and bubble size distribution.
Unified thermodynamic analysis of sorption in rubbery and glassy materials
Authors: Lipscomb G. Glenn 
Published: June 2004

AbstractA thermodynamic framework for the analysis of gas sorption in glassy polymers is established in the limit of low sorption levels. The results represent an extension of the Flory‐Huggins theory to materials with nonzero internal energy changes due to deformation; the Flory‐Huggins theory is recovered in the limit of zero polymer bulk modulus. The sorption isotherm is expressed in terms of the penetrant vapor‐phase activity, polymer physical properties, the penetrant partial molar volume, and the heat of mixing. The qualitative form of the isotherm is shown to be unrelated to the presence of excess free volume in the polymer; only quantitative predictions are influenced. The downward curvature of the isotherm is due to the thermodynamics of solid deformation. Explicit relationships between the parameters of this work and the dual‐mode model are given for the low‐sorption/high‐bulk modulus limit.
Kinetics of Carbon Dioxide with tertiary Amines in aqueous solution
Authors: Littel R. J. , Van Swaaij W. P. M. , Versteeg G. F. 
Published: June 2004

AbstractThe reaction of CO2 with TEA, DMMEA, and DEMEA has been studied at 293, 303, 318 and 333 K. All the kinetic experiments were carried out in a stirred cell reactor operated with a flat, smooth and horizontal gas‐liquid interface. A numerical method, which describes mass transfer accompanied by reversible chemical reactions, has been applied to infer rate constants from the experimental data. It is argued that the contribution of the CO2 reaction with OH− to the observed reaction rate may have been overstimated in most literature on tertiary amine kinetics as serious depletion of OH− toward the gas‐liquid interface usually occurs.For all the amines studied, the reaction order in amine was found to be about one for each temperature investigated. This is in good agreement with the base catalysis mechanism proposed by Donaldson and Nguyen (1980). All kinetic data could be summarized reasonably well in one Brønsted relationship.
Growth rate dispersion in batch crystallization
Authors: Shiau Lie‐Ding , Berglund Kris A. 
Published: June 2004

AbstractA method for describing the crystal size distribution of a batch crystallizer in the presence of growth rate dispersion is presented. The analysis is based on the assumption that individual crystals have inherent constant growth rates, but the growth rate may vary from crystal to crystal, resulting in a distribution of growth rates. The method requires the availability of growth rate, growth rate dispersion, and nucleation rate expressions for prediction of the crystal size distribution. These required rate expressions can be recovered by the use of simple linear regressions from the CSD moment data. Prediction of the unsteady‐state CSD was demonstrated using rate expressions for the sucrose‐water system. Batch fructose experiments were analyzed to demonstrate the recovery of the growth and nucleation rates from the size distribution data.
Modeling the SO2‐slurry droplet reaction
Authors: Newton Gerald H. , Kramlich John , Payne Roy 
Published: June 2004

AbstractA model of the reaction between SO2 and calcium‐based slurries is presented. The model is coupled with an extensive model of the evaporation process and considers external SO2 mass transfer and liquid‐phase mass transfer of dissolved sulfur and calcium species in both the film surrounding the calcium particles and the bulk liquid phase. The model assumes that particles do not circulate within slurry droplets and that evaporation results in an accumulation of particles at the droplet surface that causes a shift in the controlling mechanisms. Agreement between the model and data available in the literature is excellent.
Flow in a converging channel at moderate reynolds numbers
Authors: James David F. 
Published: June 2004

AbstractAn analytical solution is found for flow in a converging channel for Reynolds numbers in the range of 102 to 103. The solution applies to an axisymmetric channel, for which the shape is given by R2z=constant, where R is the channel radius at the axial distance z. This shape produces a center‐line or core velocity that increases linearly with z, thus making the extensional rate constant. The analytical solution is a pseudosimilarity solution of the axial momentum equation, and its accuracy was gauged by comparison to other results. Comparisons of velocity and pressure distributions to experimental data and to finite‐element results indicate that the analytical solution is accurate to about 5%.
Development of the AVEC model for associating mixtures using NMR spectroscopy
Authors: Karachewski Anne M. , Howell Wayne J. , Eckert Charles A. 
Published: June 2004

AbstractCommon models for excess Gibbs energy account primarily for physical forces and do not represent strong specific interactions. However, purely chemical models neglect strong nonspecific forces and combined chemical‐physical treatments involve an unreasonable number of adjustable parameters. One way to ameliorate this limitation is to make independent measurements of the parameters by a nonther‐modynamic technique. We report an investigation of hydrogen bonding, a localized and very directional specific interaction, conducted in various alcohol mixtures using Fourier transform nuclear magnetic resonance to measure the number of complexed species in solution. A chemical‐physical association model with variable equilibrium constants has been developed. The distinguishing feature of this model is that the species in solution do not have equal probability of forming yet require only a single chemical interaction parameter determined from fitting NMR data and a physical interaction parameter determined from infinite dilution activity coefficients. The AVEC model successfully predicts vapor‐liquid equilibrium and excess enthalphy as well as liquid‐liquid equilibrium, an especially stringent test.
Gas‐liquid two‐phase flow in symmetrically dividing horizontal tubes
Authors: Lightstone L. , Osamusali S. I. , Chang Jen‐Shih 
Published: June 2004

AbstractThe time‐averaged void fraction, pressure drop and flow regime transition behavior of horizontal air‐water two‐phase flows is studied experimentally and numerically for 2‐cm‐inner‐diameter tubes with various flow dividing junctions at its end. The time‐average void and pressure drop behavior along the channel is simulated using a two fluid separated flow model. The results show that two‐phase behavior (flow regime, void fraction, and pressure drop) is affected strongly by the presence of a flow division in the system. These effects extend far upstream of the junction for low‐momentum flows and far downstream for high‐momentum flows. Both numerical and experimental results show that there occurs a large increase in void just downstream of the junction owing to the halving of the fluid volume flow rates and the liquid deceleration.
Modeling of supercritical desorbers with an equation‐of‐state‐based isotherm
Authors: Akman Ugur , Sunol Aydin K. 
Published: June 2004

AbstractAn equation‐of‐state‐based sorption isotherm is developed and used in modeling isothermal supercritical fluid desorption in fixed beds. The conventional fixed‐bed desorber model when coupled with density‐dependent sorption isotherm predicts the temperature, pressure, and density effects on desorber dynamics and regeneration efficiencies that are experimentally observed in supercritical fluid regeneration of fixed beds.Experimentally observed phenomena such as the presence of pressure‐dependent optimal regeneration temperature, high‐pressure‐favored regeneration, and the reversal of temperature dependence of sorption isotherm—which formerly were attributed to supercritical fluid density and viscosity, and to the endothermicity of sorption isotherm—were fully predicted and explained in terms of a density‐dependent sorption isotherm.The proposed method also promises prediction of regeneration efficiencies in cosolvent‐aided supercritical fluid desorption.
Use of Hammerstein models in identification of nonlinear systems
Authors: Eskinat Esref , Johnson Stanley H. , Luyben William L. 
Published: June 2004

AbstractThe utility of the Hammerstein model, which is composed of a static nonlinear element in series with a linear dynamic part, was investigated to represent the dynamics of nonlinear chemical processes. Different methods to identify the parameters of Hammerstein models were tested. The methods were applied to the identification of simulated distillation columns and to an experimental heat exchanger process. The results show that the dynamics of such processes can be better represented by Hammerstein‐type models than by linear models.
Growth and transformation of TiO2 crystallites in aerosol reactor
Authors: Kobata Atsuo , Kusakabe Katsuki , Morooka Shigeharu 
Published: June 2004

AbstractRate process concerning the formation of TiO2 fine crystalline particles by the gas‐phase reaction of TiCl4 and O2 are studied using aerosol reactors. Chemical reaction of TiCl4, sintering of particles, mixing of reactants, and transformation from anatase to rutile are evaluated as the system parameters of the simulation model proposed. The crystallite size in the range of 55–65 nm at 1,273 K is predicted well by a model that assumes the maximum fusible particle size, 15 nm in this case.The defect concentration in the TiO2 crystallites strongly affects the transformation rate, and anatase particles produced at 1,173 K are transformed to rutile more rapidly than those produced at 1,373 K. The transformation is simulated quantitatively by the model with the coordinates for elapsed time, particle size and rutile fraction. The model can be applied to such particle production processes as collision, sintering and crystal transformation occurring simultaneously.
Plasma deposition and etching of diamond‐like carbon films
Authors: David Moses , Padiyath Raghunath , Babu Suryadevara V. 
Published: June 2004

AbstractDiamond‐like carbon films have been deposited from ternary mixtures of butadiene, hydrogen and argon in a parallel plate plasma reactor at constant pressure and power. These films have been etched in O2 and CF4/O2 plasma discharges. A new linear relationship between the composition of the deposition gas mixture and a dimensionless number (EN) defined in terms of etch and deposition rates and the bias voltage during deposition has been derived. EN is a function of the ion flux during deposition. Electron‐impact ionization processes are considered for relating the ion flux to the feed gas composition and ionization potentials. The etch and deposition rate data follow this linear relationship very well. The proportionality constant in this linear relationship varies with composition for CF4/O2 etching data. Film hardness and failure modes on silicon and glass substrates are also described.
Trickle‐bed reactor flow simulation
Authors: Anderson David H. , Sapre Ajit V. 
Published: June 2004

AbstractA steady‐state, two‐dimensional model for cocurrent gas and liquid flow in a trickle‐bed reactor is described. The model includes gas‐liquid interaction and isothermal, incompressible flow without phase change or chemical reaction. The momentum equation proposed by Saez and Carbonell is used, along with their expressions for relative permeabilities of gas and liquid phases. Capillary pressure equations determine the difference in the pressures of flowing phases. The results of the model simulation agree with experimental data on flow distribution, liquid spreading, and phase segregation in a two‐dimensional trickle bed with air‐water flow in both low‐ and high‐interaction flow regimes.
Airlift bioreactors: Analysis of local two‐phase hydrodynamics
Authors: Young Mark A. , Carbonell Ruben G. , Ollis David F. 
Published: June 2004

AbstractLocal two‐phase flow measurements were obtained in a pilot‐scale, external‐loop airlift bioreactor using hot‐film anemometry and resistivity probe techniques. The radial dependence of both gas and liquid velocities and of the void fraction was substantial. Developing flow effects were pronounced, as evidenced by distinct changes in the radial profiles of fluid flow properties with axial position. For high gas flow rates, liquid acceleration effects near the sparger resulted in greatly reduced slip velocities in a substantial portion of the riser. A significant reduction in mass transfer may occur under such conditions.The point equations of continuity and motion were used to develop a differential, two‐fluid model for two‐phase flow in airlift risers. The only empirical parameters in the model represent frictional effects. The developing two‐phase flow characteristic of airlift risers was observed to create significantly higher frictional effects at the wall than is routinely observed for fully‐developed flow. Model predictions were compared to our own experimental results as well as those of Merchuk and Stein (1981). Agreement between the predicted and measured values was typically within 10% for both cases.
Inversion and zero dynamics in nonlinear multivariable control
Authors: Daoutidis Prodromos , Kravaris Costas 
Published: June 2004

AbstractThis work concerns general multiple‐input/multiple‐output (MIMO) nonlinear systems with nonsingular characteristic matrix. For these systems, the problem of inversion is revisited and explicit formulas are derived for the full‐order and the reduced inverse system. The reduced inverse naturally leads to an explicit calculation of the unforced zero dynamics of the system and the definition of a concept of forced zero dynamics. These concepts generalize the notion of transmission zeros for MIMO linear systems in a nonlinear setting. Chemical engineering examples are given to illustrate the calculation of zero dynamics. Input/output linearization is then interpreted as canceling the forced zero dynamics of the system, and precise internal stability conditions are derived for the closed‐loop system.
Pressure buildup and internal stresses during binder burnout: Numerical analysis
Authors: Tsai Dah‐Shyang 
Published: June 2004

AbstractThe interstitial pressure buildup and the internal stresses on the skeleton of a cylindrical green body during burnout are analyzed numerically. The intrinsic kinetics of pyrolysis is coupled with the Carman‐Kozeny equation or the slip‐flow model of Wakao and Smith to evaluate the pressure distribution. The stress distributions before failure are estimated from elasticity theory. The stresses are tensile, and their maxima are located at the center of the cylinder. The tangential stress is larger than the radial stress. The effects of green body size, specific surface area, and pressurized atmosphere are discussed. The approximate solution is accurate for small green bodies. The pressurized atmosphere reduces the interstitial pressure and the internal stresses effectively.
Separation of azeotropic organic liquid mixtures by pervaporation
Authors: Dutta Binay K. , Sikdar Subhas K. 
Published: June 2004

AbstractWe have shown that ionomeric membranes of perfluorosulfonic acid (PFSA) polymer allow selective pervaporation of polar organic compounds from their azeotropic mixtures with less polar compounds. A composite membrane of a thin PFSA polymer film, cast on a porous Teflon support, provided desirable permeant fluxes with good selectivity. Model binary azeotropes, composed of alcohols and hydrocarbons, were separated with total pervaporation fluxes of up to 9.5 kg/h·m2 using a stirred membrane permeation cell, the product side of which was exposed to vacuum. Fluxes increased with increasing alcohol content of the feed and with temperature. But the selectivity of the more permeating component remained reasonably constant around the azeotropic point and also over the range of temperature used in the study (25–55°C). Total pervaporation fluxes depended little on downstream pressure up to 6.66 kPa (50 torr). These separation data were explained by a mathematical model based on a solution‐diffusion mechanism.
Spray‐to‐bubbly transition for distillation systems containing two liquid phases
Authors: Davies Bruce , Ali Zafar , Porter Kenneth E. 
Published: June 2004

AbstractThe tray hydrodynamics were determined for a system containing water and kerosene as immiscible liquids. Plates with hole diameters ranging from 3.18 to 12.70 mm were used in a 44.5‐cm2 perspex air‐water‐kerosene simulator. Experiments were also carried out in a 50‐mm‐ID column using different depths of oil and water mixtures to study the drop and bubble mechanisms. A spray‐to‐bubble transition occurred for the two liquid‐phase system experiments. The liquid holdup at the transition increased directly with gas velocity and hole diameter, and decreased with increasing free area. At the same hole velocity, the presence of two liquid phases caused the transition to occur at different liquid holdups than for the single pure liquid. Two different modes of coalescence were observed in the small column work. New correlations have been proposed for the liquid holdup at the transition which allow for the presence of two liquid phases.
Mathematical model of the hydrocyclone based on physics of fluid flow
Authors: Hsieh K. T. , Rajamani R. K. 
Published: June 2004

AbstractA mathematical model of the hydrocyclone, based on the physics of fluid flow, has been developed. The model equations are solved in a computer code that takes as input the hydrocyclone dimensions and feed slurry characteristics. The output of the computer code is the velocity profiles of the fluid and the separation efficiency curve. To validate the model, an LDV was used to measure the velocity profiles inside a 75‐mm hydrocyclone. Pure water and glycerol‐water mixture were used as the working media to simulate the increase of slurry viscosity in the presence of solid particles. The predicted velocity profiles agree well with the experimental measurements. Dilute limestone slurry was also classified with the same hydrocyclone, and predicted the separation efficiency curve shows good agreement with experimental observation.
Prediction of gas adsorption in 5a zeolites using Monte Carlo simulation
Authors: Razmus David M. , Hall Carol K. 
Published: June 2004

AbstractAdsorption of air in 5A zeolites was studied using Monte Carlo simulations in the grand canonical ensemble (μ, V, T constant). Site‐site potentials were used to model the adsorbate‐zeolite and adsorbate‐adsorbate interactions. The potential model contains one adjustable parameter that was fit to a single experimental isotherm data point. Adsorption isotherms and heats of adsorption were determined for pure argon, oxygen, and nitrogen at 203.15 K, 233.15 K, and 297.15 K from 0.1 bar to 4.0 bar. Multicomponent adsorption isotherms were determined for binary mixtures of oxygen and nitrogen at 203.15 K. The results for the pure‐component isotherms are in excellent agreement with experimental data. The results for the heat of adsorption are in good agreement with experimental data for argon and oxygen, but not for nitrogen. The results for multicomponent adsorption isotherms are qualitatively correct; however, the simulation was not able to quantitatively predict mixture data.