bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas holdup in slurry bubble columns: Effect of column diameter and slurry concentrations
Authors: Krishna Rajamani , De Swart Jeroen W. A. , Ellenberger Jürg , Martina Gilbert B. , Maretto Cristina 
Published: June 2004

AbstractTo study the influence of particle concentration on the hydrodynamics of bubble‐column slurry reactors operating in the heterogeneous flow regime, experiments were carried out in 0.10, 0.19, and 0.38‐m‐dia. columns using paraffinic oil as the liquid phase and slurry concentrations of up to 36 vol. %. To interpret experimental results a generalization of the “two‐phase” model for gas–solid fluid beds was used to describe bubble hydrodynamics. The two phase identified are: a dilute phase consisting of fast‐rising large bubbles that traverse the column virtually in plug flow and a dense phase that is identified with the liquid phase along with solid particles and entrained small bubbles. The dense phase suffers backmixing considerably. Dynamic gas disengagement was experimented in the heterogeneous flow regime to determine the gas voidage in dilute and dense phases. Experimental data show that increasing the solid concentration decreases the total gas holdup significantly, but the influence on the dilute‐phase gas holdup is small. The dense‐phase gas voidage significantly decreases gas holdup due to enhanced coalescene of small bubbles resulting from introduction of particles. The dense‐phase gas voidage is practically independent of the column diameter. The dilute‐phase gas holdup, on the other hand, decreases with increasing column diameter, and this dependence could be described adequately with a slight modification of the correlation of Krishna and Ellenberger developed for gas–liquid systems.
Mechanistic pressure drop model for columns containing structured packings
Authors: Brunazzin Elisabetta , Paglianti Alessandro 
Published: June 2004

AbstractA mechanistic model was developed to predict pressure drop and flooding in packed columns equipped with corrugated packing of the regular type. It was developed after considerating the interaction of falling liquid film with the gas phase, based on mass‐and momentum‐conservation equations. Among the most common structured packings, the behavior of the Mellapak and BX types was analyzed. The aim of this work is to demonstrate how mechanistic models, developed for simple geometry, can also be used to compute pressure drops in cases where the geometry is more complex, as with a structured packing. This approach, based on the geometric characteristics of the packing and measurable parameters such as liquid holdup, enables the development of a basic model by limiting the number of adjustable parameters, which are numerous in all the available models. Because of its nature, this model is extremely easy to extend to different types of structured packings.
Multimodel approach to mixed‐gas adsorption equilibria prediction
Authors: Maurer Richard T. 
Published: June 2004

AbstractA thermodynamically consistent, multimodel approach for the prediction of mixture adsorption equilibria from pure‐component adsorption isotherms is described. The ideal adsorbed solution (IAS) model is employed at low surface coverage, where potential attractive forces tend to govern adsorption behavior. An energetically quasi‐homogeneous version of the Langmuir‐Freundlich (LF) model is proposed at high coverage, where lateral adsorbate interactions and finite‐adsorbent geometric constraints tend to homogenize such attractive forces. The classical LF model is used for intermediate coverage, where both energetic attractive and geometric constraining forces contribute significantly to mixed‐gas adsorption behavior. A major benefit of this three‐regime modeling method is that physically realistic adsorptive selectivities can be adhered to at both extremes of coverage, a property not generally shared by either the IAS or LF models taken singly. This three‐regime approach yields better multicomponent equilibria predictions than IAS‐only modeling approaches for many relatively nonideal adsorption systems.
Application of a control‐law nonlinearity measure to the chemical reactor analysis
Authors: Stack Alexander J. , Doyle Francis J. 
Published: June 2004

AbstractThe optimal control structure has been introduced as a design tool to measure the control‐law nonlinearity of a given process design. In this context, control‐law nonlinearity is the optimal degree of nonlinear compensation in the controller, a system property distinct from open‐loop nonlinearity and determined by a performance objective and the region of operation as well as the nature of the open‐loop system. This approach is extended to the analysis of multivariable systems with output feedback through the application of an extended Kalman filter. Coherence estimation is used as a practical method to measure continuous, open‐loop multivariable system nonlinearity. The CSTR with van de Vusse kinetics, a system that features output feedback and a controllaw nonlinearity that changes with operating points, is analyzed. The optimal control structure approach with coherence estimation correctly indicates changes in the controllaw linearity between different operating points and changes as the regions of operation change around a particular operating point.
Rate parameters and gradient correlations for gradient‐elution chromatography
Authors: Luo Robert G. , Hsu James T. 
Published: June 2004

AbstractRate parameters and gradient correlations of proteins are very important to engineering investigations of gradient‐elution chromatography. Before carrying out computer simulations for gradient process, these rate parameters and gradient correlations must be determined from experimental data. This work presents a systematic method for estimating and determining these parameters and correlations using experimental data and computer‐simulation results based on isocratic runs. The values determined were then employed in gradient‐elution studies by putting them into the rate model to perform computer simulations. Experimental runs under gradient conditions using the parameters and correlations just referred to were carried out in a DEAE Sepharose CL‐6B ion‐exchange chromatography. Comparisons between the experimental data and the simulation results show good agreement.
Intraparticle diffusion in hydrogenation of 3‐hydroxypropanal
Authors: Zhu X. , Hofmann H. 
Published: June 2004

AbstractStrong intraparticle diffusion resistance was observed and the apparent effectiveness factors were measured for the hydrogenation of 3‐hydroxypropanal (HPA) to 1,3‐propanediol (PD) over Ni/SiO2/Al2O3 catalyst pellets at 45 to 80°C and 2.60 to 5.15 MPa in a stirred reactor with a spinning basket. A mathematical model was proposed to describe the intraparticle diffusion and to estimate the effective diffusion coefficients of HPA, PD and hydrogen under reaction conditions by a maximum likelihood function of the apparent effectiveness factors of HPA and PD. The calculated concentration distributions of HPA, PD and hydrogen in catalyst particles reveal an excess of hydrogen at 80°C and higher temperatures, but an excess of HPA at 45°C. It results in a weak dependence of the consumption formation rate of HPA and PD on the partial pressure of hydrogen at high temperature.
Mutual solubilities of hydrocarbons and water: III. 1‐hexene; 1‐octene; C10C12 hydrocarbons
Authors: Economou I. G. , Heidman J. L. , Tsonopoulos C. , Wilson G. M. 
Published: June 2004

AbstractThis article completes the analysis of high‐temperature mutual solubilities of hydrocarbons and water. Part I (Tsonopoulos and Wilson, 1983) presented benzene, cyclohexane, and n‐hexane, while Part II (Heidman et al., 1985) extended the investigation to ethylbenzene, ethylcyclohexane, and n‐octane. Part III presents experimental data up to the three‐phase critical end point for C6, C8, and C10 1‐alkenes, n‐decane, n‐butylcyclohexane, m‐diethylbenzene, p‐diisopropylbenzene, cis‐decalin, tetralin, 1‐methylnaphthalene, and 1‐ethylnaphthalene. The thermodynamic analysis of Henry's constants for hydrocarbons in water is extended to the critical temperature of water, while the solubility and volatility of water in hydrocarbons are successfully correlated with several modifications of the Redlich‐Kwong equation of state.
Wall slip in the capillary flow of molten polymers subject to viscous heating
Authors: Rosenbaum Eugene E. , Hatzikiriakos Savvas G. 
Published: June 2004

AbstractThe traditional way of determining the slip velocity of molten polymers is the classic Mooney technique, which utilizes experimental data obtained from a capillary rheometer. However, measurements of the rheological properties of polymer melts in capillary flow at high shear rates are often complicated by viscous heating, which is not taken into account by this method. A data analysis procedure based on a mathematical model for nonisothermal capillary flow of molten polymers is developed. Conduction, convection, and viscous heating are included, together with the effect of wall slip. The technique provides detailed velocity and temperature fields in the die, and can be used to determine the slip velocity at high shear rates corrected for the effect of viscous heating. It is tested for the capillary flow of several polymers, including polystyrene, polypropylene, high‐density, and linear low‐density polyethylenes.
Perturbation solution to the convection–diffusion equation with moving fronts
Authors: Vaidya Durgesh S. , Nitsche J. M. , Diamond S. L. , Kofke David A. 
Published: June 2004

AbstractElectrophoresis of a solute through a column in which its transport is governed by the convection – diffusion equation is described. Approximate solutions to the convection – diffusion equation in the limit of small diffusion are developed using perturbation methods. The diffusion coefficient and velocity are assumed to be functions of space and time such that both undergo a sudden change from one constant value to another within a thin transition zone that itself translates with a constant velocity. Two cases are considered: (1) the thickness ϵfof the transition zone is negligible compared to the diffusional length scale, so the zone may be treated as a singular boundary across which the diffusion constant and velocity suffer discontinuous changes; (2) the transition zone is considerably wider than the diffusional length scale, so the diffusion coefficient and velocity, although sharply varying, are smooth functions of position and time. A systematic perturbation expansion of the concentration distribution is presented for case 1 in terms of the small parameter ϵ = 1/Pe. A lowest order approximation is given for case 2. A suitably configured system analyzed here can lead to progressive accumulation, or focusing, of the transported solute. The degree of focusing in case 1 scales with ϵ−1, whereas in case 2 it scales with (ϵfϵ)−1/2, and thus increases much more weakly with increasing Pe. A separation based on this concept requires development of materials and devices that allow dynamic tuning of the mass‐transport properties of a medium. This would make it possible to achieve progressive focusing and separation of solutes, such as proteins and DNA fragments, in electrophoretic media with an unprecedented degree of control.
Kinetics of hydrocarbon adsorption on activated carbon and silica gel
Authors: Malek A. , Farooq S. 
Published: June 2004

AbstractExperimental breakthrough results of methane, ethane and propane in activated carbon and silica gel obtained over a wide range of gas compositions, bed pressures, interstitial velocities, and column temperatures were analyzed using a dynamic, nonisothermal, nontrace column breakthrough model. A linear driving force (LDF) approximation is used for particle uptake, and the Langmuir‐Freundlich isotherm represents adsorption equilibrium. The LDF mass‐transfer‐rate coefficient (and, hence, effective particle diffusivity) and column‐wall heat‐transfer coefficient were determined. The results show that hydrocarbon transport in the activated carbon particles used is essentially by Knudsen and surface flow, while for the silica gel used the transport is primarily by Knudsen flow. For activated carbon, the experimentally derived LDF coefficients for all three sorbates are well correlated using an average effective diffusivity value. With regard to heat transfer, the column‐wall Nusselt number is approximately constant for the range of Reynolds numbers considered. Simulations of multicomponent breakthrough in the activated‐carbon bed based on independently measured single‐component kinetic parameters and the extended Langmuir‐Freundlich isotherm agree very well with experimental results. The computational efficiency gained by adopting the simpler extended Langmuir isotherm model is also investigated.
Current distributions governed by coupled concentration and potential fields
Authors: Yang J. Deliang , West Alan C. 
Published: June 2004

AbstractResults from steady and unsteady, two‐dimensional simulations of tertiary current distributions at and below the limiting current density are presented. The simulations are based on dilute‐solution theory, with coupling of the concentrations of the ionic species through the electrical field. The electrical field is calculated from the electroneutrality constraint. Results confirm and extend previous theoretical predictions of the electricalmigration enhancement of the limiting current. To demonstrate the potential utility of general current‐distribution solvers, measured temporal variations of the rate of copper deposition in the presence of an oscillating shear flow are measured and simulated. Experiments agree well with simulations.
2‐D time‐dependent viscoelastic flow calculations using connffessit
Authors: Laso Manuel , Picasso Marco , Öttinger Hans Christian 
Published: June 2004

AbstractTwo‐dimensional time‐dependent calculations for a molecular model of finite extensibility in the journal‐bearing geometry are presented. The flow is considered to be incompressible and isothermal. The momentum conservation equation is integrated using a time‐marching procedure in which local ensembles of dumbbells act as stress calculators. The calculations are based on the Calculation of non‐Newtonian flows: finite elements and stochastic simulation technique (CONNFFESSIT) and combine deterministic (finite elements) and stochastic techniques to advance the velocity and stress fields in time. The ability of CONNFFESSIT to treat models for which no closed‐form constitutive equation can be derived is illustrated by performing calculations using FENE dumbbells. Significant differences in the stress field between the true FENE and the linearized FENE‐P are found, especially during the inception period. Steady‐state kinematics are, however, identical within error bars for both FENE and FENE‐P and for the Newtonian fluid. The essential algorithm of 2‐D CONNFFESSIT is detailed, as well as experience gathered from its parallel and vector versions.
Eddy‐viscosity vs. second‐order closures for flows in noncircular ducts
Authors: Younis Bassam A. , Cokjat Davor 
Published: June 2004

AbstractThis article deals with prediction of turbulent flows in ducts of noncircular cross sections and, in particular, assessment of the performance in such flows of two very different models of turbulence. One model is of the two‐equation, eddy‐viscosity type, which is used in conjunction with a non‐linear stress‐strain relationship. The other is a complete Reynolds‐stress transport closure that involves the solution of a differential transport equation for each of the six components of the Reynolds‐stress tensor. The flows considered are characterized by the presence of secondary motions that are largely driven by the turbulence anisotropy and whose prediction remains a severe challenge to turbulence closures. Data from several experiments involving such flows are used here to assess the overall performance of the two models. It is found that the two models yield very similar results that are also of adequate engineering accuracy—an outcome that argues in favor of the use of the nonlinear two‐equation model in practical computations.
Initial deposition of interacting particles by filtration of dilute suspensions
Authors: Koenders M. A. “Curt” , Wakeman Richard J. 
Published: June 2004

AbstractData from a range of filtration experiments on dilute suspensions are used to determine the parameters that describe the physics of suspension flow during compaction. The range of solids volume fractions used is 0.00001 < ϕ <0.1; ζ‐potentials vary between 0 and 50 mV. Relevant physical data are extracted from an analysis of the initial stages of experiments at variousϕ and ζ. Theoretical considerations on suspension flow are presented to argue that the physical character of the flow at relatively dense, strongly interacting conditions is significantly different from that of dilute systems. The latter are dominated by fluctuations in the particle velocity near the septum to give gas‐type diffusive behavior, while in the former the particles are more or less localized. This observation has implications for the diffusion coefficient, which is predicted to be quadratic in the filtration pressure for very dilute suspensions and which is roughly independent of pressure for mixtures containing strongly interacting particles. Experiments are described and analyzed, and these reinforce the main theoretical insights.
Breakthrough curves for fixed‐bed adsorbers: Quasi‐lognormal distribution approximation
Authors: Xiu Guo‐Hua , Nitta Tomoshige , Li Ping , Jin Ge 
Published: June 2004

AbstractThe quasi‐lognormal distribution (Q‐LND) approximation was used to predict breakthrough curves in fixed‐bed adsorbers for a linear adsorption system with axial dispersion, external film diffusion resistance, and intraparticle diffusion resistance for slab–, cylindrical–, and spherical‐particle geometries. The exact solution and parabolic profile approximation were also obtained for different particle geometries. Numerical results show that the Q‐LND approximation is a simple and handy solution. It predicts breakthrough curves with an accuracy comparable to the parabolic‐profile approximation over a wide range of parameters; compared with the latter, it only takes less than one hundredth the computation time and does not have a convergence problem in numerical calculations. A criterion for the applicability of the Q‐LND approximation is suggested. The effect of particle geometries on the breakthrough curves is discussed. A criterion is also provided for the Q‐LND approximation to explore the conditions where one should consider this effect on breakthrough curves.
Effect of CO2 concentration on YBa2Cu3O6+x formation
Authors: Kohav T. , Forster K. M. , Richardson J. T. , Luss D. 
Published: June 2004

AbstractTwo reversible reactions are involved in YBa2Cu3O6+x formation: a reaction between BaCO3 and CuO forming BaCuO2 and CO2, and a reaction of BaCuO2 with Y2O3 and CuO forming YBa2Cu3O6 which undergoes phase transformation to YBa2Cu3O6+x upon cooling. In‐situ isothermal time resolved HT‐XRD of a thin film was used to quantify the effect of CO2 on the kinetics of the first reaction. Increased CO2 partial pressure shifts the reactions to higher temperatures. At high CO2 partial pressure (>2 vol. %), the rate of the first reaction becomes essentially a step process with a very high activation energy. Noninstantaneous nucleation of the reaction products occurs at low CO2 partial pressure (0.5–1%) and temperatures (700°C). The data fit a 2‐D diffusion‐controlled mechanism with a zero nucleation rate for BaCO3 decomposition and a second‐order nucleation rate for YBa2Cu3O6 formation. A comparison of the kinetics of a thin film (10 mm) as determined by HT‐XRD with those of a thick sample (2 mm) determined by TG revealed that the transport of CO2 within the sample pores and to the ambient gas significantly affect the decomposition of BaCO3. For example, the formation of YBa2Cu3O6 in a thick precursor layer occurs in the 840 to 940°C range, exceeding by about 200°C that in which it is formed in thin films.
Numerical and experimental study of a homogenizer impinging jet
Authors: Kleinig Andrew R. , Middelberg Anton P. J. 
Published: June 2004

AbstractHigh‐pressure homogenization is a key unit operation used to disrupt cells containing intracellular bioproducts. Modeling and optimization of this unit are restrained by a lack of information on the flow conditions within a homogenizer valve. A numerical investigation of the impinging radial jet within a homogenizer valve is presented. Results for a laminar and turbulent (k – ϵ turbulent model) jet are obtained using the PHOENICS finite‐volume code. Experimental measurement of the stagnation region width and correlation of the cell disruption efficiency with jet stagnation pressure both indicate that the impinging jet in the homogenizer system examined is likely to be laminar under normal operating conditions. Correlation of disruption data with laminar stagnation pressure provides a better description of experimental variability than existing correlations using total pressure drop or the grouping 1/Y2h2.
Dynamic modeling for simulation and control of a circulating fluidized‐bed combustor
Authors: Muir James R. , Brereton Clive , Grace John R. , Lim C. Jim 
Published: June 2004

AbstractA dynamic model has been developed to predict the transient behavior of the temperature, the heat removal rate by the in‐bed heat exchanger, and the flue‐gas oxygen concentration for a circulating fluidized‐bed (CFB) combustor. The model was incorporated into a control simulator to reproduce the combustion process within the overall program. The simulator predicts the behavior of the combustor under manual or automatic control to allow testing of control strategies. The model is validated by comparison with step‐response tests carried out on a pilot CFB combustor. Discrepancies are attributable to unmodeled disturbances. Further validation, necessary to ensure the applicability of the simulator to control development, is provided by comparing control models identified experimentally using the pilot CFB to those obtained by simulation. Favorable comparison suggests that the dynamic model is suitable for use in control simulation.
Fluorescence capillary photometry for characterization of liquid–liquid dispersions
Authors: Weiss Christian , Köhler Volkhard , Marr Rolf 
Published: June 2004

AbstractThe behavior of droplet swarms in liquid–liquid dispersions, especially found in extraction columns, are analyzed by a new fluorescence measurement technique, which represents an extension to the capillary suction method. The measuring principle developd benefits from detectable‐emission light intensity of a fluorescent dye even in a trace concentration. The addition of this nontransferring dye to the dispersed phase enables in situ determination of bivariate drop‐size/drop‐concentration distributions, which provides important information on droplet history for the evaluation of coalescence and breakup rates. Furthermore, the measuring method represents a new approach for the measurment of droplet‐size‐dependent residence times in extraction columns.