bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas absorption with exothermic bimolecular (1,1 order) reaction
Authors: Bhattacharya A. , Gholap R. V. , Chaudhari R. V. 
Published: June 2004

AbstractGas absorption with a nonisothermal, bimolecular (1,1 order), and irreversible reaction are analyzed and approximate film theory solutions are obtained for interfacial temperature rise and enhancement factor. The model of Mann and Moyes is extended to incorporate depletion of liquid reactant concentration at the gas‐liquid interface and also the variation of dissolved gas concentration in the bulk liquid, leading to a generalized solution independent of the regime of absorption. The effect of heat generation, heat dissipation, and reaction rate parameters on enhancement factor and interfacial temperature rise is discussed. The system showed multiplicity behavior under certain conditions, but at higher values of heat dissipation parameters and for some combinations of heat generation and reaction rate parameters, unique solutions were obtained. However, even the unique solutions of enhancement factor are substantially different from the values obtained under isothermal conditions. Since depletion of liquid reactant concentration is incorporated, asymptotic values of enhancement factor (at large \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt M $\end{document}) were observed to be the same as those obtained in the instantaneous reaction regime of isothermal absorption and reaction process. The model presented does not require a priori assumption of the regime of absorption and hence can be useful in modeling nonisothermal reactors.
Control configuration selection for distillation columns
Authors: Skogestad Sigurd , Morari Manfred 
Published: June 2004

AbstractMost two‐product distillation columns can be described as 5 × 5 plants, but the control system design is usually simplified by means of the following procedure:

Choose two manipulated inputs for composition control (corresponding to a specific control configuration).
Design the level and pressure control system (usually three SISO controllers).
Design a 2 × 2 controller for composition control.
This paper provides guidelines for step 1, which is considered the most important. Ratios (e.g., L/D or V/B) are frequently chosen as manipulated inputs in step 1. It is shown that the ratio configurations are effectively complex multivariable controllers that provide, among other features, improved flow disturbance rejection.
Fines migration in porous media
Authors: Sharma M. M. , Yortsos Y. C. 
Published: June 2004

AbstractA model developed by Sharma and Yortsos (1987a) is applied to the processes of fines migration and fines injection in a porous medium. The first is a problem frequently encountered in oil reservoirs when release of fines is triggered by physicochemical interactions of the porous formation with the injected fluids. The second may be a problem in the filtration of relatively large particulates. Simple solutions are provided for both processes by considering size exclusion as the dominant particle retention mechanism. The solutions developed provide expressions for the particle concentration profiles, the open pore density and pore size distribution profiles, as well as the permeability reduction. These expressions are of importance in the evaluation of the extent and depth of formation damage and can be used as designing tools for remedial treatment, such as acidizing or fracturing.
Predicting fluid‐bed reactor efficiency using adsorbing gas tracers
Authors: Krambeck F. J. , Avidan A. A. , Lee C. K. , Lo M. N. 
Published: June 2004

AbstractGas tracers have been used frequently to predict conversion in chemical reactors. But in heterogeneous systems such as fluid‐bed reactors, tracer residence time data usually overpredict actual contact time and conversion. In this work, the general two‐phase countercurrent flow model is extended to include tracer adsorption, which is important in predicting contact time. The tracer used was SF6, whose adsorption on the solids could be varied over a wide range. The apparent reactor efficiency, calculated directly from tracer response, is shown to approach that estimated from the two‐phase model when the fluid bed approached homogeneity. This is the case for many large‐scale reactors that are operated in the turbulent fluidization regime. The use of horizontal baffles in methanol‐to‐gasoline cold flow models is shown to improve bed efficiency by staging the bed.
Dynamic modeling of deep‐bed filtration
Authors: Mackie R. I. , Horne R. M. W. , Jarvis R. J. 
Published: June 2004

AbstractPrevious attempts to model the effect of deposition on removal efficiency in deep‐bed filtration have relied heavily on the determination of empirical parameters even for monosized suspensions. A newly developed mathematical model not only significantly reduces this reliance, but takes full account of the polydispersity of suspensions. The results of eight runs on an experimental filter are compraed with the predictions of the mathematical model. Qualitative agreement is good; quantitative agreement is fair.
Solubility in binary mixtures at the immiscibility critical point
Authors: Ludmer Z. , Shinnar R. , Yakhot V. 
Published: June 2004

AbstractIt is shown that the solubility of organic solids in binary mixtures of partially miscible liquids is singular at the immiscibility critical point. The theoretically predicted maximum of solubility in the vicinity of the critical point is found experimentally. The effect is similar to the phenomenon observed near the gas‐liquid critical point. The similarity of these two critical phenomena may have interesting technical applications and may provide guidelines for identifying promising new solvents for separation processes.
A random contact point model for second virial coefficients in dilute solutions
Authors: Bloemendal Michael , Marcus Yizhak 
Published: June 2004

AbstractA simple latticelike random contact point model is presented to correlate and predict second virial (or pair interaction) coefficients of thermodynamic quantities in dilute solutions. With this model it is possible to correlate pair interaction coefficients in different solvents with one equation and a single set of group interaction parameters. Enthalpic pair interaction coefficients of alkanes and alkanols dissolved in ten different alkan‐1‐ols and water, and of amides dissolved in N,N‐dimethylformamide, N‐methylformamide, and water are discussed in terms of the model. Corresponding group interaction parameters in water, alkan‐1‐ols, and amides are found to be equal within experimental error. When applied to aqueous solutions, the model yields the empirical equations of Savage and Wood, which are thus given some theoretical basis. The model also provides values of the higher interaction coefficients on the basis of the pair terms.
Quantification of flow hydrodynamics in pulse thermogravimetric analysis systems
Authors: Dadyburjor D. B. , Dean J. W. 
Published: June 2004

AbstractA test has been designed and used to compare flow hydrodynamics in different thermogravimetric analysis (TGA) systems used as pulse microreactors. The test involves passing a pulse of injectant over the sample pan containing an adsorbent. Water and zeolite are used in the present case. The technique is easily performed and is insensitive to variations in temperature. A model is developed by which the fraction of gas pulse bypassing the sample pan within the TGA can be obtained. In gas/solid reactions, either catalytic or noncatalytic, the test should prove useful for comparing TGA extent‐of‐conversion data to similar measurements taken from other reactor configurations, carrier flow rates, and flow geometries.
Gas and solids behavior in a baffled and unbaffled slurry bubble column
Authors: O'Dowd W. , Smith D. N. , Ruether J. A. , Saxena S. C. 
Published: June 2004

AbstractNew data and analyses are presented for describing gas and solids behavior in a slurry bubble column. Axial solids concentration and bubble size distributions were measured in a 0.108 m ID slurry bubble column apparatus operated at steady state conditions. The column was operated with and without internal baffles. The slurry and gas superficial velocities ranged from 0.0077 to 0.009 m/s and from 0.031 to 0.24 m/s, respectively. The solid phase consisted of glass spheres in a narrow size range with a mean diameter of 96.5 μm; the liquid phase consisted of tap water.With a one‐dimensional sedimentation‐dispersion model, the data have been used to predict average solids loadings and axial distributions of the solids for specified operating conditions. Local bubble size and concentration measurements indicate that the slurry bubble column was operated in the churn‐turbulent flow regime throughout the entire range of operating conditions used in this study. The impact of internal baffles and solids concentration on the gas and solids behavior is discussed.
Modeling of slow dynamics in the oxidation of CO over supported silver
Authors: Shanks B. H. , Bailey J. E. 
Published: June 2004

AbstractThe oxidation of CO over aluminum‐supported Ag was studied at 147°C using transient experiments. Long‐time‐scale dynamics were observed that could not be explained by previously postulated kinetic mechanisms for this reaction system. A model is presented with kinetic parameters estimated from steady state and transient data that is able to reproduce a variety of cycled feed stream experiments. The model incorporates a slow reversible step which forms an adsorbed oxygen species that blocks reaction sites.
Monte Carlo simulation of diffusion and chemical reaction in catalyst pores
Authors: Zielinski J. M. , Petersen E. E. 
Published: June 2004

AbstractDiffusion and chemical reaction in a catalyst pore is simulated as a Monte Carlo process. In this analysis the average diffusion distance, calculated for a large number of wall collisions, and the reaction probability are computed as two independent statistical events. This formulation yields results that compare very well with the theoretical values, yet uses minimal computer time. Results reported include typical concentration profiles and effectiveness factors for first‐ and second‐order isothermal reactions using the method described. These results show promise of extension to more complex systems where analytical solutions are not available.
Study of two‐phase flow by laser image processing
Authors: Hanzevack E. L. , Bowers C. B. , Ju Chi‐Hong 
Published: June 2004

AbstractA new, unobtrusive method for liquid‐liquid two‐phase flow data collection was proved to be reliable in this research. Drop size distributions and concentration profiles were determined for a dilute water‐inkerosene system under horizontal straight pipe flow using this technique, and the Segev model for predicting concentration profiles was tested with the data collected here.The drop size distributions were found to follow a Rosin‐Rammler function for a limited droplet diameter range, and the average value of the exponent in the Rosin‐Rammler equation was determined to be 2.0. The velocity where the flow regime makes a transition from stratified to adequately dispersed flow was found to be between 2.0 and 2.2 m/s. Concentration profiles predicted by the Segev model were in general agreement with the profiles determined in this work, and using the proper choice of model parameters noticeably improves the model predictions.
Extreme solvent effects on reaction rate constants at supercritical fluid conditions
Authors: Johnston K. P. , Haynes Charles 
Published: June 2004

AbstractThe reaction rate constant was adjusted continuously over two orders of magnitude for the unimolecular decomposition of α‐chlorobenzyl methyl ether using the supercritical fluid solvent 1, 1 diffluoroethane. Activation volumes were observed as low as −6,000 cm3/mol, which is about an order of magnitude more negative than those reported previously in the literature for a homogeneous reaction. Spectral shift (solvatochromic) data were measured for phenol blue in the same fluid in order to interpret the rate data. A method is presented to predict solvent effects on rate constants at supercritical fluid conditions.
Transient response of continuous‐flow stirred‐tank polymerization reactors
Authors: Cozewith Charles 
Published: June 2004

AbstractThe transient behavior of polymer properties following a step change in feed conditions during copolymerization in a continuous‐flow stirred‐tank reactor has been investigated by both modeling and experiment. For kinetics appropriate to Ziegler catalyzed olefin polymerization, the dynamic response of polymer molecular weight and composition is predicted to be relatively slow; four to six reactor turnovers could be required to reach steady state. In addition, response time depends on the direction and magnitude of change and is generally shorter when a property value is decreased. These model predictions were confirmed by measurement of the transient response of copolymer composition and molecular weight for ethylene‐propylene‐ethylidene norbornene terpolymerization.The model equations also were used to simulate reactor startups, and it was found that steady state following a startup can be reached in about three reactor turnovers. The initial absence of polymer in the reactor causes the dynamic response to be faster for a startup than for reactor control.
Effect of natural convection on spontaneous combustion of coal stockpiles
Authors: Brooks Kevin , Balakotaiah Vemuri , Luss Dan 
Published: June 2004

AbstractSpontaneous combustion may occur in a coal stockpile when the heat generated within the pile cannot be dissipated at near ambient temperature. Under practical conditions, natural convection enhances the rate of heat removal from the bed and shifts the ignition to lower particle sizes (higher reactivities). Analysis of three limiting cases of a one‐dimensional model yields criteria predicting the conditions under which ignition occurs as well as those for which a low‐temperature (extinguished) state exists for all particle sizes. A simple asymptotic relation predicts the ignition point at large Rayleigh numbers.
Design of tubular flow reactors for monodisperse aerosol production
Authors: Kodas T. T. , Friedlander S. K. 
Published: June 2004

AbstractDesign equations are derived for calculating the properties of an aerosol generated in a tubular flow reactor operated at a constant rate of formation of condensable monomer. These equations lead to a set of characteristic dimensionless groups. Independently, it is shown that nearly monodisperse aerosols can be generated by: (1) separating particle formation and growth processes, (2) operating with a narrow residence time distribution, and (3) minimizing monomer concentration gradients. These criteria can be used in solving the design equations over ranges of the dimensionless groups suitable for monodisperse aerosol production. In general, high rates of monomer formation are desirable, subject to the desired particle size and concentration, but an upper bound may result from coagulation.
Computer‐Aided planning of purge operations
Authors: Fusillo R. H. , Powers G. J. 
Published: June 2004

AbstractA strategy is proposed for synthesizing operating procedures for purging species from chemical processing systems during start‐up. This strategy is based in part on the artificial intelligence methods of planning with constraints and symbolic functional modeling of chemical processing systems. Techniques are introduced for identifying chemical species to be purged, choosing methods and auxiliary fluids for executing purge tasks, and allocating chemical species to their final destinations. The implementation of this strategy is illustrated with the example of purging a hydrocarbon chlorination system during start‐up.
Phase equilibria of continuous fossil fuel process oils
Authors: Abbasian M. Javad , Weil Sanford A. 
Published: June 2004

AbstractFossil fuel process oils consist of such a large number of components that their only proper description is in terms of continuous distribution functions of a suitable characteristic variable. A methodology is presented to describe the oils in terms of a generalized distribution function. The characteristic variable is determined from measurements of the equilibrium ratios of two test oils, at ambient pressure. Application of the proposed methodology to a sequence of operations shows that, unlike the pseudocomponents technique, the level of accuracy can be maintained.
Tracer dispersion in sintered glass beads with a bidisperse size distribution
Authors: Hulin J. P. , Charlaix E. , Plona T. J. , Oger L. , Guyon E. 
Published: June 2004

AbstractAn experimental study was made of tracer dispersion in bidisperse sintered glass materials prepared from mixtures of two sizes of beads with mean diameters of 325 and 95 μm. The equivalent dispersion coefficient increases by a factor of 30 when the porosity decreases from 30 to 12%; this variation is similar to that measured in monodisperse samples. The variation of dispersion can be characterized by the ratio R = ℓd/L1 where ℓd is a length scale deduced from the equivalent dispersion coefficient and L1 is obtained from conductivity and permeability measurements. It is shown that the increase of ℓd/L1 correlates with the loss of porosity during the sintering process. Lightly sintered samples with a percentage of small beads around the minimum of porosity display a nearly Gaussian behavior, with a dispersion coefficient close to that obtained in homogeneous equivalent mixtures. This result is in contrast with very large anomalies observed by other authors. These results imply that dispersion in consolidated samples is sensitive to large‐scale inhomogeneities of the materials rather than to their detailed structure.
Multicomponent efficiencies in two types of distillation column
Authors: Biddulph M. W. , Kalbassi M. A. , Dribika M. M. 
Published: June 2004

AbstractA study of the efficiencies of two plate distillation columns is reported. One column had three rectangular trays with a flow path length of about 1 m, the other was a modified glass Oldershaw column with one tray of 38 mm dia. Tray efficiencies were measured in both columns and point efficiencies were deduced for the rectangular column.The systems studied were ternary and quaternary mixtures of alcohols and water. The results showed that for thermodynamically nonideal systems significant differences existed among the individual component point efficiencies. In the case of an ideal system the component point efficiencies were effectively equal, but tray efficiencies were different due to differing volatilities and composition profiles across the large trays.This study illustrates the need to allow for the above effects in large‐column designs for multicomponent systems. The possibility of using laboratory‐scale point efficiencies in these designs is explored.
Heuristic synthesis of nonsharp separation sequences
Authors: Bamopoulos George , Nath Ravindra , Motard Rodolphe L. 
Published: June 2004

AbstractThe preliminary synthesis of ordinary distillation schemes for separating a single feed into desired products is examined. Nonsharp products are emphasized, i.e., when components are desired in more than one product. Such sets lead naturally to columns with incomplete separation of the key components, including one‐section columns. Stream bypassing around separators and limited stream splitting are permitted. Sequences cannot have separators with identical key components, and only limited product fragmentation is considered. A heuristic ordering of separation options, coupled with a depth‐first application on a pictorial or a matrix representation of a stream, is proposed. Subsequently a best‐first search identifies the few better schemes. Partial sequences are (sub)optimized heuristically. Employing the present methodology on an example problem of four components and products resulted in annual cost savings of 42%, compared to the best sequence isolating the feed components.
Liquid‐liquid flows in an inclined pipe
Authors: Vigneaux P. , Chenais P. , Hulin J. P. 
Published: June 2004

AbstractExperimental measurements are reported of oil‐water flows in a 20 cm ID pipe at mean velocities between 2.7 and 35 cm/s, at deviation angles θ from vertical between 0 and 65°, and at water flow rate fractions between 30 and 100%. The distribution of the water volume fraction αw across a pipe section is obtained using local high‐frequency probes. The mean water volume fraction in the section and the slip velocity Vs between oil and water are also determined. High Vs values (up to 50 cm/s) are measured at large deviation angles; they are associated with oil droplet swarms or continuous oil phase zones. Both αw profiles and Vs values depend only on the mean water volume fraction and not on the total flow rate Qt in the range investigated. At low oil volume fractions αo, all droplets are concentrated close to the upper side of the pipe. At larger αo values, a slower linear variation of αw with the distance y from the axis is measured. A model is suggested relating the slope ∂αw/∂y in a vertical plane to the existence of internal density waves in the stratified mixture.
A nonrandom factor model for the excess gibbs energy of electrolyte solutions
Authors: Haghtalab A. , Vera J. H. 
Published: June 2004

AbstractA new approach to represent the deviations from ideality of electrolyte solutions is derived on the basis of the assumptions of specific interactions of Brönsted and of local electroneutrality of Chen. The model consists of two contributions due to long‐range forces, represented by the Debye‐Hückel theory, and to short‐range forces, represented by local compositions through nonrandom factors. With only two adjustable parameters per electrolyte, the model is valid for the whole range of electrolyte concentration, from dilute solution up to saturation. Results are compared with those obtained from two‐parameter or one‐parameter models of Meissner, Bromley, Pitzer, and Chen et al. The model presented in this work consistently produces better results and reproduces the experimental values from the dilute region up to saturation.
Turbulent mixing in baffled stirred tanks with vertical‐blade impellers
Authors: Komori Satoru , Murakami Yasuhiro 
Published: June 2004

AbstractMixing time and power consumption have been measured in baffled, paddle‐agitated cylindrical tanks with single‐ and double‐impellers, and mixing efficiency has been defined by a reciprocal of the product of the mixing time and power consumption. The mixing efficiency and mixing time of double‐impeller agitation have been compared with those of single‐impeller agitation, and they have been related, through a circulation time, to the flow patterns obtained from the measurements of mean axial and radial velocities.
Simulation of particle dispersion in a two‐dimensional mixing layer
Authors: Chein Reiyu , Chung J. N. 
Published: June 2004

AbstractParticle dispersion in a two‐dimensional mixing layer is analyzed numerically by calculating the particle trajectories in a free shear layer simulated by discrete vortices. Important global and local flow quantities reported in experimental measurements are reasonably simulated.The particle dispersion results demonstrate that the extent of particle dispersion depends strongly on the Stokes number St, the ratio of particle aerodynamic response time to the characteristic time of the mixing layer flow. Particles with relatively small St values are dispersed at approximately the fluid dispersion rate. Particles with large St values are dispersed at a rate that is less than the fluid rate. Particles with intermediate values of St may get flung outside of the vortex structures in the mixing layer and therefore get dispersed at a higher rate than the fluid. This result is in agreement with some previous experiments in plane and axisymmetric jets. It is also found that a higher dispersion rate is associated with the particles introduced to the flow from the low‐speed side and from near the middle of the mixing layer.