bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms of brine‐side mass transfer in a horizontal reverse osmosis tubular membrane
Authors: Derzansky Lewis J. , Gill William N. 
Published: June 2004

AbstractThe desalination performance of a tubular reverse osmosis membrane was studied under well‐defined hydrodynamic conditions. Experimental measurements were made of local mass transfer rates in a 2.31‐cm I.D. × 81‐cm long horizontal cellulose acetate membrane at 16 locations along the tube length for both laminar and turbulent flows. The membrane's intrinsic permeability to water and NaCl was found to vary significantly along its productive length.The experiments suggest that the dominant transport mechanisms in laminar flow are forced convection in the upstream region and combined free and forced convection in the downstream region, beyond a distance of approximately 16 tube diameters, for all feed concentrations studied. The Deissler analogy applies well to the turbulent region for Re ≧ 104; however, it increasingly overpredicts performance as Re is decreased below 104.The experimental results of other workers are interpreted successfully in terms of the mechanisms deduced in the present work.
Regulation of lumped periodic processes
Authors: Liaw J.‐S. , Bailey J. E. 
Published: June 2004

AbstractWhen a periodic process is disturbed, control action may be necessary to maintain satisfactory performance. Regulating controls to achieve this objective can be synthesized by solving a linear‐quadratic optimization problem with periodic coefficient's. Generalized proportional and proportional‐integral feedback regulators developed in this manner are tested by simulating a cyclic reactor. Very satisfactory control is achieved for 10% step disturbances in reactor feed conditions although the results are sensitive to the choice of manipulated variables.
Mechanisms of secondary nucleation in agitated crystallizers
Authors: Evans T. W. , Margolis G. , Sarofim A. F. 
Published: June 2004

AbstractExperiments were designed to identify the mechanism of the secondary nucleation of ice in a vigorously agitated crystallizer. It has been shown that the nucleation rate is proportional to the product of two factors, one characterizing crystal morphology and the other the rate of removal of potential nuclei from the surfaces of the existing crystals. Consequently, the nucleation rate attributable to different mechanisms is additive and the rate is proportional to the number of collisions per crystal. The contribution to the secondary nucleation of ice, by collisions of crystals with the impeller, baffles, and other crystals in an agitated crystallizer have been identified by measurements in a batch crystallizer in which each of the different collision mechanisms could be suppressed.
Three‐dimensional flow of fluids through nonuinform packed beds
Authors: Stanek V. , Szekely J. 
Published: June 2004

AbstractThrough the statement of the Ergun equation in a vectorial form, a formulation is presented for three‐dimensional flow of fluids through packed beds having a spatially variable resistance to flow. The equations were put in a form convenient for numerical solution by successive over‐relaxation, and a selection of computed results is presented for cylindrical beds where the nonuniform resistance to flow obeys axial symmetry. The method outlined in the paper for calculating flow maldistribution in packed beds is thought to be a necessary first step in the representation of hot spot formation and flow nonuniformities in packed bed reactors.
Minimum cost design of a multimodal fluidized reactor‐heater system involving an exponential function inside an integral equation
Authors: Wilde Douglass J. 
Published: June 2004

AbstractA simple procedure for achieving the minimum cost design of a single reaction fluidized reactor system with feed and recycle heaters is presented and proven. The problem's mathematical interest stems from its multimodality, the handling of the exponential dependence of temperature, and the presence of an integral equation constraint. The proof technique is an extension of Lagrange's method, supplemented by ideas from geometric programming, extended to exponential and the integral functions.
Gas phase axial mixing at extremely high irrigation rates in a large packed absorption tower
Authors: Woodburn Edward T. 
Published: June 2004

AbstractExtensive gas phase dispersion data are reported for extremely high liquid‐gas ratios in a cylindrical packed absorption tower operated at atmospheric pressure under counterflow conditions.The dispersion data report gas Peclet numbers in terms of superficial liquid and gas Reynolds numbers over the range

An increase in Peclet number with increasing gas rate is observed at subloading conditions.Reverse gas flow was observed in the gas phase when the liquid Reynolds number exceeded 650. Dispersion in the gas phase at liquid rates for which NReL < 650 is consistent with previously recorded correlations but becomes independent of further increases of liquid rate when NReL is > 650.The dispersion coefficients obtained by dynamic testing under reverse gas flow conditions were consistent with those obtained from steady state absorption profiles and provide a quantitative explanation for the anomalies in plug‐flow KLa at high water rates recorded by Sherwood and Holloway (1940).
Model reduction and the design of reduced‐order control laws
Authors: Wilson Robert G. , Fisher D. Grant , Seborg Dale E. 
Published: June 2004

AbstractThis paper is concerned with the problem of designing satisfactory loworder (incomplete state feedback) controllers starting with a high‐order, state‐space model. Two design approaches are considered: the control law reduction technique, recently developed by the authors (Wilson et al., 1973), and the well‐known model reduction approach. These two design techniques are used to develop a variety of low‐order controllers for a double‐effect evaporator starting with a 10th‐order model. Experimental and simulated response data from the computer‐controlled evaporator demonstrate the superiority of the control law reduction approach in this application. It is also shown that several of the previously published modal approaches to model reduction are basically equivalent since they yield identical reduced‐order models.
Modified one‐at‐a‐time optimization
Authors: Findley M. E. 
Published: June 2004

AbstractAn optimization method has been developed that searches one variable at a time under the conditions that previously searched variables are at their approximate optimum and variables to be searched later are constant. This method provides the optimum and also information on the effects of the variables. The method is based on the Partan and Powell methods and on assuming linear partial derivatives of the objective function with respect to any given variable. The procedure involves searching each variable separately with other variables either constant or varied so that they remain at their estimated optimum for the given conditions. This method provides useful information on the effects of independent variables as well as locating the overall optimum and a number of partial optimums and requires a comparable number of trials.
Convective instabilities in concurrent two‐phase flow: Part II. Global stability
Authors: Gumerman Raymond J. , Homsy George M. 
Published: June 2004

AbstractThe method of energy is used to determine global stability limits for thermally stratified two‐phase plane Couette flow. Instabilities due to surface tension variations, buoyancy effects, and shear are allowed for, but surface waves are specifically excluded from consideration. Under these assumptions, the Marangoni, Rayleigh, and Reynolds numbers completely describe the system. Stability plots, valid for disturbances of any magnitude, are presented for both streamwise oriented roll vortices and two‐dimensional transversely oriented disturbances. It is shown that rolls are the most dangerous disturbances in the sense that they cannot be shown to be stable relative to transverse disturbances at any nonzero Reynolds numbers. Comparisons are made with existing linear limits, and these are seen to be close only for moderate Reynolds numbers.
Oscillating behavior on distillation trays‐II
Authors: Biddulph Michael W. 
Published: June 2004

AbstractThis paper describes an extension of an earlier study on oscillations which can develop on distillation trays. The oscillations take the form of violent lateral movements of the gas/liquid biphase, and they are generally undesirable for good column performance. It has been found that lower density gases need higher velocities to initiate oscillation, and vice versa for higher densities. The predictive method for the onset of oscillations proposed previously appears to remain valid for the range of gas density covered, and for small hole size trays. The presence of oscillations has been shown to increase weeping significantly.
Thermodynamic consistency using orthogonal collocation or computation of equilibrium vapor compositions at high pressures
Authors: Christiansen Lars J. , Fredenslund Aage 
Published: June 2004

AbstractThe numerical method of orthogonal collocation is used within a thermodynamically consistent framework to calculate equilibrium vapor compositions from P‐T‐x data for binary systems. The method may be used for isothermal or isobaric data in both the normal liquid and in the critical region, and it applies to any choice of standard states.To use the method it is necessary to have experimental or estimated values of vapor phase fugacity coefficients for both components in the mixture and liquid molar volumes (isothermal case) or heats of mixing (isobaric case). If vapor composition data are available, each set of P‐T‐x‐y data may be checked for thermodynamic consistency by comparing y (experimental) with y (calculated). Illustrative calculations are given. The method is shown to provide an excellent procedure for obtaining Henry's constants from P‐x data for systems with one noncondensable component.
Vapor‐liquid equilibrium: Part IV. Reduction of P‐x data for ternary systems
Authors: Abbott M. M. , Floess J. K. , Walsh G. E. , Van Ness H. C. 
Published: June 2004

AbstractTotal pressure measurements taken for the ternay systems acetone‐chloroform‐methanol and chloroform‐ethanol‐n‐heptane at 50°C are reduced by Barker's method and correlated by an equation similar to one proposed by Wohl (1953).
Flexible solutions to linear programs under uncertainty: Inequality constraints
Authors: Friedman Y. , Reklaitis G. V. 
Published: June 2004

AbstractIn most industrial applications the linear model used for optimization by linear programming involves significant uncertainties and inaccuracies in the model parameters. This paper presents a framework which allows uncertainties in the matrix elements of the linear program to be taken into account without requiring detailed knowledge of the statistical characterstics of these uncertainties. Three cases for the inequality constrained problem are considered: independent variations in the array elements, column dependent variations, and row dependent variations. In each case the problem can still be solved as a linear program. In the first two cases, the problem size is doubled, while for the row dependent case a finitely terminating cutting plane algorithm is constructed.
Thermal effects in gas absorption
Authors: Verma Surjit L. , DeLancey George B. 
Published: June 2004

AbstractThe transformation of the energy equation from the mass average to the volume average reference frame exposes a pseudo Dufour effect. The theoretical model for absorption into a stagnant liquid including this effect, the heat of absorption, variable density, an interfacial velocity, and an arbitrary equilibrium condition at the interface is able to predict experimental data over a wide range of conditions. The data consisted of liquid temperature profiles and mass transfer rates into a stagnant liquid. The ammonia‐water system exhibited interfacial temperature rises from 6.9°K to 18.2°K. The interfacial temperature rise for the propane‐decane system was 1.3°K. Simpler theoretical models were able to predict the mass transfer rates or the temperature profiles.
Statistical thermodynamics of liquid mixtures: A new expression for the excess Gibbs energy of partly or completely miscible systems
Authors: Abrams Denis S. , Prausnitz John M. 
Published: June 2004

AbstractTo obtain a semi‐theoretical equation for the excess Gibbs energy of a liquid mixture, Guggenheim's quasi‐chemical analysis is generalized through introduction of the local area fraction as the primary concentration variable. The resulting universal quasi‐chemical (UNIQUAC) equation uses only two adjustable parameters per binary. Extension to multicomponent systems requires no ternary (or higher) parameters.The UNIQUAC equation gives good representation of both vapor‐liquid and liquid‐liquid equilibria for binary and multicomponent mixtures containing a variety of nonelectrolyte components such as hydrocarbons, ketones, esters, amines, alcohols, nitriles, etc., and water. When well‐defined simplifying assumptions are introduced into the generalized quasi‐chemical treatment, the UNIQUAC equation reduces to any one of several well‐known equations for the excess Gibbs energy, including the Wilson, Margules, van Laar, and NRTL equations.The effects of molecular size and shape are introduced through structural parameters obtained from pure‐component data and through use of Staverman's combinatorial entropy as a boundary condition for athermal mixtures. The UNIQUAC equation, therefore, is applicable also to polymer solutions.
Selection of decompositions for chemical process simulation
Authors: Upadhye Ravindra S. , Grens Edward A. 
Published: June 2004

AbstractA method has been developed for selection of the set of torn streams in a process simulation that leads to convergence of a direct substitution calculation in the minimum number of iterations. It is based on the establishment of families of decompositions, the members of each of which have identical convergence behavior. Explicit criteria for choice among families have been found that lead, in almost every case, to a single optimum decomposition family. These results have been verified by application to several chemical process simulation examples.
Prediction of unsymmetric convention liquid‐phase activity coefficients of hydrogen and methane
Authors: Brelvi S. Waseem , O'Connell John P. 
Published: June 2004

AbstractA corresponding states method has been developed to predict the binary parameter in the unsymmetric‐convention one‐term Margules relation for binary activity coefficients of H2 and CH4 in solvents. In addition to the solvent density, only characteristic volumes used previously for partial molar volumes at infinite dilution and pure solvent compressibility are required. Comparisons with experiment for nonpolar solvents indicate that use of the method is usually significantly more accurate than assuming ideal solution (Henry's law).
An investigation of anomalous osmosis and thermoosmosis
Authors: Goldstein W. E. , Verhoff F. H. 
Published: June 2004

AbstractMeasurements of water flux, solute flux, and electrochemical potential were made simultaneously in a membrane transport system designed for the studies in anomalous osmosis and thermoosmosis using a series of cations with a common anion. The cation exchange membrane employed was dimensionally stable. The anomalous osmosis appeared to be composed of two components, the normal osmosis and a facilitated osmosis; whereas the thermoosmosis was composed solely of a facilitated component. The anomalous water flux did not correlate with the solute flux or the electro‐chemical potential. Anomalous osmosis depended strongly upon the cation species.
Dielectric constants and Clausius‐Mossotti functions for simple liquid mixtures: Systems containing nitrogen, argon and light hydrocarbons
Authors: Pan W. P. , Mady M. H. , Miller R. C. 
Published: June 2004

AbstractDielectric constants and Clausius‐Mossotti functions (CM) have been determined for selected pure components, binary mixtures, and ternary mixtures at temperatures between 91 and 115 K and pressures near saturation. Excess Clausius‐Mossotti functions (CME) have been calculated from the pure fluid and mixture values.Mixture CME values are found to be generally less than 0.1% of the mixture CM values for systems containing only nonpolar species. Thus, dielectric constant measurements can be conveniently used as substitute density measurements for simple liquid mixtures. Methods have been developed to utilize dielectric constant measurements to accurately determine densities and heating values per unit liquid volume for liquefied natural gas mixtures.
New network permeability model of porous media
Authors: Dullien Francis A. L. 
Published: June 2004

AbstractIn this study a new mathematical model for predicting permeabilities of porous media has been developed. The model consists of a set of cubic networks of arbitrary orientations with respect to the macroscopic flow direction. The networks consist of capillary tubes which are made up of segments of different diameters. It is shown that a cubic network of capillaries has isotropic permeability properties. The permeability model requires two pore size distributions and the porosity of the sample for the calculations. The calculated permeabilities agreed with experimental results for a wide range of permeabilities of highly compacted materials to within ± 23%, without using adjustable tortuosity factors.
Multicomponent distillation simulation — distillation of air
Authors: Biddulph Michael W. 
Published: June 2004

AbstractThis paper describes the application of a mathematical model to a column distilling air to produce nitrogen, oxygen, and argon. The upper column of a plant producing 400 tonnes/day (400 Mg/day) of oxygen is considered. Apart from any direct interest in this system, the outcome illustrates the problems which arise in the study of the separation of multicomponent systems. The effect of directed flow compared with normal flow is established, and in particular the way in which some components benefit more than others. The simulation uses experimental values of point efficiency and mixing measurements, and a good comparison with plant experience is achieved.
Freeze dehydration by microwave energy: Part I. Theoretical investigation
Authors: Ma Yi Hua , Peltre Philippe R. 
Published: June 2004

AbstractA general unsteady state analysis is employed to derive a mathematical model of a freeze‐drying process using microwave heating. The model takes into account the variations of the transport and dielectric properties in the sample with both time and location as a function of temperature and pressure. The variations of the properties are described by functionals which have been derived from literature data and are built into the model.The mathematical model is used to simulate the freeze drying of beef meat with microwave energy at 2450 MHz. The simulation shows that drying rates are essentially a function of the microwave power input. The model also shows that the total pressure and the partial pressure of water vapor in the vacuum chamber directly affect the sample temperature during dehydration. The simulation shows, in particular, that, an optimal microwave freeze‐drying operation corresponds to an operation near corona and overheating/melting conditions.
A new method for nonlinearly constrained optimization
Authors: Newell J. S. , Himmelblau D. M. 
Published: June 2004

AbstractA new penalty function method of solving problems involving a nonlinear objective function subject to nonlinear equality and inequality constraints is described. It ameliorates difficulties experienced with the illconditioning of the Hessian matrix of classical penalty function methods. Experience based on the solution of 25 test problems indicates the proposed method is as good as, or better, than methods that are now being used.
General analysis for free drainage of non‐Newtonian films from flat plates when inertial and surface tension forces and normal stresses are negligible
Authors: Pendergrass John 
Published: June 2004

AbstractGeneral equations for (1) thickness, (2) specific holdup, and (3) specific flow rate of non‐Newtonian films under conditions of plane free drainage with negligible inertial and interfacial tension forces and normal stresses as functions of position and time are derived. Use of these equations reduces the heretofore tedious process of derivation for a particular rheological model of expressions for film thickness, holdup, and flow rate to a single‐step operation for film thickness and relatively simple processes for holdup and flow rate. The general equations are evaluated for popular non‐Newtonian models, with description of efficient methods for doing so, and the results for thickness, holdup, and flow rate, many new, in compact dimensionless form made available to the interested reader in a supplement.
Effects of nonseparable kinetics in alcohol dehydration over poisoned silica‐alumina
Authors: Bakshi K. R. , Gavalas G. R. 
Published: June 2004

AbstractMethanol and ethanol dehydration over fresh and poisoned silica‐alumina have been used as a model system to demonstrate experimentally certain effects of nonseparable kinetics including the change in product distribution upon flow reversal in a reactor with a poisoning gradient. The rate expression r = kKACA1/2/(1 + KACA1/2 + KWCW) describes the epxerimental data for all reactions although the constants for ether and olefin formation are entirely different and vary between fresh and poisoned catalysts. The nonseparability of kinetics and the concomitant variation of KA, KW with poisoning are briefly discussed in terms of interactions between poison molecules and surface acid‐base sites.
Effectiveness factors in gas‐liquid reactions
Authors: Kulkarni B. D. , Doraiswamy L. K. 
Published: June 2004

AbstractThe concept of the effectiveness, factor, commonly used as a means of accounting for diffusional effects in gas‐solid catalytic and noncatalytic reactions, is extended to gas‐liquid reactions. The relevant differential equations for an isothermal system with appropriate boundary conditions are solved for the case of (1) a simple first‐order irreversible reaction, (2) a consecutive reaction, and (3) a parallel reaction. The results are presented in terms of effectiveness factor plots, and methods of delineating the controlling regimes are discussed. It is shown that gas‐liquid reactions represent perhaps the most general case which reduces to gas‐solid reactions under appropriate limiting conditions.
Gas absorption accompanied by instantaneous bimolecular reaction in turbulent liquids
Authors: Méndez Francisco , Sandall Orville C. 
Published: June 2004

AbstractGas absorption accompanied by instantaneous bimolecular reaction in turbulent liquids (Re > 1200) is treated in terms of an eddy diffusion model. The species balance equations are integrated for the eddy diffusivity varying as the square of the distance from the free surface. Experimental mass transfer coefficients were measured in a wetted‐wall column for the absorption of carbon dioxide in aqueous sodium hydroxide solutions. Experimental results were obtained for carbon dioxide partial pressures of 1.0 and 1.5 atm. and for sodium hydroxide concentrations varying between 0.020 and 0.220 N over the Reynolds number range 1400 to 5400. The experimental data showed good agreement with the theoretical calculations, the mean deviation being 8.2%.