bluuebunny/crossref_metadata_2025_split huggingface dataset:
The use of secondary measurements to improve control
Authors: Weber Richard , Brosilow Coleman 
Published: June 2004

AbstractMany industrial processes are difficult to control because product quality cannot be measured economically on line. One solution to this problem is to use secondary measurements in conjunction with a mathematical model of the process to estimate product quality. This paper presents a method for designing a static estimator which predicts product quality from a linear combination of process input and output measurements. The design method includes procedures for selecting a subset of the availble output measurements so as to obtain an estimator which is relatively insensitive to modeling errors and measurement noise. Application of the estimator to a simulated multicomponent distillation column shows that the composition control achieved with an estimator based on temperature, reflux, and steam flow measurements is comparable to that achieved with instantaneous composition measurements. The composition control using the estimator is far superior to the composition control achieved by attempting to maintain a constant temperature on any single stage of the column.
A mathematical model for heat transfer in a packed bed and a simplified solution thereof
Authors: Kim D. S. , Gates L. E. , Brodkey Robert S. 
Published: June 2004

AbstractHeat transfer in packed beds can be mathematically modeled to account for the heat transfer between the particles and the gas phase, the conduction through the solid phase of particles, and the mixing or dispersion within the gas phase in the void structure of the porous media. To solve the resulting differential equations numerically is not easy. The solution for sinusoidal gas temperature input assumes linearity of the logarithm of the temperature with time. If, in addition, linearity with distance can be assumed, then the solution can be vastly simplified to finding the real root of a fourth‐order algebraic equation.
An experimental study of instabilities and other flow properties of a laminar pipe jet
Authors: Iribarne Agripina , Frantisak Frantisek , Hummel Richard L. , Smith James W. 
Published: June 2004

AbstractFlow patterns in an axisymmetrical laminar pipe jet with a flat entering velocity profile and a diametrical expansion ratio of 1:2 was investigated using nondisturbing flow visualization. A wavelike instability was discovered in the detached shear layer even at the lowest Reynolds numbers, and for Reynolds numbers greater than 350 tangential motions were observed, resulting in considerable turbulence near the mean position of re‐attachment. This turbulence even at low Reynolds explains local high rates of mass and heat transfer. The mean re‐attachment position depends on Reynolds number.Instantaneous mean velocity profiles and wall shear stresses were determined.
Using the dusty gas diffusion equation in catalyst pores smaller than 50 Å radius
Authors: Omata Hirokazu , Brown Lee F. 
Published: June 2004

AbstractWhen the dusty gas diffusion equation is applied to materials containing pores with radii below 50 Å, the observed diffusion behavior in these smaller pore systems can be quite different from that predicted by the equation. Higher temperatures and in some cases higher pressures tend to lessen the deviations between prediction and experiment. The observed deviations are probably caused by surface transport and by momentum transfer between gas molecules and pore walls during molecular flight. For bimodal materials, an additional factor can be the inapplicability of the equation to systems of parallel micro‐ and macropores. Excellent agreement between theory and experiment occurs for large‐pore unimodal systems.
Computer control using optimal multivariable feedforward‐feedback algorithms
Authors: Newell Robert B. , Fisher D. Grant , Seborg Dale E. 
Published: June 2004

AbstractThis paper presents three methods of designing feedforward compensators which can be combined with multivariable feedback controllers in order to minimize or eliminate errors caused by sustained measurable disturbances. The designs are based on a linear, time‐invariant state‐space model of the process and minimize a quadratic function of the errors and/or constrain selected steady state offsets to zero. Simulated and experimental data from a computer controlled pilot‐plant evaporator show that multivariable feedback‐plus‐feedforward control is relatively simple to implement, is practical, and gives excellent control.
The effect of angular light intensity distribution on the performance of tubular flow photoreactors
Authors: Zolner William J. , Williams John A. 
Published: June 2004

AbstractThe angular light intensity distribution (ALID) at the surface of several elliptical reflector‐photoreactors was determined experimentally using the optically dense potassium ferrioxalate actinometer. The distributions were well correlated by the model

The correlating parameter β was a function of the ratio of the light source and photoreactor tube diameters.The theoretical effect of ALID on reactor performance was determined for a reaction which proceeded via direct absorption by the reactant. The ALID effect on performance was most pronounced under conditions of high optical densities and low radial mixing rates of reactant.
A new model for granular porous media: Part II. Numerical solution of steady state incompressible Newtonian flow through periodically constricted tubes
Authors: Payatakes Alkiviades C. , Tien Chi , Turian Raffi M. 
Published: June 2004

AbstractA numerical method for the solution of the problem of steady state, incompressible Newtonian flow through periodically constricted tubes is developed. All terms of the Navier‐Stokes equation are retained, including the nonlinear inertia terms.Sample calculations for a uniform periodically constricted tube, the geometry of which is connected with the modeling of a packed bed of sand are given, including streamlines, axial and radial velocity profiles, pressure profiles, and the dimensionless pressure drop versus Reynolds number relation. The effect of some geometric characteristics of periodically constricted tubes on their friction factor is investigated numerically, and comparison of some existing experimental data with calculated ones is made.
An analysis of carrier‐facilitated transport
Authors: Smith Kenneth A. , Meldon Jerry H. , Colton Clark K. 
Published: June 2004

AbstractThe physical and mathematical characteristics of carrier‐facilitated transport in a liquid film are examined for a reaction scheme of the form A + B ⇄ AB, in which A is the permeating species and B and AB are diffusable species which are constrained not to leave the film. For thin films, a solution is developed as a perturbation from purely physical diffusion and is expressed as a second‐order power series. For thick films, a solution is developed as a perturbation from a state in which the species concentrations at any one point within the film are related by an equilibrium constraint. This development utilizes the techniques of matched asymptotic analysis. Taken together, these solutions provide an excellent estimate of the facilitation for a film of any thickness, as shown by comparison with numerical results.
Gasification: Part I. Isothermal, kinetic control model for a solid with a pore size distribution
Authors: Hashimoto Kenji , Silveston P. L. 
Published: June 2004

AbstractA model describing the development of specific surface area, volume, porosity, and mean pore radius of a porous solid with extent of gasification is developed based on consideration of pore size growth, initiation of new pores, and coalescence of adjacent pores. Use of population balances and formulation of the properties as moments of the pore size distribution leads to a mathematically simple, closed set of equations for kinetically controlled gasification. The model successfully predicts maximums in specific surface area and number of pores observed by Kawahata and Walker (1962) in the activation of devolatilized anthracite by CO2 in a fluidized bed.
The thermodynamic approach to fluidized drying and moistening optimization
Authors: Sieniutycz Stanislaw 
Published: June 2004

AbstractFor drying and moistening processes in batch fluidization and fluidization in a horizontal exchanger, the overall mathematical model describing simultaneous heat and mass exchange is given. On this basis, the problem of finding the optimal temperatures of inlet gas is formulated and investigated for the case when inlet gas humidity is constant. It is explained that when unit economical values of gas and solid phases are linear with regard to unit available energies (exergies), the economical problem of minimum costs is equivalent to the thermodynamical problem of minimum available energy (exergy) dissipation. Therefore, the performance index expression in exergy terms is formulated as a functional of the Bolza form. The dynamic programming method is used to obtain results of optimal trajectories and decisions. The dependence of optimal process time on apparatus price, which is characterized here by a Lagrangian multiplier λ, is pointed out.The results indicate that the constant gas inlet temperature policy commonly applied to the processes considered here prevents attainment of the process optimum. In fact, increasing inlet temperature until an admissible gas temperature is attained is the optimal policy.
Stability and uniqueness of a catalyst particle problem: Parameter optimization in Liapunov functions
Authors: Liou Ching‐Tien , Lim Henry C. , Weigand William A. 
Published: June 2004

AbstractIn the analysis of stability and uniqueness of steady state through the Liapunov functional technique, the Liapunov functional is not unique and different forms can lead to significantly different results. A method is proposed in which the state vector and/or the parameters in the weighting matrix S(x) are optimized to obtain less conservative results than those reported previously. For the problem of stability and uniqueness of the steady state of a chemical reaction occurring in a catalyst particle with slab geometry, several sufficient conditions for stability have been developed for both cases of unity and nonunity Lewis numbers in terms of the system parameters and steady state profiles, the system parameters and the catalyst center temperature, and the system parameters alone. These conditions are shown to be stronger than the previously reported results (Murphy and Crandall, 1970). Sufficient conditions for uniqueness have also been developed. For unity Lewis number our uniqueness condition is stronger than the previously reported result (Luss and Amundson, 1967), and for non‐unity Lewis number our uniqueness result is new.
An optimization algorithm for structured design systems
Authors: Westerberg Arthur W. , Debrosse Charles J. 
Published: June 2004

AbstractStructured design systems are systems which may be represented by generally nonlinear equality and inequality constraints, each of which contains few of the variables in the system. Assuming the existence of an automatic capabity to derive and modify as needed effective solution procedures for sets of structured equality constraints, a two‐step strategy for optimizing design systems is presented in the form of two algorithms. An earlier paper presented an algorithm for locating a first feasible point, and this paper presents a companion algorithm based on the strategy known as restriction to optimize the system once feasible.This companion algorithm divides the set of inequality constraints into three sets: the set of those currently being held as equality constraints, the set currently released but being used as search coordinates, and the set of all remaining constraints which are not currently part of the problem. Solution procedures are modified as inequality constraints and are moved from one set to another. Added constraints in the set being held tend to aid the optimization process by reducing the dimension of search space for what is usually a marginal added burden in solving an enlarged set of (structured) equations.The strategy has proved remarkably effective on three relatively simple examples, including a nonlinear 31 constraint, 10 variable alkylation problem.
A critical evaluation of methods for the prediction of critical properties of hydrocarbons
Authors: Spencer Calvin F. , Daubert Thomas E. 
Published: June 2004

AbstractA critical evaluation and modification of the available methods for the estimation of critical properties of pure hydrocarbons was undertaken to determine the most accurate method which has general applicability with minimum input data. As a result of the study, the method of Nokay as modified by the authors is recommended for the estimation of critical temperature while the method of Reidel is the best general method for critical volume. For critical pressure the Lydersen method is preferred for saturated hydrocarbons, while the method of Forman and Thodos is somewhat better for unsaturated hydrocarbons.
A critical review of correlations for the critical properties of defined mixtures
Authors: Spencer Calvin F. , Daubert Thomas E. , Danner Ronald P. 
Published: June 2004

AbstractAn extensive critical evaluation of available correlations for predicting critical properties of binary defined hydrocarbon as well as some multicomponent hydrocarbon and hydrocarbon‐nonhydrocarbon mixtures is presented using all available literature data. The Li method is recommended for critical temperature prediction based upon its accuracy and simplicity, although the Chueh‐Prausnitz method is equivalent in accuracy. The Kreglewski method is most accurate for critical pressure prediction. All methods evaluated yielded high errors for the critical properties of methane‐containing mixtures. Current correlations on critical volume are discussed, and correlational work on prediction using an excess volume approach is described.
Penetration of vapor jets submerged in subcooled liquids
Authors: Weimer J. C. , Faeth G. M. , Olson D. R. 
Published: June 2004

AbstractAn experimental investigation of the penetration distance required for complete condensation of a submerged turbulent vapor jet injected into a quiescent liquid bath of the same material was made. The bath was maintained in a subcooled condition at a temperature below the boiling temperature of the liquid at the bath pressure. The experiments were limited to choked injector Hows with the penetration regime such that buoyancy effects are negligible. Tests were run for water, ethylene glycol, and iso‐octane over a range of flow rates and bath pressures. A theoretical expression for the vapor penetration distance was developed utilizing a variable density single fluid model for the two‐phase flow, with the turbulent mixing process treated by an entrainment law. Corrections for the external expansion of the choked flow beyond the injector exit were also determined. This model was found to correlate the results of both the present experiments and those of earlier investigators over a wide range of operating conditions and injector geometries.
Volumetric properties of normal fluids at low temperatures: An extension of Pitzer's generalized correlation
Authors: Lu Benjamin C.‐Y. , Hsi Chu , Chang Shinn‐Der , Tsang Albert 
Published: June 2004

AbstractThe three‐parameter tabular correlation of Pitzer et al. for calculating the compressibility factor of pure components has been extended to lower temperatures in the region where Tr is from 0.5 to 0.80 and Pr is from 0 to 9. The compressibility‐factor is expressed linearly in the acentric factor Z = Z(0) + ωZ(1) with values of Z(0) and Z(1) tabulated in terms of Tr and Pr. The generalized correlation has been tested for 21 compounds with a total number of 463 data points. The average deviations in the calculated compressibility factors are 1.63% for the compressed liquids and 0.67% for the gases.
Catalytic oxidation of hydrogen chloride in a fluid bed reactor
Authors: Furusaki Shintaro 
Published: June 2004

AbstractThe Deacon reaction (HCI + 1/4 O2 ⇋ 1/2 Cl2 + 1/2 H2O) was studied in a catalytic fluid bed reactor. Reaction rates found from measurements in differential and integral reactors were represented by the Langmuir‐Hinshelwood type rate equation. Considering the effect of catalysts in the dilute phase, it was found that conversions in a fluid bed reactor can be calculated without any modifying parameters. It is pointed out that the wake fraction, which has been necessary to consider for fast reactions in a fluid bed reactor, is attributed to the dilute phase effect.
Gas chromatographic determination of thermodynamic properties of polymer solutions at high pressure
Authors: Brockmeier Norman F. , Carlson Ronald E. , McCoy Robert W. 
Published: June 2004

AbstractThe gas chromatographic (GC) method for thermodynamic measurements of polymer‐solvent systems at finite concentration has been improved to extend its operating range from atmospheric pressure to over 70 atm and over 240°C. This paper describes the design and opertion of the equipment and the mathematical treatment of the GC data, and presents experimental results for n‐hexane and isooctane in high density polyethylene. These results include the solubility isotherms, activity coefficients, and polymer‐solvent interaction parameters. The activity coefficients covering a range from 4 to 70 atm for n‐hexane in the polymer solution were correlated successfully as a function of composition using a two‐parameter segment interaction equation.
A theoretical model for enzymatic catalysis using asymmetric hollow fiber membranes
Authors: Waterland Larry R. , Michaels Alan S. , Robertson Channing R. 
Published: June 2004

AbstractThe behavior of an immobilized enzyme reactor utilizing asymmetric hollow fibers is simulated using a theoretical model. In this reactor, an enzyme solution contained within the annular open‐cell porous support structure of the fiber is separated from a substrate flowing through the fiber lumen by an ultrathin dense membrane impermeable to enzyme but permeable to substrate and product. The coupled set of model equations describing the behavior of this reactor represents an extended Graetz problem in the fiber lumen, with diffusion through the ultrathin fiber skin and reaction in the microporous sponge region. Exact analytic expressions for substrate concentration profiles throughout an idealized fiber which incorporate the membrane and hydrodynamic mass transfer resistances are obtained for a first‐order enzyme reaction, and numerical techniques for their evaluation are given. This analysis is extended to yield a numerical finite difference solution for nonlinear Michaelis‐Menten reaction kinetics, which is shown to agree with the analytic solution, as Km/C0, the ratio of the Michaelis constant to the initial substrate concentration, becomes large (> 100).
On the oxidation of fuel nitrogen in a diffusion flame
Authors: Sternling C. V. , Wendt J. O. L. 
Published: June 2004

AbstractThe kinetic mechanisms of fuel nitrogen conversion to NO and N2 in a diffusion flame were investigated. A simple model of a diffusion flame in which the reaction zone has a finite thickness was developed. The purpose of this model was to allow the testing of complex kinetic mechanisms of pollutant formation under conditions where the fuel and oxidant feed rates are controlled by diffusion. A simple kinetic mechanism in which fuel nitrogen was simulated by nitrogen atoms showed the correct functional dependence of nitric oxide emissions on fuel nitrogen content. The model also predicts a significant effect of combustion intensity and temperature on fuel nitrogen conversion. For the hydrogen air diffusion flame the Zeldovich reaction mechanism could account for the production of N2 as well as NO.
Steady state multiplicity and stability in an adiabatic controlled cycled stirred tank reactor
Authors: Ausikaitis J. , Engel A. J. 
Published: June 2004

AbstractSteady state multiplicity in exothermic adiabatic reaction systems has previously been demonstrated by a number of authors. Specifically, the work of Root and Schmitz proved the existence of multiple steady states in a loop reactor, but difficulty was encountered in controlling such a reaction system at the intermediate steady states.Since a close analogy can be demonstrated between loop reactors and controlled cycled reactors (CCTR), it appeared reasonable to attempt to achieve steady state multiplicity in a CCTR. When the chemical reaction of Root and Schmitz was carried out in a CCTR, it proved relatively easy to obtain experimental values of intermediate steady statesf and to control the reactor at these conditions by means of a simple on‐off temperature controller.This work suggests that chemical systems displaying steady state multiplicity can be experimentally investigated in a CCTR and that cyclic operation may be the best way for controlling such reactions systems.
Fully developed viscous—flow heat transfer in curved circular tubes with uniform wall temperature
Authors: Kalb Charles E. , Seader J. D. 
Published: June 2004

AbstractFully developed forced‐convective heat transfer to viscous flow of a constant‐property Newtonian fluid in curved circular tubes was studied theoretically for a uniform‐wall‐temperature boundary condition. Numerical solutions were obtained over a wide range of Prandtl numbers for Dean numbers as large as 1,200. The curvature ratio (radius of bend/inside radius of tube) was included as an independent parameter and, for values as small as 10, was found to have a negligible effect on the peripherally averaged Nusselt number. The average Nusselt numbers for the important Prandtl number range of 0.7 to 5 were correlated by NNu = 0.836 NDe0.5 NPr0.1 for NDe ≥ 80.
Carbon dioxide‐ethane phase equilibrium and densities from experimental measurements and the B‐W‐R equation
Authors: Gugnoni R. J. , Eldridge J. W. , Okay V. C. , Lee T. J. 
Published: June 2004

AbstractLiquid composition‐total pressure and liquid composition‐liquid density data for the carbon dioxide‐ethane system were measured at −31.7°, −17.8°, −3.9°, and 10.0°C (−25°, 0°, 25°, and 50°F ± 0.02°F), from 0 to 80 mole % CO2 at 10°C and 0 to 100% CO2 for the other isotherms. The Benedict‐Webb‐Rubin equation of state with a modified A0 mixing rule was used to correlate the composition‐pressure data, with deviations in predicted pressures of only 0.8% average and 2% maximum. Vapor‐liquid equilibrium compositions and component K values y/x were then predicted for this minimum boiling azeotrope system from 10° down to −56.7°C (50° to −70°F).
Effect of diffusional limitations on lineweaver‐burk plots for immobilized enzymes
Authors: Hamilton Bruce K. , Gardner Colin R. , Colton Clark K. 
Published: June 2004

AbstractLineweaver‐Burk plots of reaction rate data obtained with immobilized enzymes need not be linear even when intrinsic enzyme kinetics follow the simple Michaelis‐Menten rate expression. Theoretical calculations show that mass transfer effects may cause curvature which is concave or convex to the abscissa, depending upon experimental conditions. Consequently, graphical procedures commonly employed for analysis of soluble enzyme kinetics may yield misleading results when applied to immobilized enzymes. Three approaches which follow from the behavior of numerical and asymptotic solutions to the problem are proposed for extraction of intrinsic kinetic information.