bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonideal multicomponent distillation: Use of bifurcation theory for design
Authors: Fidkowski Z. T. , Malone M. F. , Doherty M. F. 
Published: June 2004

AbstractA method for the design of distillation systems for nonideal multicomponent mixtures is described, offering an alternative to extensive performance simulations. The basis is an analysis of the pinches or “fixed points” in the model equations and the results are widely applicable because approximations such as constant volatilities and ideal solutions are unnecessary. Tangent pinches are represented naturally as turning points in the diagram of pinch composition vs. reflux ratio, giving a basis for designs that alleviate the effects of tangent pinches in certain nonideal mixtures. An efficient computational approach for design is demonstrated in examples for homogeneous liquid mixtures, containing as many as four components, with and without azeotropic behavior. The results are in excellent agreement with detailed performance simulations.
Particle‐to‐bubble adhesion in gas/liquid/solid slurries
Authors: Vinke H. , Hamersma P. J. , Fortuin J. M. H. 
Published: June 2004

AbstractIn gas/liquid/solid slurries, adhesion of small particles to gas bubbles is often encountered, for example, during flotation of finely divided minerals and in slurry reactors where particle‐to‐bubble adhesion may result in an enhanced gas absorption rate (Wimmers, 1987; Lindner, 1988). The adhesion of small particles to gas bubbles in water is studied with a modified bubble pick‐up method. The extent of the particle‐to‐bubble adhesion is revealed in the angle αmax, by which the gas‐bubble surface is covered by adhering particles under static conditions. It is shown that αmax depends on the modified Eötvös number, the ratio of the particle and bubble radii, and the effective contact angle θE. It is also found that θE is affected by the curvature of the three‐phase contact ring and by the type of the gas.A “particle‐to‐bubble adhesion” model, indicated by PBA model, based on a balance of forces under static conditions, is developed to calculate the value of θE from the measured values of αmax. The measured values of cos(θE) appeared to be a linear function of the curvature 1/r of the three‐phase contact ring which is in accordance with the extended Young‐Dupré equation.
Hydrodynamics in a cocurrent gas‐liquid trickle bed at elevated pressures
Authors: Wammes W. J. A. , Middelkamp J. , Huisman W. J. , DeBass C. M. , Westerterp K. R. 
Published: June 2004

AbstractData on design and operation of trickle beds at elevated pressures are scarce. In this study the influence of the gas density on the liquid holdup, the pressure drop, and the transition between trickle and pulse flow has been investigated in a tricklebed reactor operating up to 7.5 MPa and with nitrogen or helium as the gas phase. Gas–liquid interfacial areas have been determined up to 5.0 MPa by means of CO2 absorption from CO2/N2 gas mixtures into amine solutions.A comparison of the results from nitrogen as the gas phase to those of helium shows that at equal gas densities the hydrodynamic states are the same. The gas‐liquid interfacial area increases when operating at higher gas densities. When the determined dimensionless interfacial areas agl/as are all within the range 0.25–0.8, the trickle‐bed reactor is suggested to operate in the trickle‐flow regime. The gas density has a strong influence on the liquid holdup. Due to the higher pressure gradients at elevated gas densities, the liquid holdup decreases noticeably. Besides, the boundary between the trickle‐flow and pulse‐flow regime shifts toward higher liquid throughputs: the region for trickle‐flow operationg becomes larger. For the liquid holdup and the pressure gradient in the trickle‐flow regime, correlations derived based on dimensionless numbers can be applied to high‐prssure trickle beds.
Generalized approach toward modeling resist performance
Authors: Ziger David H. , Mack Chris A. 
Published: June 2004

AbstractA generalized technique for modeling resist performance is outlined. In this approach, the fraction of resist remaining after development as a function of incident dose, or characteristic curve, is related to the development rate which is assumed to be a power law of a dominant soluble species. Soluble species are either photochemically consumed for negative resists or generated for positive. Expressions for the dependence of characteristic curves on exposure dose and chemistry are derived for various resist systems, which are consistent with current models. For similar chemical kinetics, negative resists yield fewer lumped parameters to describe their development rate and characteristic curves than positive.Under conditions of negligible surface inhibition, lumped parameters can be extracted from characteristic curves and used to simulate lithography. A generalized method to correct for absorption in the resist and reflections is outlined. Exposure latitude was accurately predicted for a commercial negative chemically amplified resist. However, prediction of linewidths from characteristic curves of positive resists is complicated by surface inhibition effects.
Continuous process improvement through inductive and analogical learning
Authors: Saraiva Pedro M. , Stephanopoulos George 
Published: June 2004

AbstractThis article presents a methodology for the continuous detection and definition of process performance improvement opportunities, especially as these pertain to the quality of operations (such as product quality). The problem is first reduced to an essentially pattern recognition formulation, for which an integrated and adaptive methodology combining analogical reasoning and symbolic induction is developed. The resulting classification of past records of data is used to support the construction of a decision support system for the generation/selection of operating suggestions leadin to performance improvements. The overall approach complements the usual set of statistical tools, commonly employed to address quality management problems. The basic methodology is also extended to handle fuzzy class definitions and function learning formulations. Case studies, covering both simulated and real industrial situations, illustrate the concepts and their practical utility.
A new scheme combining neural feedforward control with model‐predictive control
Authors: Lee Moonyong , Park Sunwon 
Published: June 2004

AbstractA new control scheme is presented for feedforward control of unknown disturbances in the model‐predictive control (MPC) scheme. In this control scheme, a neural network is connected in parallel with the MPC controller and trained online by minimizing the MPC controller output corresponding to the unmodeled effect. It is applied to distillation column control and nonlinear reactor control to illustrate its effectiveness. The result shows that the neural feedforward controller can cope well with strong interactions, time delays, nonlinearities, and process/model mismatch. The controller also offers such advantages as fault tolerance, generalization capability by interpolation, and learning capability by randdom input patterns.
Investigation of amorphous oxide film‐electrolyte junctions by AC techniques
Authors: Piazza S. , Sunseri C. , Di Quarto F. 
Published: June 2004

AbstractCurrent AC (alternating current) techniques are used often to characterize the energetics at a semiconducting solid phase/electrolyte interface. For thin layers having a strongly disordered or amorphous structure (such as oxide‐passive layers anodically grown on valve metals), interpretative models currently used for crystalline semiconductors may produce misleading data.A new interpretation of the admittance data, based on recent models for amorphous semiconductors (a‐Sc) Schottky barriers, is presented for passive films of Nb, W and Ti. The physical bases of the model are presented as well as its advantages and disadvantages. The new theory views the solid/electrolyte interface more satisfactorily and provides information on the solid‐state properties and the electronic structure of the electrode useful for interpreting the electron exchange between the solid phase and redox couples in solution.
Kinetics of COS with primary and secondary amines in aqueous solutions
Authors: Littel R. J. , Versteeg G. F. , van Swaaij W. P. M. 
Published: June 2004

AbstractThe reaction between COS and aqueous solutions of primary and secondary amines has been studied by means of the stirred cell technique. Kinetic experiments at temperatures 283 to 333 K were carried out with MEA, DGA, DEA, DIPA, MMEA, AMP, and MOR. All kinetic experiments could be described by a zwitterion reaction mechanism similar to the mechanism proposed by Caplow (1968) for the reaction between CO2 and secondary amines:

Analysis of concentrated amine solutions at high COS concentrations by various analytical techniques confirmed the conclusions from the kinetic experiments. For all amines except for MEA, the overall reaction rate was found to be determined entirely by the zwitterion deprotonation rate.
Temperature oscillations and vibrations of AC resistively heated thin filaments
Authors: Viljoen H. J. , Hlavacek V. 
Published: June 2004

AbstractResistively heated filaments are used to deposit diamond or to act as a substrate in the manufacture of ceramic fibers. This article analyzes the effects of an AC power source, in particular the oscillation in filament temperature and its influence on the kinetic rates, as well as the vibration of the filament, when it is mounted in a state of tensile stress. These effects diminish when the filament gauge is large enough and the analysis can help to decide whether an AC or a DC power source should be used.
Kinetics of phenol oxidation in supercritical water
Authors: Thornton Thomas D. , Savage Phillip E. 
Published: June 2004

AbstractAqueous solutions of phenol were oxidized in a flow reactor at temperatures between 300 and 420°C (0.89 ⩽ Tr ⩽ 1.07) and pressures from 188 to 278 atm (0.86 ⩽ Pr ⩽ 1.27). These conditions included oxidations in both near‐critical and supercritical water. Reactor residence times ranged from 1.2 to 111 s. The initial phenol concentrations were between 50 and 330 ppm by mass, and the initial oxygen concentrations ranged from 0 to 1,100% excess. The oxidation experiments covered essentially the entire range of phenol conversions. Analysis of the kinetics data for phenol disappearance using a combination of the integral method and the method of excess revealed that the reaction was first order in phenol and 1/2 order in oxygen, and influenced by pressure. The global reaction order for water was taken to be nonzero, and the global rate constant was assumed to be independent of pressure so that the only effect of pressure was to alter the water concentration and hence the reaction rate. This approach led to a global reaction rate law that was 0.7 order in water and had a rate constant with an activation energy of 12.4 kcal/mol. The implications of these rate laws to the design of a commercial supercritical water oxidation reactor are also explored.
Transfer processes in turbulent pipe flow described by the ERSR model
Authors: Fortuin Jan M. H. , Musschenga Edward E. , Hamersma Peter J. 
Published: June 2004

AbstractA model is presented for a quantitative prediction of the transfer rates of momentum, heat and mass in turbulent pipe flow. In this so‐called extended random surface renewal (ERSR) model, the tube wall is assumed to be covered by a mosaic of fluid elements of random age and laminar flow with unsteady profiles of axial velocity, temperature or concentration.Both the age distribution and the mean age of the fluid elements at the tube wall, predicted by the ERSR model, quantitatively agree with experimental results obtained from velocity signals measured with a laser‐Doppler anemometer at 5·103⩽Re⩽43·103. The time‐averaged radial profiles of the axial velocity, the temperature and the concentration in the wall region, and the heat‐ and mass‐transfer coefficients derived with the ERSR model agree with empirical results presented in literature. Furthermore, the ERSR model provides a basis for explaining the Chilton‐Colburn analogy.
Single‐pellet cell for the measurement of intraparticle diffusion and convection
Authors: Lu Z. P. , Loureiro J. M. , Rodrigues A. E. 
Published: June 2004

AbstractDynamic analysis of single‐pellet cell for the measurement of diffusion and convection in porous catalysts is revisited. A complete mathematical model for the “diffusion‐convection” cell is solved, and the relation between zero‐and first‐order moments of the cell response and operating parameters is derived. The validity region of the “simplified” boundary condition at the bottom of the pellet is quantified. The effect of the operating parameters on the cell time response to a tracer impulse is analyzed to check the practical range of operation of the system. It also is compared with the chromatographic technique.
CVD of solid oxides in porous substrates for ceramic membrane modification
Authors: Lin Y. S. , Burggraaf A. J. 
Published: June 2004

AbstractThe deposition of yttria‐doped zirconia has been experimented systematically in various types of porous ceramic substrates by a modified chemical vapor deposition (CVD) process operating in an opposing reactant geometry using water vapor and corresponding metal chloride vapors as reactants. The effects of substrate pore dimension and structure, bulk‐phase reactant concentration, reactant diffusivity in substrate pores and deposition temperature are experimentally studied and explained qualitatively by a theoretical modeling analysis. The experimental and theoretical results suggest a reaction mechanism which depends on water vapor and chloride vapor concentrations. Consequently, the diffusivity, bulk‐phase reactant concentration, and substrate pore dimension are important in the CVD process. Effects of deposition temperature on the deposition results and narrow deposition zone compared to the substrate thickness also suggest a Langmuir‐Hinshelwood reaction mechanism involved in the CVD process with a very fast CVD reaction rate. Gas permeation data indicate that whether deposition of solid in substrate pores could result in the pore‐size reduction depends strongly on the initial pore‐size distribution of the substrate.
Spin coating of colloidal suspensions
Authors: Rehg Timothy J. , Higgins G. 
Published: June 2004

AbstractThe coupled, unsteady Navier‐Stokes, convective diffusion, and thermal energy equations that describe spin coating of colloidal suspensions are solved numerically. The theoretical model, absent of any adjustable parameters, is used to explore the effects of angular velocity, initial solvent weight fraction, solvent properties and spin coating protocol on the evolution of temperature and concentration profiles in the liquid film during spin coating. The predicted coated film thickness is found to be in excellent quantitative agreement with spin coating experiments performed with both hard‐sphere and nonhard‐sphere suspensions of monodisperse latex particles in water. The coated film thickness, determined by ellipsometry, is shown to depend on the inverse square root of the angular velocity except at high ionic strength when the dependence on angular velocity is weaker. Timescales that characterize spin coating of colloidal suspensions are shown to be quite different from those that characterize spin coating of polymer solutions, and consequently simple models for predicting the coated film thickness of polymer solutions (Bornside et al., 1991; Lawrence, 1989) are shown to be inadequate for colloidal suspensions. Rapid substrate acceleration, high rotation rates, partial saturation of the overlying gas phase, and high initial solids concentration are identified as spin coating protocols that suppress a convective instability that produces radial striations in the coated film.
Phase equilibria in the system water‐methyldiethanolamine‐propane
Authors: Carroll John J. , Jou Fang‐Yuan , Mather Alan E. , Otto Frederick D. 
Published: June 2004

AbstractAqueous solutions of alkanolamines are commonly used to strip acid gases (CO2 H2S) from hydrocarbon streams. Processes for stripping acid gases from gaseous streams are well understood; however, the application to liquids is not as advanced. Experimental data available are scarce for systems containing aqueous amine solutions and the constituents of liquefied petroleum gases. To this end, new data are presented for the equilibria in the system propane–water–methyldiethanolamine (MDEA). A knowledge of the phase behavior in this system is required to model the equilibria encountered in the more complex systems of industrial importance.This work is a comprehensive study of the phase equilibria in the system propane–3 M MDEA, including vapor–liquid, liquid–liquid, and vapor–liquid–liquid equilibria. Experimental measurements were made for temperatures between 0 and 150°C and pressures up to 20 MPa. The data were correlated using the Stryjek‐Vera modification of the Peng‐Robinson equation of state. In addition, a composition‐dependent mixing rule was required to fit the data adequately.
Relative disturbance gain array
Authors: Chang Jin‐Wen , Yu Cheng‐Ching 
Published: June 2004

AbstractDisturbance rejection capabilities of different controller structures, for example, diagonal, block diagonal or full multivariable controller, are discussed. A generalized version of Relative Disturbance Gain, Generalized Relative Disturbance Gain (GRDG), is defined to evaluate the disturbance rejection capabilities of all possible controller structures. Furthermore, the relative disturbance gain array (RDGA) is introduced. Basic properties of RDGA are derived. An important one is: GRDG of all possible controller structures can be calculated directly from the array. Therefore, with RDGA, the synthesis of the controller structure can be done in a straightforward manner. Physical implications and quantitative analyses of GRDG are given. These form the basis for the synthesis. Finally, frequency‐dependent GRDG is developed which evaluates the performance further based on dynamic information. Several examples are used to illustrate the synthesis of the controller structure. The results show that better disturbance rejection can be achieved by selecting appropriate controller structure.
Natural tracking PID process control for exponential tracking
Authors: Grujić Ljubomir T. , Mounfield William Pratt 
Published: June 2004

AbstractTo cope with modeling uncertainties and randomness of external disturbances, a new tracking control called the natural control concept is designed. Its implementation is completely independent of the internal dynamics of a controlled system, its desired output and external disturbances. The design algorithm established ensures a prespecified exponential quality of output tracking. The theory presented in this article is applied effectively to the design of natural tracking control for a chemical reaction process described by the fourth‐order, linear, state‐space mathematical model.
Unbiased estimation of gross errors in process measurements
Authors: Rollins D. K. , Davis J. F. 
Published: June 2004

AbstractA new approach to gross error detection provides unbiased estimates and 100(1‐α)% simultaneous confidence intervals of process variables when biased process measurements and process leaks exist. Presented in this article are estimation equations for process variables, as well as equations that help identify biased measurements and process leaks. These equations include the power function for a global test, and two types of α‐level component tests and their power functions. Important strengths and weaknesses of this approach are compared to those of the serial compensation strategy, in particular, by varying the significance level (α), the variance‐covariance matrix (Σ), the size of measurement bias (δ), the number of biased variables, and the sample size (N). Accuracy of δ estimation and performance in detecting the presence of process leaks (γ) are also evaluated and compared. The proposed approach has unique features that can provide a basis for improving the reconciliation of variables in process operations.
Correlation of fractionation tray performance via a cross‐flow boundary‐layer model
Authors: Young Thomas C. , Stewart Warren E. 
Published: June 2004

AbstractThe nonequilibrium tray model proposed by Young and Stewart (1990) is used to correlate published fractionation data from sieve tray columns 0.45 m to 1.2 m in diameter. The model contains a dimensionless coefficient a00 to describe the interphase heat and mass transfer, and a Peclet number Pe to describe the lateral mixing of the liquid on the tray. The coefficient a00 is investigated as a function of tray geometry and hydrodynamic variables, using an error‐in‐variables extension of a multiresponse parameter estimation algorithm. Data from several sources are well correlated by a simple dimensionless relation for a00, with Pe predicted from the results of Bennett and associates (1983, 1991).
Influence of tube and particle diameter on heat transport in packed beds
Authors: Borkink J. G. H. , Westerterp K. R. 
Published: June 2004

AbstractInfluence of the tube and particle diameter and shape, as well as their ratio, on the radial heat transport in packed beds has been studied. Heat transport experiments were performed with four different packings in three wall‐cooled tubes, which differed in inner diameter only. Experimental values for the effective radial heat conductivity and wall heat‐transfer coefficient for the pseudo‐homogeneous two‐dimensional model and the overall heat‐transfer coefficient for the one‐dimensional model are presented. Values were obtained for glass spheres, alumina cylinders, and alumina Raschig rings. The effective radial heat conductivity and wall heat‐transfer coefficient can both be correlated as a linear function of the gas flow rate. The Bodenstein number for heat at fully developed turbulent flow is influenced strongly by the shape of the packing: 10.9 for glass spheres, 7.6 for alumina cylinders, and 4.2 for alumina Raschig rings. For the same packing, no significant influence is found of the tube diameter on the effective radial heat conductivity or on the wall heat‐transfer coefficient. The overall heat‐transfer coefficient can be described very well by the so‐called “lump equation,” which gives the relations among the overall heat‐transfer coefficient, effective radial heat conductivity, and wall heat‐transfer coefficient. The “lump factor,” as used in the lump equation, has a best‐fit experimental value of 7.4.
Venting of runaway reactions with gas generation
Authors: Leung Joseph C. 
Published: June 2004

AbstractPressure relief venting of a runway reaction with gas generation is examined in terms of the overall system response and the associated venting requirement. This article presents an exact formulation as well as an approximate analytical approach. The latter is shown to be particularly useful in vent‐sizing applications. Using an aqueous hydrogen peroxide decomposition example, the analytical results are demonstrated to agree well with the exact numerical results over a wide range of overpressure. In addition, the analytical result is shown to reduce to the correct limit for a pure vapor system and offers a useful vent‐sizing equation for a pure‐gassy system.