bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control of high‐purity distillation column using a nonlinear wave theory
Authors: Han Myungwan , Park Sunwon 
Published: June 2004

AbstractA new model‐based controller for profile position control of high‐purity distillation columns is presented. The controller has been developed by incorporating nonlinear wave model into the generic model control framework. An observer based on the nonlinear wave theory is also proposed to determine the profile position. The performance of the nonlinear control scheme has been tested in simulation experiments of high‐purity binary distillation columns. Tight control of profile position, which leads to fast stabilization of product compositions, has been achieved. Since the profile position control alone produces a slight offset from the desired product concentration, the composition/profile position cascade system has been used to remove the offset. The control scheme can handle significant disturbances and model‐plant mismatch.
Sensor network design for maximizing reliability of linear processes
Authors: Ali Yaqoob , Narasimhan Shankar 
Published: June 2004

AbstractA new concept of reliability of estimation of variables is introduced which relates to the estimability of variables in the presence of sensor failures. Based on this concept, a method for optimal location of sensors in a pure flow process is developed. A graph‐theoretic algorithm, SENNET, developed for this purpose, is shown to perform robustly and give globally optimum solutions for realistic processes.
Combined effects of mass transfer and inaccessible porosity in gasification reactions
Authors: Delikouras Evangelos A. , Perlmutter Daniel D. 
Published: June 2004

AbstractThe effect of inaccessible porosity on the rate of gasification reactions is illustrated under conditions where intraparticle and extraparticle resistances to mass transfer are significant. The mathematical model developed here is based on a mass balance for the reactant fluid in the porous particle, coupled with an appropriate structural model developed for the kinetics‐controlled case (Delikouras and Perlmutter, 1991). It is demonstrated numerically that the effects of inaccessible porosity generally diminish with increased diffusional resistances. In agreement with the prior kineticscontrolled case, it is shown that the effects of inaccessible porosity are more pronounced at lower values of the structural parameter ψ and at greater levels of the inaccessible fraction.
Lattice thermodynamics for binary closed‐loop equilibria: Ordinary and polymer systems
Authors: Hino Toshiaki , Lambert Stephen M. , Soane David S. , Prausnitz John M. 
Published: June 2004

AbstractThe incompressible lattice‐gas model by ten Brinke and Karasz is adopted to introduce the effect of specific interactions into a recently‐presented Monte‐Carlobased lattice expression for the Helmholtz energy of nonrandom mixing. While the lattice remains incompressible, intermolecular forces consist of two types: London dispersion forces and specific (chemical) forces. The specific interactions between similar components, as well as those between dissimilar components, are incorporated in a systematic manner. Closed‐loop temperature‐composition phase diagrams are obtained. The theory is compared with experimental data for several binary systems, including polymer solutions, which exhibit closed‐loop coexistence curves. Theoretical and experimental results are in good agreement.
Hydrodynamic cleaning of a viscous film from the inside of a long tube
Authors: Mickaily Elizabeth S. , Middleman Stanley 
Published: June 2004

AbstractA simple fluid dynamic model is developed which predicts the thinning rate of a viscous film of liquid, in contact with the smooth interior surface of a long cylindrical tube, due to the shearing action of a turbulent flow of an immiscible fluid through the tube. Experiments indicate the degree to which the model provides an accurate means of predicting viscous film removal from the tube. Similar experiments performed with electrochemically roughened tubes elucidate the limitation of this cleaning process due to surface roughness. The observed limitation is consistent with an analysis based on numerical solutions of the equations for shear flow over a rough surface.
Dynamic effects of vaporization with exothermic reaction in a porous catalytic pellet
Authors: Watson Paul C. , Harold Michael P. 
Published: June 2004

AbstractA single catalytic pellet reactor was used to investigate dynamic multiphase reaction‐transport interactions. The experiments permitted the simultaneous measurement of pellet weight(liquid holdup) and center temperature under conditions which mimic the unsteady, local events within a fixed‐bed multiphase reactor. In the liquid‐prefilled pellet experiments, the pellet (Pd/Al2O3‐clay) was prefilled with liquid reactant (AMS or cyclohexene) and then exposed to a flowing gas containing hydrogen. In the gas‐prefilled pellet experiments, the pellet was prefilled with hydrogen and then contacted by a liquid reactant pulse of prescribed flow rate and duration. The liquid‐prefilled experiments revealed an acceleration in the drying rate due to the exothermic reaction. The pore emptying process was accompanied by a significant increase in the pellet temperature. The considerably slower dynamics observed for the AMS system compared to the cyclohexene system are attributed both to differences in liquid‐phase volatility and to self‐oligimerization of the AMS. In the gas‐prefilled experiments, a pore filling with reaction process precedes the pore emptying step. The degree of catalyst overheating is highest for a liquid pulse of intermediate duration. A phenomenological mechanism of drying with exothermic reaction built on the well‐accepted theory of drying of granular media is offered to explain the trends in the data. Implications of the findings with regards to hot spot formation in the catalytic reactor are discussed.
The effect of solid interaction forces on pneumatic handling of sorbent powders
Authors: Lee Rhonda J. , Fan L.‐S. 
Published: June 2004

AbstractThis study shows that a comparison of powder characteristics–‐particle morphologies, particle size distributions, and static dielectric and Hamaker constants–‐can be used to interpret differences in dispersion and transport behavior between powders. These differences are attributed to the relative values of the solid‐solid interaction forces experienced by each powder in the process. The static dielectric constants of the powders are used as the material properties related to the relative magnitudes of the electrostatic forces. Similarly, the Hamaker constants are the material properties used to indicate the relative magnitudes of the van der Waals forces. The effects of differences in particle morphologies and size distributions are used to evaluate the dispersibility and efficiency of transport of four calcium‐based powder materials used as sorbents in flue‐gas desulfurization.
A model for gas‐liquid slug flow at reduced gravity conditions
Authors: Janicot Antoine , Dukler Abraham E. 
Published: June 2004

AbstractThe gas‐liquid slug flow pattern exists over a broad range of flow rate space at reduced gravity conditions and for that reason is expected to be widespread in many space applications. The objective of this work was to develop a model predicting the characteristics of slug flow at reduced gravity including the bubble length, shape, velocity and other properties of the slug flow. Observations derived from low‐gravity experiments suggested the use of a boundary layer‐type approach. Multiple solutions exist, and a criterion for selecting the solution which corresponds to experimental observation is indicated.
Momentum transfer across fluid‐fluid interfaces in porous media: A network model
Authors: Goode P. A. , Ramakrishnan T. S. 
Published: June 2004

AbstractTwo‐phase flow in porous media is described based on the extended form of Darcy's law, which ignores momentum transfer at fluid‐fluid interfaces. Two forms of corrections to this simple description have been proposed in the literature: one on the relative permeability dependence on viscosity ratio; the other on the velocities assumed to be proportional to both phase pressure gradients and so introducing an additional saturation‐dependent cross coefficient.In this article, to identify the correct form of transport equations, a simple cubic network model of 30 × 30 × 30 bonds is used. The cross section of the bonds is that of a four‐cusp duct. The fluid interface in each duct is located by capillary equilibrium. The duct hydraulic conductances are then obtained as a function of viscosity ratio and phase volume fraction using a finite element calculation. These individual duct results are used in the network calculations for which a percolation algorithm is applied to simulate nonwetting phase displacing wetting phase, a process also known as initial drainage. Flow calculations show that both the nonwetting‐phase relative permeability and the cross coefficient are strong functions of saturation and viscosity ratio. Also, the off‐diagonal terms may contribute to a nonnegligible fraction of the flow. The proposed generalization of the Darcy equations is applicable to all problems involving multiphase flow in porous media. The current practices for relative permeability measurements and reservoir simulation may have to be reexamined in the context of the proposed transport equations.
CO2/CH4 separation by facilitated transport in amine‐polyethylene glycol mixtures
Authors: Davis Richard A. , Sandall Orville C. 
Published: June 2004

AbstractIn this work, the separation of carbon dioxide from methane by reactive liquid membranes consisting of the secondary amines, diethanolamine, and diisopropanolamine in polyethylene glycol with an average molecular weight of 400 was studied. A mathematical model was developed to describe the transport process. This model employs the zwitterion mechanism for the CO2 amine reaction kinetics. Membrane flux experiments utilizing a flat plate device were carried out to verify the model predictions. It was found that large permeabilities and separations were achieved for low CO2 feed concentrations. The results also show that DEA based solutions give better separation than DIPA based solutions.
Simulation of a multiple substrate reactor for chemical vapor infiltration of pyrolytic carbon within carbon‐carbon composites
Authors: McAllister P. , Wolf E. E. 
Published: June 2004

AbstractA model for a pilot‐scale chemical vapor infiltration (CVI) reactor in which multiple substrates are densified simultaneously by carbon deposition from a pyrolyzing hydrocarbon is presented. Kinetic expressions and parameters and transport properties for carbon deposition from propylene determined from experimental studies and a single substrate CVI model are incorporated into the pilot reactor model. The two‐dimensional transport equations for heat, mass and momentum transfer are solved for the entire reactor to simulate the effects of varied operating conditions on substrate densification throughout the reactor during the CVI process. Of the conditions simulated, the reactor temperature was found to have the most significant impact on both the uniformity of densification and the process time required. As the temperature increased, the uniformity of densification decreased and the time at which pore blockage at the outer surface occurred was shortened. Increasing the hydrocarbon feed concentration shortened the process time, but did not affect the final level of densification, while the feed rate only affected CVI at intermediate times. Comparison between experimental pilot reactor results and model predictions were satisfactory at short and long times, but agreement was less satisfactory at intermediate times.
Nucleation mechanisms and particle size distributions of polymer colloids
Authors: Giannetti Enzo 
Published: June 2004

AbstractA theoretical model is developed for the time evolution of volume particle size distributions (PSDs) of polymer colloids during the nucleation stage. Analytic expressions for the PSD and related cumulants are presented. Negatively skewed distributions are observed only when the formation rate of mature latex particles is a monotonically decreasing function of time. When this model is tested against experimental PSD data of styrene polymerization at 50°C, agreement between theory and experiment is found only assuming a monotonically decreasing nucleation rate. The fitting is completely missed when the production rate of mature latex particles is predicted according to the coagulative nucleation scheme. Theory and experiment can combine introducing an extended coagulative nucleation model. According to this approach, the nucleation time is much shorter than predicted by earlier theories. As a consequence, most of the mechanistic information convoluted with early‐time PSDs is lost.
Gas‐Particle flow in a duct of arbitrary inclination with particle‐particle interactions
Authors: Ocone R. , Sundaresan S. , Jackson R. 
Published: June 2004

AbstractEarlier work of Sinclair and Jackson on the flow of gas‐particle suspensions in vertical pipes is extended to the case of ducts of arbitrary inclination. As a result of the compaction due to gravity, it is necessary to take into account forces transmitted between particles at points of sustained, rolling and sliding contact, and a simple frictional model of this contribution to the stress is introduced. The resulting theory is shown to predict fully developed flows with the qualitative features to be expected, even in horizontal ducts. The effects of flow rates, duct inclination, and duct width on the solution are explored.
Static instability analysis of circulating fluidized beds and concept of high‐density risers
Authors: Bi Hsiaotao , Zhu Jingxu 
Published: June 2004

AbstractAn instability analysis has been carried out to elucidate the unsteady flow conditions encountered in the typical circulating fluidized bed units in light of the conveyor‐solids feeder interaction. The results successfully predict the critical velocity and the maximum solids circulation rates reported in the literature and explain the origin of such unstable conditions. Furthermore, the simulation, for the first time, reveals the importance of unit structure in improving the performance of circulating fluidized bed systems. Finally, the concept of a high‐density circulating fluidized bed is proposed.
Unbiased estimation in dynamic data reconciliation
Authors: Rollins Derrick K. , Devanathan Sriram 
Published: June 2004

AbstractA computationally fast technique accurately estimates process variables when conditions are dynamic due to changes in steady states. The process variable estimators are unbiased and have known distributions. Thus, confidence intervals for true values of process variables are provided. The formulation of this technique was motivated by a recursive, dynamic data reconciliation technique that obtains very accurate estimators. These two techniques are compared in terms of computational speed and accuracy of estimators. The proposed technique is computationally faster, but not as accurate when variances of process measurements are large. However, the accuracy of the proposed estimators is shown to approach that of the recursive technique by iteratively recalculating estimates and when measurement variances decrease.
Reactions of polycyclic alkylaromatics: 5. pyrolysis of methylanthracenes
Authors: Smith C. Michael , Savage Phillip E. 
Published: June 2004

Abstract1‐, 2‐ and 9‐methylanthracene were pyrolyzed neat at temperatures between 350 and 450°C for batch holding times up to 300 min. The pyrolysis proceeded through three parallel primary reaction pathways: one led to anthracene via demethylation; the second to dimethylanthracenes through methyl addition; and the third to methyl‐9,10‐dihydroanthracenes through hydrogenation. The relative importance of these three paths varied for different methylanthracene isomers. The presence of these primary pathways can be rationalized in terms of recently elucidated hydrogentransfer mechanisms and other aspects of the developing free‐radical chemistry of polycyclic alkylarenes. The demethylation rate at 400°C for the methylanthracenes and seven other methylarenes was correlated with Dewar reactivity numbers, which provide a measure of the localization energy, as ln rate (arene yield/min) = 3.7– 7.1 Nts, where Nts is the Dewar reactivity number for the perpheral aromatic carbon atom bearing the methyl substituent. This correlation may be useful in molecular‐based reaction models for the conversion of heavy hydrocarbon resources such as coals and heavy oils.
Continuous‐mixture kinetics and equilibrium for reversible oligomerization reactions
Authors: McCoy Benjamin J. 
Published: June 2004

AbstractReversible oligomerization of distributions of molecules yields distributions of monomers, dimers, trimers, tetramers and higher‐order oligomers. The distributions can be functions of molecular weight, carbon number, or other variables that may be considered continuous. Rate expressions are formulated for the rates of generation of oligomers and loss of reactants due to combination (fusion) reactions and for the generation of fragments and loss of oligomers due to cracking (fission) reactions. Two types of cracking reactions are proposed: proportioned fission where products are precisely proportioned to yield monomers, dimers or trimers of given molecular weight; random fission where the fission products are distributed over all molecular weights up to that of the reactant. The zero moment of a distribution is the species concentration, which satisfies molar equilibrium and kinetics relationships. The temporal evolution of molecular‐weight moments is expressed in terms of differential equations for continuous‐flow and batch stirred reactors. By setting forward and reverse rates equal, equilibrium relations are developed for zero‐ and higher‐order moments, thus generalizing the mass‐action equilibrium concept. Equilibrium states for proportioned and random fission manifest infinitesimally narrow and infinitely broad distributions.
Effect of temperature on the phase equilibrium of aqueous two‐phase polymer systems
Authors: Hartounian H. , Floeter E. , Kaler E. W. , Sandler S. I. 
Published: June 2004

AbstractWe report experimental data showing the effect of temperature on polymer partitioning in the dextran (DEX500)‐polyethylene glycol (PEG8000)‐water system. Increasing temperature increases the concentration of PEG in the top phase and decreases the concentration of DEX in the bottom phase. A solution thermodynamic model based on local compositions with temperature‐dependent parameters correlates the experimental data well, and an efficient Gibbs‐free energy minimization algorithm for phase equilibrium calculations is described. The partial molar enthalpies and entropies of each of the solutes, calculated with the model, are negative and decrease in magnitude as temperature increases.
Computer simulation and theory for free energies in dilute near‐critical solutions
Authors: Li T. W. , Munoz F. , Chimowitz E. H. 
Published: June 2004

AbstractComputer simulation results are presented for the residual chemical potential μ, local solvent density enhancement Δρloc, and average solute potential energy u1 of a solute molecule immersed in afluid very close to its critical point. The simulation algorithm involves the Monte Carlo method in conjunction with free energy perturbation ideas. A number of ideas related to the feasibility of computer simulations in near‐critical solvents are investigated. Due to long‐range correlations near the critical point, it is not clear that simulations in this regime can be expected to yield accurate results using ensemble sizes of the magnitude typically used in simulations. Examination of system size and number of sampling steps on the simulations shows that the accuracy of the results depend to a large extent on the nature of the thermodynamic property being investigated. The solute chemical potential is suited particularly to simulation since it depends primarily on short‐range structure in the system. A comparison of the simulation results with integral equation theory calculations shows both approaches agree well with each other.
Heat‐transfer analysis of the basal melting of antarctic ice shelves
Authors: Minale Mario , Astarita Gianni 
Published: June 2004

AbstractBasal melting of Antarctic ice shelves is an important element in the overall balance of Antarctic ice. A heat‐transfer model for the basal melting of the Drygalski Ice Tongue is presented. The model does not contain any adjustable parameter. The calculated basal melting rate agrees very well with the value estimated from an overall ice balance on the ice Tongue. It is concluded that relatively simple concepts of transport phenomena may be used to model some important features of the dynamics of the Antarctic ice sheet.
u′v′ Reynolds stress in the viscous sublayer over a wide range of Re numbers
Authors: Rosén Christer , Trägådh Christian 
Published: June 2004

AbstractTo test the ability of different turbulence models to predict the turbulent momentum transport in the viscous sublayer, measurements are performed with a laser Doppler velocimeter (LDV). The main objective of the experiments is to measure the u′v′ correlation in the near wall region. The results support the correlation: −u′v′+ = Aky+3. The results of 2‐D computer simulations using four different low Reynolds number k‐ϵ turbulence models are compared with the experimental LDV data. The models tested are the original low Reynolds number k‐ϵ model of Jones and Launder (1972, 1973) and three later modifications by Chien (1980), Lam and Bremhorst (1981), and Nagano and Hishida (1987). The u′v′ correlation was found to be underestimated with all four models, but the Chien model was superior, with only a 40% underestimation in the viscous sublayer.
Rate enhancement and multiplicity in a partially wetted and filled pellet: Experimental study
Authors: Watson Paul C. , Harold Michael P. 
Published: June 2004

AbstractPhase transition during an exothermic multiphase reaction was studied experimentally using a single catalytic pellet reactor. Cyclohexene hydrogenation (to cyclohexane) and disproportionation (to benzene and cyclohexane) on Pd/Al2O3 comprised the test reaction system. The steady‐state behavior of the pellet exposed on part of its surface by a flowing liquid rivulet containing the liquid reactant (cyclohexene) and the other part by a flowing gas containing the gaseous reactant (hydrogen) was examined. Measurements included the pellet weight (liquid holdup), degree of external wetting, center and surf ace temperature and overall reaction rates. Two regimes observed are: a low‐rate regime for all hydrogen gas‐phase concentrations in which the partially wetted pellet is filled mostly with liquid and nearly isothermal; a high‐rate regime for hydrogen concentrations exceeding a critical value in which the pellet is filled only partially with liquid and the pellet temperature rise is considerable. Benzene formation was observed in this state. The difference in overall cyclohexane formation rates between the two states was as high as a factor of 20 for the same bulk conditions. Over the range where multiple states were observed, the steady state of the pellet depended on whether the pellet was pref tiled with the reactive gas mixture or with liquid cyclohexene. The range over which the high‐rate state was sustained was the largest for the most active catalyst and declined as the catalyst slowly deactivated. Data features are interpreted using the theoretical foundations of the half‐wetted catalytic slab model (Harold and Watson, 1993).