bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface tension prediction for pure fluids
Authors: Escobedo Joel , Mansoori G. Ali 
Published: June 2004

AbstractFor the surface tension of organic compounds, σ = [ 𝒫·(ρl ‐ ρv)]4 is proposed where 𝒫 = 𝒫0·(1 − Tr)0.37·Tr·exp(0.30066/Tr + 0.86442·T). ρl and ρv are molar densities of liquid and vapor, respectively, Tr = T/Tc, and 𝒫0 is a temperature‐independent, compound‐dependent constant similar to Sugden's parachor. This new expression, derived from statistical‐mechanics, represents the experimental surface tension data of 94 different organic compounds within 1.05 AAD%. We also propose 𝒫0 = 39.6431· [0.22217 − 2.91042 × 10−3·(ℛ*/T)·T/P] as a corresponding‐states expression to correlate the temperature‐independent parameter 𝒫0 for various compounds. Here, ℛ* = ℛm,ref, ℛm is the molar refraction, ℛm,ref is the molar refraction of the reference fluid (methane), and Tbr is the reduced normal boiling point. When this generalized expression is used, surface tensions for all 94 compounds can be predicted within 2.57 AAD% at all temperatures investigated.
Extension of metabolic control analysis to chemostat bioreactors
Authors: Tan Hiong Leong , Delgado Javier , Liao James C. 
Published: June 2004

AbstractA method of determining control coefficients and pseudo‐first‐order kinetic parameters is presented for cell growth, substrate consumption, and product formation in a chemostat bioreactor. From the equations that relate the control coefficients to process variables, such as feed concentrations of the limiting substrate and the product of interest, a perturbation method is developed to determine control coefficients from steady‐state measurements. This method combined with the transient response analysis provides a practical way for determining control coefficients and estimating kinetic properties in chemostat bioreactor systems. To determine the kinetic parameters, one measures cell mass, concentrations of the limiting substrate and the product of interest following a step change in the feed concentration until the system reaches a new steady state. The time courses of these variables are processed to obtain control coefficients, which yield the pseudo‐first‐order kinetic constants for cell growth, substrate consumption, and product formation. Only steady‐state responses are needed in calculation, if a step change in cell concentration in the feed stream can also be introduced without significantly perturbing cell physiology. This method is useful in characterizing the kinetics of whole cell bioreactions: results from chemostat experiments can be used to design operating strategies for batch or fed‐batch bioreactions. It is generally applicable to continuous‐stir‐tank reactors with interacting parallel reactions.
3‐D flow effects on residence time distribution in screw extruders
Authors: Chen L. , Lindt J. T. 
Published: June 2004

AbstractThis work concerns some selected 3‐D flow effects on residence time distribution (RTD) in a screw extruder. The Newtonian problem is emphasized in which the cross‐ and down‐channel flow components can be formally discoupled and treated as two parallel 2‐D problems: our stream‐function‐based analysis of the Newtonian cross‐channel flow was combined with the existing 2‐D solution for the down‐channel flow. The RTD was determined by tracing the streamlines generated from both velocity components for the industrially important cases of fully‐ and partially‐filled channels. The effect of the cross‐channel flow on the RTD is discussed in connection with the stagnation flows, the down‐channel pressure gradient, and the presence of a free surface in a partially‐filled channel. The cross‐channel pressure distribution is compared to the conventional 1‐D theory. The non‐Newtonian effects were assessed using the commercial software POLYCAD.
Computational modeling of gas/particle flow in a riser
Authors: Samuelsberg Arild , Hjertager Bjørn H. 
Published: June 2004

AbstractAxial solid velocity, solid volume fraction, and solid shear viscosity were computed in the riser of a circulating fluidized‐bed reactor using a two‐phase 2‐D computational fluid dynamic model. The time‐averaged model predictions agree well with the experimental data of Miller and Gidaspow (1992). The model predicts a core‐annulus flow in the riser, similar to that found experimentally. The maximum velocity in the core agrees well with the measurements, but the downflow in the annulus is somewhat overpredicted. The solid volume fractions profiles agree well in both core and annulus, with discrepancy in the core at the level close to the inlet. The radial profile of solid shear viscosity computed by the turbulent kinetic energy model is ten times lower in the core than that found experimentally, but with a linear function of solid volume fraction in the measurement, the computed profile agrees well with experiments.
Hydrodynamic modeling of gas/particle flows in riser reactors
Authors: Nieuwland J. J. , van Sint Annaland M. , Kuipers J. A. M. , van Swaaij W. P. M. 
Published: June 2004

AbstractComplex hydrodynamic behavior of circulating fluidized beds makes their scale‐up very complicated. In particular, large‐scale lateral solids segregation causes a complex two‐phase flow pattern which influences significantly their performance. Lateral solids segregation has been attributed to direct collisional interactions between particles as well as to interaction between gas‐phase eddies and dispersed particles. However, these phenomena have not been investigated thoroughly.This article discusses an advanced 2‐D hydrodynamic model developed for circulating fluidized beds based on the two‐fluid concept. Because theory to model the interaction between gas‐phase eddies and dispersed particles is not available, turbulence was modeled on a macroscopic scale using a modified Prandtl mixing length model. To model the influence of direct particle‐particle collisions the kinetic theory for granular flow was applied based on the Chapman‐Enskog theory of dense gases. For model validation purposes, a cold flow circulating fluidized bed was employed in which sand was transported with air as fluidizing agent. The column is equipped with pressure transducers to measure the axial pressure profile and with a reflective optical fiber probe to measure the local solids concentration and axial solids velocity. Theoretically calculated solids concentration and axial solids velocity agree satisfactorily with experiment, especially when one realizes that the model contains no adjustable parameters. In general, however, the model slightly underpredicted the experimentally observed lateral solids segregation and yielded a more peaked velocity profile compared to its experimental counterpart.
Detection of equipment faults in automatically controlled processes
Authors: Rollins Derrick K. , Cheng Yisun , Chen Victoria C. P. 
Published: June 2004

AbstractBased on the UBET, a new strategy for identifying faulty equipment for dynamic chemical processes under automatic control is presented. The strategy is designed to distinguish between measurement biases, controller biases, and process leaks. For illustration purposes, application is given to a level control process under pseudo‐steady state. This approach was inspired by the work of Rollins and Devanathan to identify biased measurements under dynamic conditions. Advantages of this method are that it is not computationally intensive, can accurately detect and specifically identify the type of fault, and can accurately determine the time when the fault occurs.
Simple and controlled extrapolation of vapor pressures toward the triple point
Authors: Růržička Květoslav , Majer Vladimír 
Published: June 2004

AbstractAlthough experimental vapor pressures are abundant in the medium‐pressure range (psat ≃ 5–100 kPa), their values are scarce and uncertain at lower pressures due to experimental difficulties in determining the data. Reliable values are, however, required by technology (separation processes dealing with mixtures containing high molar mass compounds) and environmental concerns (transport and fate of high‐boiling pollutants). The ability of frequently used vapor‐pressure equations to extrapolate the data at medium pressures toward the triple‐point temperature was tested on three groups of compounds (polar and nonpolar organic chemicals, n‐alkanes, and 1‐alkanols) for which reliable experimental data in the low‐pressure range were available. Results of a simple extrapolation were compared with those from a simultaneous correlation of vapor pressures in the medium‐pressure range and the differences between heat capacity of an ideal gas and that of the liquid available at lower temperatures. The latter is generally more reliable, as it is controlled by the exact thermodynamic constraints linking vapor pressures and the thermal data. The extent of improvement when using simultaneous correlation was examined, as well as the influence of the quality of input data on the results of extrapolation. Extrapolated values were compared with experimental vapor pressures and calorimetric enthalpies of vaporization that were selected from literature and free of any important systematic errors.
Hydrodynamic characteristics of a three‐phase inverse fluidized‐bed column
Authors: Ibrahim Yasser A. A. , Briens Cedric L. , Margaritis Argyrios , Bergongnou Maurice A. 
Published: June 2004

AbstractGas–liquid–solid inverse fluidized beds were studied, in which the gas and the continuous liquid phase flow countercurrently fluidizing particles that are lighter than the liquid. Conductivity and static pressure measurements were combined to provide the vertical profiles of the gas, liquid and solid holdup, in beds of 4‐ or 6‐mm polypropylene particles with a density of about 870 kg/m3. Various bed heights were obtained with different measurement methods. The minimum fluidization velocity was estimated using the bed static pressure gradient. A new transition velocity, called the uniform fluidization velocity, was identified using conductivity measurements. This is the superficial liquid velocity at which the fluidization quality becomes the same throughout the bed.
Estimation of three‐phase flow functions in porous media
Authors: Mejia G. M. , Watson A. T. , Nordtvedt J. E. 
Published: June 2004

AbstractSeveral important processes involve the flow of three immiscible fluids through porous media, such as the flow of oil, water and gas in petroleum reservoirs, or water, nonaqueous‐phase liquid and air in underground aquifers. Multiphase flow functions (relative permeability and capillary pressure) are important to simulate the flow in such systems. Unfortunately, there are few, if any, reliable estimates of these flow properties from laboratory experiments. One of the main reasons for this is the use of unsupported simplifications in the procedures for determining property estimates from measured data.We present a method for simultaneous estimation of three‐phase relative permeability and capillary pressure functions from laboratory experiments. The method is not limited by restrictions in the experimental design or assumptions regarding the saturation dependence or shape of the functions to be estimated. The method is demonstrated with simulated experiments. It is shown that with a suitable experimental design, regions of the functions represented by the measured data can be determined accurately.
Effect of heterogeneous mechanisms during reburning of nitrogen oxide
Authors: Chen Wei‐Yin , Ma Long 
Published: June 2004

AbstractNO reduction through heterogeneous mechanisms is a major concern when coal or lignite is used as reburning fuel. Reburning was simulated in an alumina flow reactor operated with a synthetic flue gas at a stoichiometric ratio of 1.1, at 1,100°C and with a residence time of approximately 0.2 s. Reburning fuels used include methane, one bituminous coal, two lignites, chars derived from the bituminous coal and two lignites, and the bituminous coal char impregnated with CaO. Reburning with chars indicates that heterogeneous mechanisms are more important than homogeneous mechanisms when lignites are used. This high reactivity renders lignite char an even more effective reburning fuel than the parent lignite, while char from the bituminous coal produces little activities at stoichiometric ratios above 0.75. Bituminous coal char impregnated with CaO demonstrates higher NO reduction efficiency than the original char. Effects of SR on NO reductions imply that oxygen atoms, required for the NO and HCN conversions in homogeneous mechanisms, are not required in heterogeneous mechanisms. In fact, they inhibit the surface NO reduction. The first‐level kinetic analysis indicates that the surface area is not the only contributor to a remarkable increase in NO reduction of lignite char, and chars of different origins seem to follow different mechanisms or to have different controlling steps in the overall reaction scheme.
On the kinetics of phenol oxidation in supercritical water
Authors: Krajnc Matjaž , Levec Janez 
Published: June 2004

AbstractPhenol oxidation in supercritical water was carried out in a tubular laboratory‐scale reactor operated at a temperature range of 380°C to 450°C and pressures between 230 and 265 bar. The phenol feed concentrations were between 500 and 1,000 mg/L, while oxygen was fed into the reactor at 50 to 1,000% of the stoichiometric amount needed to oxidize phenol completely to carbon dioxide. Phenol conversions from 16 to 96% were attained as the reactor residence times varied from 15 to 203 s. The oxidation obeys a parallel‐consecutive reaction scheme that involves multiring, intermediate products such as phenoxy‐phenol, biphenol, dibenzo‐dioxin, maleic acid, and succinic acid. Experimental results showed that the phenol disappearance rate is represented well by a power‐law kinetic model in which the rate is proportional to the 0.4 power of the oxygen mole fraction and roughly linearly proportional to the phenol mole fraction. The pressure effect on the disappearance rate was appropriately accounted for by introducing the molar volume of the reaction mixture, which was readily calculated by an equation of state. Total organic carbon reduction can be estimated by a lumped kinetic equation. In the P‐T region the activation energy of the phenol disappearance was 124.7 kJ/mol.
Effective viscosities in thin ionic micellar liquid films
Authors: Pollard Maria L. , Radke C. J. 
Published: June 2004

AbstractThin liquid films stabilized by surfactants above the critical micelle concentration exhibit stratification or stepwise dynamic thinning. A continuum hydrodynamic model is outlined for stepwise film thinning that incorporates equilibrium micellar structuring through self‐consistent oscillatory disjoining pressures and effective viscosities. Effective viscosities as functions of thickness are evaluated with an extension of the local average density model, considering dilute colloidal suspension shear viscosities and solvent effects. To establish local shear viscosities, structured DFT micellar profiles, coarse‐grained densities, and disjoining pressure are used. Ionic micelles and other colloidal systems with repulsive interactions show structured effective viscosities that are generally less than the corresponding homogeneous solution shear viscosity, bounded by the pure solvent viscosity and that of the bulk micellar solution. For 0.1 and 0.2‐M sodium dodecylsulfate micellar solutions, the effective viscosities are less than 5 and 10%, respectively, below the homogeneous fluid viscosity, except at small thicknesses, indicating that the micellar film thins faster than a pure water film of the same thickness.Calculated thinning curves closely resemble experimental observations in the stepwise thinning behavior, displaying decreasing slopes and increased step durations at later times. Despite the micellar structuring within the film, the ionic micelles do not contribute appreciably to the viscous resistance of the thinning film. Rather, Reynolds' film thinning is obeyed, with the equilibrium oscillatory disjoining pressures driving the stepwise dynamics. The shear viscosity of the ionic micellar film is well approximated by that of the bulk solution.
Prefractionation to reduce energy consumption in distillation without changing utility temperatures
Authors: Agrawal Rakesh , Fidkowski Zbigniew T. , Xu Jianguo 
Published: June 2004

AbstractDistillation systems composed of a prefractionator and a main column are introduced. The columns operate at different pressures, but the temperatures of the utilities are the same as for a single column performing the same separation. The energy integration of the columns is realized by condensing a vapor overhead from the prefractionator in an intermediate reboiler located in the stripping section of the main column or by boiling a bottoms liquid from the prefractionator in an intermediate condenser placed in the rectifying section of the main column.Analysis is performed to determine feasible regions of operational parameters and to minimize vapor flows. A detailed simulation example of the benzene–toluene separation shows that for certain feed compositions it is possible to reduce energy requirements of a conventional binary distillation column by almost one‐third using this new distillation system. This savings is achieved without any change in the temperature of the utilities used.
A model for drying of viscoelastic polymer coatings
Authors: Cairncross Richard A. , Durning Christopher J. 
Published: June 2004

AbstractDrying of polymeric coatings often occurs under conditions where the relaxation time of polymer molecules is significant with respect to the processing time scales. The nonequilibrium thermodynamic theory of Durning and Tabor (1986) is applied to model 1‐D drying of viscoelastic solutions with concentration‐dependent physical properties. Transport of solvent to the surface of the coating occurs by viscoelastic diffusion down the gradient of a diffusion potential with a relaxing, nonequilibrium contribution. Galerkin's method with finite‐element basis functions and a differential/algebraic equation system solver enable efficient solution of this stiff nonlinear model. Predictions show that elasticity enhances diffusion within the coating. At high Deborah numbers, however, a fall in the surface activity slows the rate of desorption. The coating thickness after a specified time under fixed total driving force is the smallest at intermediate Deborah numbers, showing that a small amount of viscoelasticity actually aids in drying. This can be interpreted as a skinning effect.
Output‐feedback control of nonlinear plants
Authors: Alvarez Jesús 
Published: June 2004

AbstractFor multiinput‐multioutput nonlinear plants whose state‐feedback control problem is solvable with complete or partial output linearization, the output‐feedback problem is addressed by combining the state‐feedback controller with a suitable closed‐loop state inferer (detector). A candidate closed‐loop detector was built to study the stability of the resulting plant‐controller interconnection. As a result, sufficient conditions for closed‐loop asymptotic nominal stability, as well as a systematic and simple design‐tuning procedure, are obtained. The stabilization of an open‐loop, unstable, free‐radical homopolymerization reactor was studied as an application example.
Fluctuation theory of hydrogen bonding in near‐critical fluids
Authors: Veytsman Boris A. , Gupta Ram B. 
Published: June 2004

AbstractRecent experiments indicate that the number of hydrogen bonds in solutions increases in the critical region of the solvent. This effect can be explained by the density fluctuations near the critical point. A theory of this unusual effect is developed. The theoretical predictions are compared with the experimental data on hydrogen bonding between perfluoro‐tert‐butanol and dimethyl ether in supercritical sulfur hexafluoride. The theory requires no adjustable parameters and is in excellent agreement with the experimental data. Possible applications of this effect for hydrogen‐bonding solutions and polymer mixtures are discussed.
A bidirectional fixed‐bed reactor for coupling of exothermic and endothermic reactions
Authors: Kulkarni Milind S. , Duduković Milorad P. 
Published: June 2004

AbstractPerformance of a bidirectional fixed‐bed reactor subject to both flow reversal and switching between exothermic and endothermic reactions is simulated. During odd semicycles (blows) an exothermic reaction heats the bed, during even semicycles an endothermic reaction cools the bed and produces the desired product in the hot zone. Such an operation is possible and efficient when the inlet gas temperature is lower than the initial bed temperature, leading to the wrong‐way behavior when the temperature front moves with a finite velocity (creep velocity) from the feed end to the exit during a semicycle. Since the dynamic nature of the fixed‐bed reactor changes with each semicycle, the front velocity during an exothermic semicycle differs from the front velocity during an endothermic semicycle and an asymptotic expression is developed for the differential creep (front) velocity that quantifies this difference. Due to a nonzero differential creep velocity, the front exhibits an effective displacement after each cycle. This asymptotic expression for the creep velocity works very well except in the inlet and outlet region of the fixed‐bed reactor. An expression developed for 100% energy efficiency shows that it can be reached only if the differential creep velocity is zero. A relation for the balanced operation of a reactor‐regenerator is discussed as well as differences in reactor performance caused by reactions occurring in the gas or solid phase.
Polymer kirkwood integral equations: Structure and equation of state of polymeric liquids
Authors: Gan Hin Hark , Eu Byung Chan 
Published: June 2004

AbstractA self‐consistent theory of chain molecular liquids from polymer Kirkwood integral equations is presented. The theory predicts the intramolecular chain distributions and the intermolecular pair correlation functions from which thermodynamic functions can be correctly predicted. The utility of the theory is demonstrated with the chain distributions from self‐consistent equations at zero density for swollen and collapsed states of the chains and numerical results for the structure and equation of state of athermal chain molecular liquids at various chain lengths and densities. Structural and thermodynamic predictions of the theory are compared with Monte Carlo simulation results. The theory agrees satisfactorily with simulation data for monomer packing fractions up to 0.25. The investigation of the chain length dependence shows that a plateau value is reached for the equation of state as the number of monomer units reaches a value between 20 and 50.
Measurement of transverse and axial apparent dispersion coefficients in packed beds
Authors: Tallarek Ulrich , Albert Klaus , Bayer Ernst , Guiochon Georges 
Published: June 2004

AbstractThe axial and transverse apparent dispersion coefficients of three solvents in two packed chromatographic columns were determined by pulsed‐field‐gradient nuclear‐magnetic resonance in a range of mobile phase velocity. The column beds were packed with 5‐ μm particles of porous C18 silica or 30‐μm particles of silica. The solvents used were methanol and acetonitrile (in an 80:20 ACN/water solution) in the former case and acetone in the latter. The coefficients were determined over a range of particle Peclet numbers from less than 0.1 to approximately 10 in the former case and 40 in the latter. The data obtained with short dispersion times were fitted to the correlations suggested by Giddings, Horvath and Lin, Huber, and Knox. These data agreed well only with the Giddings equation.