bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modified sedimentation‐dispersion model for solids in a three‐phase slurry column
Authors: Smith D. N. , Ruether J. A. , Shah Y. T. , Badgujar M. N. 
Published: June 2004

AbstractSolids distribution data for a three‐phase, batch‐fluidized slurry bubble column (SBC) are presented, using air as the gas phase, pure liquids and solutions as the liquid phase, and glass beads and carborundum catalyst powder as the solid phase. Solids distribution data for the three‐phase SBC operated in a continuous mode of operation are also presented, using nitrogen as the gas phase, water as the liquid phase, and glass beads as the solid phase. A new model to provide a reasonable approach to predict solids concentration distributions for systems containing polydispersed solids is presented. The model is a modification of standard sedimentation‐dispersion model published earlier. Empirical correlations for prediction of hindered settling velocity and solids dispersion coefficient for systems containing polydispersed solids are presented.A new method of evaluating critical gas velocity (CGV) from concentrations of the sample withdrawn at the same port of the SBC is presented. Also presented is a new mapping for CGV which separates the two regimes in the SBC, namely, incomplete fluidization and complete fluidization.
Effects of surfactants on mass transfer during spray drying
Authors: Frey D. D. , King C. J. 
Published: June 2004

AbstractA study was conducted to investigate the effects of added surfactants on mass transfer during spray drying. Measurements were made of retention of volatile components and amount of water evaporation at various points near the atomizer inside a spray dryer of pilot plant scale. Experimental data indicate that surfactants can have a substantial effect on transport processes when certain types of liquid solutions are spray dried. Experimental results are interpreted in terms of transport mechanisms and are compared with relevant previous studies on non‐spray systems.
The finite‐element solution of laminar combined convection from two horizontal cylinders in tandem arrangement
Authors: Wong King‐Leung , Chen Cha'o‐Kuang 
Published: June 2004

AbstractA finite‐element method is used to solve the full Navier‐Stokes and energy equations for the problem of laminar combined convection from two horizontal cylinders in tandem arrangement. From comparisons with the previous theoretical and experimental results of a single‐cylinder situation, it is found that the behaviors flow and heat transfer in the upstream cylinder are close to those in a single‐cylinder, but this is not the case for the downstream cylinder.
Characteristic adsorption isotherm for adsorption of vapors on heterogeneous adsorbents
Authors: Sircar S. , Myers A. L. 
Published: June 2004

AbstractThe dimensionless group [(mRT/ΔG) ln(P/P°)] is a universal function of θ (fractional filling of micropores) for different vapors adsorbed on a heterogeneous adsorbent. Adsorptive parameters are the saturation capacity (m) and the free energy of immersion of the solid in bulk liquid adsorbate (ΔG). The heat of immersion of the adsorbent determines the temperature dependence of ΔG according to the Gibbs‐Helmholtz equation ΔH = ∂(ΔG/T)/∂(1/T).
Gross error detection and data reconciliation in steam‐metering systems
Authors: Serth R. W. , Heenan W. A. 
Published: June 2004

AbstractSeveral new algorithms for the detection of gross errors in process data are presented and applied to an industrial steam‐metering system by means of computer simulation. A number of algorithms that have appeared in the literature are also applied to the steam‐metering system, and the performances of the various algorithms are compared.
Single‐Pellet, moment method for analysis of gas‐solid reactions
Authors: Doǧu Timur , Keskin Aliye , Doǧu GÜLsen , Smith J. M. 
Published: June 2004

AbstractA single‐pellet, moment technique is presented for evaluating reaction rate constants, effective diffusivities, and adsorption equilibrium constants for gas‐solid noncatalytic reactions. Experimental pulse‐response data for the reaction of SO2 with activated soda at 473 K were obtained to illustrate the method. The results show that intraparticle diffusion is the controlling mechanism for this reaction. The value of the Thiele modulus for axial transport was found to be 8.6 for a cylindrical pellet of porosity 0.56, tortuosity 2.3, and length 3 × 10−2 m.
Lagrangian dispersion in turbulent flow from laser transit anemometry
Authors: Berman N. S. 
Published: June 2004

AbstractThe Lagrangian dispersion function in turbulent flow can be determined from measurements of the probability that a particle which is observed in a small volume is not observed in a similar size volume downstream. In this work a single‐detector method is proposed to detect the particle arrivals in a multiple series of scattering volumes; the probability can be determined from the digital record over a long time compared to the turbulent integral time scale. The method is tested at locations downstream of a water spray nozzle and a submerged jet of dilute polymer solutions.
On the stability of falling films—periodic, finite‐amplitude waves
Authors: Barrdahl Runo 
Published: June 2004

AbstractAn analytical, theoretical investigation regarding periodic finiteamplitude (nonlinear) waves in a Newtonian, isothermal liquid film flowing along a vertical wall is presented. The periodic solution found provides full information regarding stability, wavelength, wave velocity, and wave amplitude as expressed exclusively in terms of physical constants and flow rate.
Adaptive control strategies for process control: A survey
Authors: Seborg D. E. , Edgar T. F. , Shah S. L. 
Published: June 2004

AbstractIn recent years there has been extensive interest in feedback control systems that automatically adjust their controller settings to compensate for changes in the process or the environment. Such systems are referred to as adaptive controllers. This survey paper reviews the current state of the art in adaptive control from a process control perspective and describes leading design techniques. Potential operating problems associated with adaptive control schemes are considered. A survey of experimental applications of adaptive control systems to process control problems is also included.
High‐Performance multivariable control strategies for systems having time delays
Authors: Jerome N. F. , Ray W. H. 
Published: June 2004

AbstractA new high‐performance multivariable time delay compensator is presented that contains the Ogunnaike‐Ray compensator as a special case, reduces to the Smith predictor for a single delay, and approaches the realizable part of the process inverse as a limit. The straightforward design procedure is illustrated with several distillation control examples.
Vapor‐liquid equilibrium of formaldehyde‐and water‐containing multicomponent mixtures
Authors: Maurer G. 
Published: June 2004

AbstractThe vapor‐liquid equilibria in the binary mixtures water‐formaldehyde and methanol‐formaldehyde are precisely correlated by introducing a physicochemical model that takes into account physical forces of interactions as well as chemical reactions. The most valuable feature of the model is its simple extension to multicomponent mixtures. From binary data alone the model is capable of accurately predicting vapor‐liqid equilibria in complex mixtures such as formaldehyde‐water‐trioxane and formaldehyde‐water‐methanol. This is demonstrated by comparing calculated data with experimental results taken from the literature or measured in this work, at temperatures between about 310 and 400 K at pressures up to 500 kPa, and formaldehyde concentrations in the liquid phase of up to about 70 mol %.
A study of separation efficiency in thermal diffusion columns with a permeable vertical barrier
Authors: Yeh Ho‐Ming , Tsai Shau‐Wei , Lin Cheng‐Shiung 
Published: June 2004

AbstractA separation theory in thermal diffusion columns with a permeable vertical barrier has been derived by making use of the orthogonal expansion method. It is shown that the undesirable remixing effect can be effectively reduced and controlled by introducing a permeable vertical barrier. Considerable improvement in separation was obtained when the position of the barrier was carefully chosen.
Gas‐liquid reaction systems: A heuristic model and its steady solutions
Authors: White Daniel , Johns L. E. 
Published: June 2004

AbstractTo identify conditions under which gas‐liquid reaction systems exhibit natural oscillations, a model is formulated in which the time scales of the elementary processes play a leading role. The steady solutions of the model problem are investigated, with the finding that at most one solution may lie in each of five temperature ranges, each range corresponding to a dominant physicochemical process.
Pole‐placement self‐tuning control of a fixed‐bed autothermal reactor. Part I: Single variable control
Authors: McDermott P. E. , Mellichamp D. A. , Rinker R. G. 
Published: June 2004

AbstractA pole‐placement self‐tuning controller has been used to control a fixed‐bed autothermal reactor conducting the water‐gas shift reaction at both an upper stable state and a middle unstable state. Excellent set‐point tracking and disturbance rejection characteristics were obtained using a single manipulated variable, the heat input at the entrance to the catalyst bed, to control a single bed temperature. Excellent set‐point tracking during the transition from the upper state to the middle state was obtained by using a technique that tuned the closed‐loop poles on‐line so as to give an optimal response.
Pole‐placement self‐tuning control of a fixed‐bed autothermal reactor. Part II: Multivariable control
Authors: McDermott P. E. , Mellichamp D. A. , Rinker R. G. 
Published: June 2004

AbstractThe multiinput/multioutput pole‐placement self‐tuning controller (MIMO PPSTC) previously developed by McDermott and Mellichamp is used to control a fixed‐bed autothermal reactor with internal countercurrent heat exchange. The performance of the controller is demonstrated using step changes in the set points and in the primary disturbance variables. It is shown that the complete temperature profile can be maintained by controlling two temperatures in the catalyst bed: one just before the hot spot and the other at the exit of the bed. Simulated results using a 36th‐order nonlinear reactor model operating at both an open‐loop upper stable steady state and an open‐loop unstable steady state are presented. Experimental results for a fixed‐bed autothermal reactor operating at an upper stable state are presented.
Mechanisms and kinetic modeling of calcium oxalate crystal aggregation in a urinelike liquor. Part I: Mechanisms
Authors: Hartel R. W. , Gottung B. E. , Randolph A. D. , Drach G. W. 
Published: June 2004

AbstractThe tendency for aggregation and disruption of aggregates of calcium oxalate dihydrate (CaOx) crystals in urinelike mother liquor was quantitatively studied in a two‐stage mixed‐suspension, mixed‐productremoval crystallizer/Couette‐flow aggregator operated in series. The degree of aggregation was obtained by comparing measured numbersize and volume‐size crystal distributions in the crystallizer and aggregator outlets. Aggregation was a strong function of CaOx supersaturation and may have changed slightly with rotation speed in the Couette‐flow aggregator. Rupture of the aggregates increased as the spindle rotation in the aggregator increased (presumably increasing turbulence). Average shear rates in these experiments were appreciably above estimated physiological levels.
Modeling of coal liquefaction kinetics based on reactions in continuous mixtures. Part II: Comparison with experiments on catalyzed and uncatalyzed liquefaction of coals of different rank
Authors: Prasad G. N. , Agnew J. B. , Sridhar T. 
Published: June 2004

AbstractExperimental kinetic data for three Australian coals are compared with predictions from the mathematical model developed in Part I. For these coals, as well as data reported for North American coals, the model is found to show good agreement, using the characteristic molecular weight as the only parameter. The effects of reaction time and temperature are coupled via a severity index that arises in the model as a dimensionless reaction time. The model is also shown to be applicable when catalysts are present. The product distribution for a particular coal seems to be a function only of the conversion even in the presence of catalysts, as long as the chemical reaction controls the rate of liquefaction.
Tracer diffusion in dense ethanol: A generalized correlation for nonpolar and hydrogen‐bonded solvents
Authors: Sun C. K. J. , Chen S. H. 
Published: June 2004

AbstractTracer diffusion coefficients were measured for benzene, toluene, mesitylene, naphthalene, and phenanthrene in dense ethanol at 0.56 ≤ TR ≤ 1.07 and ρR ≥ 1.44. The results were used to examine the temperature dependence of the degree of association between ethanol molecules across the entire range of temperature. The hard‐sphere tracer diffusion equation and the Stokes‐Einstein equation were used to develop two engineering correlations. The former approach was found to be adequate for solvents of relatively compact molecules, and the latter to be more general in its applications. The absolute deviation of prediction from observed values of tracer diffusivities is 4%, with a maximum error of 13%.
A unified approach for prediction of thermodynamic properties of aqueous mixed‐electrolyte solutions. Part I: Vapor pressure and heat of vaporization
Authors: Patwardhan V. S. , Kumar Anil 
Published: June 2004

AbstractThe overall nonideality of an aqueous mixed electrolyte solution is characterized in terms of a newly defined parameter Γ*, called the overall reduced ionic activity coefficient. It is shown that Γ* for the mixed solution is simply related to the properties of single‐electrolyte solutions. Γ* is related to the vapor pressure of a mixed‐electrolyte solution through well‐known thermodynamic equations. This leads to a predictive equation for the vapor pressure of a mixed‐electrolyte solution in terms of the vapor pressures of single‐electrolyte solutions of the components. This equation is valid over the entire concentration range encountered in practice, without any empirical constants, and has a predictive accuracy of 2%. A predictive equation for the latent heat of vaporization is also developed and tested against experimental data.
A unified approach for prediction of thermodynamic properties of aqueous mixed‐electrolyte solutions. Part II: Volume, thermal, and other properties
Authors: Patwardhan V. S. , Kumar Anil 
Published: June 2004

AbstractThe overall reduced ionic activity coefficient Γ* is useful in characterizing the overall nonideality of an aqueous mixed‐electrolyte solution. It has been shown in Part I that Γ* can be simply related to Γ of single‐electrolyte solutions containing the component electrolytes without using empirical constants. This basic relationship is used in this paper for deriving predictive equations for several properties in terms of corresponding properties of single‐electrolyte solutions containing the component electrolytes. The predictive equations need no empirical constants. The properties covered include volume properties such as density and adiabatic compressibility, thermal properties such as enthalpy and specific heats, and others such as free energy, expansibility, and depression in freezing point. Comparison with experimental data shows that the predictive equations have an accuracy varying from 0.03% for density to 2% for freezing point depression, and are valid for the entire range of concentrations encountered in practice.
A new criterion for the pairing of control and manipulated variables
Authors: Mijares Gerardo , Cole J. D. , Naugle N. W. , Preisig H. A. , Holland C. D. 
Published: June 2004

AbstractA criterion is developed for the selection of the best pairing of the control and manipulated variables of a multiloop control system. This criterion is based on the difficulty caused by the interaction terms (the off‐diagonal elements) in finding the inverse of the steady state gain matrix. From an analysis based on the proposition that the most desired or best pairing is that one for which the system most closely resembles a set of independent single‐loop systems, a quantitative measure of the best pairing is obtained. Although the development of the pairing criterion is based on purely algebraic principles, the validity of the pairing criterion is evident from analogous developments obtained within the control framework. Furthermore, it is shown that the pairing criterion may be used to determine the stability of a multiloop control system, thus enhancing the value of the criterion presented.
Mass transfer in eddies close to air‐water interface
Authors: Luk Sydney , Lee Y. H. 
Published: June 2004

AbstractDeterministic analyses applied to both velocity and concentration fluctuation data obtained in a region extremely close to air‐water interface in a free‐surface, unbaffled stirred tank allow estimation of the length and the velocity scales of individual eddies taking part in gas absorption. The mass transfer prediction by this method is superior to that by a statistical method using an integral length scale in the low‐turbulence flow employed in this work. Eddy velocities are generally lower in the diffusion boundary layer zone compared with the bulk zone. Small eddies are generally associated with low velocity scales whereas large eddies occur at high velocity scales. Local mass transfer coefficients are high in regions where small eddies are dominant.
Air‐lift reactor analysis: Interrelationships between riser, downcomer, and gas‐liquid separator behavior, including gas recirculation effects
Authors: Siegel M. H. , Merchuk J. C. , Schugerl K. 
Published: June 2004

AbstractAn approach to air‐lift reactor analysis is presented that examines the three parts of the air‐lift—the riser, downcomer, and gas‐liquid separator—as three interconnected and interrelated elements. Downcomer flow configurations are described and characterized by either straight or oscillating bubble flow patterns. The downcomer gas flow rate is determined using a two‐sparger system, and a correlation is presented relating the downcomer superficial gas velocity to the downcomer gas holdup. Gas recirculation is calculated and related to the geometric and operating conditions of the gas‐liquid separator. It is shown that an increase in residence time in the gas‐liquid separator decreases the gas recirculation rate. Correlations are presented relating gas holdup and liquid velocities to superficial gas velocity.A sparger was added near the entrance of the downcomer, in addition to the conventional placement near the entrance of the riser. Results of such a two‐sparger system are discussed in relation to reactor stability and liquid velocities.
Instantaneous concentration fluctuations in point‐source plumes
Authors: Georgopoulos P. G. , Seinfeld J. H. 
Published: June 2004

AbstractA model for the variance σ of instantaneous plume concentrations, at a level corresponding to that of the Gaussian formulas for the mean field, is developed and tested against available data. Starting from the Eulerian species transport equation, theoretical and empirical information is used to estimate parameters and simplify the form of the transport equation for σ in a meandering frame of reference. Then, introduction of a localized production of fluctuations (LPF) scheme allows construction of analytical expressions for σ that provide a direct means for calculating the concentration variance inside the instantaneous boundaries of plumes resulting from continuous point emissions in turbulent flows with uniform mean velocity.
Detection and location of a leak in a gas‐transport pipeline by a new acoustic method
Authors: Watanabe Kajiro , Himmelblau D. M. 
Published: June 2004

AbstractA new method is described for detecting and locating a leak in a gas transport pipeline lying between two pump stations by an indirect acoustic method. The basic concept is to treat the pipeline as an acoustic tube (similar to a wind instrument), and to estimate the impulse response of the acoustic wave in the pipeline solely from the acoustic signal detected at two terminal sites in the pipeline. The test signal introduced at the input site is only acoustic noise; pipeline operation need not be interrupted. If a leak occurs in the pipeline, the impulse response of the acoustic wave in the pipeline has a sharp pulse or a step at a certain time that can be directly related to the site of the leak. Using the mathematical model of the pipeline acoustics, i.e., the wave equation, a theoretical basis is developed to explain how and why the leak can be detected and located. Experiments carried out in the laboratory under conditions comparable to realistic field conditions demonstrate the validity of the proposed detection method.
The role of conduction/valence bands and redox potential in accelerated mineral dissolution
Authors: Leblanc S. E. , Fogler H. S. 
Published: June 2004

AbstractThe dissolution kinetics of a number of manganese oxides in acidic solutions were studied. Using a slurry reactor, rate laws were determined for each of the manganese oxides in the hydrohalogen acids. Significant variations in the reaction rates (up to five orders of magnitude over the HCl base rate) were obtained with different acids. The addition of anions as neutral salts to acidic solutions is shown to produce the same rate‐accelerating effect as acids containing that anion. The effect of the different acids on the oxide dissolution rates is explained using semiconductor band theory and energy diagrams.
Gas‐liquid mass transfer and pressure drop in pulp bed with flexible fibers as solid supports
Authors: Hsu C. L. , Hsieh J. S. 
Published: June 2004

AbstractThe volumetric mass transfer coefficients between oxygen and water in a pulp bed have been determined by the gas‐liquid reaction method with an enhancement factor approximately equal to one. The coefficients ranged from 0.08 s−1 at 13% to 0.34 s−1 at 19% solids content in the pulp bed, values that are close to those for comparable trickle beds. No liquid flow over the pulp bed (13–19% solids content) occurred under the operating conditions. The results showed that gas‐liquid mass transfer was affected only by the solids content of the pulp bed rather than by the oxygen superficial velocity (0.4 to 1.2 cm/s). The gas pressure drop across the pulp bed was also predicted by Ergun's equation using an estimated effective diameter for the fiber flocs.
An improved adsorption process for the production of high‐fructose syrup
Authors: Ching C. B. , Ho C. , Ruthven D. M. 
Published: June 2004

AbstractBy applying a temperature profile to the system, the concentration of the extract product in a countercurrent adsorption separation process may be increased relative to the maximum concentration attainable under isothermal conditions. To achieve the required temperature profile in a simulated countercurrent system it is necessary to heat and cool the columns in sequence as the feed and product draw‐off points are switched through the bed. The practical feasibility of operating the system in this way has been demonstrated experimentally for the separation of glucose‐fructose mixtures. By maintaining a temperature difference of 30–35°C across the bed an extract product containing 28% fructose and about 1% glucose was obtained, at steady state, from a feed containing 25 wt. % of each sugar.