bluuebunny/crossref_metadata_2025_split huggingface dataset:
Char gasification in a countercurrent reactor
Authors: Amundson Neal R. , Arri Luis Ernesto 
Published: June 2004

AbstractA model is developed for the countercurrent char gasifier of Lurgi form. Char particles are fed to the top and oxygen, inert, and steam in the bottom. The combustion zone is defined as the zone in which there is a nonzero molfraction of oxygen. In the gasification zone, the particles are assumed to be a lumped system in which the Johnson reaction kinetic expressions are assumed to be valid with the water gas shift reaction at equilibrium. All of the reactions between oxygen and carbon and water and carbon are assumed to take place in the combustion zone but with the carbon‐oxygen reaction predominating to form a shell progressive system within the particles. Radiation is taken into account, and parametric computations are made on temperatures, compositions, flow rates, and char reactivity. The maximum temperature is strongly influenced by radiation and its position is a sensitive function of the solid flow rate producing an ash layer at the bottom of varying thickness.
Synthesis of kinetic structure of reaction mixtures of irreversible first‐order reaction
Authors: Lee Hong H. 
Published: June 2004

AbstractA synthesis method for the kinetically consistent structure of reaction mixtures is developed based on elementary structures of reaction mixtures and rate expressions for product lumps of nth order. Knowledge of product lumps and experimental kinetic data on each of the lumps are required for the synthesis of kinetic structure. Rate constants for all reaction paths and initial lumps from which all the product lumps originate can be determined.
Kinetic behavior of weak base anion exchangers
Authors: Hübner Pavel , Kadlec Vaclav , Dukla Čkd 
Published: June 2004

AbstractIn this work, twelve different weak base anion exchangers were studied as to their decrease of breakthrough capacity with increasing specific loading. From the curves, the rate coefficients were calculated and correlated with the values characterizing the ion exchanger. It was found that the sorption rate of acid increases with decreasing average molality of functional groups in the ion exchanger.
On singular policies in the optimal distribution of a bifunctional catalyst: Part I. Effect of reaction kinetics
Authors: Choi C. Y. , Perlmutter D. D. 
Published: June 2004

AbstractResults are presented on the affects of kinetic changes on optimal, bifunctional, catalyst distribution policies for a consecutive two‐reaction sequence in a plug flow tubular reactor. Earlier results on singular control arising from reversible reactions are extended to include inhibition or activation. These may arise from the affects of any reactant or product on the rate or from a subsequent or preceding reaction in a sequence. The system equations are written in dimensionless form to provide efficient computations and to allow analytic interpretation of numerical results from previous studies.
An analysis of flow separation in hydrodynamic chromatography of polymer latexes
Authors: Silebi Cesar A. , McHugh Anthony J. 
Published: June 2004

AbstractAn analysis is presented for the flow separation process in hydrodynamic chromatography along with comparisons to experimental data. The flow separation model is based on calculations for the convected Brownian motion of colloidal particles in a capillary tube in the presence of a force field. The results indicate the role of the relevant experimental parameters in the separation process.
Solubilities of heavy hydrocarbons in compressed methane, ethane, and ethylene: Dew‐point temperatures for gas mixtures containing small and large molecules
Authors: Kaul Bal K. , Prausnitz John M. 
Published: June 2004

AbstractSolubilities of heavy hydrocarbons in compressed gases were measured in the region 50° to 170°C for hexadecane, bicyclohexyl, diphenylmethane, and 1‐methyl naphthalene and in the region 165° to 272°C for eicosane and squalane. Measurements were made in the pressure region 9 to 80 atm. The solubility data were reduced to yield second virial cross coefficients B12. To interpret the B12 data, a square‐well potential was used; the characteristic size of the large molecule is given by the mean radius of gyration which takes into account the variety of molecular conformations. Calculated results give good agreement with new as well as previously published B12 data.Illustrative calculations indicate how the results obtained here may be used to make dew‐point calculations in multicomponent systems containing both small and large molecules.
Kinetics of oxidation of sodium dithionite by flow thermal method
Authors: Singh D. K. , Sharma R. N. , Srivastava R. D. 
Published: June 2004

AbstractThe homogeneous kinetics and inhibition of sodium dithionite oxidation in an aqueous solution were studied by means of a flow thermal method. Results on the oxidation study of dithionite solutions at 30°C show that the reaction is first order with respect to dithionite and zero order with respect to oxygen. An activation energy of 17.5 kcal/g‐mole has been calculated for this reaction. The inhibiting effects of manganese chloride, manganese sulfate, and triethanolamine were inversely proportional to 0.8, 0.9, and 0.2 power, respectively.A free radical chain mechanism has been proposed, and the rate expressions derived are in good agreement with the experimental data.
A modification of regular solution theory to incorporate an improved approximation for pair distribution functions in mixtures
Authors: Gonsalves Joseph B. , Leland Thomas W. 
Published: June 2004

AbstractThe radial distribution functions for pairs in a fluid mixture can be closely approximated from known data on pair distribution functions pure components evaluated at a mean density determined by a properly defined average of molecular interaction parameters in the mixtures. This approximation has been used to replace the assumption about structure in mixtures inherent in the traditional regular solution theory. The result is a modified regular solution theory which gives an improvement in predicting excess thermodynamic functions and activity coefficients in mixtures involving appreciable differences in molecular size and shape.
Backmixing in gas‐liquid reactors
Authors: Shah Y. T. , Stiegel G. J. , Sharma M. M. 
Published: June 2004

AbstractThis review evaluates the present state of the art on backmixing in gas‐liquid and gas‐liquid‐solid reactors. A brief outline of numerous techniques for measuring residence time distribution (RTD) of various phases in a multiphase reactor is presented. This is followed by a brief description of differential and stagewise models for characterizing backmixing from RTD measurements. Both simple (that is, single‐parameter axial dispersion model) and more complex (that is, two‐, three‐, or four‐parameter models) models are evaluated. Backmixing characteristics of various gas‐liquid columns such as trickle beds, spray columns, mechanically agitated columns, plate columns, fluidized bed columns, etc., are subsequently evaluated. The performance of a bubble column under various reaction conditions is analyzed. Criteria for the elimination of backmixing in packed‐bed reactors are presented, and the effect of backmixing on the multiple steady states in a gas‐liquid reactor is briefly reviewed. Finally, the scale‐up problems associated with gas‐liquid reactors with various degrees of backmixing and the recommendations for the future work in RTD and macromixing models are outlined.
Theory of draw resonance: Part II. Power‐law and maxwell fluids
Authors: Hyun Jae Chun 
Published: June 2004

AbstractEmploying the same kinematic wave theory used in the previous paper on Newtonian fluids (Part I), draw resonance in isothermal spinning is solved analytically for both power law and Maxwell fluids. The critical drawdown ratios at the onset of draw resonance are again found by equating twice the throughput wave residence time to the thread‐line residence time yielding the same results reported by others through numerical calculations (Pearson and Shah, 1974; Fisher and Denn, 1976), thus confirming the premise that draw resonance is the result of the propagation of throughput waves.
The design of gas sparged devices for viscous liquid systems
Authors: Bhavaraju S. M. , Russell T. W. F. , Blanch H. W. 
Published: June 2004

AbstractDesign procedures for gas sparged contractors for both low and high viscosity liquids were developed to predict overall kLa. Bubble size close to the orifice, for moderately high gas rates, was found to increase at a rate proportional to one third power of gas rate and one tenth power of liquid viscosity. Bubble breakup phenomenon was shown to be related to liquid turbulence in the vessel rather than gas turbulence in the orifice. Procedures were developed through a simple liquid circulation model to obtain a criterion for the onset of bubble breakup. Results indicate that intense liquid mixing and high interfacial area can be achieved in low viscosity liquids by gas sparging alone. In high viscosity fluids, bubble breakup was not observed. The liquid circulation model predicts laminar flow at these experimental conditions over the complete range of gas rates observed.
Cold flow mixing rate data for pulverized coal reactors
Authors: Memmott Vincent J. , Smoot L. Douglas 
Published: June 2004

AbstractMixing rates of particles and gases in confined, coaxial jets are reported for tests with conditions simulating those of pulverized coal gasification and combustion processes. Gas velocity, particle mass flux, and gas composition were measured at various radial and axial locations downstream of the primary jet exit plane. Effects of inlet velocity, density, injection angle, particle loading level, and particle size on the rates of mixing were determined. Increasing injection angle and secondary velocity significantly increased gas and particle mixing rates, while effects of other variables were much less significant. Dispersion of particles lagged that of the gas in all cases investigated.
Mass transfer on a single sieve plate column operated with periodic cycling
Authors: Duffy G. J. , Furzer I. A. 
Published: June 2004

AbstractA single sieve plate column operated with periodic cycling was mathematically modeled using the assumption of zero weeping rate and plug flow of liquid during the liquid drain period. Zero weeping rates could only be obtained by introducing baffles to control fluid oscillations on the plate. Experimental measurements of the ratio of the slopes of the equilibrium and operating lines λ, the Murphree plate efficiency ε, the fraction of the liquid holdup transferred per cycle η, and the separation factor X on a computer controlled column provided the first reliable confirmation of the improvements in separating ability, predicted by the theory.
A rigorous method for calculating minimum reflux rates in distillation
Authors: Chien Henry H. Y. 
Published: June 2004

AbstractA computer method has been developed to calculate the minimum reflux rate for a specified distillation separation. The method makes no unnecessary simplifying assumptions of the distillation process model. The limitation of the method is that it cannot solve problems in which the minimum reflux rate is determined by a point of tangent between the operating line and the equilibrium line on a McCabe‐Thiele diagram (see Figure 1).
Synthesis of heat exchanger networks: II. Evolutionary generation of networks with various criteria of optimality
Authors: Linnhoff Bodo , Flower John R. 
Published: June 2004

AbstractAn evolutionary method is presented for the synthesis of heat exchanger networks. Starting from feasible solutions which preferably exhibit maximum energy recovery,The synthesis of such solutions has been discussed in Part I (see Linnhoff and Flower, 1978).
the method allows systematic promotion of desired design features such as low overall cost, suitability for starting‐up procedures, observation of safety constraints, etc. Seven examples based on standard literature problems are used to illustrate the method.
Dynamics and control of the activated sludge wastewater process
Authors: Attir Uri , Denn Morton M. 
Published: June 2004

AbstractThe dynamics of the activated sludge process are governed under certain conditions by interactions between the reactor and settler through sludge recycle. Settler underloading can lead to extremely sluggish system response, indicating that effective sludge height regulation is an important control objective. This objective may be in conflict with the need to maintain small variations in reactor solids concentration. An effective compromise can be achieved by using ratio control on both sludge recycle and settler underflow. This control policy does not require sludge storage.
Nucleation and growth rates of ammonium chloride in organic media: Development of an on‐line measurement technique
Authors: Shadman Farhang , Randolph Alan D. 
Published: June 2004

AbstractNucleation and growth rates of small ammonium chloride crystals precipitated from organic mother liquors were measured with an electronic particle counter using an on‐line measurement and data reduction technique. Current values for nucleation and growth rates could be obtained within a period of 3 min, thus permitting rapid scanning of variables affecting crystal size distribution. Population average sizes of 1 to 3μ were typically measured in these organic liquors. The average size of particles increased with increase in ammonium chloride solubility. Addition of surfactants (sodium dodecylbenzene sulfonate, sodium oleate) either had no effect on nucleation or inhibited growth and nucleation equally, thus did not change particle size. The average size of particles was slightly increased with addition of magnesium chloride.
A model for moving‐bed coal gasification reactors
Authors: Yoon Heeyoung , Wei James , Denn Morton M. 
Published: June 2004

AbstractA steady state model of moving‐bed coal gasification reactors has been developed. Model predictions are in agreement with published commercial plant data for Lurgi pressurized gasification reactors and a pilot plant slagging gasifier. The dependence of reactor performance on operating variables has been studied for Illinois and Wyoming coals. For a given coal, maximum efficiency is determined by the coal‐to‐oxygen feed ratio. The location of the maximum temperature, which defines the combustion zone, is an important operating variable. Efficient operation of the dry ash reactor cannot be carried out below a critical feed gas temperature because of insufficient gasification and excessive carbon loss in the ash.
Electrification of particles by impact on inclined metal plates
Authors: Masuda Hiroaki , Iinoya Koichi 
Published: June 2004

AbstractThe electrification of particles falling onto metal surfaces was well correlated with the normal component of the impact velocity, showing that the electrification was mainly caused by the deformation of contact bodies. The current generated by the electrification at higher impact velocities was proportional to the velocity, while the current at lower velocities showed a different tendency. The elastic and plastic‐elastic collision theory including particle roundness was used to explain these experimental results. Further, the coefficient of restitution, which was related to the work done by normal impulse, was determined by means of the velocity at the elastic limit obtainable from electrification data.
Prediction of the sorptional equilibrium relationship for the drying of foodstuffs
Authors: Rotstein Enrique , Cornish Alan R. H. 
Published: June 2004

AbstractAfter existing correlations were reviewed to predict the equilibrium of foodstuffs with moist air, it was found that they were not adequate. A new equilibrium expression is presented on the basis of equal chemical potentials in the external and internal phases. The resulting equation can be used over most of the range of moisture contents of sugar based foodstuffs including the high moisture region; it also provides simple analytical expressions for the partial derivatives of moisture content with respect to temperature and to water vapor activity.
Optimal determination of the vapor pressure critical exponent
Authors: Walton Clifford W. , Mullins Joseph C. , Holste James C. , Hall Kenneth R. , Eubank Philip T. 
Published: June 2004

AbstractCorrelations producing thermodynamic property tables employ the concepts of scaling with increasing frequency in the vapor‐liquid critical region. One of the important concepts is that the vapor pressure equation should provide infinite curvature and finite slope ψc at the critical point. The vapor pressure critical exponent θ describes the divergent curvature in a power law expression.This paper provides an extensive study of θ. We have determined an optimal value of θ by two general approaches: a curve fit method (CFM) which employs least‐squares analyses, and a numerical derivative method (NDM). The CFM is interpolative but requires a vapor pressure equation, while the NDM is extrapolative but is independent of the vapor pressure equation.The vapor pressure equations, which satisfy scaling concepts most closely, exhibit a very flat minima for the CFM. As a result, the values of θ which provide reasonable correlations vary over an appreciable range (depending upon the compound, form of the equation, and the temperature range). The NDM did not present any particular difficulties. Our overall weighted average for θ is 0.199 with a standard deviation of 0.052, while the overall numerical average was 0.225 with a standard deviation of 0.045; the final recommended value of θ is 0.22 ± 0.04.
An approximate theory of interfacial tensions of multicomponent systems: Applications to binary liquid‐vapor tensions
Authors: Winterfeld P. H. , Scriven L. E. , Davis H. T. 
Published: June 2004

AbstractFormulas obtained by approximation of the rigorous expression for the interfacial tension of multicomponent, polyatomic fluids are shown to provide accurate and simple estimates of the composition dependence of the surface tension of nonaqueous, binary solutions at low vapor pressures. Similar formulas are recommended for multicomponent (that is, more than two components) solutions.
Hydrodesulfurization of dibenzothiophene catalyzed by sulfided CoO‐MoO3γ‐Al2O3: The reaction network
Authors: Houalla Marwan , Nag N. K. , Sapre A. V. , Broderick D. H. , Gates B. C. 
Published: June 2004

AbstractKinetics experiments have determined the reaction network in the hydrodesulfurization of dibenzothiophene catalyzed by sulfided CoO‐MoO3/γ‐Al2O3 at 573°K and 102 atm. The predominant reaction is a direct sulfur extrusion, giving biphenyl and hydrogen sulfide; the biphenyl is subsequently hydrogenated slowly to give cyclohexylbenzene and then bicyclohexyl. Dibenzothiophene also undergoes a primary hydrogenation reaction preceding sulfur removal, but it is about one thousand times slower than the sulfur extrusion reaction.
Combined forced and free convection in a reverse osmosis system
Authors: Chang C. Y. , Guin J. A. 
Published: June 2004

AbstractThe influence of combined forced and free convection on the performance of a reverse osmosis system in a horizontal circular pipe is examined. The free convective motion, which is superimposed upon the main axial flow, is caused by buoyancy forces arising from the buildup of a dense solute boundary layer near the membrane surface. The three‐dimensional convective diffusion problem is solved by dividing it into a perturbation part accounting for the buoyancy effects present for Ra ≠ 0 and a nonperturbation part for the intrinsic convective flow pattern present even when Ra = 0.An approximate solution to the nonperturbation equations is obtained from the literature, and the perturbation equations are solved using a stream function‐vorticity scheme valid for high Schmidt numbers. The effects of rejection parameter, Rayleigh number, and pressure parameter on the Sherwood number and concentration polarization are studied. Correlations are developed for the asymptotic Sherwood number and the effective axial length at which free convection becomes significant. The numerical results are in reasonable agreement with limiting analytical solutions and with the experimental asymptotic Sherwood numbers measured by Derzansky and Gill (1974) and Hsieh et al. (1976).
Time resolution of rapid processes using numerical calculation and inversion of Laplace transforms
Authors: Hahn W. A. , Wendt J. O. L. 
Published: June 2004

AbstractA method for the interpretation of data which results from a signal altered by a process of known weighting function was developed. The method is based on the numerical evaluation and inversion of the Laplace transform. For two different weighting functions, it is shown how narrow a signal can be interpreted accurately. The method is then applied to coal volatilization data.
Experimental evaluation of analytical and Smith predictors for distillation column control
Authors: Meyer C. B. G. , Wood R. K. , Seborg D. E. 
Published: June 2004

AbstractTwo time delay compensation techniques, the Smith predictor and the analytical predictor, are used for bottom composition control of a pilot scale methanol‐water distillation column. The closed‐loop performance of the two predictor schemes is compared to that for a proportional‐integral controller in experimental and simulation studies. The predictors resulted in improved control for both set point and feed flow disturbances.
Origin and size distribution of secondary nuclei
Authors: Garside John , Rusli I. T. , Larson M. A. 
Published: June 2004

AbstractMicroscopic observations and Coulter counter measurements of the secondary nuclei produced when a parent crystal of potash alum was contacted with a solid rod suggest that these nuclei are born by an attrition mechanism which appears to be dependent on the growth rate of the crystal. The nuclei can be up to 50 μm in size. The nuclei smaller than about 4 μm are relatively insensitive to supersaturation, whereas the number greater than about 4 μm is approximately linear in supersaturation.
Continuous phase mass transfer during formation of drops from jets
Authors: Skelland A. H. P. , Huang Y‐F. 
Published: June 2004

AbstractThis study enables the extension of a recent design procedure for perforated plate extraction columns to include operation under jetting conditions. Correlations of experimental data are given for jet length, jet contraction, drop size, and mass transfer rates in continuous phase controlled liquid‐liquid systems. Systems exhibiting very low mass transfer rates were used, and this gave significantly different results from those obtained earlier with moderate rates of mass transfer.
Safety and reliability synthesis of systems with control loops
Authors: Kumamoto Hiromitsu , Henley Ernest J. 
Published: June 2004

AbstractA method of a reliability synthesis for a system with control loops is proposed by introducing a concept which we call a critical transition set. The set is an extended set of an exact failure mode and is important in that each occurrence of the system failure has to correspond to a mode in the set. This means that the system can be improved in such a way as to eliminate all the dominant modes in the set.First, the system diagram is obtained by connecting outputs of components to the inputs of succeeding components. Time delays are introduced in the feedback loops to represent the internal system state (memory). Then, the components are modeled by decision tables. The critical transition set can be obtained easily by simple tabular manipulations once the system failure is defined. Finally, the system reliability and availability improvements are made based on the set.