bluuebunny/crossref_metadata_2025 huggingface dataset:
A predictive model for rollover in stratified LNG tanks
Authors: Heestand Janet , Shipman C. W. , Meader J. W.
Published: June 2004

The incubation period preceding “rollover” within a stratified LNG tank involves intensive heat and mass transfers between layers. Numerical integration of equations describing these processes leads to predicted time‐history and boil‐off characteristics which are in excellent agreement with Sarsten's (1972) documentation of the LaSpezia rollover incident.
Characteristics of a transferred‐arc plasma
Authors: Mehmetoḡlu M. T. , Gauvin W. H.
Published: June 2004

The basic characteristics of a transferred arc argon plasma were determined using a cathode assembly suitable for transferring the electric arc to a molten metal bath or to a cooled anode. They indicated that the sustained voltage depended strongly on the arc length and much less on current. The inlet gas velocity past the cathode tip was determined to be an important operating parameter, rather than the volumetric gas flowrate.

The measurement of the axial and radial profiles of temperature was effected with ±8% accuracy by a novel diagnostic technique. Temperatures up to 18,500 K were observed on the axis of the plasma column, near the cathode tip, and decayed in both radial and axial directions. A sweeping microprobe was used to measure the axial and radial profiles of velocity. Velocities up to 190 m/s were recorded. The presence of a relatively colder flow surrounding the plasma column was detected. Mass and energy balances performed by taking this flow into account agreed with the measured input rates.
Turbulent velocity fluctuations that control mass transfer to a solid boundary
Authors: Campbell J. A. , Hanratty T. J.
Published: June 2004

The relation between the velocity and concentration fields for a fully developed turbulent flow which transfers mass to a pipe wall at large Schmidt numbers has been studied. Measurements of the fluctuations of the concentration gradient and the velocity gradient were obtained simultaneously at multiple locations on the wall. Spatial scales were calculated for the low frequency velocity fluctuations by passing the measured signals through low‐pass filters. These scales are the same size as the scales of the concentration fluctuations. This result provides additional support for the notion that mass transfer to a boundary at high Schmidt numbers in controlled by low frequency velocity fluctuations which contain only a small fraction of the total turbulent energy.
Gas absorption accompanied by an irreversible second‐order reaction in turbulent liquids
Authors: Haimour Noman , Sandall O. C.
Published: June 2004

Gas absorption accompanied by a second‐order irreversible reaction in turbulent liquid films (Re > 1,200) is described using the Danckwerts surface renewal theory. The model equations, consisting of two coupled, nonlinear partial differential equations, were solved numerically. Experimental data were obtained for the absorption of carbon dioxide into aqueous sodium hydroxide solutions flowing in a wetted wall column under turbulent flow conditions. The experimental mass transfer coefficients agree to within a mean deviation of 10.3% compared to predictions of the theoretical calculations. For this comparison, the rate of surface renewal was obtained from physical absorption experiments, the liquid viscosity and density were measured, and the reaction rate constant and all other physical properties were obtained from the literature. For the experiments the Reynolds number ranged from 1,400 to 5,300 and [OH−]b/[CO2]s varied from 9 to 29.
Discrete cell model of pore‐mouth poisoning of fixed‐bed reactors
Authors: Cho B. K. , Hegedus L. L. , Aris Rutherford
Published: June 2004

Catalyst deactivation in an isothermal fixed‐bed reactor under pore‐mouth poisoning conditions is investigated theoretically using a discrete mixing cell model. Two fundamental relationships which characterize the poisoning process in the reactor are identified and incorporated into the model to develop a simple graphical procedure for a quick, general insight into the problem. This graphical method is extended to design pellet impregnation profiles along the reactor which would give nondeteriorating reactor performance up to a given time. The effects of various system parameters on the lifetime and conversion performance of the reactor are also examined analytically, graphically and numerically.
Heat transfer to gas‐solids suspensions flowing cocurrently downward in a circular tube
Authors: Kim J. M. , Seader J. D.
Published: June 2004

Heat transfer to a gas‐solids suspension flowing cocurrently downward in a 13‐mm inside diameter tube with uniform heat‐flux boundary conditions was investigated using 329‐μm spherical glass beads in air. The gas Reynolds number varied from 0 to 30,000 with solids‐loading ratios of up to 20 at a gas Reynolds number of 10,000. The suspension Nusselt number, defined in terms of the wall‐to‐gas mixed‐mean temperature difference, decreased with increasing solids‐loading ratio at high Reynolds numbers, while it changed little from the value for gas alone at low Reynolds numbers. A possible explanation is given by considering the effects of particles on the fluid mechanical properties of the gas. Asymptotic Nusselt numbers in downflow are compared with results of other investigations for upflow.
Effect of addition of alcohols on gas holdup and backmixing in bubble columns
Authors: Kelkar B. G. , Godbole S. P. , Honath M. F. , Shah Y. T. , Carr N. L. , Deckwer W.‐D.
Published: June 2004

Gas holdup and axial dispersion coefficient data for dilute aqueous alcohol solutions and two different diameter columns at larger gas and liquid velocities compared to those of Schügerl et al. (1977) are presented. Data for cocurrent and batch systems are qualitatively explained using Zuber and Findlay's theory (1965) and bubble structure, and quantified further using a dynamic gas disengagement technique. Unified empirical correlations for the gas holdup and axial dispersion coefficients are presented.
New pressure drop correlation for sieve tray distillation columns
Authors: Bennett D. L. , Agrawal Rakesh , Cook P. J.
Published: June 2004

Pressure drop data for distillation sieve trays have been obtained with experimental trays with small outlet weir heights, including zero, and for trays with small perforations which exhibit large pressure drops due to surface tension. These data have been added to literature data to form a large composite data base with extensive variations in fluid and gas properties, flow rates, and tray designs.

A new pressure drop correlation has been developed which retains the use of the dry tray pressure drop, but provides new procedures for estimating liquid inventory and the resistance to vapor flow due to surface tension forces. This correlation gives a mean absolute error of 6.0% and an average error of −0.6%. These errors are significantly less than the errors between measurements and predictions from two other correlations using the same composite data base.
Effect of interfacial viscosities upon displacement in capillaries with special application to tertiary oil recovery
Authors: Giordano R. M. , Slattery J. C.
Published: June 2004

Washburn's equation has been generalized to explain the relative effects of the interfacial viscosities, interfacial tension, and wetting during displacement in a single, cylindrical capillary. The effect of the interfacial viscosities is to increase the resistance to displacement regardless of the wetting condition. The predictions of a prior qualitative theory for the relative effects of the interfacial viscosities and of interfacial tension during tertiary oil recovery are fully supported by this analysis. This discussion further indicates that the interfacial dilatational viscosity may be relatively more important than the interfacial shear viscosity.
New descriptions of dispersion in flow through tubes: Convolution and collocation methods
Authors: Wang J. Chih , Stewart W. E.
Published: June 2004

The convective dispersion of a solute in steady flow through a tube is analyzed, and the concentration profile for any Peclet number is obtained as a convolution of the profile for infinite Peclet number. Close approximations are obtained for the concentration profile and its axial moments, by use of orthogonal collocation in the radial coordinate. The moments thus obtained converge rapidly, and the concentration profile less rapidly, toward exactness as the number of collocation points is increased. A two‐point radial grid gives results of practical accuracy; analytical solutions are given at this order of approximation.
Particulate deposition from turbulent parallel streams
Authors: Im Kwan H. , Chung Paul M.
Published: June 2004

A theory is developed for the rate of particulate deposition from turbulent gas streams onto surfaces. Three characteristic times—the particle relaxation time, the turbulent fluctuation time, and the particle residence time—control the deposition mode. Two phenomena are primarily responsible for transport of the particles across the laminar sublayer and deposition: (1) the momentum imparted to the particle by the fluid turbulence; and (2) the thermospheresis caused by the temperature gradient near the wall. Interaction of the three characteristic times with these two phenomena is analyzed, and the particle deposition rate in turbulent pipe flow is computed. The findings are found to be in close agreement with available experimental data.
Laminar dilute suspension flows in plate‐and‐frame ultrafiltration units
Authors: Kleinstreuer Clement , Paller M. S.
Published: June 2004

A computer simulation model for suspension flows in plate‐and‐frame type membrane modules has been developed. Reduced forms of the mass transport and momentum equation were solved simultaneously to study concentration polarization and permeation flux decline. The verified simulator can be used to analyze and predict the process dynamics and can aid in the design of ultrafiltration systems.
Gas separation by permeators with high‐flux asymmetric membranes
Authors: Pan C. Y.
Published: June 2004

The permeation behavior of the high‐flux asymmetric membrane differs from that of the conventional symmetric membrane. A calculation method for predicting the gas separation performance of a permeator with asymmetric membrane is presented. The model takes into account the permeate pressure drop and is applicable to both hollow‐fiber and spiral‐wound modules. The effect of permeate‐feed flow pattern on module performance is analyzed. It is shown that for the high‐flux asymmetric membrane, the countercurrent flow pattern is not necessarily always the preferred operating mode. The mathematical model is verified by large‐scale field pilot‐plant experiments for helium recovery from natural gas using large hollow‐fiber modules (220 m2/unit).
Chain‐of‐rotators equation of state
Authors: Chien C. H. , Greenkorn R. A. , Chao K. C.
Published: June 2004

An equation of state is obtained to describe the fluid state from the supercritical gas to subcritical vapor and liquid for small and large molecules of organic and inorganic substances. The perturbation theory of the fluid state is extended to include rotational contribution of molecular motion in addition to translational and the attractive force contributions. Three equation constants describe a substance and values are presented for 22 substances. Application is made to mixtures with emphasis on their phase equilibria.
Optimal selection of intermediate storage tank capacity in a periodic batch/semicontinuous process
Authors: Karimi I. A. , Reklaitis G. V.
Published: June 2004

Batch/semicontinuous chemical plants are usually designed either by assuming infinite intermediate storage or by assuming that the units themselves act as storage vessels, while the storage vessels are sized by rules of thumb or experience. In this paper, the case of an intermediate storage vessel which links one upstream batch/semicontinuous unit to one downstream batch/semicontinuous unit is analyzed. The units are assumed to operate with fixed cycle times and capacities. Expressions for determining the minimum storage tank capacity necessary to decouple the two units are derived from a mathematical model of the periodic process. Effects of the relative starting times of the two units on the required storage capacity are determined, thus suggesting the optimum process timings to minimize the same. Application of the results is illustrated by an example.
Oil dispersion with a turbine mixer
Authors: Rounsley R. R.
Published: June 2004

A laboratory study was conducted to determine the factors influencing the dispersion of oil with a turbine mixer. Drop‐size distributions as a function of time were related to the impeller diameter, power expended in relation to the liquid volume, and the final emulsion temperature.

It was surprising that higher temperatures produced smaller mean drop diameters but at the expense of a wider distribution. An optimal batch size for the emulsion was found to exist in processing. Below this size, tank surface and internal turbulence waste much of the energy; above this size, the energy per unit volume became a critical factor.

Other trials were made to determine the effect of the turbulence of the tank surface, tank geometry, number of impeller blades, and turbine configuration. These all significantly affect drop size and should be considered in the design and selection of dispersing equipment.
Occurrence of methane hydrate in saturated and unsaturated solutions of sodium chloride and water in dependence of temperature and pressure
Authors: De Roo J. L. , Peters C. J. , Lichtenthaler R. N. , Diepen G. A. M.
Published: June 2004

Experimental results of the formation of methane hydrate in dependence of temperature and pressure in unsaturated solutions of NaCl in water will be presented in a temperature range from 261.85 to 285.98 K and pressure up to 11.0 MPa. Furthermore the four‐phase equilibrium NaCl·2H2Os CH4·nH2OsLG has been calculated from the experimental results. Also the heats of transformation of several other equilibria in the ternary system CH4H2ONaCl are obtained.
Single‐particle approach for analyzing flow systems. Part I: Visits to flow regions
Authors: Rubinovitch Michael , Mann Uzi
Published: June 2004

A methodology is presented for characterizing and analyzing general continuous flow system with special emphasis on particulate processes. The methodology is based on describing the history of individual particles (or fluid elements) in the process. The movements of particles are expressed in terms of the flow regions they visit using a Markov chain presentation. Explicit expressions as well as computational methods are derived for various process characteristics of interest. These include the distributions, means and variances of: the number of visits to any specified flow region; the total number of regions visited; and the number of visits to any specified set of regions. This methodology yields information on bulk properties as well as on individual particle behavior and deviations among particles.
Restrictive diffusion in aluminas
Authors: Chantong A. , Massoth F. E.
Published: June 2004

The effect of the ratio of solute molecular diameter to the substrate pore diameter on the diffusion of polyaromatic compounds in four different pore sizes of amorphous gamma‐aluminas was studied at atmospheric pressure and ambient temperature. Diffusion rates of the polyaromatic compounds in the aluminas decreased as the ratio of solute molecular diameter to pore diameter increased. Empirical correlations between the apparent reduction in solute effective diffusivity and the ratio of molecular diameter to pore diameter were obtained.
Regeneration of activated carbon. Part I: Thermal decomposition of adsorbed sodium dodecylbenzene sulfonate
Authors: Umehara Tadashi , Harriott Peter , Smith J. M.
Published: June 2004

Equilibrium adsorption isotherms and rates of thermal decomposition were measured for sodium dodecyl‐benzene sulfonate (DBS) adsorbed on powdered activation carbon. The rate data were obtained in a thermal gravimetric apparatus operated both at constant temperature (522 to 666 K) and with a constant rate of temperature increase from 298 to 1023 K.

About 50% of the adsorbed material could be removed at temperatures up to 748 K and only a small amount of the remaining 50% could be eliminated by further heating to 1,023 K. The residual adsorbate at 1,023 K was considerably greater than could be accounted for by inorganic materials such as Na2SO4.

The kinetics of the decomposition up to 748 K could be explained by a two‐reaction sequence, either parallel or consecutive reactions. Rates of decomposition were slower than found in earlier studies (Chihara et al., 1981) with adsorbed sucrose, and the kinetic steps were different. With sucrose, considerable decomposition occurred between 298 and 428 K. While with DBS, no decomposition was observed in this temperature range. Above 400 K, it was possible to explain the kinetics of decomposition in the case of sucrose by a single step forming residual carbon and volatile products, while with DBS, a two‐reaction sequence was required.
Studies in magnetochemical engineering. Part III: Experimental applications of a practical model for high‐gradient magnetic separation to pilot‐scale coal beneficiation
Authors: Liu Y. A. , Oak M. J.
Published: June 2004

The computer implementation and experimental verification of the practical model for high‐gradient magnetic separation (HGMS) based on particle buildup and feed characteristic, developed in Part II, are described. It is shown that the new model can be used to satisfactorily predict the grade, recovery and concentration breakthrough observed in pilot‐scale experimental studies of HGMS for the removal of sulfur and ash from water slurries of several pulverized Eastern coals. The experimentally verified model can be used to quantitatively identify the tradeoff of separation variables so as to optimize the magnetic removal of sulfur and ash from pulverized coal. The model can also be used to assess the technical and economical feasibility of the magnetic beneficiation of pulverized coal without extensive experimental tests.
Moving boundary problems in simple shapes solved by isotherm migration
Authors: Talmon Y. , Davis H. T. , Scriven L. E.
Published: June 2004

The Modified Isotherm Migration Method (MIMM) is developed for solving one‐dimensional Stefan‐type problems of multifront propagation in slabs, cylinders and spheres with a boundary condition of the third kind (radiation‐type boundary condition). The method is illustrated for all three geometries with applications to the thawing of ice and to the freezing of a 50–50 dispersion of tetradecane in water, a system in which two freezing fronts propagate simultaneously.
Kinetics of the approach to sorptional equilibrium by a foodstuff
Authors: Roman G. N. , Urbicain M. J. , Rotstein Enrique
Published: June 2004

The kinetics of equilibration of a vegetable foodstuff with moist air are studied on the basis of its cellular structure. The problem is modelled as a coupled heat and mass transfer phenomenon; since there is a significant shrinkage as moisture decreases, the model takes the effect into account by changing the basis for the mass and energy balances. The resulting nonlinear second‐order partial differencial equations are solved numerically; predicted values of moisture decrease and temperature gain with time are compared with experimental data. A sensitivity analysis of the solution to values of the transport properties shows that the value of effective diffusivity and heat and mass transfer coefficient may alter significantly the predicted equilibration kinetics and center temperature. The adopted value for heat of sorption has less influence. Changes in effective thermal conductivity and porosity bear little influence on predictions.
Fluidized‐bed reactor model with generalized particle balances. Part II: Coal combustion application
Authors: Overturf B. W. , Reklaitis G. V.
Published: June 2004

The model described in Part I is applied to study an atmospheric fluidized‐bed coal combustor. Extensive case studies are investigated on the effects of: enhanced grid region heat and mass transfer; bed void fraction; emulsion phase temperature; elutriation rates; reaction rate parameters; feed particle‐size distribution; and particle superheat. Comparison is made with experimental results reported by Babcock and Wilcox. Proper representation of the grid region and use of actual feed distributions are shown to be essential to predicting combustor performance. Better particle elutriation and single‐particle combustion submodels are found to be key requirements for improved combustor modeling.
Anomalous diffusion of vapors through solid polymers. Part II: Anomalous sorption
Authors: Neogi P.
Published: June 2004

Sorption of vapors in polymer membranes in the vicinity of and below the glass transition temperatures do not follow the Fickian (classical) diffusion. The reasons have been attributed to the molecular relaxation which affects both diffusivities and solubilities.

A time‐ and memory‐dependent diffusion coefficient has been evaluated in Part I, in a form which is analogous to the treatment in the rheology of such materials. Together with a time‐dependent solubility, the conservation equation for the sorption process has been solved. Two special cases are considered, where the relaxation times are short and where they are long. The results explain the anomalous behavior observed in the experiments. Comparison with the experiments has been made.
Vapor‐liquid equilibria for NH3 and H2O in the 100 to 150°C region: Effect of low levels of phenol on partial pressure of ammonia
Authors: Pawlikowski E. M. , Newman John , Prausnitz J. M.
Published: June 2004

Experimental results are reported for the partial pressure of ammonia in water solutions containing low concentrations of phenol. Experiments were performed in 0.6 molal phenol at 100 and 150°C. Results at 150°C indicate that the very small effect of phenol on the partial pressure of ammonia is within the limit of experimental error, 3%, and therefore could not be established from the data. However, at 100°C, the partial pressure of ammonia was decreased by nearly 10%. Computer program TIDES—a computerized thermodynamic framework for calculating vapor‐liquid equilibria for volatile weak electrolytes and other common gases—has been revised to account for the effect of low concentrations of phenol.
Influence of mixing state of carrier fluid in nonlinear equilibrium exchange systems
Authors: Schweich D.
Published: June 2004

It is shown that for a given residence time distribution of carrier fluid and a given nonlinear adsorption isotherm of a single solute, the breakthrough curve is not uniquely defined. The special case of a one‐dimensional dispersive flow is examined. It is shown that with a simple but realistic model for the residence time distribution, the classical self‐sharpening front becomes a continuously broadening front. Two extreme models are proposed to describe the behavior of any front in a flow system with a given residence time distribution. This study seems of crucial importance in systems for which this residence time distribution is the only available information about the flow pattern.
Pore‐diffusion model for cyclic separation: Temperature swing separation of hydrogen and methane at elevated pressures
Authors: Tsai M. C. , Wang S. S. , Yang R. T.
Published: June 2004

A pore‐diffusion model is developed for temperature swing separation in a packed bed of sorbent. The model is applied to interpret experimental data for separation of H2 of CH4 in a packed bed of activated carbon operated in the temperature swing mode, at pressures up to 5.52 MPa. Experimental results on the effects of total pressure, particle size, adsorption temperature, and flow rate on separation efficiency compared favorably to the model predictions. The importance of pore diffusion in separation has been clearly demonstrated.
Hydrodynamic model for gas‐liquid slug flow in vertical tubes
Authors: Fernandes R. C. , Semiat R. , Dukler A. E.
Published: June 2004

A series of equations are developed based on the physical processes thought to take place during slug flow which are used to predict the hydrodynamic character of this complex flow pattern. New experimental results are reported which appear to validate the model.
High‐temperature mutual solubilities of hydrocarbons and water. Part I: Benzene, cyclohexane andn‐hexane
Authors: Tsonopoulos Constantine , Wilson G. M.
Published: June 2004

The mutual solubilities at the three‐phase equilibrium pressure of three C6hydrocarbons (benzene, cyclohexane andn‐hexane) and water have been experimentally investigated up to 482 K. A thermodynamic analysis of these new measurements and of critically selected literature data has been carried out to the three‐phase critical end point. Information is also provided on the two‐phase critical locus. The solubility of hydrocarbons in water has been used to calculate Henry's constants, while the solubility of water in the hydrocarbons has been correlated with a modified version of the Redlich‐Kwong equation of state. Consideration is also given to the effect of pressure on the mutual solubilities.
Hydrogenation reactions of model titanium compounds under coal liquefaction conditions
Authors: Treblow M. , Spitler C. A. , Brown F. R.
Published: June 2004

Used catalyst and reactor deposits from a fixed‐bed coal liquefaction unit show high concentrations of titanium and boron. The titanium was present as anatase, a titania polymorph. Hydrogenation reactions with and without catalyst were performed with model titanium and boron compounds under liquefaction conditions. The catalyst used was Harshaw 0402T 3% CoO – 15% MoO3 on an alumina‐silica support. Rutile remained unchanged by reactor conditions. In all other runs the titanium starting material, whether organic or inorganic in nature, converted to anatase. When the deposition of the reaction products was monitored, only that anatase derived from organic titanium compounds accumulated on and in the catalyst pellets to an appreciable extent.
Bubble formation at vibrated orifices: Medium‐chamber‐volume region
Authors: Baker C. T. , de Nevers Noel
Published: June 2004

The bubble formation process at small, single, circular orifices at low gas flow rates is modified when the system is vertically vibrated in a sinusoidal fashion.

For systems with significant gas chamber volume, bubble volume in the vibrated case is smaller than in the nonvibrated case. The vibrations increase the amount of liquid weeping through the orifice into the gas chamber. A simple inviscid model adequately predicts bubble formation in the medium‐chamber‐volume region at low values of amplitude and frequency of vibration and low viscosities. The boundaries of the transition from the FR ≫ 1 to the FR = 1 regions are described in terms of “the acceleration number/Eötvös number”.
Effects of radially nonuniform distributions of catalytic activity on performance of spherical catalyst pellets
Authors: Johnson D. L. , Verykios X. E.
Published: June 2004

The performance of spherical catalyst pellets with radially nonuniform distributions of activity is simulated under parallel reaction networks closely resembling hydrocarbon oxidation reactions. Both reaction paths are assumed to be exothermic with the desired path exhibiting lower activation energy requirements than the undesired one. It is shown that nonuniform activity distributions enhance effectiveness and selectivity over a large range of values of the Thiele modulus. Multiple steady states in effectiveness and selectivity are observed for certain values of the heat of reaction parameter.
Antimisting action of polymeric additives in jet fuels
Authors: Chao K. K. , Child C. A. , Grens E. A. , Williams M. C.
Published: June 2004

Polymeric solutes in jet fuel can serve to increase greatly the droplet size and reduce flammability in fuel sprays created by high‐velocity wind shear. Photographic and spark‐ignition studies show that high molecular weight polyisobutylenes can be effective at levels below 100 ppm, where they cause only slight increases in fuel viscosity. The effectiveness of the polymers increases with molecular weight and is very well correlated by the elongational viscosity of the solution, as measured by the ductless siphon height.
Characterization of mixing in reactor systems through analysis of regional tracer dilution data obtained with a gamma camera
Authors: Castellana F. S. , Friedman M. I. , Spencer J. L.
Published: June 2004

A new approach to the characterization of flow patterns and mixing through analysis of regional tracer dilution data obtained with a gamma camera is presented. Studies performed in a small, two‐dimensional, multiple‐inlet vessel demonstrate the experimental technique and how data are analyzed to determine the intravessel spatial distribution of fluid deriving from the traced stream. Good agreement is shown between calculated values of the flow distribution and visually observed flow patterns.
Hydrodynamics and mass transfer in non‐Newtonian solutions in a bubble column
Authors: Godbole S. P. , Schumpe A. , Shah Y. T. , Carr N. L.
Published: June 2004

Until now the oxygen transfer in viscous non‐Newtonian solutions has been studied only in bubble columns of about 0.14‐m diameter. Recently Godbole et al. (1982) reported much smaller gas holdups in Carboxy Methyl Cellulose solutions (CMC) for a large‐diameter column. Therefore, the gas holdups, volumetric mass transfer coefficients, and specific gas‐liquid interfacial areas are measured in CMC solutions using a bubble column of diameter 0.305 m and height 3.4 m. The transition from churn‐turbulent to slug flow regime occured at higher viscosities and the gas holdups and volumetric mass transfer coefficients were lower in both flow regimes than reported for smaller column diameters. Empirical correlations are presented for the gas holdup, volumetric mass transfer coefficient, and specific gas‐liquid interfacial area which would be suitable for the design of fermentors.
Optimal operation of integrated processing systems: Part II: Closed‐loop on‐line optimizing control
Authors: Garcia C. E. , Morari Manfred
Published: June 2004

A method for tracking the economically optimal operating conditions of a chemical process in the presence of constraints is developed. The technique is based on an on‐line search rather than a fundamental model. The most profitable operating point is found by fitting a dynamic model of the process based on data obtained from experimental moves on the plant.

This model is used to compute gradients of the economic objective and of the constraints so that a direction of economic improvement inside the allowed operating region of the plant is always obtained. Constraint violations during the transients are prevented by a multivariable regulator. A new regulation method (Internal Model Control) is used which permits explicit handling of constraints and which can be made robust against modelling errors. This combined optimization/regulation approach is tested in a demonstrative simulation example and shown to be reliable for following a moving optimum and safely handling complex constraint moves.
Critical point measurements on nearly polydisperse fluids
Authors: Morrison G. , Kincaid J. M.
Published: June 2004

The critical temperatures, pressures and volumes of several mixtures containing CO2, C2H6, C3H8, and C4H10 have been measured using a heavy walled, variable volume, cylindrical glass vessel. In each mixturre the relative proportions of the three hydrocarbon solutes to one another were changed; total solute mole fraction never exceeded 0.1. A detailed study of the mixture CO2 + C3H8 shows that the critical temperature exhibits a minimum at a C3H8 mole fraction of 0.0265. Our mixture data are analyzed using a polydisperse model of dilute solutions.
Precipitation and dissolution of solids attending flow through porous media
Authors: Walsh M. P. , Bryant S. L. , Schechter R. S. , Lake L. W.
Published: June 2004

A model is developed that calculates the chemical equilibrium that exists between a flowing electrolyte solution and mineral assemblages. The development computes the mineral and aqueous compositions as a function of time and position in a one‐dimensional porous medium. The model considers the dissolution of solids as well as their precipitation. The application of the model to various problems has revealed that characteristic aqueous and solid phase concentration waves develop and propagate through the system in a chromatographic manner. Example calculations are presented that illustrate the widespread applicability of the model. Specifically, a calculation is presented that reproduces the genetic mineralization features that are found in sandstone‐type uranium deposits.
Stratified turbulent‐turbulent gas‐liquid flow in horizontal and inclined pipes
Authors: Shoham Ovadia , Taitel Yehuda
Published: June 2004

A two‐dimensional model for stratified turbulent‐turbulent gas‐liquid flow in inclined pipes is proposed. The gas phase is treated as bulk flow, but an exact solution is carried out for the liquid phase, applying the eddy viscosity theory to model the turbulent viscosity. The interfacial structure is taken into consideration using appropriate correlations for the interfacial shear stress. The model is capable of predicting the liquid velocity field, holdup and pressure drop given gas and liquid flow rates, physical properties, pipe size, and angle of inclination. The results are substantially better than the prediction of Lockhart and Martinelli (1949) correlation and better than the Taitel and Dukler (1976) model for stratified flow.
Complex nature of the sulfation reaction of limestones and dolomites
Authors: Chang E. Y. , Thodos George
Published: June 2004

Experimental information available in the literature for the sulfation of a wide variety of calcined limestones and dolomites has been used to establish rates of reaction over their entire range of conversion. The reaction rate was found to decay exponentially with extent of conversion and implicated parameters related to two factors, each factor representing a diffusional resistance. These factors define two generalized constants which permit the prediction of the decaying parameters associated with the sorptive capacity of the sorbent.

The sorptive capacity, x∞, which represents the ultimate conversion of the solid sorbent, has been found to depend on the pore size distribution, the chemical composition of the limestone and/or dolomite and its accessible pore surface area. The combined contribution of x∞ along with predicted parameters permit the calculation of conversion vs. time relationships that are found in close agreement with experimental measurements for the ten sorbents investigated, with the exception of one.
Breakage functions for droplets in agitated liquid‐liquid dispersions
Authors: Narsimhan Ganesan , Nejfelt Gregory , Ramkrishna Doraiswami
Published: June 2004

Photographic measurements of transient drop‐size distributions from stirred liquid‐liquid systems of low dispersed phase fraction in a batch vessel confirm consistency with a similarity behavior from population balance established earlier by Narsimhan et al. (1980). Moreover, breakage functions are presented in generalized dimensionless form accounting for dependence on physical properties of the system and power input through stirring. This information is essential for predicting drop‐size distributions in stirred liquid‐liquid systems. Experimental measurements of steady‐state drip‐size distributions obtained from stirred, continuous flow systems with known inlet drop sizes compare very favorably with theoretical predictions based on population balance analysis using the breakage functions obtained from batch experiments.
Kinetics of hydration‐dehydration reactions considered as solid transformations
Authors: Stanish M. A. , Perlmutter D. D.
Published: June 2004

A mechanism is proposed for the dehydration‐rehydration process in solid inorganic salts, and model rate equations are derived and applied to the observed behavior of potassium carbonate. Quantitative expressions for the effect of pressure on the reaction rates are derived using basic principles from nucleation and heterogeneous phase transformation theory. Model equation predictions agree with experimental dehydration and rehydration rate data at all but extreme pressures. The basic rate equation is also used to interpret the data of Eckhardt and Flanagan (1964) for the effect of pressure on the dehydration of manganous formate dihydrate. The mechanism on which the model equations are based is also consistent with the observed effects of cycling and of high temperature pretreatment on the K2CO3 rehydration rate.
Analytical solution using a pore diffusion model for a pseudoirreversible isotherm for the adsorption of basic dye on silica
Authors: McKay Gordon
Published: June 2004

An analytical solution for a two resistance mass transfer model explaining the adsorption of Astrazone Blue dye (Basic Blue 69) onto Sorbsil silica has been developed. The model includes a film mass transfer coefficient, kf1 = 80 × 10−6cm·s−1, and an internal effective diffusivity, Deff = 18×10−9cm2·s−1 which controls the internal mass transport processes based on a pore diffusion mechanism.
High‐pressure phase equilibria for the water/methane system
Authors: Larsen E. R. , Prausnitz J. M.
Published: June 2004

A semitheoretical method has been established for superimposing the residual thermodynamic properties of pure methane and of pure water over wide ranges of pressure (0.01 to 1,000 MPa) and temperature (triple point to twice the critical temperature). Using reasonable mixing rules with two binary parameters, this superposition also gives mixture properties, including high‐pressure vapor‐liquid equilibria.
Deactivation of hydrodesulfurization catalysts by metals deposition
Authors: Ahn Bum‐Jong , Smith J. M.
Published: June 2004

Primary causes of deactivation of hydrodesulfurization catalysts are partial poisoning of the interior pore surface and pore‐mouth plugging by deposition of metals from organo‐metallic compounds in the reactor feed. A model is developed to account for both causes of deactivation. It can be used to predict which occurs first: complete surface poisoning or pore‐mouth plugging. Equations are formulated for catalyst activity as a function of time for demetallization and also for desulfurization. The results depend upon particle geometry and geometry of deposited species, Thiele moduli for demetallization and desulfurization, and relative rates of desulfurization on fresh and partially poisoned catalytic surfaces. The treatment is for a single, isothermal catalyst particle.
Numerical methods of solution for continuous countercurrent processes in the nonsteady state part II: Application of numerical methods
Authors: Tan K. S. , Spinner I. H.
Published: June 2004

The numerical methods developed in Part I are applied to a number of important countercurrent processes. Examples involving simultaneous input disturbances, distributed disturbances, Langmuir isotherms, and nonlinear coupled boundary conditions are tested. These examples, if solved by previous methods, would have required interpolation or iterative procedures, but are solved efficiently and accurately by the explicit algorithms and coding sequence developed in Part I.

The solutions for a linear system are in excellent agreement with the analytic solution. Numerical solutions obtained from explicit algorithms based on a nonlinear rate expression also shows very good agreement with the analytic solutions of Thomas (1944) for a fixed bed process. In both cases good accuracy is obtained with as few as sixteen increments.
Collision rate of small particles in a homogeneous and isotropic turbulence
Authors: Yuu Shinichi
Published: June 2004

A theoretical equation is derived for the collision rate of aerosol particles in a homogeneous and isotropic turbulent system. This equation takes into account the relative velocity between fluid and particles. The calculated results indicate that the relative velocity between fluid and particles is the main factor in the turbulent coagulation (agglomeration, coalescence) of unequally sized particles in an air flow. This hold true, even when the particle sizes are less than 1 micron. For particles of equal radii the coagulation coefficient reaches its minimum value, because the effect of motion relative to the fluid now becomes zero and only the spatial variation of turbulent motion remains to cause collisions between the particles. For particles following a fluid motion completely, as in a water stream, the equation for the collision rate reduces to the Saffman and Turner equation.
Olefins and BTX‐production by thermal cracking of hydrotreated vacuum gas oil and related fractions
Authors: Clymans P. J. , Froment G. F. , Berthelin M. , Trambouze P.
Published: June 2004

Aramco vacuum gas oil was catalytically hydrotreated to conversions of 20, 40 and 60%, and subsequently fractionated into naphtha, kerosene, gas oil, and hydrotreated vacuum gas oil. These fractions were thermally cracked to test their potential as feedstock for olefins and BTX production. The olefin yields from the hydrotreated vacuum gas oil obtained from hydrotreating with 40 and 60% conversion favorably compare with those of straight‐run naphthas. Cracking in conventional naphtha/atmospheric gas oil units becomes possible. The naphtha, kerosene and gas oil fractions are preferably added to standard refinery streams.
Initial value approach to a class of reaction‐diffusion systems
Authors: Namjoshi A. N. , Kulkarni B. D. , Doraiswamy L. K.
Published: June 2004

New sets of transformations that convert an original two‐point boundary value problem into an equivalent initial value problem have been proposed and illustrated in the solution of the diffusion‐reaction problem for a monodispersed catalyst pellet. The use of the transformations reduces the computational effort considerably. The method is especially useful in the analysis of more complex cases, such as bidispersed catalyst pellets, catalysts undergoing decay, and gas‐solid noncatalytic reactions where the use of the conventional numerical techniques is quite involved and cumbersome. The method is applied to some known and to some yet‐unresolved cases and the new results obtained are discussed.
Hindered diffusion of gases in “Leaky” membranes using the dusty gas model
Authors: Macelroy J. M. D. , Kelly J. J.
Published: June 2004

The modified Enskog theory of van Beijeren and Ernst for dense fluid mixtures of rigid spheres is applied to diffusion of inert, nonadsorbing gases in microporous “leaky” membranes. Utilizing the concept of a dense dusty gas, the resulting expressions for the permeability and flux ratio illustrate the influence of steric hindrance on the transport process. The results obtained serve as corrections to the original dusty gas model of Mason and others.
Development of improved bubble disruption and dispersion technique by an applied electric field method
Authors: Ogata Sumitoshi , Tan Kazushi , Nishijima Kiyoto , Chang Jen‐Shih
Published: June 2004

With the aid of nonuniform DC electric fields, an improved bubble disruption and dispersion technique has been developed for dielectric fluid bubble column reactors. The basic mechanisms which lead to bubble disruption and dispersion in the system have been studied both experimentally and theoretically. The influence of operating variables, liquid properties and electrode geometry on the present applied electric field method has been conducted. The efficiency of power consumption by using the present technique has also been revealed.
Conditions imposed by process statics on multivariable process dynamics
Authors: Koppel L. B.
Published: June 2004

The steady‐state behavior of a multivariable process system imposes certain necessary conditions on its dynamic behavior, particularly in any feedback control system containing integral action. These conditions are derived in general and compared with previous restricted results. A more flexible design view is allowed by the general result.
Calcination kinetics and surface area of dispersed limestone particles
Authors: Borgwardt R. H.
Published: June 2004

The rates of calcination of two types of limestones, ranging in particle size from 1 to 90 μm, were measured over the temperature range 516 to 1,000°C. A kinetic model based on the B.E.T. (Brunauer‐Emmett‐Teller method) surface area of the CaCO3 correlates the results over 5 orders of magnitude in reaction rate. The B.E.T. surface area of CaO formed by rapid calcination in dispersed‐particle systems is 50 to 90 m2/g.
Hydrodynamics of fluidization: Prediction of wall to bed heat transfer coefficients
Authors: Syamlal M. , Gidaspow Dimitri
Published: June 2004

A computer model for a hot fluidized bed was developed. The large heat transfer coefficients characteristic of fluidized beds were computed without an enhancement of heat transfer by turbulence. They agreed with measurements reported by Ozkaynak and Chen (1980) within the accuracy of estimated thermal conductivity of solids.
Gas‐liquid mass transfer in fluidized particle beds
Authors: Nguyen‐Tien K. , Patwari A. N. , Schumpe A. , Deckwer W.‐D.
Published: June 2004

Gas/liquid mass transfer has been studied in air/water fluidized beds of 0.05‐8 mm glass spheres in a 0.14 m diameter reactor. The volumetric mass transfer coefficients kL a were independent of bed height, and, for particle diameters up to 1 mm, decreased linearly with solids concentration. Low solids loadings as well as large diameter particles significantly increased kL and a, respectively, as compared to the two‐phase system.
Removal of colloidal particles in electroflotation
Authors: Fukui Yoshihiro , Yuu Shinichi
Published: June 2004

The collection mechanism of polystyrene latices of 0.6 μm in diameter in electroflotation has been examined both theoretically and experimentally as extension of our previous work (1980). To avoid the change of surface state of particle bubble, the experiment was conducted under the condition that the concentration of CTAB (cetyl trimethylammonium bromide), cationic surfactant in the solution, is within the 90% of its initial concentration. It is of interest that the theory predicts the collection efficiency to vary as d.
Vacancy solution theory of adsorption using Flory‐Huggins activity coefficient equations
Authors: Cochran T. W. , Kabel R. L. , Danner R. P.
Published: June 2004

New equations for the physical adsorption of gases on solids have been developed based on the vacancy solution model of adsorption in conjunction with the Flory‐Huggins activity coefficient equations. The isotherm equation contains three regression parameters: a Henry's law constant, the limiting amount of adsorption, and a gas‐solid interaction term. Pure‐gas data over a range of temperature can be correlated using only five parameters. Gas‐mixture equilibria can be predicted using only the parameters obtained from the pure‐gas data. Pure‐component, binary, and ternary adsorption equilibrium data on activated carbons, silica, and zeolites over a wide range of conditions have been used to evaluate the model. The results show that, except for a few systems, this model predicts gas‐mixture equilibria better than any other model.