bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of the freeboard region in a fluidized bed catalytic cracking regenerator
Authors: De Lasa Hugo I. , Grace John R. 
Published: June 2004

AbstractA model is developed for a fluidized bed reactor with the dense phase region treated by conventional two‐phase models. Conversion in the freeboard is obtained based on particle trajectories predicted from drag considerations. The model is applied to an industrial‐scale catalytic cracking regenerator. It is shown that the freeboard region can have an important influence on the overall conversion in the unit.
Computation of phase and chemical equilibrium: Part II. Phase‐splitting
Authors: Gautam Rajeev , Seider Warren D. 
Published: June 2004

AbstractA phase‐splitting algorithm is coupled with the Rand method to improve its efficiency and reliability when the phase distribution is unknown at equilibrium. The coupled algorithm works well to give phase‐splits in the metastable region where most stability tests fail. Exhaustive tests show fine performance in the region near liquid‐liquid phase envelopes for systems with at least one partially miscible binary pair.
Computation of phase and chemical equilibrium: Part III. Electrolytic solutions
Authors: Gautam Rajeev , Seider Warren D. 
Published: June 2004

AbstractMethods for estimating the properties of electrolytic solutions are reviewed, with emphasis on molecule‐molecule, molecule‐ion, and ion‐ion interactions. The algorithms of Parts I and II, to search for global minimum in Gibbs free energy, are extended to handle electrolytes and compared with an algorithm using k‐values. Results are presented for SO2‐H2O and H2S‐NH3‐H2O systems and agree with experimental values.
Diffusion of gases through surfactant films: Interfacial resistance to mass transfer
Authors: Nguyen Ly L.‐A. , Carbonell R. G. , Mc Coy B. J. 
Published: June 2004

AbstractA model is proposed for mass transfer of gases across surface‐active films and into an aqueous phase. The interfacial region (1) obeys local equilibrium conditions, (2) has a capacity for the dissolved gases greater than the solubility in water, and (3) has a diffusion coefficient three orders of magnitude less than for that in water. The model is solved for and compared with three different experiments: the transient diffusion through monomolecular films into quiescent liquids studied by Plevan and Quinn (1966), the gas absorption through surfactant films into falling liquid films investigated by Emmert and Pigford (1954), and the frequency response of concentration pulses in surfactant films reported by Whitaker and Pigford (1966). The model consistently describes these experiments previously explained by three different models that either ignored the capacitance of the film or assumed local non‐equilibrium.
Axial dispersion through tube constrictions
Authors: Weaver David W. , Ultman James S. 
Published: June 2004

AbstractTracer gas dispersion was measured for laminar flow through three different tube constrictions, at orifice Reynolds numbers between 10 and 5000 and Schmidt numbers of 0.213 and 0.769. Each constriction generates a confined jet which significantly enhances axial dispersion at intermediate Reynolds numbers ranging from 100 to 1000.
Kinetics of non‐isothermal sorption in molecular sieve crystals
Authors: Ruthven Douglas M. , Lee Lap‐Keung , Yucel Hayrettin 
Published: June 2004

AbstractA mathematical model is developed to describe non‐isothermal sorption kinetics and used to interpret experimental uptake curves for CO2 in 4A zeolite and for CO2 and in C5H12 in 5A zeolite. The model assumes that the dominant mass transfer resistance is intracrystalline diffusion while the major resistance to heat transfer is the external heat transfer between the adsorbent sample and the surroundings. It gives a good representation of the kinetic behavior over a wide range of conditions. Both the extreme cases of isothermal diffusion and complete heat transfer control are demonstrated experimentally. Intermediate situations, in which the uptake rate is controlled by the combined effects of diffusion and heat transfer, are demonstrated as well. The parameters derived from the model are consistent, reproducible, and agree well with a priori estimates. The model provides a useful theoretical basis for the analysis of rapid sorption processes for which the non‐isothermal approximation is invalid.
Cluster diffusion in liquids
Authors: Cussler E. L. 
Published: June 2004

AbstractDiffusion in concentrated, non‐ideal liquid solutions may take place not only through motion of single molecules but also through movement of groups of molecules, or “clusters.” Analyzing this cluster diffusion leads to predictions that the diffusion coefficient can vary with the square root of the usual activity corrections to diffusion. These predictions seem consistent with experiments, particularly in highly non‐ideal solutions.
Studies in the synthesis of control structures for chemical processes: Part I: Formulation of the problem. Process decomposition and the classification of the control tasks. Analysis of the optimizing control structures
Authors: Morari Manfred , Arkun Yaman , Stephanopoulos George 
Published: June 2004

AbstractPart I of this series presents a unified formulation of the problem of synthesizing control structures for chemical processes. The formulation is rigorous and free of engineering heuristics, providing the framework for generalizations and further analytical developments on this important problem.Decomposition is the underlying, guiding principle, leading to the classification of the control objectives (regulation, optimization) and the partitioning of the process for the practical implementation of the control structures. Within the framework of hierarchical control and multi‐level optimization theory, mathematical measures have been developed to guide the decomposition of the control tasks and the partitioning of the process. Consequently, the extent and the purpose of the regulatory and optimizing control objectives for a given plant are well defined, and alternative control structures can be generated for the designer's analysis and screening.In addition, in this first part we examine the features of various optimizing control strategies (feedforward, feedback; centralized, decentralized) and develop methods for their generation and selective screening. Application of all these principles is illustrated on an integrated chemical plant that offers enough variety and complexity to allow conclusions about a real‐life situation.
Stochastic simulation of the motion, breakup and stranding of oil ganglia in water‐wet granular porous media during immiscible displacement
Authors: Ng K. M. , Payatakes A. C. 
Published: June 2004

AbstractThe problem of immiscible displacement of oil ganglia arises in connection with oil bank formation and attrition during enhanced oil recovery with flooding. A stochastic simulation method is developed here, which enables prediction of the fate of solitary ganglia during immiscible displacement in water‐wet unconsolidated granular porous media. This method takes into account the local topology of the porous medium; the initial size, shape and orientation of the oil ganglion and the capillary number. For each ganglion size, hundreds of realizations are performed with random ganglion shapes for a 100 × 200 sandpack. These results are averaged to obtain probabilities of mobilization, breakup and stranding as functions of capillary number and ganglion size. Axial and lateral dispersion coefficients are obtained as functions of the average ganglion velocity. The results from the solitary ganglion analysis can be used with the ganglion population balance equations developed in a companion publication (Payatakes, Ng and Flumerfelt, 1980) to study the dynamics of oil bank formation.
Effect of sludge funneling in gravity thickeners
Authors: Dixon D. Christopher 
Published: June 2004

AbstractThe performances of cylindrical and conical thickeners are compared by means of calculations, using published data on the properties of a suspension. Experimental data on the operation of cylindrical thickeners indicate that sludge funneling at the bottom of such thickeners has a large effect and is a possible cause of observed discrepancies between theory and experiment.
Conjugate unsteady heat transfer from a droplet in creeping flow
Authors: Abramzon Boris , Borde Irene 
Published: June 2004

AbstractThe phenomenon of unsteady heat transfer from a spherical droplet or solid particle moving slowly in a different fluid is analyzed, for the case in which the thermal resistances of the dispersed and continuous phases are comparable. The effect of the Peclet number (over the range 0 ⩽ Pe ⩽ 1,000) and of the internal circulation of the droplet on the development of temperature fields is investigated. The energy equations for the interior and exterior of the droplet are solved by the finite‐difference method of alternating directions. The results are compared with a number of previously published approximate models.
The critical velocity in pipeline flow of slurries
Authors: Oroskar Anil R. , Turian Raffi M. 
Published: June 2004

AbstractIn slurry transport, the critical velocity is defined as the minimum velocity demarcating flows in which the solids form a bed at the bottom of the pipe (bed load flows) from fully suspended flow. An analysis based on balancing the energy required to suspend the particles with that derived from dissipation of an appropriate fraction of the turbulent eddies is used to develop a correlation for prediction of the critical velocity. Comparison of the results with available experimental critical velocity data, relating to a rather wide variety of slurry systems, confirms that the present correlation does a superior job of prediction than all previously proposed critical velocity correlations.
Nucleation and evolution of slag droplets in coal combustion
Authors: Im Kwan H. , Chung Paul M. 
Published: June 2004

AbstractKinetics governing the nucleation and size variation of the slag droplets are first analyzed. Governing conservation equations are then formulated for the droplets and the surrounding gas‐vapor mixture. These equations are solved numerically for the environments representing a typical flow through the channel and diffuser of a coal fired, MHD, power generation system. The average droplet size, total number density and the droplet size distribution are found to be rather strongly influenced by the total slag mass fraction and the supersaturation ratio.
Mass transfer and adsorption in liquid full and trickle beds
Authors: Seirafi Hassan A. , Smith J. M. 
Published: June 2004

AbstractExperimental breakthrough curves were determined for a liquid full and a trickle bed reactor in which benzene was adsorbed from water on small activated carbon particles at 298°K and 1 atm. The step function of benzene was introduced into the water feed and the response measured in the liquid effluent. Benzene transfer also occurred from the liquid feed to the gaseous feed of pure helium.Moment analysis of data for liquid full conditions indicated that the first moment of the response curve could be used to obtain the adsorption equilibrium constant K for benzene on activated carbon. Comparison of results obtained by this new method with the K value determined from static equilibrium runs demonstrated the validity of the moment theory.Analysis of the response curves for trickle bed operation showed that the liquid‐to‐gas mass transfer coefficient (ka)L could be evaluated from either the zero or first moment. Results were obtained in both the trickling flow and pulse flow regimes. Values of (ka)L in the pulse flow regime, which were not heretofore available were sharply higher than those for trickle flow.
Hindered settling of a suspension at low Reynolds number
Authors: Reed C. C. , Anderson John L. 
Published: June 2004

AbstractThe purpose of this paper is to analyze how the settling velocity of a dispersion of spherical particles (that is, drops of arbitrary viscosity) depends on concentration. The procedure used entirely avoids the divergent integrals which previous workers in this field have been forced to deal with and yields explicit formulas for the sedimentation velocity. These formulas, accurate to first order in the particle volume fraction, depend on both the physical characteristics of the particles (size, buoyant density, viscosity ratio) as well as on any long range forces (for example, electrical double layer repulsions or van der Waals attraction) which may exist between particles. Sample calculations are given for globular proteins subject to double layer repulsions and for micron size colloids which experience van der Waals attractions in addition to the electrostatics. In the latter case, it is shown how the Hamaker constant can be extracted from sedimentation data. The analysis is extended to more concentrated suspensions by assuming that the hydrodynamic interactions among particles are pairwise additive; comparison with published data shows this analysis to be reasonably accurate, even for dense suspensions, without any adjustable parameters.
Low shear viscosity of dilute polymer solutions
Authors: Chiou C. S. , Gordon R. J. 
Published: June 2004

AbstractA modification of a viscometer originally proposed by Zimm and Crothers in 1962 is presented, which may be used to measure ultra low shear viscosity for highly dilute polymer solutions. This may provide useful information on polymer coil dimensions and relaxation time. Use of the low shear viscosity data leads to very large values of relaxation time induced by polymer addition to a concentration of only 2 to 3 wppm. This finding is consistent with the marked viscoelastic effects exhibited by these solutions.
Separation of krypton and xenon by selective permeation
Authors: Stern S. A. , Leone S. M. 
Published: June 2004

AbstractThe objective of this investigation was to study the separation of krypton and xenon from nuclear reactor atmospheres by selective permeation through silicone rubber capillaries. Effective permeability coefficients for pure krypton xenon, nitrogen, and oxygen were determined between 0 and 40°C and at pressure differences across the capillary walls (Δp) of up to 3.45 × 105 N/m2 (50 psi). The silicone rubber capillaries had an O.D. of 635 μm (0.025 in.) and an I.D. of 305 μm (0.012 in.), and were pressurized externally. The effective permeability coefficients decreased with increasing Δp, due to the elastic deformation of the capillaries, in general agreement with a deformation analysis of thick‐walled elastic tubes.Gas separation studies were made with a Kr‐Xe‐N2‐O2 mixture in a permeator containing a bundle of silicone rubber capillaries. The permeator had an effective permeation area of 0.480 m2 (5.165 ft2) at a packing density of 4132 m2m3 permeator volume (1260 ft2/ft3), and was operated in a countercurrent mode. The separation studies were conducted at −10 and 20°C and at three Δp values. The separation achieved in the permeator at Δp's of 1.38 × 105 N/m2 (20 Ib/in.2) and 2.07 × 105 N/m2 (30 Ib/in.2) was in good agreement with that predicted from a theoretical model of a permeation stage with countercurrent flow. At 3.45 × 105 N/m2 (50 Ib/in.2), the separation approached that predicted from a “perfect mixing” model. This behavior probably was due to local collapses of the capillaries at weak spots in their walls, as was evidenced also by a sharp increase in the axial pressure drop inside the capillaries.
The calculation of density by the BWRS equation of state in process simulation contexts
Authors: Mills Martin B. , Wills M. John , Bhirud Vasant L. 
Published: June 2004

AbstractThe requirements of thermodynamic data predictors in process simulation applications are especially rigorous. The calculation of vapor and liquid density by the Benedict, Webb, Rubin, Starling equation of state has been reformulated to better satisfy these requirements; the necessary mathematical and programming techniques have been developed and are presented here. The resulting algorithm is believed superior for process simulation purposes.
Suboptimal stochastic control of a continuous latex reactor
Authors: Kiparissides Costas , MacGregor John F. , Hamielec Archie E. 
Published: June 2004

AbstractA suboptimal control algorithm is derived for a continuous latex reactor subject to deterministic and stochastic disturbances to control the pathological behavior of the reactor. An extended Kalman filter based on an instantaneous local linearization technique is used to estimate the reactor states, and a quadratic performance index is used to derive the suboptimal feedback control law. This study successfully demonstrates the application of the multivariable control theory to the control of a simulated continuous latex reactor operating under limit‐cycle conditions. The mathematical model used for the control studies was previously developed and has been shown to describe the performance of an actual reactor system extremely well over its entire range of operation.
Diffusional influences on deactivation rates
Authors: Krishnaswamy S. , Kittrell J. R. 
Published: June 2004

AbstractThe interrelation between internal diffusion and concentration‐independent deactivation is examined using a simple mathematical model. Analytical procedures are developed for evaluating the performance of single catalyst particles in the presence of diffusion and deactivation. By incorporating time‐dependent effectiveness factors in design equations, reactor performance under the combined influence of diffusion and deactivation is predicted. By analogy to the effectiveness factor for non‐deactivating systems, the concept of a deactivation effectiveness factor is introduced.
High gradient magnetic filtration of fine particles from a gas stream
Authors: Gooding C. H. , Felder R. M. 
Published: June 2004

AbstractDust particles originally generated by two steelmaking processes were dispersed in an air stream and passed through a pilot‐scale high gradient magnetic filter. In accordance with theoretical predictions, the experimental results showed that collection was improved by increasing the depth or density of the steel wool filter, increasing the applied magnetic field, or decreasing the filtration velocity. Collection efficiency increased with particle size up to about 2 μm, above which the efficiency tapered off, apparently due to reentrainment effects. Collection efficiencies of greater than 99% were obtained, indicating that high gradient magnetic filtration may be a practical method of controlling particulate emission from processes in the iron and steel industry.
Vapor liquid equilibria up to 100 MPa: A new apparatus
Authors: Legret D. , Richon D. , Renon H. 
Published: June 2004

AbstractA new static cell for vapor‐liquid equilibria up to 100 MPa between 233 and 433 K is presented. A detachable sampling microcell and a special chromatographic injector are used in a new sampling system suitable for gas chromatographic analysis of mixtures with high boiling components. The test system is N2—n‐Heptane at 305.45 K.
Liquid film flowing slowly down a wavy incline
Authors: Wang C‐Y 
Published: June 2004

AbstractA viscous lamina of given mean thickness flows down a wavy incline. Assuming low Reynolds number and small perturbations due to the wavy striations, the velocity profiles and the free surface profile are determined. It is found that the amplitude and phase shift of the free surface depend, in a complicated manner, on the surface tension and the wave length and orientation of the wavy striations. The motion of a particle on the free surface experiences drift which is also a function of the surface tension, the amplitude, wave length and orientation of the wavy incline.
Regeneration of powdered activated carbon. Part II: Steam‐carbon reaction kinetics
Authors: Chihara Kazuyuki , Matsui Isao , Smith J. M. 
Published: June 2004

AbstractThe kinetics of the reaction between steam and spent activated carbon (from sucrose deposition) was studied at 1003 to 1123 K and 1 atm pressure. At these conditions some virgin carbon, upon which the sucrose was originally adsorbed, was also gasified. Rates of oxidation were essentially the same for spent and virgin activated carbon.The kinetics data fit a Langmuir‐Hinshelwood equation, originally proposed for gasification of other types of carbon, with an activation energy of 2.3 × 105 J/mol.Surface area and pore volume measurements indicated that the adsorption capacity of the original carbon could be completely restored by thermal regeneration followed by reaction with steam. However, some activated carbon is lost implying that there would be an optimum extent of steam gasification in a cyclical adsorption‐regeneration process.
The effect of pore structure on fluid‐solid reactions: Application to the SO2‐lime reaction
Authors: Bhatia S. K. , Perlmutter D. D. 
Published: June 2004

AbstractThe effect of varying pore structures on the kinetics of fluid‐solid reactions is investigated through the random pore model developed in prior papers (Bhatia and Perlmutter, 1980, 1981). By considering several idealized pore‐size distributions it is shown that a solid having a uniform pore size is intrinsically less reactive than one possessing a pore‐size distribution. For solids with bimodal pore size distributions optimal structures are shown to exist for which the reactivity is a maximum.Numerical solutions were obtained to the model equations for various values of the parameters characterizing the pore structure, the diffusion, and the chemical kinetics. The results show that the conversion‐time behavior and the expected ultimate conversion can be very sensitive to variations in surface area and porosity for reactions accompanied by an increase in volume of the solid phase.These findings are in agreement with experimental literature on the SO2‐lime reaction (Ulerich et al., 1978; Borgwardt and Harvey, 1972; Potter, 1969; Falkenberry and Slack, 1968) and the model is shown to fit the data of Borgwardt (1970), and of Hartman and Coughlin (1974, 1976). It is seen that this reaction is diffusion controlled under the conditions of Hartman and Coughlin, in consonance with their own finding using the grain model, and a prior Pigford and Sliger (1973) interpretation. The temperature behavior of the diffusion coefficient in the product layer suggests the participation of an activated process, possibly a solid state diffusion step.
A random pore model for fluid‐solid reactions: II. Diffusion and transport effects
Authors: Bhatia S. K. , Perlmutter D. D. 
Published: June 2004

AbstractThe prior random pore model for kinetically controlled fluid‐solid reaction (Bhatia and Perlmutter, 1980) is generalized to include transport effects arising from boundary layer, intraparticle, and product layer diffusion. Numerical solutions are presented for a variety of conditions. The results show that the rate and surface area maxima predicted in the kinetic regime are shifted to lower conversions as intraparticle or product layer diffusional resistances increase. In addition, with increasing temperature a decrease in the overall reaction surface is predicted, in agreement with experimental findings (Kawahata and Walker, 1962).For reactions accompanied by an increase in the volume of the solid phase, it is shown that incomplete conversion may be expected, the ultimate conversion decreasing with an increase in the intrapellet diffusional resistance. Optimal temperatures for such reactions are also identified.
Interpretation of surface flow phenomenon of adsorbed gases by hopping model
Authors: Okazaki Morio , Tamon Hajime , Toei Ryozo 
Published: June 2004

AbstractThe mechanism of surface flow of adsorbing gas molecules through the porous adsorbent is interpreted, and a new hopping model is derived by separately taking into account the hopping behaviors of monolayer and multilayer molecules. The reported experimental results containing the data measured here are correlated well. Finally, some considerations are given to the two experimental constants appearing in the model.