bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simultaneous measurement of size and velocity of bubbles or drops: A new optical technique
Authors: Semiat Raphael , Dukler A. E. 
Published: June 2004

AbstractAccurate information on both the size and velocity of a dispersed phase is of importance to many problems in heat or mass transfer and reaction. Existing experimental methods are limited in their applicability, difficult to use, provide only size or velocity, and are of low statistical reliability. A new method is developed here which overcomes most of these shortcomings and permits accurate simultaneous measurement of the size and two dimensional velocity of the dispersed phase.
Laser doppler anemometry measurements in gas‐solid flows
Authors: Lesinski J. , Mizera‐Lesinska B. , Fanton J. C. , Boulos M. I. 
Published: June 2004

AbstractLaser Doppler Anemometry (LDA) was used for the simultaneous measurement of the gas and particle velocities in a gas‐solid, two‐phase flow. The flow configuration consists of an air jet at ambient temperature in which a spherical glass powder of a mean particle diameter of 97.0 or 13.7 μm was injected from one side using a secondary air jet. Both principal and secondary jets were also seeded with talcum powder with a mean particle diameter of about 1 μm which served as a tracer.The probability density distribution function (PDF) of the LDA output showed two distinct peaks corresponding to the particle and gas velocities. As the particles were accelerated by the flow, the slip velocity between the gas and the particles decreased causing the gap between these two peaks to narrow. The measured mean particle velocity profiles were in agreement with the predictions of a theoretical model.The objectives of the present investigation was to obtain experimental data on the dependence of the particle trajectories and their mean velocities on the injection conditions in a free jet stream. The principal question, however, was whether such data could be obtained using Laser Doppler Anemometry (LDA). In other words, whether LDA could be effectively used in two‐phase flow systems for the simultaneous measurement of the gas and particle velocities? Obviously, the answer to this last question can affect far beyond this particular study and more than justified the effort for this detailed investigation. It should be pointed out that, while LDA has been known for sometime, and the necessary equipments for an LDA system are available on a commercial bases, relatively little attention has been given to its application to other than single‐phase, fluid‐flow measurements.
Properties of bismuth oxide catalysts for oxidative dehydrogenation dimerization of propylene
Authors: White M. G. , Hightower J. W. 
Published: June 2004

AbstractThe electronic properties of bismuth oxide shed light on the mechanism of its catalytic activity for the oxidative dehydrogenation dimerization of propylene. Variations in the electrical conductivity and thermoelectric power, as the gas phase contacting a pellet of this p‐type semiconductor was changed, provided information about the nature of species adsorbed at reaction temperature.
A stochastic model for turbulent diffusion of particles or drops
Authors: Lee N. , Dukler A. E. 
Published: June 2004

AbstractA stochastic model is presented for turbulent diffusion of particles or drops in a turbulent field. The model is free of arbitrary adjustable constants and is applicable to realistic situations where the flow is nonhomogeneous such as in boundary layers or in pipe flow. New experimental data is presented for dispersion of glass beads in the boundary layer of the University of Houston Environmental Wind Tunnel. Good agreement with the theoretical model is demonstrated.
Estimation of activity coefficients in concentrated sulfite‐sulfate solutions
Authors: Rosenblatt G. M. 
Published: June 2004

AbstractThe electrolyte theory of Pitzer and coworkers is used to estimate geometric mean‐ion activity coefficients in strong electrolyte solutions at 25–55°C. By using Pitzer's equations with ion‐pair parameters estimated in this paper, one can calculate activity coefficients to moderately high ionic strengths in aqueous mixtures containing the following ions: Na+, K+, Mg2+, Ca2+, Cl−, ClO, ClO, HCO, HSO, CO, SO, SO, and S2O. Mixtures containing these ions are present in CaO/CaSO4 flue gas desulfurization units and in laboratory experiments aimed at understanding the chemistry occurring in such units. The computed activity coefficients are relatively insensitive to the values of the estimated quantities. The basis of the estimates, as well as their effect on calculated activity coefficients, is discussed. It is concluded that activity coefficients are estimated with an accuracy of ±25% or better.
Kinetics of nonisothermal sorption: Systems with bed diffusion control
Authors: Ruthven D. M. , Lee Lap‐Keung 
Published: June 2004

AbstractA theoretical model is presented to describe the kinetics of nonisothermal sorption for a system in which the main resistance to mass transfer is the macrodiffusional resistance of the absorbent particle bed while the main resistance to heat transfer is the resistance at the external surface of the adsorbent sample. The model is used to interpret experimental kinetic data for the sorption of several hydrocarbons in 10X and 13X zeolite crystals. By varying the configuration of the sample bed and the size of the zeolite crystals it is shown that, for n‐heptane and iso‐octane in 13X, the intracrystalline diffusional resistance is negligible even in 40‐μm crystals. The assumption of intracrystalline diffusion control which has been made in earlier kinetic studies of similar systems is therefore incorrect.
Studies in the synthesis of control structures for chemical processes. Part V: Design of steady‐state optimizing control structures for integrated chemical plants
Authors: Arkun Yaman , Stephanopoulos George 
Published: June 2004

AbstractThis paper addresses the question of how to design the steady‐state optimizing control system for a large scale interconnected chemical plant. The integrated design approach is structured within the framework of the hierarchical control theory and is based on the concepts of constraint control, hierarchical decomposition and nonlinear mathematical programming. Theoretical developments lead to the generation of alternative operational policies of practical value. An imbedded branch and bound screening strategy is given to select the best policy, which will be implemented on‐line by the optimizing plant controllers. The general design approach has the broad applicability to any interconnected large scale system, and its application is demonstrated on a gasoline polymerization plant.
Revision of kynch sedimentation theory
Authors: Tiller Frank M. 
Published: June 2004

AbstractMuch of the theory of gravity sedimentation has been based on the work of Coe and Clevenger (1916) and Kynch (1952). They provided methods for obtaining rates of sedimentation in batch, static tests which are presently used for design of continuous thickeners. Kynch assumed that a first order partial differential equation controlled the entire sedimentation process. His equation was based on: (1) continuity balance; and (2) sedimentation velocity being a unique function of solid particulate concentration. A general solution was presented in the form of volume fraction of solids ϕs = f(x − vt). During the constant rate fall of the upper interface, the boundary condition of uniform initial concentration combines with the Kynch equations to adequately describe the sedimentation phenomena. Kynch ignored the sediment rising from the bottom of the settling chamber, and assumed that the characteristics y = x − vt originated at the origin of coordinates (height, time) during the first falling rate period. The characteristics actually originate at the surface of the rising sediment where the upward liquid velocity affects the rate of fall of the particulates. New equations have been derived based upon the assumption that the characteristics emanate from the rising sediment.
Effects of molecular size and configuration on diffusion in microporous membranes
Authors: Deen W. M. , Bohrer M. P. , Epstein N. B. 
Published: June 2004

AbstractEffects of molecular size and configuration on hindered diffusion were examined by measuring diffusion of two series of uncharged macromolecules through track‐etch membranes with uniform and well‐defined pore geometry. At any given Stokes‐Einstein radius, diffusivities in small pores were lower for ficoll (crosslinked structure) than for dextran (more nearly linear structure).
Optimal operation of integrated processing systems. Part I: Open‐loop on‐line optimizing control
Authors: Garcia Carlos E. , Morari Manfred 
Published: June 2004

AbstractA new algorithm for the continuous tracking of the optimal economic operating conditions of an integrated chemical plant has been developed. The method does not make use of fundamental models of the plant but is based on an on‐line search using experimental moves of the independent variables. The results of these moves provide the data for the identification of a dynamic process model. This model allows one to determine the gradient of the objective function and thus guides the next move of the independent variable eventually leading to the optimum. The advantages of the new technique over other methods are demonstrated in simulation examples:

The speed of tracking is equally fast or faster than the relaxation speed of the system after a step change.
The noise insensitivity allows safe tracking of the optimum despite significant measurement errors.

As a key feature a decentralized form of the algorithm is developed making it suitable for distributed microprocessor implementation.
Analysis of particulate removal in venturi scrubbers—role of heat and mass transfer
Authors: Placek T. D. , Peters L. K. 
Published: June 2004

AbstractIn a previous paper, a theoretical model of venturi scrubber performance was presented in which the operating variables, scrubber geometry, and droplet and dust size distributions are specified. The present paper examines the roles that heat and mass transfer have in determining the particle collection efficiency. The mechanisms of inertial impaction, interception, and diffusiophoresis are analyzed simultaneously to account realistically for heat and mass transfer effects on particle collection. Operation at elevated gas temperatures can substantially reduce collection, primarily due to the increase in gas density which occurs as the gas contacts the spray liquid. Mass transfer effects are important only when condensation onto the drops occurs, such as that during the scrubbing of saturated gas streams or when using cold liquid sprays. Under these conditions, mass transfer effects increase the collection efficiency.
Unsteady heat transfer in laminar non‐Newtonian boundary layer over a wedge
Authors: Gorla Rama Subba Reddy 
Published: June 2004

AbstractThe transient thermal response of a power‐law type non‐Newtonian, laminar boundary layer flow over a wedge is investigated. Consideration is given to the case of a step change in surface temperature. Details of the transient heat flux and the temperature field are obtained and have been presented graphically. The range of Prandtl numbers investigated is from 5 to 1000 while the viscosity index was allowed to vary from 0.1 to 5.0.
An analysis of bacterial growth in fluidized‐bed adsorption column
Authors: Andrews G. F. , Tien Chi 
Published: June 2004

AbstractAn analysis is presented to described the dynamics of fluidized bed adsorption columns. A microbial film model (recently proposed by the authors) is used to characterize the bacterial activity and its interaction with adsorption and solids mixing. Solids mixing and mixing in the liquid phase are included in the analysis, as is the effect of microbial film growth on the settling velocity of the adsorbent particles. The interplay of film growth, bed stratification and solids mixing is discussed in detail.
Numerical solution for the flow of highly viscous fluid in agitated vessel with anchor impeller
Authors: Kuriyama M. , Inomata H. , Arai K. , Saito S. 
Published: June 2004

AbstractFluid motion in an agitated vessel with an anchor impeller is characterized by flow in a horizontal plane induced by the vertical arms of the impeller rotating near the vessel wall. A numerical algorithm of the two‐dimensional flow in the horizontal plane is established using an iterative method for the determination of the boundary values of stream function. The computational results of the velocity profiles and agitation power are compared with those of the experiments, and it is shown that the numerical method used in this study is very useful to analyze the flow past the vertical arms of an anchor impeller.
A study of fast tracer desorption in molecular sieve crystals
Authors: Kärger Jörg 
Published: June 2004

AbstractA modification of the customary NMR (Nuclear Magnetic Resonance) pulsed field gradient technique is shown to allow the observation of tracer desorption phenomena in a time interval of 4 … 1 000 ms. The processes observed are only limited by molecular transport in the individual crystallites. Other influences, such as intercrystalline transport resistances and the finite rate of adsorbate supply or adsorption heat dissipation, as known from traditional sorption experiments, can be excluded.The method is applied to several zeolitic adsorbate‐adsorbent systems: methane…hexane/NaX; ethane/NaCaA. The tracer desorption curves show the expected dependences on paraffin chain length, sorbate concentration and crystallite size. Comparison with the coefficients of intracrystalline diffusion shows that desorption is limited by intracrystalline transport, excluding the existence of structural surface resistance for these systems. Application of the technique to small zeolite crystallites allows the observation of molecular transport phenomena considerably slower than accessible until now by customary NMR techniques.
Effect of lateral heat losses on the stability of thermal displacement fronts in porous media
Authors: Yortsos Y. C. 
Published: June 2004

AbstractPrevious studies have shown that heat transport by horizontal conduction in thermal displacement processes in porous media has a stabilizing effect on condensation fronts. This paper expands the stability analysis by also including the description of heat transfer lateral heat losses by conjungate (vertical) conduction. A marginal stability condition is derived in terms of a parameter Λ representing the relative magnitude of heat transfer by conjugate conduction. It is shown that lateral heat losses ask a significant stabilizing effect on the front. This effect should be important in thermal oil recovery processes such as steam injection and in‐situ combustion.
Finite difference calculation of current distributions at polarized electrodes
Authors: Prentice G. A. , Tobias C. W. 
Published: June 2004

AbstractThe changing geometry of electrodes undergoing electrodeposition or dissolution can be simulated by successive solutions of Laplace's equation with nonlinear boundary conditions. To overcome the instability in the finite‐difference calculation caused by nonlinear boundary conditions, a weighting algorithm to compute the new surface potential on successive iterations has been developed.
Theoretical and experimental study of radiant heat transfer in a solar fluidized‐bed receiver
Authors: Flamant G. 
Published: June 2004

AbstractThe temperature profile, total emissivity, flux density distribution, and effective mean penetration distance were determined from measurements in high‐temperature solar fluidized beds. A theoretical model is proposed to describe the complex heat transfer phenomena in the radiation penetration zone of the fluidized layers. The results correlated well at incipient fluidizing conditions for beds of silicon carbide and chamotte but were found imprecise for beds of zirconia and silica sand.
Intraparticle‐forced convection effect in catalyst diffusivity measurements and reactor design
Authors: Rodrigues A. E. , Ahn Bum J. , Zoulalian André 
Published: June 2004

AbstractIntraparticle forced convection was considered in order to explain experimentally observed changes in effective diffusivity (apparent) with flowrate, when measures are carried out in fixed beds.A complete model taking into account intraparticle diffusion and forced convection together with film diffusion is derived in order to analyze diffusivity measurements by physical methods, both in perfectly mixed reactors and fixed beds.The experiments were carried out with hydrogen tracer in a partial oxydation catalyst.Implications of the use of such “apparent” effective diffusivities in reactor design are discussed, showing that errors of 100% can be made.
Factors affecting secondary nucleation rate of sodium chloride in an evaporative crystallizer
Authors: Grootscholten P. A. M. , De Leer B. G. M. , De Jong E. J. , Asselbergs C. J. 
Published: June 2004

AbstractCrystallization kinetics of sodium chloride have been studied in a Continuous Mixed Suspension Mixed Product Removal evaporative crystallizer at 50°C. A marine propeller was found to give a substantially lower nucleation rate than a pitched blade impeller under identical conditions. The crystal turnover time did not affect the effective nucleation rate.
In situ gravimetric studies of the regenerative mechanism for water‐gas shift over magnetite: Equilibrium and kinetic measurements in CO2/CO and H2O/H2 gas mixtures
Authors: Kubsh J. E. , Dumesic J. A. 
Published: June 2004

AbstractIn situ gravimetric measurements were used to study oxygen removal from (or incorporation into) chromia‐promoted magnetite in CO2/CO and H2O/H2 gas mixtures at 637 K. The equilibrium and kinetic data could be described by two reversible, oxidation‐reduction reactions: surface‐oxygen removal by CO and surface oxygen replenishment by H2O, with the corresponding reverse reaction involving CO2 and H2. These reactions form a regenerative mechanism that is able to predict qualitatively both the measured rate and rate expression for water‐gas shift. It is concluded that this regenerative mechanism is a primary pathway for water‐gas shift over magnetite.
Oscillatory behavior of a gas bubble growing (or collapsing) in viscoelastic liquids
Authors: Yoo Hee Ju , Han Chang Dae 
Published: June 2004

AbstractA theoretical study was carried out to achieve a better understanding of the oscillatory behavior of a gas bubble growing (or collapsing) in a viscoelastic liquid, by taking into account both the hydrodynamic and diffusion effects. The Zaremba‐DeWitt model was chosen to represent the rheological properties of the suspending medium. The finite difference method was employed to solve the governing system equations.The computational results show that, in the case of very fast diffusion (i.e., constant bubble pressure), the oscillatory behavior of a bubble takes place only when the ratio of the initial pressure difference between the gas bubble and the liquid phase to the elastic modulus of the suspending medium is below a certain critical value. On the other hand, in the case of very slow diffusion, the oscillatory behavior of a bubble persists, regardless of the magnitude of the rheological properties of the suspending medium. Our study indicates further that the diffusivity of a gas has a profound influence on the occurrence of oscillatory behavior, that the elastic property of the suspending medium enhances oscillatory behavior while its viscosity plays the opposite role, and that even a Newtonian medium can give rise to an oscillatory pattern of bubble growth (or collapse), although it dampens out very quickly.
Selective absorption of H2S from larger quantities of CO2 by absorption and reaction in fine sprays
Authors: Bendall E. , Aiken R. C. , Mandas F. 
Published: June 2004

AbstractHighly selective transfer of hydrogen sulfide (H2S) from much larger quantities of carbon dioxide (CO2) has been accomplished by absorption and reaction into fine sprays of buffered carbonate solution. Selectivity after the intensely agitated atomization zone is dramatically improved once the droplets have formed and stagnate internally. H2S transfer in this latter zone is virtually independent of the presence of CO2, even at CO2:H2S ratios of 100; CO2 transfer, however, is adversely affected by the presence of H2S. The gas film resistance for mass transfer is effectively eliminated with the 50 μm mean droplet diameter. The data indicate approximately constant hydrodynamics throughout the formed droplet zone and allow good theoretical prediction of enhancement factors for this complex system. Thus the design of more efficient equipment is possible if the gas‐liquid contacting method is tailored to take advantage of differences in the transfer and reaction rate properties of gases to be separated.
Nonlinear taylor instability of a plane interface between two incompressible fluids with interfacial mass transfer
Authors: Chang I‐Hwa M. , Bankoff S. G. 
Published: June 2004

AbstractA principal mechanism for rapid mixing and fragmentation in vapor explosions, such as have occurred in the LNG, aluminum, steel and paper industries, is thought to be nonlinear Taylor instability. An analysis, based on a generalized coordinate method developed by Dienes for a fluid with an arbitrary constitutive law, is here extended to a two‐fluid model, with or without mass transfer between the fluids. Numerical results indicate that in a steam‐water system entrainment starts in times of order 10−4s at 100 G acceleration normal to the interface. For gas‐liquid systems the presence of the second fluid changes the instability growth only slightly. Condensation of steam, even when limited only by the kinetic theory interfacial resistance, also has minor effects on the growth rate. However, condensation on the entrained drops will have a major effect on the acceleration.
A residence‐time model for trickle‐flow reactors incorporating incomplete mixing in stagnant regions
Authors: Kan Kin‐Mun , Greenfield P. F. 
Published: June 2004

AbstractA model for the liquid‐phase residence time in a trickle‐flow reactor has been derived and experimentally verified using a tracer input. The model, termed the Ideal Plug Flow Stagnancy Model, postulates that the prime liquid‐phase dispersive mechanism in such reactors is the interchange between the dynamic and stagnant regions. Unlike previous models, however, it does not require the assumption of perfect mixing in the stagnant zones. While the results of the study confirm that the mixing is incomplete, they show clearly that back mixing rather than molecular diffusion is the dominant exchange mechanism.
Disruption mechanism of aggregate aerosol particles through an orifice
Authors: Yuu Shinichi , Oda Takashi 
Published: June 2004

AbstractBased on the drag force of two spheres in contact and the probability density of size ratios of particles which constitute an aggregate particle, the population balance equation describing the change of the particle‐size distribution due to the disruption of aggregate particles is derived and the numerical solutions of this equation are obtained.Experiments were carried out with fly ash particles dispersed in air stream through an orifice at various flow rates. The measured size distributions can be represented by the numerical solutions of the population balance equation.