bluuebunny/crossref_metadata_2025_split huggingface dataset:
Complex transitional flows in concentric annuli
Authors: Hanks R. W. , Peterson J. M. 
Published: June 2004

AbstractDetailed measurements of radial variations of turbulence intensity were made with a hot film anemometer in a concentric annulus of aspect ratio Ri/Ro = 0.0416 for a Reynolds number range 1,200 ⩽ Re ⩽ 3,000 using a Newtonian polyglycol water solution. Measurements were also made of excess entrance pressure gradients and the axial variation of pressure gradients.Based on the results of these measurements, it is concluded that the proposition of Lea and Tadros (1931), Rothfus (1948) and others that a transitional flow regime develops with a zone of turbulence near the inner core surrounded by a zone of laminar flow near the outer wall is false. The two‐critical Reynolds number transitional regime proposed by Hanks and Bonner (1971) is verified to exist but their mathematical model for the interpretation of its cause is disproved. It is shown that at the lower critical Reynolds number predicted by Hanks and Bonner (1971) and by Hanks (1980) a transition does occur. It is conjectured that the new flow may be a type of complex laminar bifurcation flow described by Joseph (1976), although the present data do not permit a definite conclusion to be reached. This complex laminar flow in turn undergoes a transition to turbulent flow at a second critical Reynolds number, higher than the first, in qualitative accord with Hanks and Bonner's (1971) and Hanks' (1980) predictions, although the latter are not quantitatively correct because they are based on inadequate models of the transitional flow field.
Bed‐surface contact dynamics for horizontal tubes in fluidized beds
Authors: Chandran Ravi , Chen J. C. 
Published: June 2004

AbstractThe local contact characteristics between the bed emulsion and the tube surface for horizontal tubes immersed in fluidized beds were investigated experimentally. The measurements indicated that the contact dynamics change significantly with circumferential position, gas flow rate, particle size and system pressure. From the experimental data, quantitative information on the local fluidization behavior were generated for use in heat transfer models.
Measurement and prediction of dissociation pressures of isobutane and propane hydrates below the ice point
Authors: Holder G. D. , Godbole S. P. 
Published: June 2004

AbstractA gravimetric technique has been developed for measuring three phase vaporice‐hydrate (VIH) equilibria. This technique has been used for measuring VIH dissociation pressures for propane and isobutane hydrates to temperatures as low as 241.4 K. Kihara parameters, based upon the experimental dissociation pressure data, have been obtained. Because the range of experimental three phase equilibrium data has been considerably extended, the parameters based on this data should be more useful in predicting hydrate dissociation pressures.
Effects of London‐van der Waals forces on the thinning of a dimpled liquid film as a small drop or bubble approaches a horizontal solid plane
Authors: Chen Jing‐Den , Slattery J. C. 
Published: June 2004

AbstractWhen a small drop or bubble approaches a solid surface, a thin liquid film forms between them, drains, until an instability forms and coalescence occurs. Lin and Slattery (1982a) developed a hydrodynamic theory for the first portion of this coalescence process: the drainage of the thin liquid film while it is sufficiently thick that the effects of London‐van der Waals forces and electrostatic forces can be ignored. Here the effects of the London‐van der Waals forces are included. The resulting theory describes the evolution of the film profile, given only the bubble radius and the required physical properties. The inclusion of a positive disjoining pressure results in better descriptions of the film profiles measured by Platikanov (1964) for air bubbles pressed against glass plates. When the disjoining pressure is negative, an unstable draining film evolves and finally ruptures. Unfortunately, there are no experimental data with which to compare our predicted coalescence times.
Laminar tube flow with a thermosetting polymerization
Authors: Castro J. M. , Lipshitz S. D. , Macosko C. W. 
Published: June 2004

AbstractTwo models describing the laminar flow of a polymerizing liquid through a tube have been developed and tested experimentally. One model is a full finite difference solution of the balance equations. The other is an approximate analytical solution which assumes that flow ceases after viscosity increases about tenfold. The models are compared to two experimental cases: (1) the pressure rise needed to keep the flow rate through the tube constant and (2) the flow rate decrease when pressure at the tube entrance is held constant. The finite difference model is more accurate in the early stages of polymerization while the approximate analytical model is more accurate at long times. The models have application to runner flow in reaction injection molding, to nozzles in thermoset molding, to thermoset dispensing equipment and to continuous reactive polymer processes in general.
Trickle‐bed reactors: A review
Authors: Herskowitz Mordechay , Smith J. M. 
Published: June 2004

AbstractFixed‐bed, catalytic reactors in which gas and liquid phases flow concurrently downward, termed trickle beds, are becoming more widely used in chemical processing, particularly in the petrochemical industry. Shah (1979) has summarized the advantages of trickle‐bed reactors and mentioned some of the processes in which the reactors are used. Shah's monograph and earlier reviews (Satterfield, 1975; Goto et al., 1977; Hofmann, 1978; Gianetto et al., 1978) have discussed factors affecting reactor performance.In the last few years additional experimental and theoretical studies that contribute to improved design and scaleup of trickle‐bed reactors have been published. The scope of this paper is to review critically these improvements. Progress in understanding local rates of reaction is considered first. Then recent developments in reactor design are analyzed.
Determination of multicomponent sorption equilibria using perturbation gas chromatography
Authors: Glover C. J. , Lau W. R. 
Published: June 2004

AbstractPerturbation chromatography previously has been used experimentally as an efficient method for obtaining sorption equilibria for systems with up to two vapor phase components at finite concentration. The objective of this work was to obtain a theoretical result that could be used for experimental determinations of sorption of multiple interfering species at finite concentration. Results obtained are applicable for both non‐stoichiometric and stoichiometric situations for systems that may have flowing phase velocity and volume changes associated with interphase transport and also may have interactions among the sorbed components. The dependence of each effluent peak characteristic velocity upon all of the component equilibrium isotherms requires that the equilibria be considered as a whole by simultaneously fitting a set of composition grid perturbation response data to appropriate isotherm surface equations.
Effect of the product layer on the kinetics of the CO2‐lime reaction
Authors: Bhatia S. K. , Perlmutter D. D. 
Published: June 2004

AbstractThe kinetics of reaction between CO2 and lime is investigated in the range of 673 to 998 K with a view to examining the effects of product layer deposition and variations in the limestone calcination atmosphere. The reaction is initially rapid and chemically controlled and goes through a sudden transition to a much slower regime controlled by diffusion in the product CaCO3 layer. The magnitude of the estimated product layer diffusivity is in the range of 10−18 to 10−21 m2/s, the corresponding activation energy is 88.9 ± 3.7 kJ/mol below 688 K and 179.2 ± 7.0 kJ/mol above that temperature, suggestive of solid state diffusion. Plausible mechanisms are discussed.
Behavior of particles in a liquid‐solids fluidized bed
Authors: Yutani N. , Fan L. T. , Too J. R. 
Published: June 2004

AbstractThe mechanics of particle motion in a fluidized bed were studied by focusing on the microscopic behavior of the particles. The local displacements of nylon particles fluidized by liquid were measured by the micro‐capacitance method, and the resultant time series was analyzed by determining its auto‐correlation function and the corresponding power spectrum. This has given rise to a stochastic or statistical model of particle displacements in the fluidized bed. This model visualizes the particle motion in a fluidized bed to consist of the random movement, generating irregular signals, and the linear movement, generating wave‐like signals.
A predictive model for rollover in stratified LNG tanks
Authors: Heestand Janet , Shipman C. W. , Meader J. W. 
Published: June 2004

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractGas 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

AbstractCatalyst 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

AbstractHeat 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

AbstractGas 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

AbstractPressure 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

AbstractWashburn'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

AbstractThe 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractAn 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

AbstractBatch/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

AbstractA 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

AbstractExperimental 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

AbstractA 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.