bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tortuosity factors for diffusion in catalyst pellets
Authors: Wang Chang‐Tai , Smith J. M. 
Published: June 2004

AbstractThe dynamic pulse‐response technique was used to measure effective diffusivities under nonreacting conditions in two, unsulfided, extrudate‐type, hydrodesulfurization catalyst pellets of different porosities. Pore‐volume distribution data showed a bidisperse pore structure with a broad pore‐size range (100 μm to 3 nm).The main purpose of the study was to evaluate various methods for calculating the tortuosity factor, τ. For this particular catalyst, the most constant and unreasonable values of τ were obtained by supposing that diffusion occurred in all the pore volume (micro and macropores) and by summing the combined Knudsen and bulk contributions over each increment of pore volume.
Effect of a phase transition on the solubility of a solid
Authors: Choi P. B. , Mclaughlin Edward 
Published: June 2004

AbstractTheoretical investigation shows that a transition in the solid state from form I to form II affects the solubility of a solid in a liquid. Experimental results for the solubility of phenanthrene in pyridine, which has a lambda‐point transition between 331 and 361 K, conform generally to the theoretical predictions.
Mechanism of turbulent mass transfer at a solid boundary
Authors: Campbell J. A. , Hanratty T. J. 
Published: June 2004

AbstractMass transfer between a turbulent fluid and a solid boundary is considered for the case of large Schmidt numbers. The variation of the mass transfer coefficient with time, K(t), is calculated by solving the mass balance equation using a random velocity input. An interpretation of the mass transfer process which is radically different from that given by classical approaches is obtained.
Plasma—particle momentum and heat transfer: Modelling and measurements
Authors: Vardelle M. , Vardelle A. , Fauchais P. , Boulos M. I. 
Published: June 2004

AbstractMeasurements were made of the two‐dimensional flow and temperature field in a d.c. plasma jet under different operating conditions. The particle velocity and the in‐flight particle temperature were also measured for narrow cuts of alumina powders, of mean particle diameters of 18, 23, 39 and 46 μm, injected in the jet. The results are compared with the predictions of a one‐dimensional mathematical model. The measured and computed particle velocities are in good agreement. This is, however, not the case for the particle temperature where considerable differences are observed. An attempt is made to determine the parameters which are often unduly neglected in modelling work and to identify the areas where further work is needed.
Fault diagnosis in nonlinear chemical processes. Part I. Theory
Authors: Watanabe K. , Himmelblau D. M. 
Published: June 2004

AbstractWe propose a two‐level identification strategy to detect and diagnose process faults and their causes. The strategy can be applied to processes represented by process models nonlinear in the states but linear in the coefficients. Relations to calculate both the observer for the states and the least squares estimator for the coefficients are specified in detail.
Four environment model of mixing and chemical reaction. Part II. Comparison with experiments
Authors: Mehta R. V. , Tarbell J. M. 
Published: June 2004

AbstractThe four environment model, which was developed in Part I, has been compared with three extensive sets of experimental data from plug‐flow and stirred‐tank reactors with unmixed feedstreams and a single chemical reaction. The data sets have been accurately reproduced with a single value of the micromixing parameter (RS), and the “best fit” value of RS for each data set was close to the value estimated from the Corrsin‐Rosensweig turbulent mixing theory. This lends support to the turbulence analogy suggested in Part I. Simulations of competing reactions of the parallel‐consecutive type are used to discriminate between the four and three environment models with the four environment model providing much more realistic predictions.
Hydrodynamics of two‐phase cocurrent downflow through packed beds. Part I. Macroscopic model
Authors: Rao V. G. , Ananth M. S. , Varma Y. B. G. 
Published: June 2004

AbstractPressure drop and liquid saturation are two important design parameters in cocurrent gas‐liquid downflow through packed beds. A macroscopic model based on momentum balance is formulated for the condition of no radial pressure gradients. The model includes the effect of bubble formation on the pressure drop and holdup and is compared with the experimental data of the earlier investigators and of the present study. The model provides a functional form for correlating pressure drop and liquid saturation but some parameters have to be determined by fitting the experimental data.
Hydrodynamics of two‐phase cocurrent downflow through packed beds. Part II: Experiment and correlations
Authors: Rao V. G. , Ananth M. S. , Varma Y. B. G. 
Published: June 2004

AbstractTwo‐phase pressure drop and dynamic and total liquid saturation are experimentally determined for air‐water system under cocurrent downflow through packed beds using packing differing widely in geometry. The experimental data of the present study as well as that available in literature is satisfactorily correlated in terms of: (a) Lockhart‐Martinelli parameters; and (b) the Reynolds numbers defined for the respective phases and the bed porosity, taking into account the flow behavior of the phases through the packed bed.
Energy storage capacity of reversible liquid‐phase Diels Alder reaction between maleic anhydride and 2‐methyl furan
Authors: Sparks B. G. , Poling B. E. 
Published: June 2004

AbstractCalorimetry was used to determine the heat of reaction and equilibrium constant at 318 K for the reaction between maleic anhydride (A) and 2‐methyl furan (B). The values were −60 kJ/gmol and 614 cm3/gmol, respectively. The motivation for this work was to find a single phase‐reacting system that could be used to store solar energy. Thus, the energy storage capacity was calculated for a mixture of A and B, both initially at 7 kmol/m3, in dioxane. The maximum apparent heat capacity of 7.37 J/cm3·K occurred at 334 K. This maximum value is 76% higher than the heat capacity of pure water.
New simultaneous modular method for calculating multistage multicomponent separation processes
Authors: Fonyo Z. , Nishimura H. , Yamashita Y. 
Published: June 2004

AbstractA new flexible method has been developed for modelling multistage multicomponent separation processes. The method is based on the simultaneous modular approach and can be referred to as a quasilinear two‐level modelling. The network is solved within each iteration as a linear one, and after each network solution the split streams are updated modularly using nonlinear submodels. The method is suited for modelling the most important separation processes with arbitrary structure and permits to use different models for the subunits or processing units. Illustrative examples and computational results are presented showing the efficiency, flexibility and capability of the method.
Modeling of acid hydrolysis of solasodine glycosides. Part II: Formation of solasodiene
Authors: Crabbe P. G. , Fryer Colin 
Published: June 2004

AbstractThe undesirable conversion of solasodine product to solasodiene which occurs during the acid hydrolysis of solasodine glycosides has been mathematically modelled. The model incorporates acid loss which results from reaction of acid with alcohol solvents. The model has been used to obtain kinetic data for the reaction at a number of different reaction conditions.
Pyrolysis of oil shale: Experimental study of transport effects
Authors: Galan M. A. , Smith J. M. 
Published: June 2004

AbstractThe thermal decomposition of kerogen in a Colorado shale was studied in a TGA‐type apparatus in which the temperature was first increased at a constant rate and then held constant at a plateau value. Data were obtaiend at plateau temperatures from about 573 to 703 K and at 101.3 kPa.The objective of the research was to determine the influence of transport effects on the observed rate of decomposition. The results show that, for the shale studied, transport of heat and mass influenced the rate, if the particle size was greater than about 0.4 × 10−3 m and if more than two to three layers of particles were placed in the weighing basket.
Turbulence structure of dilute drag‐reducing polymer solutions in a rectangular open channel flow
Authors: Usui Hiromoto , Sano Yuji 
Published: June 2004

AbstractThe drag reduction phenomenon in a rectangular open channel flow was examined by measuring the longitudinal velocity by means of a laser Doppler anemometer. Statistical analysis of the fluctuating velocity showed that the most significant effect of the polymer additive (polyethylene oxide) on the large‐scale turbulent motion appeared in the turbulent core of an open channel flow. The scale of bursting phenomenon was enlarged by the polymer additive, and the typical ejection process was detected as the remarkable negative fluctuating velocity throughout the buffer and turbulent core regions except near the free surface.
Single‐particle approach for analyzing flow systems. Part II: Regional residence times and local flow rates
Authors: Rubinovitch Michael , Mann Uzi 
Published: June 2004

AbstractThe analysis of Part I (Rubinovitch and Mann, 1983) is continued here, considering the movements of a single particle in an arbitrary flow system in terms of the total times it resides in various flow regions. Results from the theory of Markov chains are used to derive expressions for the joint distribution of number of visits and total residence time in a flow region and for the total regional residence time distribution. Further, the relationships between the local particle flow rate, number of visits to a flow region, and net flow rate through the system are derived. Specifically, it is shown that

equation image
This relation is valid for any general flow system and any general region in the system. It holds true irrespective of the number of inlets and outlets to the region or of the nature of the internal mixing in the region. It is further shown how this relation leads to an experimental method for measuring local flow rates.
Heat transfer in three‐phase fluidized beds
Authors: Chiu Tai‐Ming , Ziegler E. N. 
Published: June 2004

AbstractWall‐to‐bed heat transfer coefficients in three‐phase fluidized beds with glass beads and clyindrical γ‐alumina particles were determined experimentally. In the present study, the relative increase in heat transfer coefficient was found equal to the relative decrease in liquid holdup in three‐phase fluidized beds. Modified Stanton number has been correlated with modified Reynolds number.
New approach to approximation of quantities involving physical properties derivatives in equation‐oriented process design
Authors: Lucia Angelo , Macchietto Sandro 
Published: June 2004

AbstractA new method for approximating quantities that involve physical properties derivatives in equation‐oriented process design is presented. It is a hybrid algorithm that makes combined use of Newton's method and the Schubert update. In doing so, available analytical derivative information is used in an optimal way.This hybrid algorithm is surprisingly close, in terms of the number of iterations required for solution, to an implementation of Newton's method that uses finite difference approximations of any unavailable physical properties derivatives. However, the number of rigorous thermodynamics calculations is usually about 50% fewer for the hybrid method. This can result in a substantial savings for problems in which the physical properties calculations dominate the simulation time. Two examples are presented to support these claims.
Heat transfer around a horizontal tube in freeboard region of fluidized beds
Authors: Biyikli S. , Tuzla K. , Chen J. C. 
Published: June 2004

AbstractAn experimental investigation was carried out to measure local and average heat transfer coefficients for horizontal tubes located in freeboard region of air fluidized beds. Tests were carried out at room temperature and atmospheric pressure in a rectangular fluidized bed, with mean particle diameters of 275 to 850 μm.Both local and average heat transfer coefficients were found to vary with particle diameter, flow rate, static bed depth, and elevation in the freeboard region.
Modeling of sintering and redispersion of supported metal catalysts
Authors: Handa P. K. , Matthews J. C. 
Published: June 2004

AbstractA model, which utilizes a Monte Carlo simulation, of the sintering and the redispersion of supported metal catalysts is presented and compared with experimental data from a Pt/Al2O3 system. The model is based on an atomic migration mechanism, but includes instantaneous diffusion and coalescence of crystallites of size <1 nm in reducing and inert atmospheres. It was found that behavior in reducing, oxidizing and inert atmospheres could be predicted.
Regeneration of activated carbon. Part II: Gasification kinetics with steam
Authors: Umehara Tadashi , Harriott Peter , Smith J. M. 
Published: June 2004

AbstractThe kinetics of the reaction between steam and thermally‐regenerated activated carbon containing DBS residue was studied at 973 to 1,062 K and atmospheric pressure. The results fit a Langmuir‐Hinshelwood rate equation originally developed for the oxidation of other types of carbon with steam. The rates of reaction were relatively high. Auxiliary experiments with added Na2SO4 indicated that the non‐volatile inorganic residue from DBS has a catalytic effect.Readsorption measurements on regenerated samples demonstrated that thermal regeneration alone resulted in considerable loss (35%) in adsorption capacity but that thermal regeneration followed by steam gasification could completely restore the adsorption capacity for DBS on the remaining virgin carbon.
Heat and power networks in process design. Part I: Criteria for placement of heat engines and heat pumps in process networks
Authors: Townsend D. W. , Linnhoff Bodo 
Published: June 2004

AbstractThe general problem of heat and power integration in process networks is complex and to date not fully understood. The subject covers site combined heat and power, on‐plant power generation, heat pumps, and refrigeration systems. This paper is the first of a two‐part series and explains the concept of “appropriate” heat engine and heat pump placement in process networks based on a fundamental new insight. “Appropriate” placement takes advantage of integration opportunities with the remainder of the process and yields marginal efficiencies far greater than could be achieved through stand‐alone heat engines. Conversely, “inappropriate” placement can never offer an advantage over stand‐alone systems. Part II describes procedures for preliminary design, involving heat engine, and heat pump equipment selection and performance assessment.
Kinetics and transport effects in the dehydration of crystalline potassium carbonate hydrate
Authors: Stanish M. A. , Perlmutter D. D. 
Published: June 2004

AbstractThe reaction kinetics and physical transport processes governing the thermal dehydration of solid K2CO3·3/2H2O particles were investigated. Isothermal reaction rate data were gathered using a thermogravimetric balance in which narrowly‐sized K2CO3·3/2H2O crystals were dehydrated under a water vapor atmosphere at different pressures and temperatures. The magnitudes of the heat and mass transfer resistances external to and within the solid product were estimated from solutions of the relevant pseudosteady‐state transport equations. In the temperature range 320 to 358 K, the vacuum dehydration of K2CO3·3/2H2O crystals smaller than 710 μm (−25 +30 mesh) are accurately modeled by the spherical shrinking‐core equation for the chemical rate control regime. In the presence of water vapor, external heat transfer to the particles was sufficient to prevent significant self‐cooling; heat and mass transfer resistances within the particles were negligible. The activation energy for K2CO3·3/2H2O dehydration is approximately 91 kJ/mol in vacuum; the reaction becomes extremely slow at relative pressures (P/Peq) > 0.35.
Kynch theory and compression zones
Authors: Fitch Bryant 
Published: June 2004

AbstractKynch's theories of sedimentation are reinterpreted, modified, and extended to be valid for batch sedimentation in which a zone of compacting sediment forms at the bottom of the column. The development has several steps: First, it is shown that a concentration discontinuity, any part of whose chord plots above the curve on a Kynch plot of settling flux vs. particle concentration, will be unstable and immediately give rise to a different concentration distribution. From this it is deduced that Kynch characteristics, or loci of constant concentration, must propagate either from the origin of a height vs. time plot, or tangentially from the locus of the compression or suspension‐sediment discontinuity. A Kynch‐like construction is derived to relate the settling rate at the top of the suspension (measured by its subsidence rate) to the concentration arriving at the surface at that time. It makes use of two tangents, one to the settling curve (as in Kynch), and another to the locus of the compression discontinuity. Finally a construction, analagous to that of Talmage and Fitch, is deduced for determining required thickener area.
Forced convection in three‐dimensional flows: III. Asymptotic solutions with viscous heating
Authors: Stewart W. E. , McClelland M. A. 
Published: June 2004

AbstractMatched asymptotic solutions are given for the temperature profiles and heat transfer rates in laminar three‐dimensional flows with viscous dissipation. The results are asymptotically valid for small thermal diffusivity α; they hold for Newtonian or non‐Newtonian fluids. The fluid properties are evaluated at an average temperature for the system; this is satisfactory for moderate temperature differences. Heat transfer formulas for various thermal boundary conditions are included. Several examples are analyzed, including the frictional heating of a polymer melt in flow through a wire‐coating die.
Dense‐phase feeding of pulverized coal in uniform plug flow
Authors: Sprouse K. M. , Schuman M. D. 
Published: June 2004

AbstractA series of high‐pressure pneumatic dense‐phase flow experiments were conducted using pulverized coal as the granular solids. This granular material was transported by nitrogen gas out of a conical feeder tank, through a length of stainless‐steel tubing and into a pressurized receiver tank. Only the nitrogen gas trapped in the interstices of the coal particles inside the feeder tank was used to transport the coal. Six different transport stainless‐steel tube geometries were used. A detailed analysis of the system is performed. This analysis reasonably predicts the expected solids flow rate for a given set of operating conditions and the minimum pressure drop required to maintain flow.
Dynamic simulation of azeotropic distillation towers
Authors: Prokopakis G. J. , Seider W. D. 
Published: June 2004

AbstractAlgorithms are presented for integration of the stiff ordinary differential equations using an adaptive semi‐implicit Runge‐Kutta (ASIRK) integrator; an A‐stable, single‐step, noniterative algorithm with step‐size control. Unusual open loop responses are encountered for simulations of azeotropic distillation towers and the results suggest two control variables. The results support the contention that one steady‐state regime of operation is unstable.
Sedimentation of multisized particles in concentrated suspensions
Authors: Selim M. S. , Kothari A. C. , Turian R. M. 
Published: June 2004

AbstractA model is developed for predicting the sedimentation velocity in suspensions of multisized nonflocculating solids, in which the retarding effect of the smaller particles on the setting velocities of the larger ones is taken into account. Tests of the model, and comparisons with other models, demonstrate that it provides improved prediction of data on suspensions comprising both discrete particle size mixtures and continuous size distributions, and that it is applicable to continuous countercurrent solid‐liquid operations.
Hydration of propylene oxide using ion‐exchange resin catalyst in a slurry reactor
Authors: Jaganathan R. , Chaudhari R. V. , Ramachandran P. A. 
Published: June 2004

AbstractKinetics of hydration of propylene oxide using an ion‐exchange resin catalyst in a slurry reactor was studied. The kinetics of homogeneous, uncatalyzed reaction was studied separately and used to obtain heterogeneous reaction kinetics. The homogeneous reaction was found to be 0.43 order with respect to propylene oxide concentration. The heterogeneous reaction was found to have intraparticle diffusional resistance under certain conditions. The intrinsic kinetic parameters and effective diffusivity were obtained from these data. The heterogeneous reaction was found to be 0.55 order with respect to propylene oxide concentration. The activation energies obtained for homogeneous and heterogeneous reactions were 51.5 and 53.4 kJ/mol, respectively. A theoretical model incorporating all the mass transfer resistances has been proposed.
Solid/liquid washing theory: Calculations for nonequilibrium stages
Authors: Tomiak A. 
Published: June 2004

AbstractCalculations for nonequilibrium stages were systematized via material balances for multicomponent mixing, which is applicable in the absence of sorption.The resulting treatment is quite complex with unequal stages but much simpler when the stages are equal. It allows solving complex solid/liquid washing problems from experimental simple washing data obtained with solute‐free wash liquor.
Rate processes in cycling a reversible gas‐solid reaction
Authors: Stanish M. A. , Perlmutter D. D. 
Published: June 2004

AbstractRate studies are reported of the effect of rehydration‐dehydration cycling on the vapor hydration behavior of solid K2CO3. Isothermal rate data were obtained at different temperatures and water vapor pressures for the reaction of narrowlysized anhydrous particles. Effects of different particle preparation histories on the rehydration rate were investigated and correlations of rate with particle pore structure explored. Rehydration rates of dehydrated K2CO3·3/2H2O were found to depend on the conditions of the prior dehydration. Rehydration is comparatively very slow at relative pressures below P/Peq ≃ 1.5; rates increase linearly with pressure above P/Peq ≃ 3. Hydration rates of K2CO3 particles obtained as anhydrous are substantially slower than those of identically‐sized crystals produced by prior dehydration of K2CO3·3/2H2O; after one rehydration‐dehydration cycle, rehydration rates are increased by as much as two orders of magnitude and this distinction between sources virtually disappears. Diffusional resistances based on calculated water vapor diffusivities are qualitatively consistent with the observed effects of cycling but do not by themselves account fully for the observations.
Modeling and simulation of an entrained flow coal gasifier
Authors: Govind Rakesh , Shah Jogen 
Published: June 2004

AbstractA mathematical model has been developed to simulate the Texaco downflow entrained‐bed pilot‐plant gasifier using coal liquefaction residues and coal‐water slurries as feedstocks. This model describes the physical and chemical processes occurring in an entrained coal gasifier. The gasification kinetics describes different complex reactions occurring in the gasifier and the hydrodynamics describes mass, momentum and energy balances for solid and gas phases. Temperature, concentration and velocity profiles along the reactor height were obtained by solving the mass, momentum and energy balances. Parameter studies were made to provide a better understanding of the reactor performance for various inlet feed conditions utilizing the model.