bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusive transport across corrugated plates and tubes
Authors: Wang C.‐Y.
Published: June 2004

The steady diffusion across a constant thickness corrugated barrier is analyzed through the intrinsic coordinate system. Perturbation solutions are found when the thickness is small compared to the minimum radius of curvature. For a given perimeter length, diffusive transfer is decreased, while for given maximum geometric dimensions, diffusive transfer may be increased by corrugations.
Model of solid gas reaction phenomena in the fluidized bed freeboard
Authors: Chen L. H. , WEN C.Y.
Published: June 2004

A comprehensive model incorporating elutriation, entrainment and reaction is presented to describe the chemical reaction and hydrodynamics occurring in the freeboard of a fluidized bed. A comparison of experimental data on the amount of particles elutriated and the concentration profiles of SO2 and NOx obtained from the freeboard of fluidized bed coal combustion (FBC) by the Babcock & Wilcox Company with the calculation based on the proposed model to include the effect of interaction among the entrained particles is desirable. More experimental data with chemical reactions in the freeboard are needed to validate the model for applications to fluidized bed catalytic reactors.
Feasible specifications in azeotropic distillation
Authors: Prokopakis G. J. , Seider W. D.
Published: June 2004

Feasible operating conditions are obtained for an azeotropic distillation tower using a nonlinear programming algorithm. The boil‐up rate, fractional recovery of product, and bottoms purities of entrainer and by‐product are adjusted to locate an overhead vapor stream that condenses into two liquid phases, but is in equilibrium with a single liquid phase on the top tray. A new objective function is introduced and minimized, subject to inequality constraints, using Powell's algorithm (1977). Results are obtained for dehydration of alcohol with benzene.
A design approach based on phase plane analysis: Countercurrent reactor/heat exchanger with parametric sensitivity
Authors: Akella L. M. , Lee Hong H.
Published: June 2004

A design approach based on a phase diagram of inlet temperatures is proposed for the countercurrent reactor/heat exchanger for highly exothermic reactions with inherent parametric sensitivities. The phase diagram shows the region of safe operation on a plane of feed and coolant inlet temperatures, free from runaway conditions. The boundaries surrounding the safe operation region are defined by design parameters. Simple procedures applicable to arbitrary expressions of global rate are developed for the phase diagram. The multi‐pronged design problem of selecting the design parameters and operating conditions for the maximum possible conversion within the constraints due to the parametric sensitivities is condensed into the represented by a phase diagram and an analysis on the phase plane. A design alternative which eliminates the necessity of the preheater for highly exothermic reactions is discussed and the advantages are quantitatively illustrated to assert that this design should be seriously considered as a viable alternative.
Correlation for the third virial coefficient usingTc,Pcand ω as parameters
Authors: Orbey Hasan , Vera J. H.
Published: June 2004

An empirical correlation for the third virial coefficient of nonpolar gases is developed. The correlation requires a knowledge of the critical temperature, critical pressure and acentric factor of the compounds for the prediction of third virial coefficients in the absence of experimental data. The use of the correlation for mixtures of nonpolar gases, including quantum gases, requires one binary parameter for each binary interaction. Predictions are in good agreement with reported experimental data and with the values obtained with existing correlations.
Corrected flowrates estimation by using θ convergence promoter for distillation columns
Authors: Pierucci S. J. , Ranzi E. M. , Biardi G. E.
Published: June 2004

The main task of the θ convergence promoter is to afford a better estimate of liquid and vapor molar fractions in each tray of the column.

The assumptions implied by the promoter prove to be reliable for conventional columns, while they may cause numerical instability when dealing with nonconventional configurations. In these cases, corrected molar fractions may be computed only after making a supplementary assumption, which in principle is not unique. So, the paper presents a new methodology which gives rather satisfactory results.
Tortuosity factors for diffusion in catalyst pellets
Authors: Wang Chang‐Tai , Smith J. M.
Published: June 2004

The 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

Theoretical 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.
Avoiding unwarranted inflection points in fitting of data
Authors: Taitel Yehuda , Tamir Abraham
Published: June 2004

This paper presents a method for correlating univariable experimental data, which avoids unwarranted inflection points by means of mathematical constraints fitted to sections of the data. The method was applied successfully to correlate thermodynamic data which are otherwise difficult to fit in without inflection points.
Mechanism of turbulent mass transfer at a solid boundary
Authors: Campbell J. A. , Hanratty T. J.
Published: June 2004

Mass 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

Measurements 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

We 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

The 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

Pressure 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

Two‐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

Calorimetry 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

A 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

The 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

The 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

The 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

The 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

Wall‐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

A 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

An 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

A 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

The 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

The 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

The 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

Kynch'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

Matched 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

A 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

Algorithms 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

A 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

Kinetics 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

Calculations 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

Rate 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

A 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.
Decomposition of systems of nonlinear algebraic equations
Authors: Shacham Mordechai
Published: June 2004

A new method for decomposing irreducible subsets, in the solution of systems of nonlinear algebraic equations, is presented. This method consists of two steps: (1) elimination of the nonlinearity from some of the equations by replacing nonlinear expressions by new variables; and (2) formulation of a problem of smaller dimension by tearing the linear subset of equations. It is shown that these modifications do not change considerably the convergence rate of the Newton‐Raphson and Broyden's methods while reducing the problem's dimension. Computer time reduction up to 80% is demonstrated in the examples solved. An algorithm for elimination of nonlinear expressions, which uses Boolean matrices instead of formula manipulation, is also presented.
Mass transfer and pressure drop in a cocurrent reciprocating plate extraction column
Authors: Noh S. H. , Baird M. H. I.
Published: June 2004

A 5‐cm‐diameter reciprocating plate extraction column has been operated in cocurrent flow. The pressure drop for water flow, and the local and average mass transfer products for the system acetic acid/kerosene/aqueous sodium hydroxide have been measured. Under well‐agitated conditions, the mass average transfer product is predictable by a model, which is also applicable to data reported earlier by Karr for a 2.54‐cm‐diameter column.
Estimation of critical properties with group contribution methods
Authors: Klincewicz K. M. , Reid R. C.
Published: June 2004

Currently available group‐contribution methods for Tc, Pc, and Vc were evaluated using the Ambrose (1980) critical property data compilation. The Ambrose estimation methods were found to be the most accurate. Linear regression methods were also employed to develop alternate estimation methods which were found to have an accuracy comparable to those of Ambrose.
Calculation of aerosol collection in fluidized filter beds
Authors: Ushiki K. , Tien Chi
Published: June 2004

A method is proposed for calculating aerosol collection in fluidized filter beds. The method employs the bubble assembly model of fluidization and considers the bed to be a series of compartments, each of which comprises two or three phases. Aerosol collection is assumed to occur in these phases in accordance with existing theories of particle deposition. The validity of the method is tested against available experimental data.
Effective utilization of equations of state for thermodynamic properties in process simulation
Authors: Mathias P. M. , Boston J. F. , Watanasiri S.
Published: June 2004

Thermodynamic property computations using equations of state first require computation of the density root. Since higher level calculations such as single‐stage flash, distillation and data regression are usually performed iteratively, properties are often demanded at conditions where the appropriate density root does not exist. A strategy of returning suitable pseudoproperties under such conditions is proposed. It has been successfully used in ASPEN (Advanced System for Process Engineering), a general process simulator developed at the Massachusetts Institute of Technology.
Multivariable computer control of a butane hydrogenolysis reactor: Part II: Design and on‐line implementation of a stochastic controller using an identified multivariate noise model
Authors: Jutan Arthur , Wright J. D. , MacGregor J. F.
Published: June 2004

A multivariable stochastic controller is implemented on a pilot scale, plug flow, butane hydrogenolysis reactor. In the synthesis of the controller, a multivariate time series model of the process disturbances is used. The success of this controller is compared to a previous controller where the process disturbances are not directly modeled.
Dispersion, mass transfer and chemical reaction in multiphase contactors: Part II: Numerical examples
Authors: Hatton T. A. , Lightfoot E. N.
Published: June 2004

A Numerical study, based on the theoretical developments of Part I of this series, has demonstrated that the chemical activity of a solute can have a significant effect on the convective dispersion behavior of multiphase reactors, and that the dispersion parameters estimated using inert tracers for the individual phases may not be representative of the parameters that should be used in the design of reactive systems. Moreover, the use of different transverse averaging procedures for the individual phases can give rise to additional interaction effects between the phases which are not accounted for in the traditional axial dispersion models. The predicted differences in dispersion parameter values depending on whether the solute is inert or not, are in qualitative agreement with published experimental results.
Kinetics of short contact time coal liquefaction. Part I: Effect of operating variables
Authors: Abichandani J. S. , Wieland J. H. , Shah Y. T. , Cronauer D. C.
Published: June 2004

The liquefaction kinetics of Powhatan No.5 mine coal (Pittsburgh Seam) in the presence of SRC‐II recycle solvent at short contact times (<10 min) and temperature and pressure ranges of 573–723 K and 10.3–13.8 MPa is examined in a well‐mixed reactor. In the initial stages of liquefaction, while overall coal conversion (tetrahydrofuran solubles) increases with temperature, oil (pentane solubles) is lost with an increase in temperature. An increase in solvent‐to‐coal ratio results in an increase of conversion. The initial coal particle size distribution, total pressure, and nature of gas phase (nitrogen or hydrogen) have no significant effect on the production of any of the product of liquefaction for contact times up to 10 min. A lumped kinetic model is presented to describe the product distribution.
Fractionation with condensation and evaporation in wetted‐wall columns
Authors: Davis J. F. , Tung Hsien‐Hsin , Mah R. S. H.
Published: June 2004

A model is presented to describe the behavior of falling film fractionators with evaporation or condensation. Experimental measurements of vapor composition, vapor temperature and wall temperature profiles were made. Close agreement suggests that the model is applicable to both adiabatic and nonadiabatic conditions.
Coiled configuration for flow inversion and its effect on residence time distribution
Authors: Saxena A. K. , Nigam K. D. P.
Published: June 2004

Flatter velocity profiles and more uniform thermal environents are extremely desirous factors for improved performance in flow reactors and heat exchangers. One means of achieving this in laminar flow systems is to use mixers and flow inverters. These improve performance but at higher initial and operating costs. This paper introduces a new and more effective device for flow inversion which is achieved by changing the direction of centrifugal force in helically‐coiled tubes. Transient response experiments carried out under the conditions of both negligible and significant molecular diffusion reveal drastic narrowing of the residence time distribution (RTD). The effectiveness of the present device can be assessed by the fact that even at a Dean number of 3 the value of dispersion number as low as 0.0013 is obtained under the condition of significant diffusion, and in the case of negligible diffusion the value of dimensionless time at which the first element of tracer appears at the outlet is as high as 0.85.
Excess enthalpies for (water + methane) vapor up to 698.2 K and 12.6 MPa
Authors: Wormald C. J. , Colling C. N.
Published: June 2004

A new flow mixing calorimeter has been used to make measurements of the excess enthalpy of water vapor + methane at temperatures up to 698.2 K and pressures up to 12.62 MPa. Tests on the calorimeter and consistency tests on the measurements suggest that the results are free from significant error. The measurements are fitted to an equation from which excess volumes and compressibility factors for the mixture are calculated.
Gas‐Liquid mass transfer in fixed‐bed reactors with cocurrent downflow operating in the pulsing flow regime
Authors: Blok J. R. , Koning C. E. , Drinkenburg A. A. H.
Published: June 2004

Liquid‐side mass transfer coefficients were measured for cocurrent two‐phase downflow in 5 and 10 cm diameter columns pakced with 2.5 and 4 mm Raschig rings. Experiments were specifically carried out in the pulsing flow regime. The mass transfer coefficients were determined via absorption of CO2 into buffer solutions with the advantage of a high absorbing capacity. Thus columns of 1 m length could be used. Relations are proposed based on the hydrodynamic phenomena observed in pulsing flow. From these relations a correlation for kL is found in terms of flow rates and packing characteristics that satisfies the experimental data.
Low‐density polyethylene vessel reactors: Part I: Steady state and dynamic modelling
Authors: Marini Luigi , Georgakis Christos
Published: June 2004

By the use of a perfectly mixed model and an imperfectly mixed one for lowdensity polyethylene vessel reactors, we show that increases in the initiator consumption with polymerization temperature are due to mixing limitations at the initiator feed. With all its parameters independently estimated, the imperfectly mixed model provides an excellent agreement with experimental data for several initiators, feed flow rates and polymerization pressures. In the temperature region of industrial interest for each type of initiator, the open‐loop reactor dynamics drastically change from open‐loop unstable, at low temperatures, to open‐loop stable at high polymerization temperatures.
Low‐density polyethylene vessel reactors: Part II: A novel controller
Authors: Marini Luigi , Georgakis Christos
Published: June 2004

By the use of an imperfectly mixed model developed for LDPE vessel reactors, we show that a linear controller cannot perform satisfactorily in the entire range of operating conditions of industrial interest. Based on the concept of reaction rate control, a novel controller is developed which provides satisfactory closed‐loop dynamics independent of steady‐state conditions. A nonlinear controller is shown to be more effective in avoiding reactor light‐off.
Finishing stages of PET synthesis: A comprehensive model
Authors: Ravindranath K. , Mashelkar R. A.
Published: June 2004

A comprehensive mathematical model for the finishing stages of polyethylene terephthalate (PET) synthesis is developed. The model takes into account the variables which have significant influences on polymerization but have not been hitherto taken into account, e.g., changing interfacial concentration and the presence of side reactions. The model is applicable to industrial polymerizations, and the predictions agree well with the literature and with certain pilot‐plant and commercial data.
Droplet coalescence and breakage rates in a packed liquid extraction column
Authors: Hamilton J. A. , Pratt H. R. C.
Published: June 2004

Coalescence rates for MIBK (methyl isobutyl ketone) droplets in water in a packed column have been measured directly using a novel colorimetric technique. Second‐order coalescence and first‐order breakage rate constants were derived from the results using a discrete population balance model and were correlated in terms of droplet diameter and dispersed‐phase holdup. It is shown that the rate constants can be used to predict the steady‐state droplet‐size distribution and coalescence rates. They were also used in a theoretical study of mass transfer for a typical polydisperse system, which showed that repeated droplet coalescence and breakage leads to some reduction in column height.
The VIM theory of molecular thermodynamics: Part I: Analytic equation of state of nonpolar fluids
Authors: Alem A. H. , Mansoori G. A.
Published: June 2004

Variational inequality minimization (VIM) theory of statistical mechanics is used to derive analytic equations of state for nonpolar fluids. Pair‐ and tripletintermolecular potential energy functions are taken into account in the formulation of this equation of state. The VIM theory has made it possible to derive rather simple expressions for the thermodynamic properties of nonpolar fluids. Predictions of the thermodynamic properties of argon and methane in the liquid phase, in the vapor phase, and in the critical region by the VIM equation of state are shown to be in excellent agreement with the experimental data.
Hydrodynamics of fluidization in a semicircular bed with a jet
Authors: Ettehadieh Bozorg , Gidaspow Dimitri , Lyczkowski R. W.
Published: June 2004

A hydrodynamic model of fluidization was developed that computes void fractions, pressure and solid and gas velocities in cylindrical fluidized beds. Cmputed time‐averaged gas velocity distributions of a jet compared well with Westinghouse experimental data without the use of any fitted parameters. The main empirical input was a drag correlation from the literature.
A dual mechanism for low‐stress hemolysis in laminar blood flow
Authors: Beissinger R. L. , Williams M. C.
Published: June 2004

Human blood is sheared in cone‐and‐plate and parallel‐plate rotational viscometers, the latter with variable plate spacings h. Plasma is analyzed for hemoglobin and LDH content before and after shearing to determine the extent of shear‐induced blood damage within the low‐stress regime (stress ⩽ 13 Pa). Geometrical variations in the test apparatus can be accommodated by correlating blood damage with the radially‐averaged shear rate. Data on expired blood are shown to imply that much of the damage arises in the bulk fluid, with a smaller contribution from surface effects. Models are proposed to explain these results, obtained over a shear rate range to 5,000 s−1; parallel‐plate platen separation is 0.25 < h < 1.00 mm, cone‐and‐plate angle is 0.5°, and both systems have platens 100 mm in diameter.
Coalescence time for a small drop or bubble at a fluid‐fluid interface
Authors: Chen Jing‐Den , Hahn Pil Soo , Slattery J. C.
Published: June 2004

When a small drop or bubble is driven through a liquid phase to a fluid‐fluid interface, a thin liquid film which forms between them drains, until an instability forms and coalescence occurs. Lin and Slattery (1982b) developed a hydrodynamic theory for the first portion of this coalescence process: the drainage of the thin liquid film which occurs while it is sufficiently thick that the effects of London‐van der Waals forces and electrostatic forces can be ignored. Here we extend their theory to include the effects of the London‐van der Waals forces. To simplify the analysis, we follow the suggestion of Buevich and Lipkina (1975, 1978) in developing an expression for the rate of thinning at the rim or barrier ring of the draining film. A linear stability analysis permits us to determie the coalescence time or the elapsed time between the formation of a dimpled film and its rupture at the rim.

For comparison, this same linear stability analysis is applied to the thinning equations developed by MacKay and Mason (1963) for the plane parallel disc model and by Hodgson and Woods (1969) for the cylindrical drop model.

For all three models, our linear stability estimate for the coalescence time tc is in better agreement with the available experimental data than is the elapsed time t∞ between the formation of a dimpled film and its drainage to zero thickness at the rim in the absence of instabilities.
A rotating annular chromatograph for continuous separations
Authors: Begovich J. M. , Sisson W. G.
Published: June 2004

Preparative, multicomponent liquid chromatographic separations have been achieved by using a slowly rotating annular sorbent bed with fixed multiple feed points and fixed product withdrawal locations. The cation exchange separation of copper, nickel, and two cobalt complexes has been extensively used to study the effects of rotation rate, eluent rate, bed loading, and column size on separation performance. Experimental results have been compared with three theoretical models: plate theory, an analytical solution which incorporates multicomponent Langmuir isotherms, and an extension of the analytical solution to include dispersion effects.
Influence of hydrodynamics on crystal growth and dissolution in a fluidized bed
Authors: Budz Jerzy , Karpinski P. H. , Nuruc Zbigniew
Published: June 2004

Mass transfer coefficients for the growth and the dissolution of potassium alum and sodium thiosulfate in a laboratory‐scale fluidized‐bed apparatus were determined and correlated in a form of the Frössling equation. The surface reaction rate for potassium alum was found to be dependent onthe crystal size.
Incomplete state feedback for time delay systems: Observer applications in multidelay compensation
Authors: Ogunnaike B. A. , Ray W. H.
Published: June 2004

This paper demonstrates how a recently developed observer for time delay systems may be used to estimate needed state variables for implementation of multivariable time delay compensation. The general results are illustrated by an example of a multireactor plant in which only one reactor concentration can be measured. The observer worked well in simulation for both multivarible PID control and multidelay compensated PID control and allowed both schemes to function with estimated state variables in the feedback loop.
Numerical methods of solution for continuous countercurrent processes in the nonsteady state part I: Model equations and development of numerical methods and algorithms
Authors: Tan K. S. , Spinner I. H.
Published: June 2004

Simple, efficient and noniterative algorithms are developed for the calculation of the dynamics of continuous countercurrent processes described by hyperbolic differential equations. The algorithms are derived using the method of characteristics and are particularly useful for either general quadratic or hyperbolic isotherms such as the Langmuir isotherm. The use of characteristic coordinates for the numerical solution avoids accumulating errors that would arise from computations based on a rectangular grid of real time and space coordinates.

The proposed methods can provide an efficient framework for extension to transport processes with general nonlinear rate expressions. The algorithms and methods initially derived for simple models can be extended to more complex systems such as countercurrent flow with accumulating stationary phases and response to distributed disturbances.

The application of the algorithm and methods to a number of countercurrent mass and heat transfer processes will be illustrated in Part II, where the accuracy and efficiency of the proposed methods will also be demonstrated by comparison to available analytic solutions. An example demonstrating the extension of the method to a system with complex coupled boundary conditions will also be discussed.
Fluidized combustion of char and volatiles from coal
Authors: Turnbull Eion , Davidson J. F.
Published: June 2004

This paper reviews the literature about fluidized combustion of char and volatiles from coal. While the rate of combustion of particles bigger than about 2 mm is mainly limited by the rate of diffusion of oxygen, there is usually an effect of chemical rate. As particle diameter decreases, the influence of chemical rate increases. Char particles are porous and combustion occurs in pores near their exterior. Char reactivity can be modelled by an effective pore area for combustion.

At high bed temperatures (>1,150 K), the rate of combustion of volatiles is limited by the rate of mixing of fuel and oxygen. At low bed temperatures (<1,000 K), combustion reactions are inhibited by the inert particles in the bed.