bluuebunny/crossref_metadata_2025 huggingface dataset:
Oscillatory behavior of a gas bubble growing (or collapsing) in viscoelastic liquids
Authors: Yoo Hee Ju , Han Chang Dae
Published: June 2004

A theoretical study was carried out to achieve a better understanding of the oscillatory behavior of a gas bubble growing (or collapsing) in a viscoelastic liquid, by taking into account both the hydrodynamic and diffusion effects. The Zaremba‐DeWitt model was chosen to represent the rheological properties of the suspending medium. The finite difference method was employed to solve the governing system equations.

The computational results show that, in the case of very fast diffusion (i.e., constant bubble pressure), the oscillatory behavior of a bubble takes place only when the ratio of the initial pressure difference between the gas bubble and the liquid phase to the elastic modulus of the suspending medium is below a certain critical value. On the other hand, in the case of very slow diffusion, the oscillatory behavior of a bubble persists, regardless of the magnitude of the rheological properties of the suspending medium. Our study indicates further that the diffusivity of a gas has a profound influence on the occurrence of oscillatory behavior, that the elastic property of the suspending medium enhances oscillatory behavior while its viscosity plays the opposite role, and that even a Newtonian medium can give rise to an oscillatory pattern of bubble growth (or collapse), although it dampens out very quickly.
Selective absorption of H2S from larger quantities of CO2 by absorption and reaction in fine sprays
Authors: Bendall E. , Aiken R. C. , Mandas F.
Published: June 2004

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

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

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

Based on the drag force of two spheres in contact and the probability density of size ratios of particles which constitute an aggregate particle, the population balance equation describing the change of the particle‐size distribution due to the disruption of aggregate particles is derived and the numerical solutions of this equation are obtained.

Experiments were carried out with fly ash particles dispersed in air stream through an orifice at various flow rates. The measured size distributions can be represented by the numerical solutions of the population balance equation.
Unified treatment of structural effects in fluid‐solid reactions
Authors: Bhatia S. K. , Perlmutter D. D.
Published: June 2004

By considering reaction and diffusion through a product layer and concomitant movement of pore and reaction surfaces, a general rate equation is derived for fluid‐solid reactions. Application to the random pore model extends the prior results (Bhatia and Perlmutter, 1980, 1981a) to account for nonlinear concentration gradients in the product layer, by assuming that the product is deposited as overlapping cylindrical annulae. For the Petersen (1957) model, new results are derived which account for product layer diffusion. A comparison of numerical conversion‐time predictions from the grain model (Szekely et al., 1976), the Petersen model, and the random pore models suggests that they are more strongly affected by the representation of the reaction surface than by that of the pore surface. The model is applied to the data of Borgwardt (1970) on the SO2‐lime reaction, and the results are compared with a previous interpretation using a linear concentration gradient approximation.
Hydraulic deliquoring of compressible filter cakes. Part 1: Reverse flow in filter presses
Authors: Tiller Frank M. , Horng Liou‐Liang
Published: June 2004

Removal of liquid from filter cakes can be accomplished by mechanical or hydraulic methods after cake formation is complete. This paper deals with the latter procedure. The local porosity in porous beds (Tiller and Cooper, 1962) is a function of hydraulic pressure distribution and cake compressibility. Calculation of average porosity requires an integration of local values as determined by liquid flow patterns. As most compressions of filter cakes are irreversible, the local porosity is a function of the maximum effective pressure (frictional pressure loss) reached during cyclical operations. Reversal of flow through a cake develops radically changed pressure distributions which can be utilized to reduce local porosities. Analytical expressions are presented for reduction of average porosity brought about by reversing flow of liquid in plate‐and‐frame and recessed plate filter presses.
Improved bubble velocity equation for bubbling fluidized beds
Authors: Weimer A. W. , Clough D. E.
Published: June 2004

An improved bubble velocity equation is developed for gas‐solid fluidized beds. Model parameters are evaluated from reported experimental results of bubble flow. Finally, this improved equation is compared to the commonly applied velocity relationship of Davidson and Harrison (1963).
Modeling of acid hydrolysis of solasodine glycosides. Part I: Formation of solasodine by glycoside hydrolysis
Authors: Crabbe P. G. , Fryer Colin
Published: June 2004

Solasodine from Solanum plants is a potential raw material for steroid drug manufacture. Acid hydrolysis of the naturally occuring glycosides of solasodine is a major step in production of the aglycone. As part of a detailed study of the hydrolysis of solasodine glycosides, the hydrolysis procedure has been mathematically modelled. Two models are presented and have been used to obtain kinetic data for the reactions at a number of different reaction conditions. The subsequent conversion of solasodine to solasodiene is considered in Part II of this paper; the combined reactions and guidelines for commercial hydrolysis are presented in Part III.
Modeling of acid hydrolysis of solasodine glycosides. Part III: Combined glycoside hydrolysis and solasodiene formation—guidelines for commercial hydrolysis
Authors: Crabbe P. G. , Fryer Colin
Published: June 2004

Kinetic models for glycoside hydrolysis and solasodiene formation are combined, and using previous experimental data the effect of changes in reaction conditions on hydrolysis times and the proportion of solasodiene in the final hydrolysed product are established. These are used to give a set of guidelines for commercial hydrolysis. The use of the models for new commercial situations is explained.
Selective propylene oxidation over a copper‐tin oxide catalyst
Authors: Self D. E. , Oakes J. D. , White M. G.
Published: June 2004

The mixed oxide system of copper and tin and the active single oxide, Cu2O, were compared for reducibility of the copper ion, relative number and type of active sites, and reaction kinetics. The enhanced selectivity of the mixed oxides may result from the formation of highly selective sites at the expense of less selective sites. The reducibility of the copper ion in the mixture is influenced by the oxidation state of the tin ion. The reactant and product reaction orders are the same for both catalysts but the mixed oxides are more sensitive to inhibition by water. The catalyst composition affects the energetics of the reaction over the copper‐tin oxide catalysts.
Advanced multivariable control of a pilot‐plant distillation column
Authors: Ogunnaike B. A. , Lemaire J. P. , Morari M. , Ray W. H.
Published: June 2004

This paper reports an experimental study of the multivariable control of a pilot‐plant distillation column having a side stream as well as overhead and bottom products. A recently developed multivariable controller for systems having multiple time delays is implemented for the first time on an experimental process. The controller consists of a new multivariable time delay compensator coupled with traditional PI controllers. Realization is accomplished with a PDP 11 minicomputer. Improved system performance was observed with the delay compensator, especially in disturbance rejection.
Studies in magnetochemical engineering. Part II: Theoretical development of a practical model for high‐gradient magnetic separation
Authors: Liu Y. A. , Oak M. J.
Published: June 2004

High‐gradient magnetic separation (HGMS) is an existing commercial technology which promises to be an effective means for the large‐scale separation of both weakly magnetic and practically nonmagnetic, micron‐sized particles. It utilizes the strong magnetic forces created typically by placing filamentary ferromagnetic packing materials inside a separator matrix magnetized by a uniform background magnetic field. In this paper, a practical mathematical model for HGMS is developed for quantitatively predicting the grade and recovery of the separated product and the capacity (concentration breakthrough) of the separator. Computer implementation and experimental verification of the new model for HGMS applied to pilot‐scale coal beneficiation are described in Part III.
One variety of quick estimation schemes for parameters in kinetic models
Authors: Watanabe K. , Himmelblau D. M.
Published: June 2004

Quick estimation of the parameters in a process model can play a significant role in kinetic studies. This work is aimed at developing a quick estimation strategy by means of process discretization and evaluating errors engendered by the strategy. A systematic error evaluation method and guidelines to select the best discretization relation used in the strategy are described.
Anomalous diffusion of vapors through solid polymers. Part I: Irreversible thermodynamics of diffusion and solution processes
Authors: Neogi P.
Published: June 2004

The solubility and diffusivity of vapors in polymers below and in the vicinity of glass transition temperature are known to be explicitly time‐dependent. It is assumed here that the polymers are in nonequilibrium states, characterized by an internal order. The latter relaxes with time and moves towards equilibrium. The changes in the internal order bring about changes in the properties of the polymer‐solute system.

The time dependence of diffusivity and solubility has been derived for isothermal processes not far from equilibrium. Well‐known procedures for analyzing relaxing systems are used to obtain the above results, and the knowledge of how the internal order is related to the molecular properties is not required.
Simplification of quasilinearization method for parameter estimation
Authors: Kalogerakis Nicolas , Luus Rein
Published: June 2004

An alternate development of the quasilinearization method for parameter estimation is presented to enable a more efficient implementation of the algorithm. Similarity of this algorithm to Gauss‐Newton method is shown and attention is given to systems having a nonlinear relationship between the observed and state variables. To overcome the problem of a small region of convergence, the use of direct search optimization is proposed for the first few iterations, followed by the simplified quasilinearization algorithm.
Reconciliation of process flow rates by matrix projection. Part I: Linear case
Authors: Crowe C. M. , Campos Y. A. Garcia , Hrymak A.
Published: June 2004

Flow rate measurements in a steady‐state process are reconciled by weighted least squares so that the conservation laws are obeyed. A projection matrix is constructed which can be used to decompose the linear problem into the solution of two subproblems, by first removing each balance around process units with an unmeasured component flow rate. The remaining measured flow rates are reconciled, and the unmeasured flow rates can then be obtained from the solution of the conservation equations. The basic case contains constraints which are linear in the component and the total flow rates. The method is extended to cases with bilinear constraints, involving unknown parameters such as split fractions.

Chi‐square and normal statistics are used to test for overall gross measurement errors, for gross error in each node imbalance which is fully measured, and for each measurement adjustment.
Studies in chemical process design and synthesis: Part V: A simple heuristic method for systematic synthesis of initial sequences for multicomponent separations
Authors: Nadgir V. M. , Liu Y. A.
Published: June 2004

A simple heuristic method for the systematic synthesis of initial sequences for multicomponent separations is proposed and applied to a number of synthesis problems which have been solved previously using other methods. Based on reported costs, it is shown that the initial sequences synthesized for the test problems by the new heuristic method are cheaper than those obtained by other ordered heuristic methods. These initial sequences are also either identical to or at most a few percents higher in costs than those optimum sequences obtained by other algorithmic, heuristic‐algorithmic and heuristic‐evolutionary methods. The new method is straightforward to apply by hand and it does not require any mathematical background and computational skill from the user.
One‐dimensional model of the physico‐chemical processes occurring inside a burning coal surface
Authors: Massaquoi J. G. M. , Riggs J. B.
Published: June 2004

A one‐dimensional model has been developed to account for the physicochemical processes occurring inside a burning wet coal surface. The model considers the vaporization of coal moisture and the existence of a moving evaporation front, pyrolysis and char/gas reactions in the hot zone, molecular diffusion and Darcy flow through the dry porous coal, transpiration cooling effect of the water vapor and pyrolysis gases, temperature‐dependent reaction kinetics and coal thermal conductivity, and variable porousity of the coal due to pyrolysis and char/gas reactions.

The model and associated assumptions have been verified with experimental data from the combustion and drying of coal. The results also show that the model prediction of the heat transferred from the coal surface into the coal is much higher than that calculated by the simple heat conduction equation.

The fraction of the water in the coal that reacts with char is shown as a function of the linear burn velocity and the surface temperature. In addition, the effect of variations in coal moisture and the thermal conductivity on the thickness of the dry zone are also shwon.
Excess second virial coefficients and critical temperatures: Acetone + methyl acetate
Authors: McElroy P. J. , Hashim H. , Tatt Wong Loke
Published: June 2004

For the system acetone + methyl acetate measurements are reported of excess second virial coefficients (at 75 and 100°C) and critical temperatures for nine different compositions. The efficacy of the correlations due to Tsonopoulos and to Hayden and O'Connell are discussed and the former correlation (with one modification) is shown to give a better prediction of unlike interaction terms. The implication of the results for excess Gibbs Free Energy estimation is discussed.
Oxidative absorption of H2S and O2 by iron chelate solutions
Authors: Neumann D. W. , Lynn Scott
Published: June 2004

Hydrogen sulfide is oxidized to elemental sulfur by ferric ion chelated with nitrilotriacetic acid (NTA) in aqueous solution at pH 3.5 to 4.5. The reaction appears to be fast relative to gas‐ and liquid‐phase diffusion, and the transfer of H2S from a gas stream is correlated well by the theory of absorption with instantaneous chemical reaction. The ferrous ion formed in this reaction may be reoxidized with oxygen absorbed from a stream of air. The presence of NTA catalyzes the reaction of O2 and Fe2+ in the same pH range, and diffusion is again controlling. Design calculations based on laboratory data for both absorption steps show that cocurrent gas‐liquid contactors are advantageous for achieving high reaction rates (e.g., ∼99.99% H2S removal), high gas velocities (10 to 20 m/s), low pressure drops [1 to 3 kPa (10 to 30 cm H2O)], and moderate column heights (10 to 15 m).
Computer‐aided synthesis and design of plant utility systems
Authors: Petroulas T. , Reklaitis G. V.
Published: June 2004

A design synthesis procedure is developed for preliminary design of utility systems. Given known steam sources (waste heat and auxiliary boilers) and sinks (heating, process injection, and driver horsepower needs), the algorithm determines the optimal header pressure levels, the distribution of steam turbines in the network, and the steam flows between all devices so as to maximize the real work recovered from the sources. Any number of pressure levels can be accommodated at only modest increase in computational effort.
Fate of solids fed pneumatically through a jet into a fluidized bed
Authors: Kececioglu Ifiyenia , Yang Wen‐Ching , Keairns D. L.
Published: June 2004

Solid tracer particles were fed pneumatically through a jet into a fluidized bed to simulate the feeding of solids via a pneumatic transport line into a fluidized‐bed reactor operating in the slugging‐bed mode. The fluidized bed was defluidized instantaneously at different times after the initiation of the tracer particle injection. The bed was then sampled layer by layer to provide the radial and axial concentration profiles of the tracer. Regular and high‐speed movies (1,000 frames per second) were taken to study the operation of the fluidized bed and the phenomena of the gas‐solid two‐phase jet.

Experimental results on solid mixing, jet constriction and slugging frequencies, slugging bed height, slug length, jet penetration, and jet half‐angle at three nominal jet velocities of 52, 37, and 25 m/s and corresponding solids loadings are presented. Additional experimental results on jet constriction and slugging frequencies, and slug volume (axial slug size) obtained for a wider range of jet velocities confirm the hydrodynamic trends observed during the tracer particle injection experiments. The results indicate that solids mixing increases, and well‐mixed conditions are reached earlier, with an increase in jet injection velocity. The obtained mixing times were correlated successfully in terms of the excess gas velocity. The experimental data on jet penetration and slug motion were satisfactorily correlated by modified versions of existing theoretical relations. The modifications included the effect of the injected solids on jet penetration and jet half‐angle and also the effect of our semicircular column geometry and single wall‐slug configuration on the observed slug motion.
Determination of catalyst surface area from desorption characteristics of physisorbed gases
Authors: Miller D. J. , Lee H. H.
Published: June 2004

A new experimental method for the measurement of catalyst surface area of supported catalysts has been developed using selective physisorption. The desorption characteristics of a gas are studied separately on the catalyst, the support, and the supported catalyst by carrying out thermal desorption experiments in a continuous flow sorptometer. Differences in the coverage vs. temperature curves, obtained from the thermal desorption experiments, are a measure of the selectivity of the physisorbing gas, and allow calculation of the fraction of total surface area occupied by the catalyst.

Two systems have been studied utilizing the thermal desorption with carbon dioxide as adsorbate: potassium carbonate/carbon black and silver/alumina. Supported catalyst surface area was determined for each system; the results were confirmed using physical mixtures of the two components (where the actual area of each component is known) and oxygen chemisorption for the silver/alumina system. The experimental technique allows for straightforward calculation of the catalyst area.
Dispersion, mass transfer and chemical reaction in multiphase contactors: Part I: Theoretical developments
Authors: Hatton T. A. , Lightfoot E. N.
Published: June 2004

The convective dispersion theory of Gill and Sankarasubramanian is extended to allow for multiphase mass transfer interactions in column‐type contactors, and for multisolute, reversible and irreversible, homogeneous and wall‐catalyzed heterogeneous chemical reactions in the individual phases. This theory can now be applied in any transverse average, not just the area average used in the past, and additional interactions between the phases not normally accounted for in the traditional axial dispersion model are indicated.
Dynamic behavior of a porous char particle burning in an oxygen‐containing environment: Part I: Constant particle radius
Authors: Sotirchos S. V. , Amundson N. R.
Published: June 2004

The transient combustion of porous char particles is modelled. The model takes into account the reactions of carbon with CO2 and O2 and the oxidation of CO in the gas phase. It reveals strong effects of the intraparticle thermal gradients and of the pore structure evolution scheme on the burning time and predicts an optimum particle size that gives minimum burning time.
Structural analysis and solution of systems of algebraic design equations
Authors: Book N. L. , Ramirez W. F.
Published: June 2004

A new method for expressing the structure of a system of equations is developed using a type of occurrence matrix entitled the functionality matrix. The functionality matrix indicates not only the occurrence of variables in equations but also the functional form in which they occur. Since the difficulty of solving an equation for a variable is related to its functional form, analysis of the functionality matrix provides explicit information on the difficulty of solution of the solution of the equation.

A methodology for the solution of design problems by digital computers is described. This methodology operates on the functionality matrix which describes the set of design equations. Algorithms using this methodology interact and guide the designer in an efficient selection of design variables and redundant equations. Once design variables and redundant equations are selected, a computational method is presented for ordering and solving the equations.
Mass transfer in AC electrolysis part I: Theoretical analysis using a film model for sinusoidal current on a rotating hemispherical electrode
Authors: Cheng C. Y. , Chin D‐T.
Published: June 2004

A film model is presented for the analysis of mass transfer to a rotating hemispherical electrode when sinusoidal alternating current (AC) together with direct current (DC) are flowing across the electrode surface. The concentration of a diffusing ion is separated into two independent components: a constant DC component and a periodic AC component. The DC concentration is obtained by solving the steady‐state convective mass transport equation with the perturbation method. The periodic AC concentration distribution is analyzed by the solution to the one‐dimensional transient diffusion equation based on the concept of Nernst diffusion layer. The limiting AC current densities corresponding to a zero surface concentration of a reactive ion are investigated for various DC current densities and AC frequencies. The resulting periodic concentration overpotential wave and its phase shift with respect to the applied AC are examined. A comparison with a previous rigorous model indicates that the film model is a good approximation to the mass transfer calculation in the regimes of a dimensionless AC frequency K = (ω/Ω)Sc1/3 greater than 2 and less than 0.01.
Evolution of pore volume distribution during gasification
Authors: Su Jow‐Lih , Perlmutter D. D.
Published: June 2004

A general equation is derived that predicts the evolution of pore volume distribution during isothermal gasification in the regime of kinetic control, starting from a given initial condition. The development takes into account pore enlargement as well as pore intersections. Equations are also derived for the special cases of (1) uniform pore size and (2) bimodal distribution. The results are used to interpret the experimental data of Tomkow et al. (1977) and Kawahata and Walker (1962).
hydrodynamic parameters for gas‐liquid cocurrent flow in packed beds
Authors: Sáez A. E. , Carbonell R. G.
Published: June 2004

The hydrodynamics of cocurrent gas‐liquid flow in packed beds is analyzed by extending the concept of relative permeability to the inertial regime.

The relative permeabilities of the gas and liquid phases are functions of the saturation of the liquid phase. These functions are found from an analysis of experimental data. The relations obtained are used to develop empirical correlations for predicting liquid holdup and pressure drop in gas‐liquid cocurrent downflow in packed beds over a wide range of operating conditions. The correlations proposed give very good results when compared to experimental data yielding, in general, mean relative deviations lower than existing correlations. In addition, a new equation is proposed for predicting static holdup in packed beds which is based on a more physically realistic characteristic length than that used in previous studies.
Initiation of roll waves in gas‐liquid flows
Authors: Andreussi Paolo , Asali J. C. , Hanratty T. J.
Published: June 2004

Measurements of the effect of liquid viscosity on the initiation of roll waves in a horizontal gas‐liquid flow are presented. These results are interpreted by an analysis based on the calculation of the growth of long wavelength disturbances.
Evaluation of changeover control policies by singular value analysis—Effects of scaling
Authors: Lau Henry , Jensen K. F.
Published: June 2004

A method for assessing control performance at different operating conditions in a chemical process is developed using singular value analysis. The control potential of the system is established by analyzing the singular values of the steady‐state system matrix. Dynamic considerations and interaction analysis can be included in the framework of the method described. The approach enables the process engineer to consider controllability of the process as well as economics in synthesizing a changeover control policy. Singular values depend on the scaling of the system, i.e., the definition of the physical dimensions of the system. The effects of scaling on the analysis are first investigated by scaling the steady‐state system matrix with empirical methods, equilibration, and geometric scaling. Using the insights gained from these studies a scaling method, variable normalization and equation equilibration, which is intuitively appealing and suited for the purpose, is devised. Two typical systems, continuous stirred tank reactor and a polymerization reaction system, demonstrate the usefulness of this method.
The influence of temperature on surface and microscopic properties of surfactant solutions in relation to fluid displacement efficiency in porous media
Authors: Sharma M. K. , Shah D. O. , Brigham W. E.
Published: June 2004

The surface properties, microscopic structure of foam, and flow through porous media behavior of mixed surfactant solutions (sodium lauryl sulfate plus lauryl alcohol) have been studied at various temperatures in relation to enhanced heavy oil recovery processes. The studies reported here suggest that temperature has a remarkable influence on the microscopic structure of foam and the flow through porous media behavior of the surfactant solutions. The surface tension and bubble size decreased as the temperature increased. The foam volume increased, whereas foam half‐life (or foam stability) decreased with increasing temperature. A linear increase in bubble size with time was observed at different temperatures. The rate of change in bubble size increased with temperature. A significant reduction in effective air mobility and an improvement in fluid displacement efficiency were observed with increasing temperature. All measured parameters changed strikingly in the temperature range of 20–40°C, whereas they exhibited small changes between 40 and 80°C for the surfactant system investigated. The effect of temperature on half‐life of foam and on the effective air mobility was most pronounced as compared to that on other parameters. An attempt is made to correlate quantitatively the foam volume of surfactant solution with fluid displacement efficiency in porous media.
Reduced‐order, multivariable models with pure time delays
Authors: Iwai Zenta , Fisher D. G. , Seborg D. E.
Published: June 2004

Marshall's method of model reduction (1966) neglects the modes of the high order system which contribute little to the overall system response. This approach is extended to handle complex and/or repeated eigenvalues and is then modified so that pure time delays can be included in the control variables of the reduced order model. Open‐ and closed‐loop examples show that the inclusion of the time delays tends to compensate for the eliminated modes and leads to better agreement between the high and low order models.
The effect of interfacial tension gradients on the flow structure of single drops or bubbles translating in an electric field
Authors: Chang L. S. , Berg J. C.
Published: June 2004

Stream functions, interfacial velocities, and terminal velocities are computed for spherical drops or bubbles supporting interfacial tension gradients and translating in creeping flow in an electric field imposed in the direction of translation. In particular, the case in which a trace of surfactant is present is considered, and it is found that such material may produce quasi‐stagnant zones along the interface either near the poles or the equator. Terminal velocities may be either increased or decreased relative to the value obtained in the absence of the electric field.
Mass transfer in a liquid‐liquid CFSTR
Authors: Bapat P. M. , Tavlarides L. L.
Published: June 2004

The performance of a two‐phase liquid‐liquid continuous flow stirred tank reactor (CFSTR) was evaluated experimentally by simultaneous determination of dispersed phase drop size distribution and extraction efficienty as a function of reactor operating conditions. The results provided a basis against which predictions made by a previously developed simulation technique (Bapat et al., 1984) were compared. The close agreement between the experimental and the simulation results validates the drop rate models and the simulation algorithm employed in this work.
Rates of pyrolysis of colorado oil shale
Authors: Pan Zhenglu , Feng H. Y. , Smith J. M.
Published: June 2004

Both intrinsic kinetics and rates of decomposition in larger particles were determined for a Colorado shale by weight‐loss measurements in TGA‐type equipment. The data for small granular particles indicated first‐order intrinsic kinetics up to a fractional weight change that depended on the temperature level. In the experiments with larger particles, gas, particle‐surface, and particle‐center temperatures measured in separate runs showed that both gas‐to‐particle and intra‐particle temperature differences were significant.

A heat transfer model was evaluated by using the intrinsic kinetics data, measured heat transfer coefficients, and shale properties from the literature, to predict weight loss and particle‐center temperatures for the larger particles. Comparison with observed results showed good agreement in general, although there was some deviation in weight‐loss results at low temperatures.

The combined set of intrinsic kinetics data and rates for larger particles should be useful for further studies of pyrolysis models.
Characterization of a membrane permeation system for controlled drug delivery studies
Authors: Tojo K. , Sun Y. , Ghannam M. M. , Chien Y. W.
Published: June 2004

Hydrodynamic characteristics of an in vitro membrane permeation system for controlled drug delivery studies were investigated by measuring dissolution rates of benzoic acid in various aqueous solutions of polyethylene glycol 400. The mass transfer coefficient was well correlated in terms of three dimensionless numbers: Sherwood, Schmidt, and Reynolds numbers. By using the correlation equation, the intrinsic permeation rate of testosterone through silicone membranes was precisely extracted from the experimental data obtained under various nonideal flow conditions.
Thermal regeneration of diesel‐particulate monolithic filters
Authors: Bissett E. J. , Shadman Farhang
Published: June 2004

A mathematical model is developed to describe the process of thermal regeneration in diesel‐particulate monolithic filters. The model shows that a typical regeneration cycle consists of four stages: preheating, ignition, transport‐controlled combustion, and cooling. The total regeneration time and the peak temperature are the important regeneration characteristics and can be controlled by initial particulate loading, total filtration area, and channel wall thickness.
A simultaneous transport‐reaction model for controlled drug delivery from catalyzed bioerodible polymer matrices
Authors: Thombre A. G. , Himmelstein K. J.
Published: June 2004

A simultaneous diffusion‐reaction model is presented for the analysis of the kinetics of a chemically eroding poly(orthoester) matrix incorporated with a bioactive agent and with a catalyst to promote the erosion. Simulation results are consistent with experimentally observed hollow residuals and provide a basis for analyzing various design options.
Hydrodynamics and mass transfer characteristics of a scheibel extractor. Part II: Backmixing and stage efficiency
Authors: Bonnet J. C. , Jeffreys G. V.
Published: June 2004

The transfer of acetone between the toluene phase (dispersed) and the aqueous phase (continuous) has been measured along the length of a four‐stage Scheibel column packed with material preferentially wetted by the dispersed phase. (A Scheibel stage is defined as one mixing section plus one packing section.) The column concentration profiles were obtained by applying a new technique developed for this investigation.

A parameter model‐fitting exercise has been developed to select the most appropriate mathematical model that quantifies the extent of backmixing in the dispersed and continuous phases and evaluates the stage efficiency.

Overall dispersed phase mass transfer coefficients were estimated using the drop size and holdup data presented in Part I, and these have been compared with the published correlations based on single drop mechanisms.
Mobility control in the displacement of residual oil by an unstable foam
Authors: Hahn Pil‐Soo , Ramamohan T. R. , Slattery J. C.
Published: June 2004

A qualitative analysis is developed for the displacement of an unstable foam in a porous structure. The effects of the magnitude of the London‐van der Waals forces, of the surface tension, of the surface viscosities, of the quality (volume fraction of the gas), of the bubble size, and of the viscosity of the foaming agent solution are investigated. A number of qualitative conclusions are drawn regarding three aspects of mobility control: distribution of bypassed oil, speed of displacement, and displacement efficiency.

Ideally, any change in formulation should increase both the speed of displacement and the displacement efficiency. This is possible only by decreasing the surface viscosities. With all of the other variables, whenever either the speed of displacement or the displacement efficiency is increased, the other is decreased. Whether both the speed of displacement and the displacement efficiency actually increase on reducing the surface viscosities depends on whether the effects of the surface viscosities are dominant.
A generalized methodology for estimating minimum fluidization velocity at elevated pressure and temperature
Authors: Yang Wen‐Ching , Chitester D. C. , Kornosky R. M. , Keairns D. L.
Published: June 2004

A generalized methodology for estimating minimum fluidization velocity at elevated pressure and temperature was developed on the basis of a general correlation for pressure drop through fixed beds of spherical particles proposed by Barnea and Mizrahi (1973) and extended by Barnea and Mednick (1975). Comparison with experimental results shows good agreement.
Multiplicity in continuous MSMPR crystallizers. Part I: Concentration multiplicity in an isothermal crystallizer
Authors: Tavare N. S. , Garside John
Published: June 2004

A theory for the identification of criteria within which a continuous isothermal mixed‐suspension, mixed‐product removal (MSMPR) crystallizer can exhibit concentration multiplicity (i.e., multiple steady states) is developed. Power law growth and power law magma‐dependent nucleation kinetic models are used to describe the crystallization kinetics. Applications to specific cases together with figures delineating regions of multiplicity are presented. The stability of these steady states is analyzed by using small perturbations around the steady state. Growth ratedispersion is shown to be unimportant in establishing this concentration multiplicity.
Real‐time estimation of dynamic particle‐size distributions in a fluidized bed: Theoretical foundation
Authors: Cooper D. J. , Clough D. E.
Published: June 2004

Significant noise (random error) is common in an on‐line signal when measuring the particle size distribution in a fluidized bed. The application of optimal estimation theory to obtain a filtering algorithm that can rectify such measurements is detailed. Off‐line simulation studies demonstrate that the filtering algorithm yields a measure of particle size distribution that is well‐behaved, accurate, and able to track in real time as conditions change in the bed.
Kinetics of CO oxidation over Co3O4/γ‐Al2O3. Part I: Steady state
Authors: Perti Deepak , Kabel R. L.
Published: June 2004

Steady state experiments and their interpretation were performed to explore the kinetics of CO oxidation over a supported Co3O4 catalyst. The rate of reaction was found to depend on temperature and the partial pressure of oxygen but not on the partial pressure of carbon monoxide. It is shown that catalyst dynamics must be accounted for to achieve real understanding.
Liquid holdup and heat transfer coefficient in liquid‐solid and three‐phase fluidized beds
Authors: Chiu Tai‐Ming , Ziegler E. N.
Published: June 2004

Liquid holdups and wall‐to‐bed heat transfer coefficients in three‐phase fluidized beds with glass beads and cylindrical γ‐alumina particles were determined experimentally. It was found that the product of heat transfer coefficient and liquid holdup in three‐phase fludized beds is equal to that in corresponding liquid‐solid fluidized beds. A generalized correlation equation for heat transfer coefficients in both liquid‐solid and three‐phase fluidized beds was proposed based on the above relationship.
Deterministic variability analysis for intermediate storage in noncontinuous processes. Part I: Allowability conditions
Authors: Karimi I. A. , Reklaitis G. V.
Published: June 2004

Noncontinuous processes involving batch and semicontinuous processing operations are typically subject to significant levels of process parameter variations. Intermediate storage is commonly used to mitigate the effects of these variations. A taxonomy and analysis is presented of the various types of parameter variations: elementary and composite, single and multiple, homogeneous and mixed, overlapping and nonoverlapping. Sufficient conditions are developed which insure that continuity of periodic operation can be maintained in the presence of these various types of process variations. These conditions serve as the basis of storage sizing procedures developed in the companion paper.
A generalized equation of state for the thermodynamic properties of polar fluids
Authors: Wu G. Z. A. , Stiel L. I.
Published: June 2004

The generalized relationships of Lee and Kesler for the thermodynamic properties of nonpolar fluids have been combined with an accurate equation of state for water which is utilized as the reference substance for polar fluids for reduced temperatures from 0.4 to 2.5 and reduced pressures to 10. The input data required are the critical temperature, critical pressure, acentric factor, and a polarity factor Y obtained from experimental pressure‐volume‐temperature data. Comparisons between calculated and experimental thermodynamic properties indicate that highly accurate results are obtained by the method of this study for most polar fluids. A modified procedure is presented for the compressibility factors of substances with large acentric factors such as alcohols. Tabulated values of the polar fluid correction terms are presented for the compressibility factor, fugacity coefficient, and enthalpy, entropy, and heat capacity departures for the complete range investigated.
Periodic cycling of distillation columns using a new tray design
Authors: Szonyi L. , Furzer I. A.
Published: June 2004

Computer simulations of periodically cycled columns predicted improvements in column performance of greater than 200% for systems with nonlinear equilibrium curves. Experiments distilling methanol‐water mixtures have verified those predictions for periodic cycling with a single plate. The extension of the theory to multiple‐plate columns fails in usual distillation apparatus due to liquid mixing during the liquid flow period. To overcome this problem a new tray design consisting of a sieve plate and inclined surfaces has introduced an effective liquid time delay. Although the predicted efficiencies of 200% were not realized due to vapor movement hindering the tray action, a wide range of operating conditions provided good overall column efficiencies of 140%.
Measuring simultaneous mixing and reaction in batch reactors by dilatometry
Authors: Ghodsizadeh Yousef , Adler R. J.
Published: June 2004

A dilatometric technique is reported for studying simultaneous mixing and reaction as a function of time in batch systems. Volume‐averaged fractional conversion is determined from small volume changes without sampling or flow disturbances.

Data are obtained for very fast and intermediate speed reactions in a turbulent, unbaffled, stirred laboratory reactor.
Theory and application of an extended horizon self‐tuning controller
Authors: Ydstie B. E. , Kershenbaum L. S. , Sargent R. W. H.
Published: June 2004

A robust version of the self‐tuning regulator is developed. The regulator, which requires relatively little knowledge of system characteristics (estimated order of transfer function polynomials and an upper bound for transportation delays), has been shown to yield stable control and convergence for linear, time‐invariant systems. Simulations and practical tests on a large pilot‐scale process have shown that the inclusion of a variable forgetting factor and an “extended horizon” control criterion provides the regulator with a sufficient degree of robustness and flexibility to perform well in a nonlinear time‐varying environment. The regulator makes use of intuitively easy‐to‐understand concepts and leaves few degrees of freedom for the potential user. Furthermore, extensive experiments and simulation studies have shown it to be insensitive to choice of initial conditions and dynamic characteristics set by the user.
Hydrodynamic characteristics of a gas‐liquid‐solid fluidized bed containing a binary mixture of particles
Authors: Fan Liang‐Shih , Matsuura Akinora , Chern Song‐Hsing
Published: June 2004

Hydrodynamic characteristics were investigated in a cocurrent gas‐liquid‐solid fluidized bed containing a binary mixture of particles. The binary mixtures used were ten combinations of eight types of spherical particles differing in diameter and/or density. The density variation of the particles in the mixture was found to exhibit a stronger effect on the extent of solids mixing or segregation than did the size variation of the particles in the mixture. Additionally, a solids layer inversion phenomenon was found to occur in a bed of small, heavy alumina beads and large, lighter glass beads. The minimum fluidization velocity of binary mixtures correlated well empirically with the superficial gas velocity, weight fraction of jetsam particles, and particle terminal velocities of jetsam and flotsam particles. Bed expansion and gas holdup for a binary mixture were analyzed for three solids mixing states, namely, complete segregation, partial intermixing, and complete intermixing. The analysis indicates that the serial model, or segregation model, predicts the bed voidage satisfactorily even when the bed is at the complete intermixing state.
Further development of selective physisorption for measuring catalyst surface area
Authors: Toor I. A. , Lee H. H.
Published: June 2004

Platinum supported on silica is used as a model supported catalyst for the purpose of demonstrating that the selective physisortion method yields the fractional catalyst surface area of supported catalysts, inclucing metal compounds catalysts for which the method is primarily intended. The selective physisorption results with nitrous oxide as adsorbate are compared with hydrogen chemisorption results for this purpose. Experimental and theoretical refinements of the method developed earlier in our laboratory are presented that allow rather accurate determination of the catalyst surface area. The refinements also make the method effctive even when the catalyst covers a small portion of the total surface area. Because of the nature of physisorption, the method should be applicable to any supported catalyst including metal compounds catalysts, provided a suitable adsorbate is used. Adsorbates other than nitrous oxide and carbon dioxide which are suitable for selective physisorption, are suggested.