bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinematic waves in the isothermal melt spinning of Newtonian fluids
Authors: Kim Byung Min , Hyun Jae Chun , Oh Joo Seok , Lee Seung Jong
Published: June 2004

The hyperbolic nature of the continuity equation in the melt spinning process causes several kinematic waves to travel in the spinline. Since different traveling waves possess different speeds, the system invariably has many characteristic times. This study computes the traveling times of these waves, finds their interrelationships, and then derives the criterion for the instability of periodic oscillation known as draw resonance. The period of oscillation is greater than the fluid residence time, but equal to the time during which both the maximum and minimum spinline cross‐sectional area waves travel in sequence from the spinneret to the take‐up. The onset of draw resonance occurs when two successive unity‐throughput waves are also able to travel the same distance within the same period of oscillation. This happens when the drawdown ratio takes on the critical value of 20.218 for the isothermal spinning of Newtonian fluids, agreeing with the value reported by earlier researchers.
Effect of droplet size on the rheology of emulsions
Authors: Pal Rajinder
Published: June 2004

The effect of droplet size on the rheological behavior of water‐in‐oil and oil‐in‐water emulsions was investigated using a controlled‐stress rheometer. Results indicate that the droplet size has a dramatic influence on emulsion rheology. Fine emulsions (water‐in‐oil or oil‐in‐water) have much higher viscosities and storage moduli than the corresponding coarse emulsions. The shear‐thinning effect is much stronger in the case of fine emulsions. When coarse droplets are replaced by fine droplets (keeping total volume fraction of the dispersed phase constant), the resulting emulsion exhibits a minimum in rheological properties (viscosity, storage and loss moduli, time constant) at a certain proportion of fine droplets. However, the minimum in viscosity occurs only at low shear stresses. At high stresses, the viscosity of the mixed emulsion increases as the proportion of fine droplets increases. The study of the aging effect on the rheological behavior shows that water‐in‐oil emulsions age much more rapidly than the oil‐in‐water emulsions.
Comparison of isotherm models for hydrocarbon adsorption on activated carbon
Authors: Malek A. , Farooq S.
Published: June 2004

A number of equilibrium isotherm models can be utilized for correlating experimental equilibrium results. Seven different isotherm models are studied using equilibrium data of methane, ethane and propane in activated carbon. Besides comparing the goodness of data fit, the limiting behaviors as well as the pressure and temperature derivatives of the equilibrium isotherm models are also investigated. Performance of multicomponent extensions of these isotherm models and their combinations with the ideal adsorbed solution theory are also compared with experimental data. This systematic evaluation of the more important equilibrium isotherm models provides the general basis for making a preliminary selection of an effective model for a given application. Although an accurate and thermodynamically consistent model is desirable, these requirements may often be compromised for computational simplicity in dynamic process modeling studies.
Kinetics of ozone photolysis in aqueous solution
Authors: Gurol Mirat D. , Akata Aysegul
Published: June 2004

The kinetics of ozone photolysis were investigated experimentally in well‐characterized aqueous solution and by a conceptual kinetic and mechanistic model developed based on possible reaction pathways. The primary quantum yield of ozone photolysis at 245‐nm wavelength was measured at 20°C as 0.48 ± 0.6. The rate of ozone photolysis increased with increasing light intensity, ozone concentration and pH, and decreased with increasing inorganic carbon concentration in water. The model was able to predict the experimentally observed rate of ozone photolysis quite well for various combinations of UV light intensity, initial ozone concentration and water characteristics. In the mechanistic model, the formation of the hydroxyl radical, which is the primary oxidant in the O3/UV process, was tied to the decomposition of ozone; therefore, the model can now be extended to predict the oxidation rates of water contaminants by the hydroxyl radical generated in the O3/UV process.
Asphalt flocculation and deposition: II. Formation and growth of fractal aggregates
Authors: Rassamdana Hossein , Sahimi Muhammad
Published: June 2004

Extensive small‐angle X‐ray and neutron‐scattering data, as well as results of precipitation measurements, are analyzed to delineate the structure of the asphalt and asphaltene aggregates that are formed when a solvent is injected into a system containing crude oil. The two types of data strongly suggest that both small and large aggregates have a fractal structure, with well‐defined fractal dimensions. If the system is aged long enough at low enough temperature, large asphalt particles will have the structure of diffusion‐limited cluster–cluster aggregates with a fractal dimension Df ≃ 1.8, while the small ones are similar to diffusion‐limited particle aggregates with a fractal dimension df ≃ 2.5. High temperatures increase the rotational motion of the particles, disturb the structure and mechanical stability of the aggregates, and decrease their fractal dimension. Aging and concentration effects of the asphalts in the solution, and the type of the solvent on the structure of the aggregates are also investigated. Implications of these results for the structure, mechanical stability, and molecular‐weight distribution of asphalts and asphaltenes are detailed. A new molecular‐weight distribution for asphalt aggregates predicts the experimental data excellently.
Strategy for dynamic process modeling based on neural networks in macroscopic balances
Authors: Van Can Henricus J. L. , Hellinga Chris , Luyben Karel Ch. A. M. , Heijnen Joseph J. , Te Braake Hubert A. B.
Published: June 2004

Gray box models combine the short development time of data‐driven black box models with extrapolation properties of knowledge‐driven first principles models (white box), which in (bio)chemical engineering are always based on macroscopic balances. By modeling the inaccurately known terms in a macroscopic balance with a black box model, one naturally obtains a so‐called serial gray box model configuration. The identification data must cover only the input‐output space of the inaccurately known terms, and the accurately known terms can be used for reliable extrapolation. In this way, the serial gray box configuration results in accurate models with known extrapolation properties with a limited experimental effort. This strategy is demonstrated for the modeling and control of a pressure vessel using real‐time experiments. For this case, the strategy is superior to a black box modeling approach that requires much more data and to a parallel gray box approach that results in a model with poor extrapolation properties. Moreover, neural networks are an accurate and convenient modeling tool for the black part in gray box model configurations, because a very fast noniterative training algorithm is used for training neural networks.
Homogeneous multicomponent azeotropic batch distillation
Authors: Ahmad Berit S. , Barton Paul I.
Published: June 2004

Mixed waste‐solvent streams generated in pharmaceutical and specialty chemical manufacturing typically form multicomponent azeotropic mixtures. This highly nonideal behavior often prevents separation and recovery of the solvents. Batch distillation remains an important separation technology for these industries. The sequence of pure component and azeotropic cuts produced in batch distillation depends strongly on the feed composition. For ternary‐ and four‐component mixtures the separation behavior can be studied graphically in residue‐curve maps. For mixtures with more components, this approach is infeasible. Other tools are therefore required. Deficiencies in earlier work on ternary systems are demonstrated and addressed as well as a complete set of concepts to describe batch distillation of an azeotropic mixture with an arbitrary number of components. The body of theory is derived from the fields of nonlinear dynamics and topology.
Model for SrCsCaMgNa ion‐exchange uptake kinetics on chabazite
Authors: Depaoli Susan M. , Perona Joseph J.
Published: June 2004

Many nuclear facilities throughout the world must separate strontium‐90 and cesium‐137 from natural waters containing calcium, magnesium, and sodium. Our research showed that chabazite, a zeolite with a hexagonal ring structure, is cost‐effective for this purpose. A batch kinetic uptake model for this five‐component ion‐exchange system was developed and tested against experimental data. The pore‐diffusion model of Yao and Tien is used with the equilibrium model of Perona. The resulting model is fast and stable, and represents the experimental data well.
Modeling of phase separation in PEG–salt aqueous two‐phase systems
Authors: Kenkare Paresh U. , Hall Carol K.
Published: June 2004

A molecular model based on the integral equation theory of statistical thermodynamics is used to study phase separation in PEG–salt aqueous two‐phase systems. PEG molecules are modeled as hard spheres that attract each other through a temperaturedependent Yukawa potential, which mimics the effect of PEG–water hydrogen bonding on the attraction between PEG molecules. The salt ions are modeled as charged hard spheres interacting through a Coulombic potential. Excess thermodynamic properties due to Coulombic and Yukawa interactions are calculated by analytical solutions to the Ornstein–Zernike equation for the mean spherical approximation closure. Yukawa parameters for PEG–PEG interactions are determined by fitting the theoretical phase diagram for a pure Yukawa fluid to the experimental phase diagram for a PEG–water mixture. The model predicts experimentally observed trends: increasing the temperature increases the slope and length of the tie lines; increasing the PEG molecular weight increases the miscibility gap; and increasing the anion charge lowers the salt concentration at which phase separation occurs. Theoretical results allow us to infer the relative importance of ion–PEG interactions, ion–solvent interactions, and the interpenetrable nature of PEG molecules on the phase separation in PEG–salt aqueous two‐phase systems.
Molar mass distribution and solubility modeling of asphaltenes
Authors: Yarranton Harvey W. , Masliyah Jocob H.
Published: June 2004

Attempts to model asphaltene solubility with Scatchard‐Hildebrand theory were hampered by uncertainty in molar volume and solubility parameter distribution within the asphaltenes. By considering asphaltenes as a series of polyaromatic hydrocarbons with randomly distributed associated functional groups, molar volume and solubility parameter distributions are calculated from experimental measurements of molar mass and density. The molar mass distribution of Athabasca asphaltenes is determined from interfacial tension and vapor pressure osmometry measurements together with plasma desorption mass spectrometry determinations from the literature. Asphaltene desnities are calculated indirectly from mixtures of known concentration of asphaltene in toluene. Asphaltene density, molar volume, and solubility parameter are correlated with molar mass. Solid‐liquid equilibrium calculations based on solubility theory and the asphaltene property correlations successfully predict experimental data for both the precipitation point and the amount of precipitated asphaltenes in toluene‐hexane solvent mixtures.
Characteristics of high‐pressure liquid–solid fluidization
Authors: Lin Tsao‐Jen , Fan Liang‐Shih
Published: June 2004

Fundamental characteristics of liquid–solid fluidization at high pressures (up to 21 MPa) and moderate temperatures (up to 89°C) are investigated. Properties under study include minimum fluidization velocity (umf), bed voidage at minimum fluidization, and bed expansion. Devices for in‐situ measurements of physical properties of the liquid in the bed are developed, and measurements are carried out to quantify the pressure and temperature effects on the fluidization behavior. The results indicate that under high pressures and moderate temperatures, liquid–solid fluidization behavior is affected significantly by the variation of liquid density and viscosity with pressure. As the pressure increases, the liquid viscosity and density increase, yielding an increased drag force and buoyancy force on the particles, and hence a decreasing umf and an increasing bed expansion for a given liquid flow rate. An increase in temperature has an opposite effect on the physical properties of the liquid, increasing umf and decreasing the bed expansion for a given liquid flow rate. Various correlations proposed in the literature for umf and bed expansion, including those by Richardson and Zaki (1954) and Chitester et al. (1984), are applicable to high‐pressure and high‐temperature conditions when proper account is made of the liquid physical properties under bed operating conditions.
Permeation studies on oriented single‐crystal ferrierite membranes
Authors: Lewis John E. , Gavalas George R. , Davis Mark E.
Published: June 2004

Large, high‐quality, single crystals of pure‐silica ferrierite are synthesized, and the structure is described. Selected individual crystals (approximately 600 μm X 500 μm X 20 μm) are mounted in a membrane configuration so that only the 10‐membered‐ring channels (5.4 Å X 5.4 Å X 4.2 Å) or the 8‐membered‐ring channels (4.6 Å X 3.7 Å X 3.0 Å) are accessible for gas‐molecule permeation. The first examples of transport exclusively through 8‐ or 10‐membered‐ring channel systems are reported and obtained through crystal orientation in the membrane. A series. of adsorption experiments are conducted to help select suitable probe molecules and evaluate the role of adsorption in the permeation process for single‐crystal membranes. Methane, n‐butane, isobutane and nitrogen probe molecules are used to study intracrystalline sorption and transport effects for different crystal orientations, pressures and temperatures. Both pure‐gas selectivities and mixed‐gas separation factors are reported. A mixed‐gas separation factor of n‐butane/isobutane = 116 for the 10‐membered‐ring orientation of the crystal at 383 K and a transmembrane pressure difference of 1.01 X 105 Pa are found using this technique. In addition, molecular sieving is observed for the 8‐membered‐ring orientation of the crystal since methane, but not butane, transport is observed for this crystal orientation.
Simulations of a LDPE reactor using computational fluid dynamics
Authors: Read Nolan K. , Zhang Simon X. , Ray W. Harmon
Published: June 2004

Computational fluid dynamics methods are used to provide three‐dimensional simulations of a low‐density polyethylene (LDPE) autoclave reactor under normal operating conditions. For the conditions used, the reactor is not very well mixed; thus, the common model approximation of a perfectly stirred reactor is not warranted. The simulations verify the sensitive nature of the polymerization reactors and indicate a need for optimizing operating parameters.
Simulation of decoking of thermal cracking coils by steam/air‐mixtures
Authors: Schools Evy M. , Froment Gilbert F.
Published: June 2004

A rigorous approach was developed for the simulation of the decoking of an industrial cracking furnace. A one‐dimensional heterogeneous reactor model, which accounts for the interfacial gradients between the process gas and the coke surface, was used to simulate reactor coils. Both the combustion and steam gasification of the coke layer were taken into account. The reactor model for the decoking was coupled with a detailed firebox simulation model. The initial profile of the coke layer thickness, required for the decoking calculations, was obtained by a run‐length simulation. The evolution with time of the temperature distribution inside the cracking coil and in the furnace was generated simultaneously, which made it possible to understand the decoking operation in detail and to predict its duration accurately.
Dynamics of semibatch polymerization reactors: I. Theoretical analysis
Authors: Teymour F.
Published: June 2004

The dynamics of semibatch reactors is often neglected in the literature despite their industrial importance. This article analyzes the stability and dynamic behavior of semibatch polymerization reactors operated according to a flow scheduling strategy designed to impart a steady‐state nature to the dynamics of these essentially transient reactors. It can also improve the operation of these reactors, especially the quality of the polymer produced (such as molecular weight distribution and polymer composition). In the proposed strategy of flow rate scheduling, the intensive states of the reactor can be made to reach steady‐state values. A comparison of the dynamics of the proposed and classical operating strategies illustrates this possibility. Further dynamic analysis reveals the emergence of phenomena characteristic of continuous operation in a CSTR. Examples are multiplicity of the trajectories, limit cycle oscillations, as well as nonhomogeneous oscillations belonging to a period doubling cascade. Operation in a sequential semibatch mode is discussed, as well as the importance of selecting parameters for the fillup and discharge operation. In this mode of operation either periodic or chaotic behavior is obtained. The effect of both on polymer properties is studied in detail.
Enhanced SO2 abatement with water‐hydrated dolomitic particles
Authors: Al‐Shawabkeh Ali , Matsuda Hitoki , Hasatani Masanobu
Published: June 2004

A dolomitic calcine was hydrated with liquid water and then recalcined as an effective sorbent toward SO2 removal. The hydrated/recalcined sorbent was tested for SO2 removal in a thermogravimetric analyzer under conditions applicable to an atmospheric fluidized‐bed combustor: 1,123 K, 20 vol. % excess air, and 3,000 ppmv SO2. Specific pore surface areas and volumes of hydrated/recalcined dolomites, hydrated at 80°C for 1 h, increased by four and five times, respectively, compared to unhydrated dolomitic calcines. Due to these improved pore characteristics, the SO2 capture achieved by the hydrated/recalcined calcine, was 1.3–1.6 times higher than that of the unhydrated one after a 1‐h exposure to SO2 concentrations of 0.11–0.31 vol. % at 1,073–1,173 K. In the hydrated/recalcined calcine CaO utilization was enhanced due to the absence of significant pore diffusional limitations, at least during the early reaction times, evidenced by the high apparent activation energy of 198 kJ/mol. On the contrary, the lower CaO utilization in the unhydrated calcine was presumably due to severe pore diffusional limitations, which dropped the apparent activation energy from 149 to 85 kJ/mol at > 1,123 K.
Recent advances in modeling thermodynamic properties of aqueous strong electrolyte systems
Authors: Loehe Joseph R. , Donohue Marc D.
Published: June 2004

Theoretical and engineering models for the thermodynamic properties of strong electrolyte solutions have advanced significantly since 1985. This progress is notable in the ability to calculate selected properties of single and mixed strong electrolyte solutions over a wide range of temperatures and compositions, including effects of various nonelectrolytes, solvents and supercritical components. Theoretical studies have begun to consider more realistic fundamental interactions between various components in these systems. There have been several successful conversions of theories based on the mean spherical approximation and perturbation methods into engineering equations, without large numbers of empirical parameters. Other theoretical models seem almost ready for application to real systems. The capability to estimate a wide variety of thermodynamic properties accurately with a consistent set of equations and a small number of adjustable parameters has been achieved by several groups over limited temperature and composition ranges. Much work remains to be done, however, to understand completely the interplay and relative importance of various contributing energy effects.
Molecular interactions in chloroform‐diluent mixtures
Authors: Choi K. , Tedder D. W.
Published: June 2004

Plausible stoichiometries for solvation and association complexes in binary mixtures of chloroform and one of six organic diluents (n‐hexane, p‐dioxane, acetone, diethyl ether, tri‐n‐butyl phosphate, or triethylamine) are examined parametrically. A range of stoichiometric assumptions based on hydrogen bonding are examined, but only a few such combinations yield statistically significant fits to the experimental vapor–liquid equilibria and NMR chemical shift data. Hydrogen bonding considerations and the “true” chemical species are much more important than nonspecific physical factors such as molecular sizes, shape differences, and regular solution terms. Thermodynamic equilibrium constants are presented for the most significant chloroform solvation complexes. Nonspecific dilution shift is important and more helpful in fitting NMR data than the assumption of a chloroform dimer. Physical effects and an orientation factor are used to predict excess enthalpy in chloroform/n‐hexane mixtures where no solvation or association reactions occur. Model parameters are used to predict excess molar volumes and enthalpies. Commonly reported stability constants are concentration dependent.
Removal of oil films from stainless steel tubes
Authors: Yan Jenn‐Feng , Sáez A. Eduardo , Grant Christine S.
Published: June 2004

The removal of oil films from the inner surface of a stainless steel tube cell using aqueous cleaning solutions was studied. The two oils used in the cleaning experiments, Sunquench 1042 and heavy mineral oil, contained P32 labeled tributyl phosphate (TBP) as a radioactive tracer. The β‐ particles emitted from the radioactive TBP were detected by a CaF2 scintillator and used as a measure of the amount of oil remaining in the tube cell. Cleaning experiments performed at different flow rates, surface treatment, and surfactant concentrations indicated that initially the oil films were removed rapidly. At the end of the experiments, the oil removal rate reduced significantly, eventually becoming negligible. The stainless steel morphology affected oil removal significantly, and the rougher tube tended to retard the oil removal. The rate and extent of the decontamination were significantly increased in the presence of sodium dodecyl sulfate, a nonionic surfactant. Experimental data were compared to a hydrodynamic model based on the removal of a liquid contaminant from a solid surface by an immiscible fluid. The model deviated from the experimental data due to the presence of instabilities at the oil‐water interface.
Digital particle imaging velocimetry of viscoelastic fluids
Authors: Pakdel Peyman , McKinley Gareth H.
Published: June 2004

We investigate the utility of digital particle imaging velocimetry (DPIV) for performing kinematic measurements in non‐Newtonian flows. With the advances in numerical techniques for simulation of viscoelastic flows, acquisition of spatially dense 2‐D kinematic data in steady and time‐dependent deformations can be useful in verifying predictions of the corresponding computational studies. Furthermore, kinematic measurements of the velocity field and rate of deformation in prototypical industrial processes can significantly enhance the rational design and optimization of polymer processing unit operations. Application of a high seeding density DPIV technique in viscoelastic media is discussed, and quantitative data are obtained in a number of industrially relevant flow geometries. The issues of velocity‐position assignment and the effects of a velocity gradient across DPIV correlation regions are discussed. A simple yet effective averaging technique preserves the order of accuracy and assigns the velocity vectors to their appropriate positions using an overlapping discretization scheme. The examples studied experimentally include steady flow in circular pipes, flow past obstructions, flow in a lid‐driven cavity, and time‐dependent free‐surface extensional flows in a liquid filament. With the exception of the first example, these flow geometries constitute an important collection of configurations in which quantitative experimental data for non‐Newtonian fluids are scarce or nonexistent.
Turbulence in flocculators: Effects of tank size and impeller type
Authors: Ducoste Joel J. , Clark Mark M. , Weetman Ronald J.
Published: June 2004

Past research shows that for the same power per unit volume, flocculation performance varies with tank size and impeller type. This study was performed to characterize effects of scale and impeller design on turbulence produced in the flocculation process. The study was performed with a Rushton turbine and an A310 foil impeller in three square tanks of 5‐, 28‐ and 560‐L volume. Fluid velocities were measured using a dual‐channel laser Doppler velocimeter with an enhanced burst spectrum analyzer. Flocculation tanks were operated at a constant average unit‐mass energy‐dissipation rate of 0.0016 m2/s3. The results show that the turbulence intensity and local turbulent energy‐dissipation rate were higher for the Rushton turbine than for the A310 impeller. The turbulence intensity was found to increase with increasing tank size regardless of impeller type. The local turbulent energy dissipation rate decreased for the Rushton turbine and remained constant for the A310 impeller with increasing tank size.
Efficient sampling technique for optimization under uncertainty
Authors: Diwekar Urmila M. , Kalagnanam Jayant R.
Published: June 2004

The concept of robust design involves identification of design settings that make the product performance less sensitive to the effects of seasonal and environmental variations. This concept is discussed in this article in the context of batch distillation column design with feed stock variations, and internal and external uncertainties. Stochastic optimization methods provide a general approach to robust/parameter design as compared to conventional techniques. However, the computational burden of these approaches can be extreme and depends on the sample size used for characterizing the parametric variations and uncertainties. A novel sampling technique is presented that generates and inverts the Hammersley points (an optimal design for placing n points uniformly on a k‐dimensional cube) to provide a representative sample for multivariate probability distributions. The example of robust batch‐distillation column design illustrates that the new sampling technique offers significant computational savings and better accuracy.
Simulation and design of fluid catalytic‐cracking riser‐type reactors
Authors: Theologos K. N. , Nikou I. D. , Lygeros A. I. , Markatos N. C.
Published: June 2004

Two‐phase flow, heat transfer, and reaction in fluid catalytic‐cracking riser‐type reactors are studied using a 3‐D mathematical model. This study was carried out based on the model of Theologos and Markatos, which incorporates a detailed ten‐lump reaction kinetics scheme and accounts for gradual feedstock vaporization inside the reactor. Predictions obtained using the new model are compared against industrial reactor operating data. A design study was also carried out to illustrate that the model developed is capable of predicting feed‐injector geometry effects on overall reactor performance. It shows that by increasing the number of feed‐injection operating nozzles at the bottom of the reactor, selectivity of primary products is improved.
Extraction of nitric acid from aqueous media with Oϕ D(iB)CMPO–n‐dodecane
Authors: Spencer Barry B. , Counce Robert M. , Egan B. Zane
Published: June 2004

A study of the extraction characteristics of nitric acid with octyl(phenyl)‐N,N‐diisobutylcarbamoylmethyl phosphine oxide [OϕD(iB)CMPO or, simply, CMPO] was conducted. In the experimental program, CMPO was dissolved in n‐dodecane to produce the organic extracting medium. The objectives of the project were to infer extraction stoichiometry and to estimate equilibrium constants for the extraction of nitric acid with the CMPO extractant.

Experiments were performed over a limited range of concentrations to avoid conditions favoring formation of a third phase. Aqueous nitric acid concentrations were limited to 0.30 M at 25°C, 1.0 M at 40°C, and 3.0 M at 50°C. The data indicate that CMPO extracts nitric acid with a 1:1 stoichiometry. The value of the equilibrium constant is estimated at 2.66 ± 0.09 at 25°C. The enthalpy of the extraction is estimated to be ‐ 5.46 ± 0.46 kcal/mol.
Oxidative dehydrogenation of butane using membrane reactors
Authors: Téllez C. , Menéndez M. , Santamaría J.
Published: June 2004

The oxidative dehydrogenation of butane was studied at temperatures between 450 and 550°C using a conventional fixed‐bed reactor and inert membrane catalytic reactors with different feed arrangements. When inert membrane reactors were employed, a ceramic membrane was used to distribute oxygen to a fixed bed of V‐Mg‐O catalyst. The membrane reactor was found to be more efficient than a fixed‐bed reactor under most of the conditions investigated. In addition, in the membrane reactor the formation of hot spots decreased considerably, leading to a more stable and safer operation.
Macro‐ and microscopic fluid transport in living tissues: Application to solid tumors
Authors: Netti Paolo A. , Baxter Laurence T. , Boucher Yves , Skalak Richard , Jain Rakesh K.
Published: June 2004

Transvascular and interstitial fluid movements are involved in many important biological processes such as convective macromolecular transport and contribute to the mechanical behavior of tissue. Although intimately coupled, there is a tendency in the literature to regard these two fluid‐transport mechanisms separately; if the interaction is considered, the description is usually confined to the local level (e.g., transvascular or interstitial perivascular). A general framework presented here combines transvascular and interstitial fluid movement with the mechanics of soft tissue and integrates macro‐and microscopic views of the phenomena. On the macroscopic level, interstitial fluid transport is described by adapting the field equations of the poroelastic theory using average field variables defined on a scale of several blood vessel diameters (∼ 1 mm), while transvascular transport is described by a generalized Starling's law. As an example, the model equations have been specialized for a spherical solid tumor and an analytical solution is presented for the transient redistribution of interstitial fluid following a rapid change in vascular pressure or flow. The model describes the overall average profiles of the interstitial fluid pressure and velocity, as well as the dilatation, displacement and stress of the solid matrix. Moreover, on a smaller length scale the model can describe the local fluid movement (perivascular) using the average field variables as boundary conditions. The basic theory provides new insight into understanding the fluid transport in biological tissues and a valuable tool for determining relevant fluid‐transport parameters. Implications for improving drug delivery to solid tumors are also discussed.
On‐line control of a semibatch emulsion polymerization reactor based on calorimetry
Authors: de Buruaga Isabel Sáenz , Echevarría Antonio , Armitage Philip D. , de la Cal José C. , Leiza José R. , Asua José M.
Published: June 2004

In this work, on‐line calorimetry was used to estimate the conversion and the copolymer composition in emulsion polymerization systems. Real‐time feedback control of the polymer composition during the semibatch emulsion copolymerization of vinyl acetate and butyl acrylate was carried out. Both homogeneous copolymers and copolymers with previous defined composition profiles were obtained. It was shown that the feedback control was able to avoid monomer accumulation in the reactor, and hence potentially dangerous thermal runaways, without any deleterious effect on the polymer composition, when a sudden inhibition was caused by deliberately adding a solution of hydroquinone. The use of feedback control for the maximization of the production rate under safe conditions in the unseeded emulsion copolymerization of vinyl acetate and VeoVa10 (an alkyl vinyl ester from Shell) is also presented.
Yield stress of suspensions loaded with size distributed particles
Authors: Kapur Prakash C. , Scales Peter J. , Boger David V. , Healy Thomas W.
Published: June 2004

A new theoretical approach is proposed for the yield stress of concentrated, flocculated particulate suspensions. Explicit cognizance is taken for the three‐dimensional, mechanically rigid particle network held together by interparticle forces wherein the mean coordination number in the assemblage increases and the separation between the particles decreases with an increase in the volume fraction of the solid phase. The Rump‐Molerus model relting isotropic normal stress and isotropic normal interparticle force in a bed of single‐sized spheres is modified to incorporate the size distribution of particles and extended to the suspension network. The model estimates the yield stress as a function of solids loading for various kinds of size distribution and is in reasonable agreement with experimental data when the surface properties of the particle are held constant.
Fugacity coefficients for free radicals in dense fluids: HO2 in supercritical water
Authors: Mizan Tahmid I. , Savage Phillip E. , Ziff Robert M.
Published: June 2004

The fugacity coefficients of the hydroperoxyl radical in supercritical water are estimated through molecular simulations. A potential function for the radical is first derived from ab initio self‐consistent field molecular orbital calculations at the unrestricted Hartree‐Fock level and from data in the literature. Molecular dynamics simulations of the hydroperoxyl radical are then performed in supercritical water and the fugacity coefficient of the radical is calculated by the free‐energy perturbation method using the dynamic coupling parameter window‐modification technique. The values of the fugacity coefficients at 773 K differ from unity. This methodology facilitates the incorporation of thermodynamic nonidealities in mechanism‐based kinetic models for free‐radical reactions in supercritical water.
Modeling and experimental study of a sequential phosphazene reaction by phase‐transfer catalysis
Authors: Wu Ho‐Shing , Meng Shang‐Shin
Published: June 2004

The substitution reaction of hexachlorocyclotriphosphazene, N3P3Cl6, with phenol was performed to synthesize the partially substituted (phenoxy) chlorocyclotriphosphazenes, N3P3Cl6 − i(OC6H5)i, i = 1 – 6 by phase‐transfer catalysis (PTC) in an organic phase/alkaline solution. The steric hindrance effect plays a crucial role in this reaction. The reaction system was controlled by both chemical kinetics and mass‐transfer effects. The mass transfer of the catalyst between two phases was investigated by a pseudosteady‐state liquid–liquid PTC (LLPTC) model. Also, the intrinsic reaction‐rate constants of the series substitution and the overall mass‐transfer coefficient of the catalyst from the organic phase to the aqueous phase were determined by a combined model. In addition, the corresponding energies, enthalpies, and entropies of activation of the series substitution were also estimated.
Gas‐holdup measurements in bubble columns using computed tomography
Authors: Kumar Sailesh B. , Moslemian Davood , Duduković Milorad P.
Published: June 2004

A computed tomographic scanner was developed for imaging gas‐holdup distributions in two‐phase flow systems such as bubble columns and fluidized beds. The scanner has been used to study the effects of various operating parameters (such as column diameter, superficial gas velocity, and distributor type) on the gas holdup and its distribution in an air–water bubble column. The experimental investigation shows that the column dimensions have no significant effect on the void fraction when the column diameter is greater than 0.15 m. Differences in the holdup distribution due to the kind of distributor used are significant only at low gas flow rates. Surface tension of the liquid has a profound influence on the gas holdup and its distribution.
Chaotic behavior of gas‐solids flow in the riser of a laboratory‐scale circulating fluidized bed
Authors: Marzocchella Antonio , Zijerveld Robert C. , Schouten Jaap C. , van den Bleek Cor M.
Published: June 2004

A cold model of a circulating fluidized bed with a 0.030‐m‐ID, 2.77‐m‐high riser was operated in a wide range of operating conditions. Several solids were tested, from 57 μm to 1,830 μm in size and from 1,100 kg/m3 to 2,540 kg/m3 in density. Pressure fluctuations were measured at several points along the riser, and time series were processed to evaluate chaotic invariants (Kolmogorov entropy and correlation dimesion). Axial profiles of average values of pressure and voidage were also evaluated. At fixed operating conditions, the Kolmogorov entropy changed along the riser, which appeared to be a fuction of the local voidage and showed a minimum when voidage decreases from 1.00 until about 0.90. Changes of the Kolmogorov entropy with local voidage were interpreted based on interactions among solids and gas turbulence structure. Three regions were identified in the voidage range investigated: particles‐controlled region, clusters‐controlled region, and bottom‐bed‐controlled region.
Structural stability of chemical process plants
Authors: Hangos Katalin M. , Perkins John D.
Published: June 2004

The problem of analyzing the stability of chemical process plants is considered. The idea of exchange plants has been extended with more general binary transfer terms and binary equilibrium, resulting in the idea of binary exchange‐equilibrium plants. Their structural stability is analyzed using results on conservation matrices. It was found that binary exchange‐equilibrium plants with no azeotropes are stable irrespective of the connections of their operating units. The general results are illustrated in examples of practical importance: heat‐exchanger networks and binary distillation columns with constant molar flows.
Oscillating temperature pulses during CO oxidation on a Pd/Al2O3 ring
Authors: Liauw M. A. , Somani M. , Annamalai J. , Luss D.
Published: June 2004

Back‐and‐forth‐moving temperature fronts separating regions with high and low temperatures (amplitudes up to 100 K) formed on a Pd on alumina ring during the atmospheric oxidation of carbon monoxide. The back‐and‐forth front movement reflects the intrinsic nonuniformity of the catalytic system and the impact of global coupling. The ignition and extinction fronts usually moved at different velocities, in agreement with theoretical predictions. Complex spatiotemporal patterns were observed due to small‐amplitude temperature fronts that moved on the high‐temperature region at a much higher velocity than the high‐amplitude fronts. The qualitative motion features were affected by changes in the excess oxygen concentration. The nonuniform states existed mainly for feed conditions for which the only uniform state was an extinguished one.
Reactivation of the HZSM‐5 zeolite‐based catalyst used in the MTG process
Authors: Gayubo Ana G. , Aguayo Andrés T. , Benito Pedro L. , Landeta Alberto , Castilla Marta , Bilbao Javier
Published: June 2004

The recovery of the acidic structure and activity during the regeneration step by coke combustion of an HZSM‐5 zeolite‐based catalyst used in the methanol‐to‐gasoline (MTG) process in reaction–regeneration cycles was studied. The reactivation kinetics (activity us. coke combustion time) was determined as a function of temperature and time on stream of the reaction step. The validity of the reactivation kinetic model was proven by using it for the simulation of the cyclic operation under conditions of catalyst partial reactivation, together with the kinetic model for the MTG process.
Analysis of microwave thawing of slabs with effective heat capacity method
Authors: Basak Tanmay , Ayappa K. G.
Published: June 2004

Microwave thawing of materials, which melt over a finite temperature range, are analyzed using the effective heat capacity method. The state of the material, solid, liquid or mush is deduced from the equilibrium liquid volume fraction vs. temperature relationship for the substance, and the microwave power is calculated from Maxwell's equations. Using Galerkin finite elements, the microwave power, temperature and liquid volume fractions were obtained for microwave thawing of tylose slabs. Thawing progresses from the inside and/or outside depending on the slab thickness. For slabs ⩾ 5 cm, thawing progresses predominantly from the surface of the sample. Resonances, during which the microwave power absorption is high, causes the 2‐cm slab to thaw quicker than 1‐cm slabs. A power law for the thawing time vs. sample thickness yields an exponent of 1.56 for microwave thawing and 2 for conventional thawing. To control the temperature rise in the liquid regions, simulations were carried out with an on‐off control on the microwave power. On‐off control results in greater power savings for thick samples.
Shear and compressive rheology of aggregated alumina suspensions
Authors: Channell Glenn M. , Zukoski Charles F.
Published: June 2004

The shear and compressive properties of aggregated alumina particles are determined as functions of volume fraction and the strength of the interparticle attraction. Over a range of volume fractions, yield stresses, τy, elastic moduli, the strain delimiting the extent of the linear elastic response, and compressive yield stress, Py, are well described by power‐law functions of volume fraction, while the role of interparticle attractions can be accounted for by expressing these mechanical properties as (ϕ/ϕg − 1)n, where ϕg captures the strength of particle attractions and n the microstructure. The links between compressive and shear properties are well described by linear elastic models where the Py and τy are a function of Poisson's ratio which, for the suspensions investigated, has a value near 0.49.
Measurement of ultrasonic forces for particle–liquid separations
Authors: Woodside Steven M. , Bowen Bruce D. , Piret James M.
Published: June 2004

The magnitude and direction of the ultrasonic radiation forces that act on individual particles in a standing‐wave field were determined using a microscope‐based imaging system. The forces are calculated from measured particle velocities assuming that the drag force, given by Stokes' law, is exactly counterbalanced by the imposed ultrasonic forces. The axial primary radiation force was found to vary sinusoidally with axial position and to be proportional to the local acoustic energy density, as predicted by theory. The magnitude of the transverse primary force was determined by two independent methods to be about 100‐fold weaker than the axial force. Separation concepts exploiting the transverse force for cell retention have been successful despite the great disparity in magnitude between the axial and transvers‐force components. This may be explained by the reduced hydrodynamic forces on aggregated particles in transverse flow due to their alignment in the sound field.
Synthesis of reactive crystallization processes
Authors: Berry David A. , Ng Ka M.
Published: June 2004

A systematic method is presented to synthesize reactive crystallization processes. It shows how to selectively crystallize a desired solid product(s) after a reaction step and how to use compound formation to effect separation of a mixture. The method is based on the generation of phase diagrams with liquid‐phase reactions. Using transformed coordinates, systems with three or fewer degrees of freedom can be conveniently analyzed, regardless of the number of components and reactions. Features of the solid–liquid phase diagram that are relevant to process synthesis are identified. The method is illustrated with systems with multiple components, complex reactions, and multiple phases.
Polymer trace devolatilization: II. Case study and experimental verification
Authors: Yang Chi‐Tai , Smith Theodore G. , Bigio David I. , Anolick Colin
Published: June 2004

In this work, the bimodal/film model is compared with the cell model based on a case study using polystyrene/styrene devolatilization. It shows improvements over the cell model: (1) it requires a lower initial number of bubbles, which is more physically realistic and (2) it takes into account the observation of a limiting foam volume growth for a specific polymer in devolatilization. A stripper dispersion experiment was designed to investigate the effect of dispersed nitrogen stripper bubbles on the foam dynamics and devolatilization efficiency. The variables examined include polymer viscosity, initial volatile concentration, and the initial number and size of dispersed stripper bubbles. Polymer viscosity was the dominant factor in limiting the maximum foam volume expansion. The number and size of dispersed stripper bubbles show positive and negative effects (which are only secondary) on the maximum foam volume expansion, respectively. The initial volatile concentration has no effect on limiting the maximum foam volume expansion.
Effect of inlet conditions on scalar statistics in pipe mixing
Authors: Guilkey James E. , McMurtry Patrick A. , Klewicki Joseph C.
Published: June 2004

Recent experimental validation of theoretical and numerical predictions regarding scalar variance decay in a pipe have revealed that the traditional plug‐flow reactor picture of pipe flow omits key physical mechanisms. In particular, the far‐field decay exhibits a power law rather than exponential decay. These observations are examined by performing a set of experiments where the manner in which the scalar constituents are introduced into the pipe is varied. Significant differences are noted in the behavior of the variance decay until the very far field is reached, where an invariant power‐law form emerges.
Radial distribution of the flow velocity, efficiency and concentration in a wide HPLC column
Authors: Farkas Tivadar , Sepaniak Michael J. , Guiochon Georges
Published: June 2004

The use of optical fibers in a fluorescence–detection scheme permits the accurate determination of the radial distribution of the transit time, the column efficiency, and the analyte concentration at the exit of a chromatographic axial–compression column (50 mmID). The results obtained demonstrate that the column is not homogeneous, but suggest a nearly cylindrical distribution of the packing density. The average velocity close to the column wall is 7% lower than along its axis and the HETP 25% higher. The lack of homogeneity of the column packing is another source of band broadening not taken into account in chromatography so far. It causes the apparent HETP derived from the conventional elution chromatogram recorded on the bulk eluent to be larger than the local HETP and the band profile to be unsymmetrical with a slight tail reminiscent of kinetic tailing.