bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of filament drawdown on aerodynamic drag and heat transfer in fiber spinning
Authors: Miller C.
Published: April 2004

The momentum and thermal boundary layer equations are solved numerically to assess the effects of filament drawdown on aerodynamic drag and heat transfer in melt fiber spinning. It is found that, relative to the case without drawdown (constant filament velocity and diameter), the aerodynamic drag on the filament increases substantially, but the heat transfer rate is suppressed. Moreover, the air velocity profile eventually becomes fully developed (unlike the zero drawdown case), and the (velocity) boundary layer thickness, rather than continuing to grow with distance beneath the spinneret, eventually becomes proportional to the filament diameter, and thus decreases with increasing axial distance. Quantitative results are presented for the dimensionless drag force per unit length along the filament (the Drag number) and the Nusselt number as functions of the dimensionless axial distance and a new dimensionless parameter, the Drawdown Reynolds number. © 2004 American Institute of Chemical Engineers AIChE J, 50: 898–905, 2004
CFD study of fluid flow and wall heat transfer in a fixed bed of spheres
Authors: Nijemeisland Michiel , Dixon Anthony G.
Published: April 2004

A study is presented of the relationship between the local flow field and the local wall heat flux in a packed bed of spheres. Computational fluid dynamics is used as a tool for obtaining the detailed velocity and temperature fields, for gas flowing through a periodic wall segment test cell. Results from the wall segment are demonstrated to reproduce those obtained from a full bed of spheres with tube‐to‐particle diameter ratio of N = 4. Attempts to correlate the local wall heat flux with local properties of the flow field, such as velocity components, velocity gradients, and components of vorticity, led to the conclusion that local heat transfer rates do not correlate statistically with the local flow field. Instead, a conceptual analysis was used to suggest that local patterns of wall heat flux are related to larger‐scale flow structures in the bed. © 2004 American Institute of Chemical Engineers AIChE J, 50: 906–921, 2004
Factors affecting solids segregation in circulating fluidized‐bed riser
Authors: Hirschberg B. , Werther J.
Published: April 2004

Axial and radial segregation effects due to differences in particle sizes and solids densities were studied in a 0.2‐m‐dia. riser at gas velocities between 3.5 and 7 m/s and solids circulation rates between 8 and 40 kg/(m2·s). Two bed materials (a quartz sand/iron powder mixture and a quartz sand with a broad size distribution) with identical terminal velocity distributions were used. Local mean particle sizes and local mass fractions of the iron powder (for the mixture) decreased with height. Measurements of the solids streams revealed that the downflowing solids consist preferentially of large and/or heavy particles, while the reverse happens in the upward solids flow. The single particle terminal velocity is the decisive parameter affecting solids segregation. The comparison of both bed materials indicates that two bed materials will exhibit the same segregation patterns only if the distributions of the particles' terminal velocities in both materials are the same.
Transport processes of water and protons through micropores
Authors: Din Xue‐Dong , Michaelides Efstathios E.
Published: April 2004

Molecular dynamics simulations were performed to study the movement of water molecules and protons in two pores: a small pore of radius 9.36 Å and a larger one of radius 12.24 Å. Inside the ionic solution, the wall charge densities are approximately −0.1 C/m2 and −0.2 C/m2. Water and proton distributions in the pore are affected strongly by the water content and the wall charge density. In the case of low wall charge density, if there is a sufficient number of water molecules in the pore, the protons are strongly hydrated to the water molecules and do not directly contact the wall. In the case of high wall charge density, most of the protons are attracted to the wall. Then, the wall charge and the absorbed protons together behave like a weakly charged wall. We found that the Poisson–Boltzmann theory fails to predict the proton distribution in these pores. The calculated electroosmotic drag coefficient, proton diffusion coefficient, and pore conductance are compared with the simulation results for the Nafion‐117 membrane. This study suggests that if the Nafion‐117 membrane is modeled as a large number of identical cylindrical pores, the effective wall charge densities in the pores will never reach the value of −0.2 C/m2.
Fractionation of BSA and lysozyme using ultrafiltration: Effect of gas sparging
Authors: Ghosh Raja , Li Qiangyi , Cui Zhanfeng
Published: April 2004

Fractionation of proteins by ultrafiltration is an interesting challenge. With a particular membrane, the protein – protein and protein – membrane interactions largely decide which protein passes through and which is retained. System hydrodynamics also affects protein fractionation as the transmission behavior of a protein is altered by concentration polarization. Therefore, disruption of the concentration polarization layer would help to maintain the native selectivity of the membrane and hence aid in protein fractionation. An attempt is made to use gas sparging, a technique proven effective in controlling concentration polarization to enhance the selectivity of separation of BSA (MW 67,000) and lysozyme (MW 14,100). The effects of gas flow rate, liquid flow rate and feed concentration on the selectivity of fractionation are examined. Gas sparging enhances protein fractionation; under suitable solution conditions, nearly complete separation of BSA and lysozyme was achieved with gas sparged ultrafiltration. The permeate flux was also increased by gas sparing. The mechanism of enhancement is explained in terms of disruption of the concentration polarization layer and enhanced mass transfer due to bubble‐induced secondary flow.
Dual diffusion and finite mass exchange model for adsorption kinetics in activated carbon
Authors: Do D. D. , Wang K.
Published: April 2004

A model allowing for the finite mass exchange between the two phases is proposed for the description of adsorption kinetics in activated carbon. This model based on Do's earlier structural model for activated carbon involves three mass‐transfer processes: pore diffusion, adsorbed phase diffusion, and finite mass interchange between the fluid and adsorbed phases. The solid phase is heterogeneous, which is characterized by the micropore size distribution. The interaction between the adsorbate molecule and the micropore is calculated from the Lennard‐Jones potential theory. The model developed for nonpolar adsorbates is tested with the experimental data of seven adsorbates (paraffin gases, aromatics, carbon dioxide, and sulfur dioxide) on pellets of different shapes and sizes and at various operating conditions. The finite kinetics play an important role in the overall kinetics. Failure to account for this finite kinetics makes the model unable to describe correctly the desorption behavior, since under such conditions, the ability of the particle to release adsorbed molecules is dictated mostly by the resistance at the pore mouth of the micropore.
A break‐even analysis of distillation–membrane hybrids
Authors: Pressly Thomas G. , Ng Ka M.
Published: April 2004

The use of distillation–membrane hybrids is examined for the separation of two component mixtures exhibiting a tangent pinch, azeotrope, or low relative volatility. The merits of various process alternatives are discussed. A procedure for screening calculations is presented that allows the determination of the break‐even cost for a membrane, above which the hybrid would be too costly to be competitive. This approach is applicable to the screening of all the types of membranes and can be used to target the desirable membrane properties. Screening calculations are performed for water–acetic acid, ethanol–water, and propylene–propane systems to demonstrate the inherent trade‐offs of the hybrids and the effect of phase behavior on the performance.
FIR model identification: Parsimony through kernel compression with wavelets
Authors: Nikolaou Michael , Vuthandam Premkiran
Published: April 2004

Although finite impulse response (FIR) models are nonparsimonious, they are frequently used in model predictive control systems because they can fit arbitrarily complex stable linear dynamics. However, identification of FIR models from experimental data may result in data overfitting and high modeling uncertainty. To overcome this, FIR models may be determined by regularization‐based least squares and indirectly after prior identification of other parametric models such as ARX. In both cases, some prior knowledge about the model is essentially assumed to be known. ARX models, although parsimonious in terms of the number of identified parameters, perform poorly for bad choices of model structure and order. A methodology for the direct identification of parsimonious FIR models is proposed. In this way, most advantages of the FIR structure are retained without its disadvantages. The idea relies on the effective use of some prior information about the model through wavelet‐based signal compression. The proposed methodology is compared with other FIR identification methodologies, on the basis of the closeness of the identified FIR to the true FIR, steady‐state gain estimation, and analysis of the prediction residuals on a cross‐validation set of fresh data. Simulation studies on a single‐input‐single‐output process show that this method performs very well in all tests considered. Certain industrial practices are shown to be special cases of the proposed formalism.
Determining the model order of nonlinear input/output systems
Authors: Rhodes Carl , Morari Manfred
Published: April 2004

A method for determining the proper regression vector for recreating the dynamics of nonlinear systems is presented. The false nearest neighbors (FNN) algorithm, originally developed to study chaotic time series, is used to determine the proper regression vector for input/output system identification and inferential prediction using only time‐series data. The FNN algorithm for solving these problems is presented, and the problem of analyzing noise corrupted time series is discussed. The application of the algorithm to a number of examples including an electrical‐leg stimulation experiment, an industrial pulp‐digester model, a polymerization model, and a distillation‐column simulation is presented and the results are analyzed.
Automatic synthesis of thermodynamically feasible reaction clusters
Authors: Holiastos Konstantinos , Manousiouthakis Vasilios
Published: April 2004

Reaction clusters serve to carry out reactions whose thermodynamic yield is too low for practical large‐scale application. They therefore play an important role in the economics of the process and can decisively control its environmental impact. Reaction cluster synthesis must address such economic and environmental considerations. This was successfilly accomplished in this work, which is the first employing an optimization technique for this task. The problem formulation ensures that all mass balances are satisfied, that all reactions are thermodynamically feasible, and that they follow certain user‐defined characteristics of a generalized chemical reaction. In addition, given a set of chemical species, all clusters are identified that can represent this reaction; the ones found first are the most promising candidates. The formulation is flexible, accommodating a different number of reactions per cluster and allowing specification of many attributes by the user.
Novel concept prototype of low‐power‐consumption electrically heatable catalyst
Authors: Nakouzi Sabine R. , Narula Chaitanya K. , McBride James R. , Nietering Kenneth E. , Visser Jacobus H. , Adamczyk Andrew A.
Published: April 2004

Electrically heated catalyst devices (EHCs) are important for treating exhaust gases in the 20 to 120 s warmup period after a cold start when about 70% of the total hydrocarbon (HC) and carbon monoxide (CO) emissions from a modern gasoline powered vehicle are released. Although known for several years, EHCs have not been deployed because these devices are cost‐ and energy‐intensive. An alternate EHC prototype proposed here is based on our reasoning that only the platinum group metals and the molecules undergoing oxidation need to be at light‐off temperatures and it is not necessary to waste energy to heat the whole catalyst. The concept prototype, fabricated on a glass coupon, resistively heats the fluorine doped tin oxide film beneath the washcoat to bring a palladium‐titania washcoat to the CO and HC light‐off temperatures. The electrically powered concept prototype showed light‐off temperatures of 250°C and 260°C for CO and HC, respectively, in laboratory tests with simulated exhaust gases at 25°C. A device based on this concept is estimated to attain the 1‐kW target power consumption required for the deployment of the EHC.
Role of transition metal oxides in metal dusting: Density functional study
Authors: Cheng Hansong , Reiser David B. , Mathias Paul M. , Dean Sheldon
Published: April 2004

Density function theory was applied to study the mechanisms and energetics of two major metal dusting processes represented by Boudouard and steam‐carbon reactions on the FeO(100) surface. Cluster models were utilized to represent the surface. The chosen cluster model was validated by examining CO adsorption binding energies on clusters of various sizes. We show that the lattice relaxation has a relatively small effect on the adsorption. The reaction process involving direct abstraction of O from the surface by CO was excluded from consideration of the overall dusting processes due to unfavorable energetics. Minimum energy path calculations were carried out to investigate the reaction mechanisms. It was found that both the Boudouard and steam‐carbon reactions are thermochemically and kinetically unfavorable on transition metal oxide surfaces. Detailed insight into the reaction mechanisms was obtained by following the reaction trajectories and analyzing the electron population distribution along the reaction paths. This study elucidates the empirical observation that metal oxide can often minimize metal dusting.
Preparation of spherical oxalate particles of rare earths in emulsion liquid membrane system
Authors: Hirai Takayuki , Okamoto Norihiko , Komasawa Isao
Published: April 2004

Submicron‐sized spherical oxalate particles of rare earths were prepared by using an emulsion liquid membrane (ELM, water‐in‐oil‐in‐water (W/O/W) emulsion) system, consisting of Span 83 (sorbitan sesquioleate) as a surfactant and EHPNA (2‐ethylhexylphosphonic acid mono‐2‐ethylhexyl ester) as an extractant (cation carrier). Rare‐earth ions were extracted from the external water phase and stripped into the internal water phase to make submicron‐sized oxalate particles. In the case of Ce, Pr, Nd, Sm, and Gd, well‐defined spherical oxalate particles (0.2 – 0.6 μm dia.) were obtained, following the formation of primary particles of about 20 nm. In contrast, less spherical or rather tabular particles were formed for La, Dy, and Y, possibly owing to their formation in the external phase following some breaking of the water‐in‐oil (W/O) emulsion drop. Oxalate particles of Yb were not obtained in this system. Effects of the internal water droplet size, the rare‐earth ion concentration in the external water phase, and the volume ratio of organic membrane phase to internal water phase of the W/O emulsion (O/A ratio), on the size of spherical particles, were investigated. A simulation study based on the model of transport mechanism of rare‐earth ions through the organic membrane phase revealed that the particle size was determined by the distribution of rare‐earth ions into the internal water droplets, as confirmed by the experimental results. The control of the particle size was found to be feasible by control of the feed rare‐earth concentration and size of the internal water droplets.
Hydrogen‐bond cooperativity in 1‐alkanol + n‐alkane binary mixtures
Authors: Gupta Ram B. , Brinkley Ray L.
Published: April 2004

Hydrogen‐bond cooperativity is an effect when hydrogen bonding is influenced by the previously formed hydrogen bond on the molecules. Using Fourier‐transform infrared spectroscopy, we have measured the extent of self hydrogen bonding in 1‐hexanol and 1‐pentanol dissolved in n‐hexane. Conventional theories without hydrogen‐bond cooperativity, such as the statistical‐association‐fluid theory, lattice‐fluid‐hydrogen‐bonding theory, and associated perturbed‐anisotropic‐chain theory, cannot represent the experimental data accurately. The extended lattice‐fluid‐hydrogen‐bonding theory that includes hydrogen‐bond cooperativity agrees well with the experimental data. Study suggests that the equilibrium constant for the second hydrogen bond on 1‐alkanol molecules is 10 times larger than that for the first hydrogen bond formation. Hence, strong hydrogen bond cooperativity exists in 1‐alkanol self association. Equations of state dealing with 1‐alkanol mixtures need to be modified to account for this strong hydrogen‐bond cooperativity.
Kinetics of protein deposition and replacement from a shear flow
Authors: Mandrusov E. , Yang J. D. , Pfeiffer N. , Vroman L. , Puszkin E. , Leonard E. F.
Published: April 2004

Kinetics of plasma protein deposition and replacement from a shear flow of full strength and diluted blood plasma onto prewetted glass were studied both numerically and experimentally. A band of fibrinogen moving down the adsorbing surface was predicted and observed. The band was shown to define the region where blood platelets subsequently adhered to the surface. Since platelet adhesion is a fundamental component of thrombosis, this observation is potentially pertinent to the long‐sought mechanism that determines where thrombus forms during shear flow of blood through artificial devices. The discrepancies between the mathematical model and experimental observations are explained by the presence of the natural convection, arising from density differences between plasma and the wetting fluids.
Blowdown of pipelines carrying flashing liquids
Authors: Fairuzov Yuri V.
Published: April 2004

A mathematical model is developed to simulate a blowdown of a long pipeline conveying a flashing multicomponent mixture. The effect of the thermal capacitance of the pipe was incorporated into the model by employing a novel approach in the formulation of the energy equation for the fluid flow in the pipeline. The model was validated by comparison with previously published experimental data for the blowdown of a pipe containing a two‐component mixture. A detailed study was performed to investigate the effect of heat transfer between the fluid flow and the pipe wall on the process of depressurization of a long pipeline. Numerical simulations were carried out to assess the effect of friction on the blowdown time. The results obtained lead to a better understanding of the blowdown phenomenon and can be used for predicting the consequences of controlled or uncontrolled releases of flashing liquids from long pipelines.
Flow and axial dispersion simulation for traveling axisymmetric Taylor vortices
Authors: Howes Tony , Rudman Murray
Published: April 2004

Numerical experiments using a finite difference method were carried out to determine the motion of axisymmetric Taylor vortices for narrow‐gap Taylor vortex flow. When a pressure gradient is imposed on the flow the vortices are observed to move with an axial speed of 1.16 ± 0.005 times the mean axial flow velocity.

The method of Brenner was used to calculate the long‐time axial spread of material in the flow. For flows where there is no pressure gradient, the axial dispersion scales with the square root of the molecular diffusion, in agreement with the results of Rosenbluth et al. for high Peclet number dispersion in spatially periodic flows with a roll structure. When a pressure gradient is imposed, the dispersion increases by an amount approximately equal to 6.5 × 10−4 W2d2/Dm, where W is the average axial velocity in the annulus, analogous to Taylor dispersion for laminar flow in an empty tube.
Numerical simulation of intense reaction propagation in multiphase systems
Authors: Pape Ronald , Gidaspow Dimitri
Published: April 2004

A numerical model was evaluated including Arrhenius reaction kinetics to simulate multiphase flows with intense reactions and severe property gradients. Although these problems are common in chemical engineering, such an extreme case as detonation propagation in a dispersed particulate flow was investigated. The model was evaluated with respect to the form of the conservation relations being simulated, frame invariance verification, constitutive relations, numerical stability, numerical diffusion, and model verification using available experimental results and equilibrium thermochemical predictions. The model was adequate with respect to numerical issues of particular concern such as stability and numerical diffusion. To simulate experimental results realistically, Arrhenius reaction kinetics alone were insufficient. When considering important physical mechanisms in the reaction modeling based on single particle heat transfer, the multiphase model simulates experimental results realistically.
Electrochemical membrane flue‐gas desulfurization: K2SO4/V2O5 electrolyte
Authors: Schmidt Douglas S. , Winnick Jack
Published: April 2004

The viability of a new electrolyte was demonstrated in the bench‐scale electrochemical removal of SOx from flue‐gas streams at high temperatures. At current densities up to 20 A/m2, approximately 99% current efficiciency was achieved when removing 90% of inlet SOx at 480°C. As current densities increased to 100 A/m2, current efficiencies were 64% at 480°C and 73% at 520°C. While species present in this K2SO4/V2O5 molten salt are not well understood, a simple mechanism was used to develop a model to describe the observed removal results. This model was then used to predict preliminary economic viability of this system based on known electrochemical technology.
Complete separation conditions for a local equilibrium TCC adsorption unit
Authors: Chiang Anthony S. T.
Published: April 2004

A new technique presented can offer analytical solutions for the local equilibrium true countercurrent model to study the simulated moving‐bed (SMB) separation process. This equilibrium theory could be vey useful for predicting both optimal and robust operation conditions for the SMB separation process, if the results can be easily calculated. However, analytical solution was available only in the limiting case of binary separation. With this analytical solution for multicomponent systems, the application of equilibrium theory will be more practical. While developing these solutions, a new way of applying the well‐known ω‐transformation to nonlinear adsorption system was conceived. This approach may have broader applications than are presented here.
Wavelet‐based modulation in control‐relevant process identification
Authors: Carrier John F. , Stephanopoulos George
Published: April 2004

The identification of models from operating data for process controller design requires that the information from the process be extracted in pieces that are localized in both time and frequency. Such an extraction process would allow the separation of valuable signal information from the effects of nonstationary disturbances and noise. The wavelet transform provides an efficient approach for such a decomposition, which is organized in a multiscale, hierarchical fashion. By using the method of modulating functions in conjunction with the wavelet decomposition, it is demonstrated that recursive state‐space models, which are multiscale in character and suitable for the design of model‐predictive controllers, may be readily constructed with lower levels of modeling error than yielded by traditional techniques. The method is especially suitable for the identification of time‐varying and nonlinear models, where the nonlinear process is represented by a set of linear models. The multiscale character of the wavelet basis makes it particularly suitable for multirate, multivariable processes. A series of examples illustrates various aspects of the proposed approach and its inherent advantages.
Safety verification using a hybrid knowledge‐based mathematical programming framework
Authors: Srinivasan R. , Dimitriadis V. D. , Shah N. , Venkatasubramanian V.
Published: April 2004

Hazard and operability analysis (HAZOP) is widely used to perform hazards analysis of chemical plants. It is labor‐ and knowledge‐intensive and could benefit from automation. Toward that goal, a knowledge‐based framework for automating HAZOP analysis (HAZOPExpert) was proposed. Recently, Dimitriadis et al. proposed a quantitative model‐based approach that uses a dynamic model of the plant and a description of process disturbances and parameters for hazard eualuation. These two different approaches have their own merits and demerits. The qualitative analysis performed by HAZOPExpert is thorough and computationally efficient, but can lead to ambiguous conclusions. The quantitative approach can perform an exact analysis without ambiguities, but a complete analysis can be computationally prohibitive. Thus, these two frameworks appear to complement each other. This article presents an integrated approach for hazard identification and evaluation, which overcomes the shortcomings of purely qualitative and quantitative methods. In the integrated framework, the overall features of a particular hazardous scenario are extracted by inexpensive qualitative analyses. If necessary, a detailed quantitative analysis is then performed, and that too only on those parts of the plant identified by the qualitative analysis as hazardous. The results of this framework are compared to those of purely qualitative reasoning using an industrial case study.
Miscibilization of reactive polymers during early‐stage spinodal decomposition
Authors: Yashin Victor V. , Spontak Richard J.
Published: April 2004

Reactive compatibilization constitutes an important method by which to control the size scale of phase separation in immiscible polymer blends. If a polymer pair exhibits a miscibility window at experimentally accessible temperatures, then reactive chain coupling can also be used to enhance the miscibility of the blend during spinodal decomposition in the biphasic region. We consider here the simultaneous phase separation and chemical reaction of A and B homopolymer blends in which end‐functionalized A chains react with a variety of functionalized B chains to form either AB diblock, ABA triblock, or n‐armed B‐g‐A graft copolymers. Analytical expressions for the structure factors and Onsager kinetic coefficients are developed for each of these copolymer architectures in the kinetically controlled mean‐field limit of early‐stage spinodal decomposition. Multifunctional conversion‐architecture‐phase stability (CAPS) diagrams are introduced to facilitate comparison of the effect of copolymer architecture on reaction‐driven blend miscibilization.
Morphology development in shear flows of straight and folded molten fibers
Authors: Zhang D. F. , Zumbrunnen D. A. , Liu Y. H.
Published: April 2004

The morphological evolution of straight and folded molten fibers in shear flows was systematically investigated. Shear flows represent local flow conditions within actual batch mixers and extruders. Folded fibers were of interest, since folding may occur during melt processing and since folded fibers resemble portions of more complex extended structures arising in polymer blends. A general, three‐dimensional numerical model of the time‐dependent fluid flows within the molten‐fiber phase and major‐phase fluid was developed. Interactions between both fluids via fully dynamical, three‐dimensional interfaces were considered. The relation of morphological changes in the fibers to the flow field for specified interfacial tensions and viscosity ratios are presented.
Comparison of converging and diverging radial flow for measuring cell adhesion
Authors: Goldstein Aaron S. , DiMilla Paul A.
Published: April 2004

Radial flow between parallel surfaces produces a spatially dependent wall shear stress that permits investigation of cell adhesion for a range of shear simultaneously. The maximum for this range is limited by accurate prediction of fluid mechanics at small radial positions. Numerical and analytical models for predicting fluid mechanics demonstrate that corner and inertial effects at small radial positions are not only significant but differ with the direction of flow (i.e., converging vs. diverging). For diverging flow from an axially oriented inlet, the recirculation zone downstream of the corner disturbs streamlines at small radial positions. With converging flow this recirculation zone is confined to the axially oriented outlet. Also, inertia contributes positively for converging flow, enhancing the magnitude of shear stress, but negatively for diverging flow. Experiments with cells support the validity of this analysis: the strength of cell adhesion does not vary with direction or magnitude of flow.
Quick analysis of enantioselectivity by a chromatographic reactor
Authors: Wu Jau‐Yann
Published: April 2004

The transient behavior of enzyme‐catalyzed reaction in a proposed chromatographic reactor was investigated, and application of the technique to evaluate the capability of the enzyme in the process of kinetic resolution was developed. The theoretical result reveals that the enantioselectivity of the enzyme can be obtained directly from the amount of substrates eluted without any further treatment if a large amount of enzyme is provided. Because of its simplicity in operation and data analysis yet without any adverse consequences induced by enzyme deactivation, the technique presented can facilitate the development of an optimal condition for enzymatic kinetic resolution.
Simulation of structural phenomena in mixed‐particle fluidized beds
Authors: Seibert Kevin D. , Burns Mark A.
Published: April 2004

A statistical mechanical simulation was developed and used to predict the macroscopic and microscopic behavior of fluidized beds. In particular, the model was used to study structural phenomena in liquid fluidized beds that contain a distribution of particle sizes and/or densities. Bed structural phenomena, such as density‐based and size‐based segregation, classification, expansion, inversion, and solids dispersion have all been successfully simulated. Experimental data for the segregation of glass beads of different sizes and different densities agree well with predictions made from the simulation (without adjustable parameters). Classification and dispersion simulations also show good agreement with experimental data.
Modeling strategies for enantiomers separation by SMB chromatography
Authors: Pais Luís S. , Loureiro José M. , Rodrigues Alírio E.
Published: April 2004

Modeling strategies for simulated moving bed adsorbers were studied to compare the simulated moving bed model (SMB) that considers the real shift of the injection and collection points to the true moving bed approach (TMB) that considers liquid and solid flow in opposite directions. The prediction of these two models is compared in terms of steady‐state performance, steady‐state internal concentration profiles, and transient behavior of the extract and raffinate purities. The influence of the degree of subdivision of the bed in the SMB model predictions is also analyzed and compared with the TMB performance. Model results are compared with experimental results obtained for the chromatographic separation of binaphthol enantiomers.
Emulsion‐liquid‐membrane extraction of copper using a hollow‐fiber contactor
Authors: Hu Shih‐Yao B. , Wiencek John M.
Published: April 2004

A novel extraction technique using an emulsion liquid membrane within a hollow‐fiber contactor was developed and utilized to extract copper using LIX 84 extractant. Emulsion liquid membranes are capable of extracting metals from dilute waste streams to levels much below those possible by equilibrium‐limited solvent extraction. Utilizing an emulsion liquid membrane within a hollow‐fiber contactor retains the advantages of emulsion‐liquid‐membrane extraction, namely, simultaneous extraction and stripping, while eliminating problems encountered in dispersive contacting methods, such as swelling and leakage of the liquid membrane. Mathematical models for extraction in hollow‐fiber contactors were developed. The models satisfactorily predict the outcome of both simple solvent extraction and emulsion‐liquid‐membrane extraction of copper by LIX 84 in a hollow‐fiber contactor over a wide range of conditions. Emulsion‐liquid‐membrane extraction performs exceptionally well when the extraction is close to equilibrium limit. It is also capable of extracting a solute from very dilute solutions. Stability of the liquid membrane is not crucial when used in hollow‐fiber contactors; the surfactant in liquid membrane can be reduced or even eliminated without severely impairing the performance.
Solvation effect on kinetic rate constant of reactions in supercritical solvents
Authors: Chialvo A. A. , Cummings P. T. , Kalyuzhnyi Yu. V.
Published: April 2004

A statistical mechanical analysis of the solvation effects on the kinetic rate constants of reactions in near and supercritical solvents is presented to understand the experimental findings regarding the thermodynamic pressure effects. This is an extension of the solvation formalism of Chialvo and Cummings to the analysis of the microscopic basis for the macroscopic pressure and temperature effects on the kinetic rate constants of reactions conducted in the compressible region of the solvent phase diagram. This analysis is illustrated with integral equations calculations involving Lennard–Jones infinitely dilute quaternary systems to describe the species in solution during the reaction of triplet benzophenone (3BP) with a cosolvent (either O2 or 1,4‐cyclohexadiene) in supercritical CO2 along the supercritical isotherms Tr = 1.01 and 1.06. The role of the species molecular asymmetries and consequently their solvation behavior in determining the thermodynamic pressure and temperature effects on the kinetic rate constant of reactions at near‐critical conditions are discussed.
Differential pressure sticking of drill string
Authors: Sherwood J. D.
Published: April 2004

The frictional forces acting on a drill string in a borehole can be large if the drill string is embedded in a pastelike filter cake formed at the borehole wall by the drilling fluid. In extreme conditions, the drill string can become stuck, leading to expensive delays in the drilling process. The hydraulic pressure within the wellbore is usually higher than the pore pressure within the rock. This excess pressure is responsible both for the growth of the filter cake, and for the normal force that can hold the drill string against the borehole wall. We obtain estimates of the normal and frictional forces acting on the drill string, based on an analysis of the pressure and concentration profile within the filter cake. The forces can be minimized by ensuring that the cake is highly compressible, so that the bulk of the pressure drop between the borehole and porous rock occurs across a thin boundary layer at the base of the cake. The forces acting on a sphere (rather than a cylindrical drill string) are also modeled, and are compared against experiment. The predicted fictional force is smaller than observed experimentally, but the predicted t3/4 growth of the force with time t agrees with experiment.
Polymer cross‐linking in post‐gel region for continuous and batch reactors
Authors: Cozewith C. , Teymour F.
Published: April 2004

Tetrafunctional chain coupling of polymers is an important process for introducing long‐chain branching to modify flow behavior and for forming cross‐linked networks. Reactor modeling for polymers branched beyond the gel point is a difficult problem because of the divergence of the moments of the MWD to infinity. A newly developed technique, numerical fractionation, based on the method of moments is applied to modeling chain coupling (cross‐linking) kinetics in continuous flow stirred tank (CFST) and batch reactors. The resulting model is applicable from 0 to 100% gelation and predicts the amount of sol fraction and its molecular weight and MWD as a function of operating conditions. This technique is easier to apply to reactor simulation than others for calculating properties of polymers in the post‐gel region. An examination of CFSR dynamics during reactor startup indicates a wide range of behavior depending on the critical residence time for gel formation. At residence times close to the critical, long times are needed to reach steady state, but at residence times much greater than the critical, the reactor can reach steady state in less than three turnovers. For both the batch and CFST reactors, polymer properties are determined by only two parameters: initial polymer MWD and reduced reaction time or reduced residence time. Consequently, at a given sol fraction, the molecular weight and MWD of the sol polymer are fixed. Narrowing the initial polymer MWD increases the amount of gel present at a given reaction time. Considerable differences are shown in the rate of the chain coupling reaction and properties of the sol phase between the two reactor types.
Thermodynamic properties prediction of vinyl acetate systems at high pressures
Authors: Prasad B. G. Shiva , Woollatt Derek
Published: April 2004

Vinyl acetate (a polar compound) has become a key ingredient in many industrial and consumer products. However, very little is known about its thermodynamic properties. This article presents a simple modification of Wu and Stiel's (1985) method (originally) developed for predicting thermodynamic properties of polar compounds up to Pr = (10) for extending its range of applicability to very high pressures of the order of Pr = 80. The predictions show good agreement with the experimental data for specific volume in the case of vinyl acetate, and specific volume, enthalpy and entropy for mixtures of ethylene and vinyl acetate for compositions up to 50 wt. % of vinyl acetate. Further validation for other polar systems would determine if this method is applicable to polar compounds in general.
Comparison of models on the prediction of binary equilibrium data of activated carbons
Authors: Ahmadpour A. , Wang K. , Do D. D.
Published: April 2004

A pure‐component equilibrium adsorption isotherm of methane, ethane, propane, and CO2 at different temperatures and the binary adsorption data of methane with the other three species measured at 500 torr (66.7 kPa) and temperatures of 273 K and 303 K are presented and discussed. These measurements were carried out on three nutshell‐derived KOH chemically activated carbon (AC) samples and one commercial activated carbon. The binary adsorption data of another commercial AC (Nuxit‐al) from the literature are also used for comparison purposes. The single and binary experimental data were applied to six models: IAST, loading‐dependent isosteric heat, micropore‐size distribution (MPSD), energy distribution (ED), extended Langmuir, and extended Sips models. The models were found to describe the experimental data of the commercial ACs with a reasonably good accuracy, but only the model assuming isosteric heat as a function of loading could reasonably predict the data of KOH chemically activated carbons.
Liquid jet‐array cooling modules for high heat fluxes
Authors: Oh Chang H. , Lienhard V John H. , Younis Hesham F. , Dahbura Rudy S. , Michels Dirk
Published: April 2004

Liquid jet‐array cooling modules had been designed for operation at very high heat fluxes and were used to remove fluxes as high as 17 MW/m2. Experimental results, numerical studies, and thermal stress analyses are reported. Modules having actively cooled areas of 10 cm2 were developed. Cooling is provided by an away of small‐diameter water jets operating at speeds of 47 m/s. These jets impinge on the rear side of a 2‐to 4‐mm‐thick metallic faceplate from which the heat load is absorbed. Cooling is entirely convective without boiling. The behavior of cooling jet arrays is summarized, including numerical simulations for our specific cases. Finite‐element studies of the stresses in candidate faceplate materials are described for typical thermal and mechanical conditions. A thin‐film high‐flax resistance heater provides the heat load for testing module prototypes. The thermal resistances of the system are quantified experimentally and incorporated in our numerical model. The dominant thermal resistance is associated with the heating element. The modules are believed to be serviceable to fluxes above 20 MW/m2, although dificulties with the heating element prevented this level from being reached.
Olefin/paraffin separations by adsorption: π‐Complexation vs. kinetic separation
Authors: Rege Salil U. , Padin Joel , Yang Ralph T.
Published: April 2004

Monolayer dispersed AgNO3 on silica gel was prepared by thermal dispersion. This sorbent exhibited superior adsorption properties for olefin/parafin separations by selective adsorption of olefins through π‐complexation. This sorbent, along with Ag+ ion‐exchanged resin, was subjected to simulation studies for olefin/parafin separations by pressure‐swing adsorption. Kinetic separations (due to differences in olefin/parafin diffusivities) using zeolite 4A and molecular‐sieve carbon were also studied, Using 50/50 mixtures of C2 H4/C2 H6 and C3H6/C3H8, separations using these sorbents were compared directly based on olefin product purity, recoveiy, and throughput. The monolayer AgNO3/SiO2 sorbent showed superior separation results for C3H4/C3H8, and the Ag+‐exchanged resin showed best results for C2H4/C2H6. In both cases, over 99% product purities could be obtained at reasonably high recoveries and throughputs. For C3H6/C3H6 separation on AgNO3/SiO2, multiplicity of cyclic steady states were observed within certain regions of feed and purge velocities. within these regions, two stable cyclic steady states were reached starting ffom different initial‐bed conditions while all operating conditions were identical.
Lumen mass transfer in hollow‐fiber membrane processes with nonlinear boundary conditions
Authors: Qin Yingjie , Cabral Joaquim M. S.
Published: April 2004

Hollow‐fiber membrane separation or reaction processes, with a nonlinear boundary condition at the lumen interface, are analyzed numerically. Sixteen different nonlinear boundaly conditions in the literature were simplified to four dimensionless boundary conditions, in which only two parameters are needed to incorporate the effect on mass transport of membrane and shell resistances, lumen inlet Concentration, shell concentration, phase and/or chemical equilibria, and interface reaction kinetics. The lumen mass‐transfer coefjicients were obtained by solving the continuity mass‐conservation equation with the corresponding boundary conditions. The calculated results demonstrate that the lumen mass‐transfer coefjicient is a function of lumen‐inlet concentration and shell concentration, as opposed to the case when a linear boundary condition occurs at the lumen interface. By using the empirical correlations of the lumen local mass‐transfer coefjicient, an ordina ry differential equation substituting a partial differential equation can be applied to obtain the lumen dimensionless mixed‐cup concentration with an absolute error of less than 0.005 in most cases, thus making it possible to design and evaluate the hollow‐fiber membrane separation or reaction processes.
Internally staged permeator prepared from annular hollow fibers for gas separation
Authors: Li K. , Wang Dongliang , Li Dongfei , Teo W. K.
Published: April 2004

A polysulfone/polyethersulfone annular hollow‐fiber (tube) membrane was prepared using a phase‐inversion process, which is useful for further preparation of an internally staged permeator (ISP) for gas separation. This study focused on the techniques of fabricating the polysulfone/polyethersulfone annular‐hollow‐fiber membranes and its membrane permeators for gas enrichment. Two homogeneous polymer solutions comprising polysulfone/DMAc and polyethersulfone/NMP/water, respectively, were prepared and extruded with a triple‐orifice spinneret into an annular‐hollow‐jiber membrane that possesses two distinct skin layers and is capable of providing two separation stages internally for gas separation. The performance of the ISP fabricated from the prepared annular hollow‐fiber membrane was evaluated theoretically and experimentally under co/countercurrent and countercurrent flow patterns for various binaly gas mixtures. The mathematical models generally describe satisfactorily the observed experimental results. A parametric study reveals that while, in general, better separation is available at lower values of overall stage cuts, highly purified permeate products could be achieved at higher values of overall stage cuts if the concentration of a permeating component in the feed stock is relatively high.
Back mixing in a reciprocating plate column with stable density gradients
Authors: Rao Nadella V. Rama , Baird Malcolm H. I.
Published: April 2004

Axial dispersion coeficients were measured in an aqueous phase flowing downward through a 5.08‐cm‐dia. Karr‐type reciprocating plate column. The steady tracer injection method was used, in which the concentration profile was measured upstream of tracer injection. The tracer solution was a strong (150–170 g/L) solution of sodium chloride, whereby a significant stable density gradient (density decreasing with height) was created in the upstream section. The operating variables included frequency (0 to 7.1 Hz), amplitude (0.7 to 1.4 cm), and plate spacing (2.65 to 7.65 cm). Some data were also obtained under two‐phase conditions with a refined kerosene (Isopar M) dispersed in the aqueous phase as droplets. Some control experiments were done using a neutrally buoyant tracer solution containing sodium chloride and methanol. There was no evidence that the stable density gradient had any effect in reducing the values of the axial dispersion coejjicient, although earlier published work had shown that an unstable density gradient did increase axial miring.
Synchronization of batch trajectories using dynamic time warping
Authors: Kassidas Athanassios , MacGregor John F. , Taylor Paul A.
Published: April 2004

The application of dynamic time warping (DTW) to the analysis and monitoring of batch processes is presented. This dynamic‐programming‐based technique has been used in the area of speech recognition for the recognition of isolated and connected words. DTW has the ability to synchronize two trajectories by appropriately translating, expanding, and contracting localized segments within both trajectories to achieve a minimum distance between the trajectories. Batch processes often are characterized by unsynchronized trajectories, due to the presence of batch‐to‐batch disturbances and the existence of physical constraints. To compare these batch histories and apply statistical analysis one needs to reconcile the timing differences among these trajectories. This can be achieved using DTW with only a minimal amount of process knowledge. The combination of DTW and a monitoring method based on Multiway PCA/PLS is used for both off‐line and on‐line implementation. Data fiom an industrial polymerization reactor are used to illustrate the implementation and the performance of this method.