bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanics of column beds: II. Modeling of coupled stress‐strain‐flow behavior
Authors: Yew Bee Gaik , Ureta Jorge , Shalliker R. Andrew , Drumm Eric C. , Guiochon Georges 
Published: April 2004

AbstractThe rheological behavior of a bed of packing material during its consolidation was investigated using an elastic‐plastic model, the Frictional Material Model. This model takes into account the behavior of the packing material under compression stress, its consolidation, its internal friction, its friction against the column wall, and the dependence of the bed's permeability on the local void fraction. The complexity of the problem arises from the nonlinear behavior of the relationships between the critical parameters controlling the column bed behavior and the external stresses applied to this bed. Solutions of the model were calculated for combinations of axial compression and seepage stresses, the latter corresponding to the flow of the mobile‐phase stream under typical conditions used in HPLC. The results demonstrate the importance of the internal angle of friction of the packing material used on the degree of radial and axial heterogeneity of the beds of chromatographic columns packed with this material.
Positioning of salt gradients in ion‐exchange SMB
Authors: Houwing Joukje , Jensen Thomas B. , van Hateren Stef H. , Billiet Hugo A. H. , van der Wielen Luuk A. M. 
Published: April 2004

AbstractSalt gradients can be used to improve the efficiency of ion‐exchange separations in simulated moving‐bed systems. The gradient, formed by the use of feed and desorbent solutions of different salt concentrations, introduces regions of increased and decreased affinity of, for example, proteins for the matrix. Several gradient shapes can be formed, depending on the flow‐rate ratios and salt concentrations used. Only some of these effectively increase throughput or decrease desorbent consumption. Correct gradient positioning is essential, but not trivial, because salt is adsorbed in the resin. A procedure developed selects the flow‐rate ratios that allow correct positioning of gradients based on wave theory and incorporates the nonlinear Donnan isotherm of salt on ion‐exchange resins. Predictions are verified by experiments combined with a mathematical equilibrium stage (true moving‐bed) model. Upward and downward gradients are compared with respect to the use of desorbent and salt.
Enhancement of large‐particle gas‐fluidization by adding liquid
Authors: Nagahashi Y. , Lee D. H. , Grace J. R. , Epstein N. , Yokogawa A. , Asako Y. 
Published: April 2004

AbstractThere are circumstances where fluidization of particles by a gas can be promoted by the addition of small quantities of liquid, contrary to many reported cases where liquid impedes gas‐solid fluidization. Enhancement occurs only when the particles are larger than about 3 mm in diameter, the liquid and particles have similar densities (within ∼25%), and the particles are poorly wetted by the liquid. When these conditions are met, the liquid causes the minimum gas fluidization velocity Ugmf to decrease and particle motion to be more vigorous. For low liquid loadings, Ugmf and the pressure drop across the bed are then predicted well by a “modified liquid‐perturbed gas model.”
Performance of immobilized photocatalytic reactors in continuous mode
Authors: Dijkstra M. F. J. , Koerts E. C. B. , Beenackers A. A. C. M. , Wesselingh J. A. 
Published: April 2004

AbstractA packed‐bed (PBR), fiber (FR), membrane (MR), and tubular (TR) photocatalytic reactor have been modeled to compare their performance on a pilot scale. The influence of radial dispersion in the PBR and mass‐transfer limitation in the PBR, FR, and TR has been taken into account. The oxygen concentration in the liquid has a large influence on the performance and, therefore, air or pure oxygen should be added. The MR and PBR have a better performance than the TR and FR. Only a small degree of mass‐transfer limitation occurs in the PBR. Radial dispersion hardly influences the performance of the PBR. External mass‐transfer limitation influences the conversion in the TR and FR severely. The PBR, MR, and TR show a much better energy efficiency than the FR.
Thermal machines based on surface energy of wetting: Thermodynamic analysis
Authors: Laouir A. , Luo L. , Tondeur D. , Cachot T. , Le Goff P. 
Published: April 2004

AbstractThis work proposes an original thermodynamic‐energetic analysis of the feasibility and ideal performance of thermal machines based on the wetting phenomenon proposed by V. A. Eroshenko. The extension or contraction of a liquid film is taken as a “tutorial” example to introduce the basic thermodynamic relations of this 2‐D transformation. It implies both mechanical and thermal effects, and this coupling allows conversion of heat to work (thermal engine) or conversely to pump heat (refrigeration/heat pump effect). A similar approach is then developed for the interface between a liquid and a highly microporous solid, having a large internal surface area. The thermodynamic behavior of this interface involves as state variables the surface tension of the liquid, the contact angle, and their dependence on temperature. Depending on the relative magnitude and sign of these quantities, and, therefore, on the working couple and the temperature range, a variety of machine cycles are feasible, or excluded, and a method is proposed for a comprehensive inventory. Order‐of‐magnitude calculations of the energy densities are presented based on the existing experimental data for several systems involving water as the fluid. The tentative conclusions are that the energy densities are very small on a mass basis compared to conventional systems based on vaporization, but the contrary is true on a volume basis because the phase transformation (extension of the surface) occurs in a condensed state. There may, therefore, be some niches for thermal machines of this type, but they remain to be identified and validated.
Physical model analysis of foam–TCE displacement in porous media
Authors: Jeong Seung‐Woo , Corapcioglu M. Yavuz 
Published: April 2004

AbstractA glass micromodel was experimented to study the coupled effects of the apparent viscosity and mobility of surfactant foam (SF) on the displacement of residual trichloroethylene (TCE) during SF flooding. The SF floods operated under moderate interfacial tension (4.9 dyne/cm) of surfactant solution with TCE and pressure gradient (20–200 kPa) conditions showed relatively different foam behaviors to the higher pressure gradient conditions. The apparent viscosity of SF seems to be less affected by changes in surfactant concentration and affected more by the gas fraction in SF or the bubble size of SF. As the total SF flow rate and the gas injection velocity increased, the apparent SF viscosity decreased and the SF mobility increased. The latter characteristic led to an increase in the TCE displacement efficiency although SF under low‐pressure gradients resulted in flow channeling. The experiment results imply that the SF flood for environment application would be affected by operating conditions and distribution of residual contaminants.
CFD Simulations of bubbling/collapsing fluidized beds for three Geldart Groups
Authors: Gelderbloom Susan J. , Gidaspow Dimitri , Lyczkowski Robert W. 
Published: April 2004

AbstractA multiphase computational fluid dynamics (CFD) model was applied to a commonly used industrial experiment known as the collapsing fluidized‐bed experiment. The experiment involves several hydrodynamic regimes including the bed expansion, bubbling, sedimentation, and consolidation of the fluidized bed. The CFD model is capable of predicting all four of these regimes. The three Geldart Groups, C, A, and B were simulated in a bubbling and subsequently collapsing fluidized bed. Results show that hydrodynamic Models A and B, the use of the modified Ergun equation or the MFIX code drag models, and solids rheology have limited impact on the bubbling‐ and collapsing‐bed simulations. The major finding of this study is that the solids modulus, G, is the controlling parameter during the consolidation regime. The simulated bubble sizes and bed collapse rates for all three Geldart groups were found to be within reported experimental error. The computed high turbulent intensity of Geldart Group A particles also agrees with data in the literature measured using an acoustic shot noise probe. It is also demonstrated that the traditional interpretation of the collapsing bed as consisting of separate bubble escape and sedimentation regimes is incorrect and that, in fact, they occur simultaneously.
Analysis of multicomponent adsorption kinetics on activated carbon
Authors: Ding L. P. , Bhatia S. K. 
Published: April 2004

AbstractAn integrated mathematical model for the kinetics of multicomponent adsorption on microporous carbon was developed. Transport in this bidisperse solid is represented by balance equations in the macropore and micropore phases, in which gas‐phase diffusion dominates the mass transfer in the macropores, with the phenomenological diffusivities represented by the generalized Maxwell–Stefan (GMS) formulation. Viscous flow also contributes to the macropore fluxes and is included in the MS expressions. Diffusion of the adsorbed phase controls the mass transfer in the micropore phase, which is also described in a similar way by the MS method. The adsorption isotherms are represented by a new heterogeneous modified vacancy solution theory formulation of adsorption, which has proved to be a robust method for adsorption on activated carbons. The model is applied to the coadsorption and codesorption of C2H6 and C3H8 on Ajax and Norit carbon, as well as the displacement on Ajax carbon. The effect of the viscous flow in the macropore phase is not significant for the cases studied. The model accurately predicts the overshoot behavior and rollup of C2H6 during coadsorption. The prediction for the heavier compound C3H8 is always satisfactory, though at higher C3H8 mole fraction, the overshoot extent of C2H6 is overpredicted, possibly due to neglect of heat effects.
Thermoresponsive transport through porous membranes with grafted PNIPAM gates
Authors: Chu Liang‐Yin , Niitsuma Takuya , Yamaguchi Takeo , Nakao Shin‐ichi 
Published: April 2004

AbstractBoth thermoresponsive flat membranes and core‐shell microcapsule membranes, with a porous membrane substrate and grafted poly(N‐isopropylacrylamide) (PNIPAM) gates, were successfully prepared using a plasma‐graft pore‐filling polymerization method. PNIPAM was proven to be grafted homogeneously onto the porous membrane substrates, in the direction of both the membrane thickness and surface. Regardless of the solute molecular size, temperature had an opposite effect on diffusion coefficients of the solute across the PNIPAM‐grafted membranes with low graft yields as opposed to those with high graft yields. The PE‐g‐PNIPAM membranes change from positive thermo‐response to negative thermoresponse types with increasing pore‐filling ratios at around 30%. Phenomenological models were developed for predicting the diffusion coefficient of the solute across PNIPAM‐grafted membranes at temperatures, both above and below the lower critical solution temperature (LCST). Predicted diffusional coefficients of solutes across both the PNIPAM‐grafted flat and PNIPAM‐grafted microcapsule membranes fit the experimental values. To obtain an ideal result for the diffusional thermoresponsive controlled release through PNIPAM‐grafted membranes, the substrates strong enough to prevent any conformation changes are more suitable for preparing thermoresponsive membranes than weak ones.
CFD modeling of flow patterns and hydraulics of commercial‐scale sieve trays
Authors: Gesit Getye , Nandakumar K. , Chuang K. T. 
Published: April 2004

AbstractA computational fluid dynamics (CFD) model was used to predict the flow patterns and hydraulics of a commercial‐scale sieve tray. The model considers the 3‐D two‐phase flow of gas and liquid in which each phase is treated as an interpenetrating continuum having separate transport equations. Interaction between the two phases occurs via an interphase momentum transfer. For the CFD analysis, the commercial packages CFX5.4 and CFX4.4 of AEA Technology were employed. Velocity distributions, clear liquid height, froth height, and liquid holdup fraction in froth were predicted for various combinations of gas and liquid flow rates. Tray geometry and operating conditions were based on the experimental work that Solari and Bell carried out in a 1.22‐m diameter air–water simulator in 1986 at Fractionation Research Inc. Predicted results were found to be in good agreement with the experimental data of these authors. The objective of the work was studying the extent to which CFD can be used as a prediction and design tool for industrial trays. The simulation results are such that CFD can be used as an invaluable tool in tray design and analysis.
Polymer‐zeolite composite membranes for direct methanol fuel cells
Authors: Libby Brett , Smyrl W. H. , Cussler E. L. 
Published: April 2004

AbstractDirect methanol fuel cells require membranes with the dual properties of high proton conductivity and low methanol crossover. Such membranes have a high selectivity, that is a high ratio of proton conductivity to methanol permeability. This research reports such a membrane made of polyvinylalcohol and loaded with mordenite, a proton conducting, methanol impermeable zeolite. Protons travel directly through both the polymer and zeolite phases, but methanol has a more tortuous path around the zeolite particles. The composite membranes show up to twenty times higher selectivity than Nafion, the current benchmark. The improved behavior, a result of the proper tailoring of the polymer and dispersion phase, is predicted using Maxwell's theory for diffusion in composite media.
Modeling of morphogenesis of polyolefin particles: Catalyst fragmentation
Authors: Grof Zdeněk , Kosek Juraj , Marek Miloš , Adler Pierre M. 
Published: April 2004

AbstractThe growth of polyolefin particles in heterogeneous catalyzed polymerization reactors is simulated often by reaction‐transport models that introduce certain ad hoc effective spatial scales to the description of particle morphology and transport processes inside the particles. Because predictive capabilities of such models with respect to particle morphogenesis are limited, a multiscale model of a growing particle is developed. Maximum relevant information can be systematically extracted from particle microscopy images using the method of reconstructed porous media. The spatially 3‐D replicas of the particle pore space allow to calculate the effective transport and mechanical properties. Two new modeling techniques approximate catalyst particle fragmentation: Delaunay triangulation generalized into a 3‐D space with non‐Euclidean metrics and disconnection of the skeleton representation of the solid phase. Predictive mesoscopic modeling of particle morphogenesis is also discussed.
Aggregation structure and thermal conductivity of nanofluids
Authors: Xuan Yimin , Li Qiang , Hu Weifeng 
Published: April 2004

AbstractNanofluids are obtained by suspending metallic nanoparticles in conventional base liquids. Such a new class of heat‐transfer fluid is superior to the base liquids in energy‐transport performance, which depends on the distribution, volume fraction and thermal properties of the suspended nanoparticles. The theory of Brownian motion and the diffusion‐limited aggregation model are applied to simulate random motion and the aggregation process of the nanoparticles. A theoretical model is developed to predict the thermal conductivity of nanofluids. Comparison between the theoretical and experimental results shows the validity and accuracy of the theoretical model.
Transport properties for turbulent dispersion from wall sources
Authors: Mitrovic Bojan M. , Papavassiliou Dimitrios V. 
Published: April 2004

AbstractThe dispersion of a passive contaminant by turbulence is not only intrinsically interesting, but also is fundamental to practical heat‐ and mass‐transfer problems. The mechanism of turbulent dispersion from the wall and effects of the molecular Prandtl number are examined. Transport properties for scalar dispersion from an instantaneous line source at the wall of a parallel‐plate channel in which fully developed turbulent flow occurs, as well as from a continuous line source, are studied. Numerical experiments using a direct numerical simulation (DNS) of the flow, combined with Lagrangian scalar tracking (LST) of trajectories of thermal markers in the flow field, are conducted. The method is applied for a wide range of molecular Prandtl (Pr) or Schmidt (Sc) number fluids (0.1⩽Pr⩽50,000, which corresponds to liquid metals, gases, refrigerants, lubricants and electrochemical fluids). Results from the DNS/LST method are compared with experimental data, which are available for low Pr or Sc fluids. The turbulent diffusivity and turbulent Prandtl number for the plume that results from a line source are calculated, and an appropriate scaling is proposed. Finally, a model is developed for the prediction of the mean temperature or mean concentration profile as a function of Pr or Sc.
Mass‐transfer effects during separation of proteins in SMB by size exclusion
Authors: Houwing Joukje , Billiet Hugo A. H. , van der Wielen Luuk A. M. 
Published: April 2004

AbstractThe chromatographic fractionation of proteins by size‐exclusion chromatography in a simulated moving bed (SMB) is studied. During experimental fractionation of a mixture of bovine serum albumin (BSA) and myoglobin on Sepharose Big Beads, mass‐transfer effects are shown to limit the performance of the SMB. The internal profiles, as well as the extract and raffinate compositions, are described well by a steady‐state equivalent true moving‐bed (TMB) model that incorporates mass‐transfer effects. The selection of the particle size in SMB is a trade‐off between productivity and mass transfer. Based on the equivalent TMB model, the optimum particle size and configuration of the SMB can be selected, at which preset performance criteria (purity, recovery) are met at specified flow‐rate ratios, total column length, and pressure drop. For the current feed and apparatus, an optimal particle size of approximately 145 μm is calculated for achievement of purities and overall recoveries of 95%.
Accounting for batch reactor uncertainty in the nonlinear MPC of end‐use properties
Authors: Valappil Jaleel , Georgakis Christos 
Published: April 2004

AbstractThere are significant incentives in controlling the end‐use properties in batch reactors to reduce the variability in the final product quality. The presence of model errors and other uncertainties poses a problem in achieving this objective using model‐based control. A methodology to account for the model uncertainties in nonlinear model predictive control is presented here. This methodology also allows establishing a trade‐off between robustness and optimality in the controller. This is based on determining the uncertainty in the predicted final values of the properties, in the form of elliptical confidence regions. The controller then ensures that the complete confidence region is within the target range for the product. A semiinfinite programming problem is solved to find the input values for the rest of the batch, utilizing techniques that reduce the complexity of the problem. A Parameter Adaptive Extended Kalman Filter is used to estimate the important unmeasured and observable properties. An emulsion polymerization process for styrene is chosen as a case study and the methods developed here are demonstrated on this example process.
Product‐centered processing: Pharmaceutical tablets and capsules
Authors: Fung Ka Y. , Ng Ka M. 
Published: April 2004

AbstractA systematic procedure is presented for synthesizing and developing a manufacturing process for pharmaceutical tablets and capsules. The product quality factors—functional, physical and sensorial—are first identified. The dosage form and excipients are then selected, and the process flowsheet is synthesized along with the suitable equipment and operating conditions. Finally, the product and process are evaluated to ensure that the product possesses the desired quality factors. Design heuristics and physical models are provided to assist decision‐making. Examples involving Vitamin C, antacid, and ginseng are provided to illustrate the procedure.
Process uncertainty: Case of insufficient process data at the operation stage
Authors: Ostrovsky G. M. , Datskov I. V. , Achenie L. E. K. , Volin Yu. M. 
Published: April 2004

AbstractFlexibility analysis is of prime importance in chemical process systems, since it permits the creation of chemical processes, which can satisfy all design specifications in spite of changes in internal and external factors during the operation stage. The modern foundations of flexibility analysis were developed in the 1980s by Grossman and coworkers. They formulated solution approaches for the main problems of flexibility analysis (feasibility test), flexibility index, and the two‐stage optimization problem. All the formulations are based on the supposition that during the operation stage there are enough experimental data to accurately determine uncertain parameter values, but in practice, these assumptions are not likely to be met. This article discusses extensions of the feasibility test and the two‐stage optimization problem (TSOP), which take into account the possibility of accurately estimating some of the uncertain parameters while estimating with less accuracy the remaining uncertain parameters. To solve the TSOP, the split and bound approach was developed based on a partitioning of the uncertainty region and estimation of bounds on the performance objective function. Three computational experiments show the importance of taking into account the possibility (or lack thereof) of obtaining values of greater accuracy for uncertain parameters at the operation stage.
Framework for evaluating the feasibility/operability of nonconvex processes
Authors: Goyal Vishal , Ierapetritou Marianthi G. 
Published: April 2004

AbstractA large number of publications available on determining the feasible region and the operability limits for a design are all limited due to the assumption that the feasible space is convex, but almost all of the problems appearing in chemical engineering are nonconvex in nature. Determining the region where the design is feasible and safe to operate is of extreme importance. To address this problem, a novel algorithm was developed based on the idea of systematically evaluating the infeasibility areas using the outer approximation procedure introduced earlier, and the simplicial approximation approach to approximate the expanded feasible space constructed with the exclusion of the nonconvex constraints. This approach is general and deals with any nonconvex regions, as long as the nonconvex constraints are either concave or quasi‐convex, as illustrated through a series of example problems. A new metric is introduced to accommodate the need for comparison between various designs.