bluuebunny/crossref_metadata_2025_split huggingface dataset:
HEN optimizations without using logarithmic‐mean‐temperature difference
Authors: Akman Uğur , Uygun Korkut , Uztürk Derya , Konukman Alp Er Ş. 
Published: April 2004

AbstractA simple 1‐1 shell‐and‐tube heat‐exchanger model without the logarithmic‐mean‐temperature difference ΔTlm is proposed for heat‐exchanger network (HEN) optimizations. The model consists of two algebraic equations and allows to determine hot and cold outlet temperatures independent of each other. HEN optimization problems are classified as feasible‐ and infeasible‐path formulations, and compared with regard to problems originating from the use of ΔTlm in exchanger energy‐balance equations. The ΔTlm‐free model eliminates numerical failures in computing the logarithmic terms with negative arguments due to possible inconsistent initialization/progress of exchanger interconnection temperatures during HEN optimizations. The ΔTlm‐free model does not require inclusion of approach‐temperature inequality constraints since positive approach temperatures are guaranteed. It also eliminates iterative solution of nonlinear energy‐balance equations in feasible‐path formulations and is represented as linear equality constraints in infeasible‐path formulations for fixed areas, heat‐capacity‐flow rates, and bypass flows. As demonstrated with two representative HEN optimization problems, the ΔTlm‐free model significantly reduces numerical difficulties and decreases computation time in the optimization phase of synthesis/design, retrofit, and flexibility‐analysis of HENs. Thus, it permits handling large HEN problems.
Adaptive parameter estimation for microbial growth kinetics
Authors: Zhang T. , Guay M. 
Published: April 2004

AbstractAn adaptive parameter estimation algorithm for a class of biochemical processes expressed by a nonlinearly parametrized Monod's growth kinetics model is presented. Contrary to conventional least‐square or gradient‐type identification techniques, the proposed parameter estimation algorithm is developed based on Lyapunov's stability theory. A novel class of parameter‐dependent Lyapunov functions is utilized to remove the difficulty associated with estimating the unknown parameters that appear nonlinearly. A persistence of excitation (PE) condition is investigated to guarantee the convergence of the estimation scheme. Simulations are provided to verify the effectiveness of the new approach and the theoretical discussion.
Prediction and quantification of micromixing intensities in laminar flows
Authors: Cerbelli S. , Alvarez M. M. , Muzzio F. J. 
Published: April 2004

AbstractA new approach presented here predicts and quantifies the nonuniform spatial distribution of passive interfaces in both periodic and aperiodic chaotic mixing processes. Based on a coarse‐grained calculation of line element stretching, it bypasses the direct numerical simulation of continuous interfaces, which is computationally impractical even in simple model flows. The evolution of the structures created by the Lagrangian displacement and deformation process is decoupled into the product of a time‐invariant, spatially‐dependent function expressing the nonuniform density of interface throughout the flow domain and a temporally‐dependent function expressing the exponential growth of the interface, characterized by a global exponent (topological entropy) unambiguously different from the Lyapunov exponent. The Sine Flow agreed excellently with the Journal Bearing, when results from direct tracking of the interface were compared to those using stretching calculations to predict interface density.
CFD of multiphase flow in packed‐bed reactors: I. k‐Fluid modeling issues
Authors: Jiang Y. , Khadilkar M. R. , Al‐Dahhan M. H. , Dudukovic M. P. 
Published: April 2004

AbstractThe Eulerian k‐fluid CFD model was used to simulate the macroscale multiphase flow in packed beds. The geometric complexity of the bed structure is resolved by statistically describing the porosity distribution. The complicated multiphase interactions are computed using the Ergun type of formula developed based on bench‐scale hydrodynamic experiments. The work is presented in two sequential articles. Part I discusses implementation issues of the k‐fluid CFD model for packed beds. The drag exchange coefficients are obtained from the model of Holub et al. for the particle‐fluid interfaces Xks and from the model of Attou et al. (1999) for the gas–liquid interface, Xgl. The effect of particle external wetting on flow distribution was incorporated into the model through the capillary pressure evaluated by either the J‐function of Leverett (1941) for air–water or by the expression of Attou and Ferschneider (1999) for other fluids. In the framework of CFDLIB, the choice of the grid size and boundary conditions are discussed. An appropriate relationship between the section size and variance of the sectional porosity distribution was used for flow simulation. Part II discusses the extensive numerical results, and the CFD model is compared with experimental data in the literature.
CFD of multiphase flow in packed‐bed reactors: II. Results and applications
Authors: Jiang Y. , Khadilkar M. R. , Al‐Dahhan M. H. , Dudukovic M. P. 
Published: April 2004

AbstractNumerical simulations of multiphase flow using the k‐fluid CFD model described in Part I of this issue are presented for packed beds at various operating conditions. Both steady‐state and unsteady‐state (e.g., periodic operation) feed conditions were studied numerically. Predictions of the k‐fluid CFD model are comparable with the experimental data in the literature for liquid upflow in a cylindrical packed bed. In addition to the mean porosity and the longitudinally averaged radial porosity profile, the variance of the porosity distribution is needed for predicting the probability density function of the sectional flow velocity. In the trickling flow regime, the k‐fluid CFD model provides reasonable predictions of the global liquid saturation and the pressure gradient. Relevant applications of the k‐fluid CFD model are identified in quantifying the relationship between bed structure and flow distribution in various‐scale packed beds. The combined flow‐reaction modeling scheme is proposed through the “mixing‐cell” network concept, in which the k‐fluid CFD simulation can provide the information on sectional flow distribution.
Topology of ternary VLE diagrams: Elementary cells
Authors: Hilmen E. K. , Kiva V. N. , Skogestad S. 
Published: April 2004

AbstractThe classification of ternary vapor‐liquid equilibrium (VLE) diagrams is a key to simple azeotropic distillation analysis. All ternary mixtures reported so far to be occurring in nature can be qualitatively represented by a combination of only four elementary cells. This greatly reduces the number of VLE diagram structures that need to be analyzed in order to reveal the qualitative characteristics of any ternary azeotropic mixture.
Wavelet‐based adaptive grid method for the resolution of nonlinear PDEs
Authors: Cruz Paulo , Mendes Adélio , Magalhães Fernão D. 
Published: April 2004

AbstractTheoretical modeling of dynamic processes in chemical engineering often implies the numeric solution of one or more partial differential equations. The complexity of such problems is increased when the solutions exhibit sharp moving fronts. A new numerical method is established, based on interpolating wavelets, that dynamically adapts the collocation grid so that higher resolution is automatically attributed to domain regions where sharp features are present. The effectiveness of the method is demonstrated with some relevant examples in a chemical engineering context.
Microwave heating of endothermic catalytic reactions: Reforming of methanol
Authors: Perry W. Lee , Datye Abhaya K. , Prinja Anil K. , Brown Lee F. , Katz Joel D. 
Published: April 2004

AbstractIn an endothermic reaction, such as methanol‐steam reforming, the reaction rate can be limited by the ability to supply heat to the reactor. Heat transfer from the reactor wall normally supplies the required energy in such processes. Drawbacks, such as operating temperature constraints and practical heat‐transfer restrictions, limit this practice. In such situations, microwave heating could provide an effective and efficient method for transferring heat to the catalyst. To explore this possibility, the methanol‐steam reaction performed by conventional heating and microwave heating was studied. Mathematical modeling was performed for 1‐D heat transfer in a single catalyst pellet and for 2‐D heat transfer in a tubular packed‐bed reactor. The single catalyst pellet model indicated that productivity could increase significantly using microwave heating. The 2‐D model showed that microwave heating could minimize radial heat‐transfer effects. Conducting the methanol‐steam reaction in a microwave‐heated reactor experimentally verified the improved productivity.
Synthesis of controlled‐release products in supercritical medium
Authors: Guney Ozge , Akgerman Aydin 
Published: April 2004

AbstractControlled‐delivery products have recently received considerable attention. They prolong the drug's therapeutic effect, keeping its concentration between the therapeutic and toxicity limit. The final product must be free of residual solvent, even with nontoxic solvents, to provide its constant property that does not change with natural evaporation of the solvent. A major cost item in the synthesis of controlled‐release drugs is to remove this solvent to acceptable limits. To eliminate the production step involving the organic solvent from the overall process, the drug was introduced into the polymer matrix using supercritical carbon dioxide (scCO2) as the carrier solvent and swelling agent. This study focuses on the impregnation of a biodegradable polymer matrix with 5‐fluorouracil for chemotherapy and β‐estradiol estrogen hormone therapy. Swelling of the polymer matrix, solubility of drug components in scCO2 and the adsorption isotherm/partition coefficients in the presence of scCO2 were studied. To investigate the single‐component supercritical adsorptive synthesis of controlled‐delivery products, accurate experimental techniques to measure drug‐component solubilities in supercritical fluids and adsorption isotherms in the presence of supercritical fluids were developed. Solubility data of these drugs in scCO2 at 35–55°C and 101–220‐bar were reported. The adsorption equilibrium constants/partition coefficients were presented for these drug components on poly‐dl‐lactide‐co‐glycolide (PLGA) at the same conditions. To understand the effect of operating variables on the total drug loading and to predict the drug‐loading breakthroughs, a flow over a flat plate model was developed that accounts for the polymer swelling, the partitioning of the drug component between the supercritical and polymer phases, and the polymer diffusivity. Experimental isotherm data with and without the polymer were incorporated into the model to isolate the system response from the polymer response to determine impregnation efficiencies.
Modeling and extractive properties of quaternary salt in a two‐phase system
Authors: Wu Ho‐Shing , Tseng Ming‐Shu 
Published: April 2004

AbstractThermodynamic equilibrium parameters of seven kinds of 1:1 electrolytes of quaternary salts in an organic and aqueous phase, including an extraction constant for ion‐pair and free‐ion, distribution constant, and dissociation constant in an organic solvent/aqueous solution, were determined by a numerical iteration method. Temperature, the kinds of solvents and quaternary salts, and the concentration of quaternary salts were evaluated to understand the thermodynamic properties. The free energies of extraction constant, distribution constant, dissociation constant, and the transfer of dissociated ions and ion pairs for quaternary ions were obtained as well. The amount of coextracted water and thermodynamic parameters were correlated with the solvent property. The equation of hydrophile–lipophile balance for selecting proper quaternary salt was also developed.
New efficient algorithm for solving thermodynamic chemistry
Authors: Carrayrou Jérôme , Mosé Robert , Behra Philippe 
Published: April 2004

AbstractModeling thermodynamic equilibrium of complex nonlinear chemical systems with the most used Newton‐Raphson method can lead to nonconvergence. From the mathematical properties of the set of equations, a chemically permitted interval is defined. By imposing this interval, the robustness of the Newton‐Raphson method is increased at a low computing time cost. The new method, the positive continuous fraction, does not depend on the first derivative of the objective function to find the solution. A new algorithm is thus built by the association of this very robust method with the fast Newton‐Raphson method and the definition of the chemically allowed interval. This combined algorithm is very impressive in terms of reliability, robustness, and speed.
Effect of polymer coatings from CO2, on water‐vapor transport in porous media
Authors: Hénon Florence E. , Carbonell Ruben G. , Desimone Joseph M. 
Published: April 2004

AbstractA variety of perfluorinated polyethers were coated onto surfaces of marble, sandstone and limestone samples from solutions in supercritical carbon dioxide. These polymers make ideal protectants for civil infrastructure by making stone surfaces hydrophobic and preventing penetration and deterioration of the stone by acid rain. The effective diffusivities of water vapor through coated and uncoated stones were measured as a function of polymer applied per unit area of sample. An analysis of the diffusive transport of water through the stones led to estimates of the penetration depths of the polymers and the percentages of blockage of the pores in the coated layers as a function of polymer surface coverage. Penetration depths were seen to strongly depend on the mean size and porosity of the stones. It is important for water‐vapor diffusion to occur through the samples to prevent water condensation inside polymer‐coated structural materials.
Unsaturated liquid percolation flow through nonwetted packed beds
Authors: Liu D. Y. , Wang G. X. , Litster J. D. 
Published: April 2004

AbstractThe unsaturated flow of liquid through packed beds of large particles was studied using six different liquids, all with contact angles greater than 90° on the bed packing (wax spheres of 9, 15 and 19.4 mm diameter). The liquidflow was discrete in nature, as drops for low flow rates and rivulets for high flow rates. For unsaturated liquid flows, the actual percolation velocity, not superficial velocity, should be used to characterize the flow. The percolation velocity did not vary with packed‐bed depth, but was a strong function of liquid flow rate, liquid and particle properties. Effects of liquid and particle properties (but not flow rate) are well captured by a simple correlation between the liquid‐particle fiction factor and Reynolds number based on actual percolation velocities. Liquid dispersion, characterized by the maximum dispersion angle, varies significantly with liquid and particle properties. The tentative correlation suggested here needs further validation for a wider range of conditions.
Inverse problems in population balances: Growth and nucleation from dynamic data
Authors: Mahoney Alan W. , Doyle Francis J. , Ramkrishna Doraiswami 
Published: April 2004

AbstractParticulate process modeling is critical for system design and control used widely in the chemical industly. Previous methods have focused on the assumption of appropriate models that can capture system behavior. A new technique presented is based on viewing the population balance from an inverse problem perspective that allows to determine appropriate models directly from experimental data. Under suitable assumptions (deterministic growth rate, no aggregation), the population balance equation may be solved by the method of characteristics, which associates the number density for any size at any time with a single point from the initial or boundary condition. The key to using this is the recognition that these characteristics correspond to the size history of individual particles and can be associated with constant cumulative number densities (quantiles) of the population. These quantiles are easily identifiable from experimental data. The variation of size and number density along these characteristics provides decoupled equations used to determine the growth rate. Validity of the determined growth law is checked by the collapse of the experimental data onto initial and boundary conditions.
Visualization of high‐dimensional phase diagrams of molecular and ionic mixtures
Authors: Wibowo Christianto , Ng Ka M. 
Published: April 2004

AbstractA general method for visualizing high‐dimensional phase diagrams of systems containing a mixture of molecular and ionic species is presented. Based on geometric modeling with homogeneous coordinates, canonical coordinates are developed to represent cuts and projections, which, being reaction‐invariant, do not depend on the degree of ionization. Examples are provided to illustrate the application of this method for identifying useful transforms with potential applications in separation system synthesis.
On the theory of optimal sensor placement
Authors: Chmielewski Donald J. , Palmer Tasha , Manousiouthakis Vasilios 
Published: April 2004

AbstractOn the Theory of Optimal Sensor PlacementAn optimal sensor placement is defined as a sensor configuration that achieves the minimum capital cost while observing prespecified performance criteria. Previous formulations of this problem have resulted in the definition of a mixed‐integer nonlinear program (MINLP) with dimensions dependent on the value of the integer decision variables. The main contribution of this work is an equivalent reformulation of the design problem such that the dimension of the NLP is independent of all decision variables. Additionally, the traditional sensor‐placement problem, based on static process conditions, is extended to linear dynamic processes. The final contribution is the exact conversion of the general NLP into a convex program through the use of linear matrix inequalities. The aggregation of these results show that the sensor‐placement problem can be solved globally and eficiently using standard interior‐point and branch‐and‐bound search algorithms.
Online estimation and control of polymer quality in a copolymerization reactor
Authors: Park Myung‐June , Hur Su‐Mi , Rhee Hyun‐Ku 
Published: April 2004

AbstractThe validity of an online state estimator for a semi‐batch MMA/MA solution copolymerization reactor was established using online densitometer and viscometer. Using the conventional extended Kalman filter (EKF) as the state estimator, the experiment was conducted under both isothermal and nonisothermal conditions for application to the control of copolymer properties. Further analysis was made by using ofline measurement data for the mol fraction of MMA in the remaining monomers and the solid content. The EKF was found to provide a good estimate for the state of the copolymerization system. A model predictive controller was designed and implemented to obtain copolymers with uniform copolymer composition and the desired weight average molecular weight by adopting the feed flow rate of MMA and the reaction temperature as control inputs. The controller was proven effective with a satisfactory performance for the control of polymer properties in the semi‐batch copolymerization reactor.
Analyzing enhancement of CO2, reforming of CH4, in Pd membrane reactors
Authors: Raybold Troy M. , Huff Marylin C. 
Published: April 2004

AbstractIt is demonstrated that H2, removal through Pd foil membranes can enhance the CO2, reforming of CH4. At 550°C and low flows over Pt/γ ‐Al2O3, pellets, conversions were twice that of a conventional reactor, while H2O formation was suppressed, resulting in H2/CO effluent ratios of 1.0. Larger sweep flows enhanced the reaction somewhat, and the replacement of Pt/γ ‐Al2O3, with Pt/ZrO2 mitigated catalyst deactivation in H2‐poor operating environments. A quantitative correlation was established between reaction enhancement and the overall H2 removal to production ratio. Based on this correlation, a simple membrane reactor equilibrium model was developed for comparison against experimental data. Subsequently, a unique and useful “on‐the‐fly” method of gauging membrane limitations, catalyst limitations, and modes of deactivation within a membrane reactor was demonstrated.
Modeling monomer transport by convection during olefin polymerization
Authors: Parasu Veera U. , Weickert G. , Agarwal U. S. 
Published: April 2004

AbstractDuring olefin polymerization on heterogeneous catalyst, a catalyst particle undergoes fragmentation, and the formed polymer gets deposited on the fragments. These polymer‐coated fragments (microparticles) together form a porous polymer particle (macroparticle). The multigrain model (MGM) gives a detailed description by accounting for the monomer diffusion phenomena at both levels. The original approach to solution involved a sequential shell‐by‐shell determination of monomer concentration profiles, with both radial boundaries of the shells moving with the particle growth. A fixed boundaly system of simultaneous differential equations enables easier computer implementation of the MGM model. Further, in a new development presented here, the interstitial spaces between the microparticles make up the pores through which monomer transport occurs not only by diffusion, but also by convection. The convection is driven by the pressure gradient created by the monomer consumption within the particle. Consistent with recent experimental observations, significantly higher monomer transport rates are thus predicted.
Miniature fuel cells fabricated on silicon substrates
Authors: Kelley S. C. , Deluga G. A. , Smyrl W. H. 
Published: April 2004

AbstractNovel miniature fuel cells were fabricated from micromachined silicon wafers. The cells used methanol and air as reactants, and a thin polymer electrolyte as separator. The assembled cells had a working volume of 12 mm3 and could be scaled down in size by three orders of magnitude by simple adjustments of the masking and etching procedures. Electrodeposition of Pt‐Ru as the anode catalyst (oxidation of methanol) was successful in lowering the loading to 0.25 mg/cm2 without loss of performance. Cell performance approached that of the best, state‐of‐the‐art, large fuel cells, when scaled for size. In particular, single miniature cells yielded 822 Wh/kg and 924 Wh/L when operated at 70°C. The same chip design was also used for the hydrogen/air system, and the cell current, power, and specific energy density were higher than those of methanol/air, Further tailoring of the chips for spefici fuels could lead to further improvements.
Thermodynamics of gas‐solid flow
Authors: Collado Francisco J. , Sevilla Eduardo , Valcárcel Carlos 
Published: April 2004

AbstractNew thermodynamic fundamentals for vertical pneumatic conueying are proposed with derivation based strictly on mass conservation and continuum concept. For a 1‐D, vertical, steady gas‐solid flow, these new mass and energy balances allowed the derivation of a new nondimensional energy factor containing the pressure drop. This energy factor correlated quite well with the difference between the inlet gas velocity and solids terminal velocity, when tested against high‐pressure, 15‐m‐high, vertical pneumatic transport data from Institute of Gas Technology. The energy factor was also checked against atmospheric‐pressure data of the 5‐m lift line of the Pennsylvania State Uniuersity. The new energy factor covers quite well both the atmospheric‐ and high‐pressure sets of data (923 tests) including two heights, lean‐ and dense‐phase transports, several pipe diameters, broad and narrow particle‐size distributions, and different materials. The dissipation terms in gas‐solid flow were also clearly identified.