bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhanced conductivity of fuel cell plates through controlled fiber orientation
Authors: Blunk Richard H. J. , Lisi Daniel J. , Yoo Yeong‐Eun , Tucker Charles L. 
Published: April 2004

AbstractManufacturers of polymeric composite bipolar plates have been relying on high loadings (60 to 90 v/o) of discrete and conductive graphite/carbon filler particles to meet fuel‐cell plate conductivity targets. Unfortunately, at these loadings, the plate materials are inherently brittle and result in high scrap rates and the inability to mold thin plates (less than 1 mm) required for high stack volumetric power densities. Low loadings of high‐aspect‐ratio conductive fillers, a fiber/flake alignment process, and a conductive‐tie layer (CTL) were used to simultaneously increase the plate conductivity and toughness. The alignment process reduces the bulk resistance in the current‐flow direction, and the CTL reduces the contact resistance at the plate‐to‐diffusion medium interface. Although a significant reduction in plate resistance is realized, high filler loadings are still required to meet conductivity targets.
Effect of pore‐network connectivity on multicomponent adsorption of large molecules
Authors: Ismadji S. , Bhatia S. K. 
Published: April 2004

AbstractThe effect of pore‐network connectivity on binary liquid‐phase adsorption equilibria using the ideal adsorbed solution theory (IAST) was studied. The liquid‐phase binary adsorption experiments used ethyl propionate, ethyl butyrate, and ethyl isovalerate as the adsorbates and commercial activated carbons Filtrasorb‐400 and Norit ROW 0.8 as adsorbents. As the single‐component isotherm, a modified Dubinin–Radushkevich equation was used. A comparison with experimental data shows that incorporating the connectivity of the pore network and considering percolation processes associated with different molecular sizes of the adsorptives in the mixture, as well as their different corresponding accessibility, can improve the prediction of binary adsorption equilibria using the IAST. Selectivity of adsorption for the larger molecule in binary systems increases with an increase in the pore‐network coordination number, as well with an increase in the mean pore width and in the spread of the pore‐size distribution.
Simulation‐optimization framework for stochastic optimization of R&D pipeline management
Authors: Subramanian Dharmashankar , Pekny Joseph F. , Reklaitis Gintaras V. , Blau Gary E. 
Published: April 2004

AbstractThe simulation‐based optimization framework (Sim‐Opt) uses a twin‐loop computational architecture, which combines mathematical programming and discrete event simulation, to address this problem. This article extends our earlier work to present methods for integrating information from the inner loop (Sim‐Opt time lines, reactive adjustment) and using it in the outer risk‐control loop (Stochastic Optimization loop) to obtain statistically significant improvements in the solutions to the underlying stochastic optimization problem. Two classes of information can be obtained from the inner loop time lines: the first pertaining to portfolio selection and the second resource crowding associated with the chosen operation policy. Methods presented quantify the information on these two classes, and a three‐step heuristic incorporates this information in the outer risk‐control loop to drive the system toward improving solutions with respect to the mean net present value (NPV) of the portfolio and the probability of delivering a positive NPV. This method was used on a pharmaceutical product development case study, consisting of 11 projects, 154 activities, 14 resource types and a 20‐year planning horizon with respect to patent expiration. Basic algorithm engineering efforts are also described to significantly improve the performance of formulation generation, the generation of a heuristic lower bound and the identification of cut families to effectively apply branch‐and‐cut methods.
Kinetics of the reaction of CO2 with aqueous potassium salt of taurine and glycine
Authors: Kumar P. S. , Hogendoorn J. A. , Versteeg G. F. , Feron P. H. M. 
Published: April 2004

AbstractThe kinetics of the reaction between CO2 and aqueous potassium salts of taurine and glycine was measured at 295 K in a stirred‐cell reactor with a flat gas–liquid interface. For aqueous potassium taurate solutions, the temperature effect on the reaction kinetics was measured at 285 and 305 K. Unlike aqueous primary alkanolamines, the partial reaction order in amino acid salt changes from one at low salt concentration to approximately 1.5 at salt concentrations as high as 3,000 mol·m−3. At low salt concentrations, the measured apparent rate constant (kapp) for potassium glycinate is comparable to the values in literature. In the absence of reliable information in the literature on the kinetics and mechanism of the reaction, the applicability of the zwitterion and termolecular mechanism (proposed originally for alkanolamines) was explored. For the zwitterion mechanism, the forward second‐order reaction rate constant (k2) of the CO2 reaction with amino acid salt seems to be much higher than for alkanolamines of similar basicity, indicating that the Bronsted plot for amino acid salts might differ from that of alkanolamines. The contribution of water to the deprotonation of zwitterion seems to be more significant than reported values for aqueous secondary alkanolamines.
Experimental tests of two‐phase fluid model of drying consolidation
Authors: Brown L. A. , Zukoski C. F. 
Published: April 2004

AbstractDrying of aggregated slurries proceeds through a stage of consolidation prior to bed desaturation. During this period, volume fraction profiles develop within the bed. The magnitude of volume fraction variation is controlled by the rate of mass transfer and the strength of the bed. A two‐phase fluid model for stress balances in conjunction with the compressive yield stress constitutive equation is explored to describe the temporal evolution of bed volume fraction profiles. For this purpose, the compressive rheology of the saturated bed is characterized through independent experiments that fix all adjustable parameters. Excellent agreement is found between model predictions and experimental results.
Synthesis of multicomponent distillation column configurations
Authors: Agrawal Rakesh 
Published: April 2004

AbstractA systematic procedure presented here draws distillation column configurations to separate an ideal to near ideal n–component mixture into n product streams with each enriched in one of the components. The method synthesizes all feasible basic configurations using n–1 distillation columns with each column having only a condenser at the top and a reboiler at the bottom. It also generates all feasible thermally coupled schemes with classical two‐way liquid and vapor communication between the distillation columns. The method is simple and easy to use. The advantage of such a method is that it could be incorporated in a search algorithm to systematically find an optimum distillation scheme for a given application.
Unsteady‐state residence‐time distribution in perfectly mixed vessels
Authors: Rawatlal Randhir , Starzak Maciej 
Published: April 2004

AbstractWhile addressing some difficulties in the modeling of unsteady‐state residence‐time distribution (RTD), the care of perfectly mixed systems was considered. By an extension of the boundary condition domain, the traditional unfeasible concept of fresh and original populations was discarded to achieve a solution valid for all the fluid elements in a single vessel. This result enabled the development of the unsteady‐state RTD for N vessels in series in the form of a joint probability density function. The relationship between the joint RTD and the combined RTD was also established. Numerical simulations were performed under various time varying flow patterns. The proposed solution can be applied to RTD‐based models of chemical reactors operating under unsteady‐state conditions. Potential applications in polymer reaction engineering are briefly outlined.
Oxidative destruction of dichloromethane over protonic zeolites
Authors: López‐Fonseca R. , Cibrián S. , Gutiérrez‐Ortiz J. I. , Gutiérrez‐Ortiz M. A. , González‐Velasco J. R. 
Published: April 2004

AbstractVarious protonic zeolites (H‐Y, H‐ZSM‐5, and H‐MOR) were tested for the total combustion of dichloromethane (DCM) as a model reaction for the catalytic destruction of chlorinated organic pollutants. The order of catalytic activity decreased in the following order: H‐MOR > H‐ZSM‐5 > H‐Y. Strong Brønsted acidity played a determining role in controlling the active catalytic behavior as revealed by TPD of ammonia and IR measurements of adsorbed pyridine. DCM oxidative decomposition gave rise to CO and HCl as main products along with small amounts of CO2and Cl2. In addition, methyl chloride was detected as a reaction intermediate between 250 and 500°C. The presence of water in the feed stream led to an inhibition of the zeolite activity and resulted in a noticeable change in the reaction product distribution. Water effectively promoted the selectivity toward environmentally desirable reaction products, that is, HCl and CO2, and completely suppressed the formation of methyl chloride.
Solidification in heat packs: II. Role of cavitation
Authors: Rogerson Mansel A. , Cardoso Silvana S. S. 
Published: April 2004

AbstractWhen the metallic trigger in a commercial heat pack is flexed to initiate solidification, the acceleration of the liquid near the solid surface can cause cavitation and collapse of small vapor bubbles. It is investigated whether such cavitation is responsible for the operation of the metallic trigger in the subcooled sodium acetate solution in a heat pack. Using cavity collapse theory and the results in Part I for the nucleation pressure of a sodium acetate solution, it is shown that cavitation can generate pressures greater than the nucleation pressure of the solution. However, the period of time during which the solution is exposed to such high pressure is not sufficient to lead to nucleation, and hence the metallic trigger does not induce solidification as a result of cavitation. Experimental results, using sonication, tribonucleation, and shock waves, confirm the theoretical findings.
Vaporization ratio in differential ebulliometers for measuring limiting activity coefficients
Authors: Raal J. David , Ramjugernath D. 
Published: April 2004

AbstractAccurate limiting activity coefficients can be obtained from differential ebulliometry if vapor and liquid holdups in various parts of the equipment are correctly accounted for in calculating the equilibrium liquid composition from the known charge composition. Available procedures require the difficult‐to‐determine dynamic vaporization rates (V/F) or (V/L). Two new procedures proposed determine V/F ( = ϕ): 1. a trial‐and‐error procedure satisfying all three of the equations governing the ebulliometer operation yielding the true liquid equilibrium composition x1, ϕ, and the overall composition in the Cottrell pump, Z1; 2. one procedure based on the measured superheat temperature at the base of the Cottrell pump. A possibly limiting assumption is that local equilibrium exists at this point, but the method has good rigour otherwise. It is, however, very sensitive to measured pressures and temperatures, which need to be of the highest accuracy. The procedure is illustrated for the n‐hexane (1)–ethanol (2) and n‐hexane (1)–ethyl‐acetate (2) systems, and requires liquid density, heat capacity and accurate latent heats over a small temperature interval. Measurements suggest that about 72% of the total vaporization takes place at or before the entrance to the Cottrell pump with only about 28% in the equilibrium chamber for the n‐hexane–ethyl acetate system. For the n‐hexane–ethyl alcohol systems, they are 89% and 11%. The iterative procedure is recommended because it is more reliable and, although computationally extensive, has more rigor.
Gas–liquid two‐phase flow through packed beds in microgravity
Authors: Motil Brian J. , Balakotaiah Vemuri , Kamotani Yasuhiro 
Published: April 2004

AbstractExperimental data on flow pattern transitions, pressure drop, and flow characteristics for cocurrent gas–liquid flow through packed columns in microgravity is analyzed. The pulse flow regime exists over a wider range of gas and liquid flow rates under microgravity conditions. Furthermore, maps used to predict transition boundaries in normal gravity do not apply in microgravity. The flow regime data are compared to the widely used Talmor map and a new transition criterion between bubble and pulse flow in microgravity is proposed. The pressure‐drop data clearly show that interfacial effects can increase the pressure drop by as much as 300% compared to those predicted by the single‐phase Ergun equation. A two‐phase friction factor is correlated to the superficial gas and liquid Reynolds numbers and the Suratman number. New data are also presented on the influence of gravity on the pulse amplitude and frequency.
Promotion of deactivated sintering by dry‐particle coating
Authors: Mohan Michelle Ramlakhan , Dave Rajesh N. , Pfeffer Robert 
Published: April 2004

AbstractDry‐particle coating was used to examine the feasibility of increasing the sintering temperatures of different particulate materials (hosts) by applying a discrete coating of a highly refractory material (guest). Increasing the sintering temperature reduces the sintering rate of the material, and hence the phenomenon is called “deactivated sintering.” Several host particles, such as glass beads, PMMA, γ‐alumina, and an alumina–silica composite, were coated with submicron‐size silicon carbide in three different dry‐particle coating devices: magnetically assisted impaction coating, mechanofusion, and hybridizer. The coated products were characterized using several techniques, including particle‐size analysis, SEM, EDX, BET, optical microscopy, and dilatometry studies to compare the coating performance of each device. By coating the host particles with silicon carbide, it was possible to appreciably increase the sintering temperatures of all four of the particulate host materials. Simple phenomenological sintering models based on volume diffusion for crystalline materials and viscous flow for amorphous materials were combined with dilatometry data to explain the phenomenon of deactivated sintering. For γ‐alumina, there was a significant reduction in the effective diffusivity due to the addition of a surface coating of SiC, whereas for SiC‐coated glass beads and PMMA, an increase in the effective viscosity was postulated as the cause of deactivated sintering.
Optimal region for design and control of ternary systems
Authors: Cheng Yu‐Chang , Yu Cheng‐Ching 
Published: April 2004

AbstractThe trade‐off between steady‐state economics and dynamic controllability of recycle plants is analyzed for ternary systems. For this analysis, a boundary is first established in the composition space to identify the correct flow sheet, and then optimal trajectories for recycle plants with direct and indirect sequences are derived as the conversion varies. In the optimality regions, at any conversion, the correct separation sequence, as well as optimal reactant distribution, can also be obtained. For dynamic controllability, the reachable composition space is identified as the recycle ratios vary. The results clearly indicate that trade‐off between steady‐state design and dynamic control is not likely to occur, if the plant is designed along the optimal trajectories with the correct flow sheet. Rigorous nonlinear simulations also reveal that no single control structure works well over the entire composition space.
2‐D wavelet‐based adaptive‐grid method for the resolution of PDEs
Authors: Santos J. C. , Cruz P. , Magalhães F. D. , Mendes A. 
Published: April 2004

AbstractAn efficient interpolating wavelet‐based adaptive‐grid numerical method is described for solving systems of bidimensional partial differential equations. The grid is dynamically adapted in both dimensions during the integration procedure so that only the relevant information is stored, saving allocation memory. The spatial derivatives are directly calculated in a nonuniform grid using cubic splines. Numerical results for five typical problems presented illustrate the efficiency and robustness of the method. The adaptive strategy significantly reduces the computational times and the memory requirements, as compared to the fixed‐grid approach.
Three‐liquid phase equilibria in water+benzene+caprolactam+(NH4)2SO4 mixtures
Authors: Huan Zhou , Van Bochove Gerard H. , De Loos Theo W. 
Published: April 2004

AbstractLiquid–liquid–liquid equilibrium (LLLE) data are reported for the water+benzene+caprolactam+ammonium sulfate system at 293.1 K, 313.1 K, and 328.1 K. The experiments show a distinct pattern of phase behavior with increasing salt concentration and temperature. The tricritical point of the system was not determined, but was estimated to be around 332 K. The results are modeled using a modification of the extended electrolyte NRTL model. The model was able to represent the LLLE data satisfactorily.
Maximum carrying capacity and granular temperature of A, B and C particles
Authors: Gidaspow Dimitri , Mostofi Reza 
Published: April 2004

AbstractThe observed cyclic operation of a riser near choking was calculated using a computational fluid‐dynamic model used previously to predict its flow regimes. An approximate analytical expression for the maximum carrying capacity of Geldart A, B and C particles was developed and compared to data in the literature. In the new theory, an unknown parameter is the pseudosonic velocity of the particles. To estimate this quantity, new granular temperatures were measured and compared to data from the literature for Geldart A, B and C particles. In the riser flow regime (2% to 20% solid volume fraction), the turbulent intensity of the particles is approximately 0.5, in agreement with the theory. The theoretical value involves the ratio of particle viscosity to the granular conductivity.
Kinetics of particle formation in the gas antisolvent precipitation process
Authors: Elvassore Nicola , Parton Tiziana , Bertucco Alberto , Di Noto Vito 
Published: April 2004

AbstractAn original experimental setup based on UV‐vis spectroscopy was developed to study the precipitation kinetics of a biodegradable polymer by gas antisolvent processes (GAS). Poly(L‐lactide) acid (PLA) precipitations were carried out in a high‐pressure optical cell equipped with sapphire windows, working at 1–80 bar and 301.15–307.15 K. The particle formation and precipitation kinetics were investigated in situ by measuring UV‐vis absorbance of polymeric particles at a wavelength of 600 nm. They were measured in a batch system at different pressurization rates (different supersaturation conditions). To rationalize the precipitation kinetics in GAS processes, a population balance model was developed considering particle nucleation, growth, aggregation, and settling. Nucleation and growth were represented by the McCabe model, whereas both independent‐ and nonindependent‐kernel Smoluchowski's coagulation equations were used for aggregation. Settling was approximated by a first‐order kinetic. Absorbance measurements were related to the second moment of the simulated particle‐size distribution, and the kinetic parameters were estimated based on spectroscopic data. The model gave a correct phenomenological representation of all experimental data and fairly predicted the particle‐size distribution of the precipitated PLA microparticles.
Comparing true countercurrent and simulated moving‐bed chromatographic reactors
Authors: Lode Florian , Mazzotti Marco , Morbidelli Massimo 
Published: April 2004

AbstractSimulated Moving Bed reactors (SMBR) combine chemical reaction and adsorptive separation within one single continuous and countercurrent unit. This integration promises substantial improvements in process performance, especially when applied to equilibrium‐limited reactions involving such heat‐sensitive products as fine chemicals and pharmaceuticals. In this work, the interplay among the relevant process design parameters (dimensionless ratios of the fluid and solid flow rates, and the Damköhler numbers for each section of the unit) is investigated. For this, an analytical solution of differential mass‐balance equations for the corresponding true countercurrent process (TCC), using as a model system the reaction A⇌B+C with each species exhibiting linear adsorption behavior, was developed. Based on this solution, criteria were derived for the optimum process design with respect to productivity and solvent consumption. Comparing these results with numerical simulations of an SMBR unit shows that the TCC model does not apply to SMBR units with a finite number of columns per section, that is, units of practical relevance, because the two units exhibit different residence time distributions and, hence, lead to different degrees of conversion.
Core–shell structure and segregation effects in composite droplet polymer blends
Authors: Reignier Joël , Favis Basil D. 
Published: April 2004

AbstractCore–shell morphology formation within the dispersed phase was studied for composite droplet polymer‐blend systems comprising a high‐density polyethylene matrix, polystyrene shell and different molecular weights of poly(methyl methacrylate) core material. The blends were prepared in the melt using an internal mixer, and the morphology was analyzed by electron microscopy. Changing the viscoelastic properties of the core in the dispersed phase dramatically affects PS‐PMMA segregation within the dispersed composite droplet itself. A high‐molecular‐weight‐PMMA core contains a large quantity of occluded PS inclusions, while the low‐molecular‐weight PMMA results in a perfectly segregated PS shell and PMMA core. These phenomena were attributed to the viscosity of the PMMA. Using the latter system, a direct microscopic study of the shell formation process demonstrates unambiguously that under conditions of perfect segregation, the onset of complete shell formation corresponds to a shell thickness that is close to two times the radius of gyration of polystyrene. Thus, the thinnest possible shell in such a system possesses a molecular‐scale thickness. The system with the high‐molecular‐weight‐PMMA core demonstrates an onset of complete shell formation that is displaced to higher concentrations due to the poor segregation effect. By counterbalancing the effects of viscosity ratio and interfacial effects on the composite droplet size, it is possible to generate perfectly segregated core–shell dispersed‐phase morphologies of almost identical size with a controlled shell thickness ranging from 40 to 300 nm.