bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling of the heat‐transfer process in a differential scanning calorimeter
Authors: Sen B. 
Published: June 2004

AbstractThe model developed predicts a priori potential errors associated with the energy trace recorded by an isoperibol differential power scanning calorimeter in the measurement of heat of adsorption of H2 on Pt and Pd catalysts. The uptake of H2 by the catalyst sample was approximated by a diffusion‐limited quasi‐steady‐state moving boundary model. This approximation is valid only if the parameter [(adsorption capacity of cat. sample)/(inlet conc. of H2)] is extremely large (∼ 24). The effect of flow rate, amount of H2 adsorbed, sink temperature, and the thermal conductivity of the adsorbate mixture was examined. Model predictions indicate that the error in the energy trace recorded by the DSC is appreciable: if a large difference exists between the thermal conductivity of the inert carrier, Ar (K = 0.017 J/m·K·s), and the adsorbate, H2 (k = 0.174 J/m·K·s); if the heat sink temperature is much lower (∼ 90 K) than the measurement temperature. However, these errors can be eliminated by matching the thermal conductivity of the inert carrier and adsorbate, such as He (k = 0.143 J/m·K·s) and H2 (k = 0.174 J/m·K·s). The results agree well with the experimental observations of Vannice et al. (1987) on high‐purity Pt and Pd powder and supported Pt catalysts, if the H2 uptake by the catalyst sample in the calorimeter is small (⩽2 μmol).
Recovery of short‐lived chemical species in a Couette flow reactor
Authors: Ouyang Q. , Swinney Harry L. , Roux J. C. , De Kepper P. , Boissonade J. 
Published: June 2004

AbstractA new technique for studying and recovering short‐lived chemical intermediate species has been developed using a Couette reactor, which is an open one‐dimensional reaction‐diffusion system. Reaction occurs in the annulus between concentric cylinders with the inner one rotating and the outer one at rest. Fresh reagents are in contact with the ends of the annulus, but there is no net axial flow. The axial transport arising from the hydrodynamic motion is effectively diffusive, but has a diffusion coefficient 3 to 5 orders of magnitude larger than that of molecular diffusion. The oxidant (ClO2−) and reductant (I−) of an autocatalytic reaction are fed at opposite ends of the reactor. The reactants diffuse toward each other and react, forming a steady, sharp chemical front and a stable spatial concentration band of unstable intermediate species (HOCl) in the front region. Unstable intermediate species are thus stabilized at a well‐defined spatial position where they can be recovered and studied. The experiments and numerical simulations demonstrate that the faster the reaction rate, the stabler the chemical front and the more effective the recovery of unstable intermediate species.
Kinetics and column dynamics for adsorption of bulk liquid mixtures
Authors: Sircar S. , Rao M. B. 
Published: June 2004

AbstractA framework is developed to describe kinetics and column dynamics of ad(de)sorption from bulk liquid mixtures using surface excess as the variable to quantify the extent of adsorption. It is found that the transient rate of change of surface excess with time from a multicomponent liquid mixture can be expressed in terms of a surface excess linear‐driving‐force model. A local‐equilibrium model can be developed to describe the column dynamics of ad(de)sorption from liquid mixtures. Both self‐sharpening and proportionate pattern mass‐transfer zones can be formed depending on the shape of the surface‐excess isotherm and the selectivity of adsorption. Analysis of column dynamics for liquid mixture adsorption can be carried out analogous to that for adsorption from gas mixtures, when a constant pattern mass‐transfer zone is formed. The length of the mass‐transfer zone and the composition‐time column effluent profile can also be derived analytically for such a case. Experimental kinetics and column dynamics data for ad(de)sorption of ethanol‐water mixtures on a large‐pore activated carbon are analyzed using these models.
A kinetic model of membrane formation by CVD of SiO2 and Al2O3
Authors: Tsapatsis Michael , Gavalas George R. 
Published: June 2004

AbstractSilica and alumina layers deposited onto the walls of porous Vycor tubes by chloride hydrolysis in an opposing reactants geometry have been characterized by scanning electron microscopy and electron microprobe analysis. The layers are asymmetric, having a long tail toward the side of the chloride flow and a sharp boundary at the other side. The deposit thickness is several tenths of microns, while the totally plugged region is of order of 1 micron.A model has been developed describing reaction, diffusion and evolution of the porous structure in the Vycor substrate due to the accumulation of the solid product. The deposition reaction is described by transient kinetics in terms if the concentrations of silanol and chloride groups in the product layer, as well as the concentrations of the gaseous reactants. The model is capable of generating deposit profiles in good agreement with those measured by electron microprobe analysis.
Modified MWR approach: Application to agglomerative precipitation
Authors: Bhatia S. K. , Chakraborty D. 
Published: June 2004

AbstractA modified method of weighted residuals approach is presented that combines expansions based on limiting forms of the true solution to solve the population balance equation accurately for continuous agglomerative precipitation. A modified moment method is used that employs fractional moments and is stable for the infinite domain problem. Solutions are obtained for various values of the agglomeration parameter, and the results are fitted to Pade approximations providing simple relationships that can be used for data fitting, thus obviating further need to solve the population balance equation with a constant aggregation kernel. This method is applied to experimental data on the precipitation of nickel ammonium sulfate and calcium carbonate to yield kinetic parameters.
Chromatography of liquid‐phase adsorption on octadecylsilyl‐silica gel
Authors: Miyabe Kanji , Suzuki Motoyuki 
Published: June 2004

AbstractIntraparticle diffusion and adsorption equilibrium on octadecylsilyl‐silica gel (ODS) were studied. As an adsorbate, p‐tert‐octylphenol (PTOP) was employed. The intraparticle diffusion coefficient was measured by the chromatographic technique and the moment analysis at zero and several surface coverages. Adsorption isotherms can be correlated by the Langmuir equation. The isosteric heat of adsorption and the activation energy of surface diffusion were constant regardless of the amount adsorbed. These results suggest that ODS has an energetically homogeneous surface. The effect of solvent on isosteric heat of adsorption in the liquid system was discussed qualitatively by the solvophobic theory. Surface diffusion coefficient of PTOP on ODS was of the order of 10−7 to 10−6 cm2/s. Surface diffusion was dominant for the intraparticle diffusion in ODS, and its coefficient increased with an increase in the amount adsorbed. Positive concentration dependence of the surface diffusion coefficient was interpreted in terms of diffusion by potential chemical driving force.
Direct catalytic hydrodechlorination of toxic organics in wastewater
Authors: Kovenklioglu Suphan , Cao Zhihua , Shah Dinesh , Farrauto Robert J. , Balko Edward N. 
Published: June 2004

AbstractThe in‐situ catalytic hydrodechlorination of chlorinated hydrocarbons in waste‐water‐generating HCl and a hydrocarbon‐free chlorine is demonstrated as a viable wastewater remediation technique. Catalyst screening studies with a shaker‐type hydrogenation reactor have shown that the commercial Pd/C catalyst is highly effective in hydrochlorinating various chlorinated hydrocarbons in synthetic wastewater at room temperature and near atmospheric pressure. 1, 1, 2‐trichloroethane hydrodechlorination experiments in an autoclave reactor shows that initial rates are well correlated with first‐order dependence of the reactant hydrocarbon adsorbed on carbon. Initial rates are also independent of hydrogen pressure, and adsorption on the carbon support is Langmuir type. Activation energies calculated at different catalyst loadings varied from 29 to 38 MJ/mol.1,1,2‐trichloroethane hydrodechlorination activity is much lower for Pd/Al2O3 than Pd/C because the reactant hydrocarbon does not adsorb on alumina. When the carbon support does not readily adsorb the reactant hydrocarbon, the hydrodechlorination rates dropped significantly. These results confirm the role of the carbon support in providing the major path to reaction and thereby significantly increasing reaction rates compared to direct adsorption from solution onto the palladium.
Gas‐phase backmixing in bubble‐column reactors
Authors: Shetty S. A. , Kantak M. V. , Kelkar B. G. 
Published: June 2004

AbstractGas‐phase backmixing and holdup for the air‐water system were measured in 0.15‐ and 0.25‐m‐dia. bubble columns. Novel experimental and analytical techniques were used to analyze the gas‐phase residence time distribution. A Levenberg‐Marquardt‐type optimization scheme was used to obtain the two reactor model parameters: Peclet and Stanton numbers. Operating variables included the column diameter and the superficial gas‐ and liquid‐phase velocities.A two‐bubble‐class hydrodynamic model has been proposed to predict the gas‐phase backmixing in bubble column reactors. The model assumes a bimodal distribution of the gas phase with large bubbles flowing in a plug‐flow manner and the small bubbles partially backmixed. The model only needs easily measurable parameters and has been validated by comparing experimental as well as literature data on gas‐phase backmixing with the model predictions. The model is more realistic than the conventional single‐bubble‐class model and provides a rational approach to predict the gas‐phase backmixing in scaling‐up bubble‐column reactors.
Structure H clathrate hydrate equilibria of methane and adamantane
Authors: Lederhos J. P. , Mehta A. P. , Nyberg G. B. , Warn K. J. , Sloan E. D. 
Published: June 2004

AbstractThe first phase equilibrium data are presented for Structure H hydrates. The data represent the initial formation of these hydrates from methane, with adamantane— a previously determined Structure H former. Temperature and pressure conditions are consistent with hydrocarbon production/transportation/processing facilities. Structure H hydrates are shown to contain molecules indigenous to petroleum. which may not be present in natural gas.
Parallel computational microhydrodynamics: Communication scheduling strategies
Authors: Fuentes Yuris O. , Kim Sangtae 
Published: June 2004

AbstractThe behavior of multiparticle systems in a viscous fluid, as governed by the Stokes equations, is computed by the coordinated use of multiple processors on a distributed memory parallel computer. The completed double‐layer boundary integral equation method (CDL‐BIEM) is used to convert the hydrodynamic mobility problems to a fixed‐point problem, amenable to either synchronous or asynchronous iterative solution schemes. Parallel computational strategies, based on assigning particles to processors, are considered, and rules are derived to specify how often processors should exchange information. A spectral communication scheduling strategy, based on the spectral radius in pair‐interaction problems, converges with fewer global iterations and effectively reduces the level of interprocessor communications, suggesting algorithm scalability to massively‐parallel computers with hierarchical access to distributed memories. Stochastic schedules, which specify the probability that the information exchange occurs at every iteration, were also considered. For the same test problems, these strategies performed better than the point Jacobi iterations, but not as well as their deterministic counterparts. Scheduling strategies are extrapolated to larger problems, based on projections of memory and performance capabilities of the next generation of high‐performance parallel supercomputers.
Measurement of individual cell migration parameters for human tissue cells
Authors: DiMilla Paul A. , Quinn John A. , Albelda Steven M. , Lauffenburger Douglas A. 
Published: June 2004

AbstractWe present an approach for determining in vitro the means and distributions of a set of phenomenological parameters, including cell speed and persistence time, which can be used to evaluate the effect of isotropic variations in the extracellular environment on the motility of human tissue cells. Using time‐lapse videomicroscopy and semi‐automated image analysis, we tracked the paths traveled by slow‐moving, isolated human vascular smooth muscle cells over 48 hours on surfaces of petri dishes coated with 10 μg/mL of the adhesive extracellular matrix proteins type IV collagen, fibronectin or laminin. By applying a persistent random walk model to experimental data for mean‐squared displacement as a function of time for these cells, we rigorously distinguished individual cells with different motile characteristics not obvious based on qualitative comparisons between the structures of individual cell paths. We also positively identified the presence of immotile cells. Based on the behavior of 34 to 77 cells on each substrate, we found mean cell speeds and persistence times on the order of 10 micron/h and 3 hours, respectively, on all three ECM substrates, while the fraction of motile cells varied from 65% on laminin to 78% on collagen. On all three surfaces experimental number distributions of speed and persistence time could be described by normal and exponential waiting time distributions, respectively. Our approach provides a framework for addressing questions concerning the mechanistic relationship between cellular and environmental properties and cell motility.
Investigation of the chemistry of a diazo micromixing test reaction
Authors: Wenger Kevin S. , Dunlop Eric H. , MacGilp Iain D. 
Published: June 2004

AbstractThe azo coupling of 1‐naphthol with diazotized sulfanilic acid has been studied in detail focusing on the practical use of this reaction as a micromixing test reaction, as developed by Bourne and coworkers. The reaction is a fast, competitive, consecutive reaction whose final product distribution is affected greatly by mixing. Problems that occur in the isolation of the pure‐dye products and quantification of the product distribution are addressed. Previously unreported information is given about the structure and properties of one of the products as well as the existence of an additional unknown product. The reaction was used to characterize the spatial heterogeneity of micromixing in a 14‐L stirred‐tank fermenter. Results show large differences in the product distribution dependent on the depth and radial position of the feed pipe in the tank.
Modeling of bubble‐size distribution in free rise polyurethane foams
Authors: Niyogi Debdarsan , Kumar R. , Gandhi K. S. 
Published: June 2004

AbstractThe existing models of the foaming process in reaction injection molding are inadequate for predicting the bubble‐size distribution, which influences many properties of interest. This work attempts to develop a model for the bubble‐size distribution under conditions of free rise.The population balance equation for bubbles, coupled with the system of energy balance and reaction kinetics equations through the blowing agent evaporation rate expression, is solved to obtain the bubble‐size distribution. A simple mass‐transfer coefficient approach for expressing growth rate of bubbles is used, although various growth laws can be accommodated without affecting the solution procedure. Determining factors for the bubble size and its distribution are the foaming period and the growth law. With increase in initial blowing agent concentration, the foaming period increases and bigger bubbles are obtained. The bubble‐size distribution becomes broader as the foaming period increases.
Synthesis of reverse‐osmosis networks for waste reduction
Authors: El‐Halwagi Mahmoud M. 
Published: June 2004

AbstractThe purpose of this work is to introduce the novel notion of synthesizing reverseosmosis networks (RONs) for waste‐reduction applications. The RON design task aims at synthesizing a network of reverse‐osmosis units, booster pumps and energy recovery devices that can separate a set of waste streams into lean (product) streams and rich (retenate) streams at minimum total annualized cost. A systematic and generally applicable procedure for tackling RON synthesis problems is developed. First, a structural representation is devised to embed all potential network configurations. Then, the problem is formulated as an optimization program whose objective is to minimize the total annualized cost of the network while satisfying all environmental and technical requirements. The solution to this program provides the optimal arrangement, types and sizes of the reverse‐osmosis units, the booster pumps, and the energy‐recovery turbines to be employed in the network. Furthermore, the solution also provides the optimum stream distribution, operating conditions, and separation levels. The applicability of the proposed synthesis technique is demonstrated by tackling case studies and comparing the optimal solutions with current industrial practices.
Coalescence of charged droplets in agitated liquid‐liquid dispersions
Authors: Tobin T. , Ramkrishna D. 
Published: June 2004

AbstractExperimental studies have been performed to assess the effect of drop charge on turbulent drop coalescence. Although it is well known that surface charge can affect coalescence rates of Brownian particles in a quiescent medium, no studies have been found in the literature which explicitly examine charge effects on larger drops in turbulent media.Results demonstate that drop charge can substantially inhibit coalescence between drops in agitated dispersions. Moreover, this effect can arise solely from latent drop charges, which are attributed to the preferential adsorption of hydroxide ions onto the water‐organic phase interface. Ionic strength and pH thus are shown to play a major role in determining coalescence rates between agitated drops.Results also demonstrate that reliance on measurement of average drop sizes for the purpose of determining coalescence rate dependencies is a precarious practice. Strong size‐dependent effects such as obtained here have the potential to suggest erroneous conclusions when conclusions are based on measurements of average drop sizes rather than of drop‐size distributions.
Theory of hydrogen bonding in supercritical fluids
Authors: Gupta Ram B. , Panayiotou Constantinos G. , Sanchez Isaac C. , Johnston Keith P. 
Published: June 2004

AbstractThe degree of hydrogen bonding and macroscopic thermodynamic properties for pure and mixed fluids are predicted with the hydrogen bonding lattice fluid (LFHB) equation of state over a wide range in density encompassing the gas, liquid and supercritical states. The model is successful for molecules forming complex self‐associated networks, in this case pure methanol, ethanol, and water, and the mixture 1‐hexanol‐SF6. In supercritical water, significant hydrogen bonding is still present despite all the thermal energy and is highly pressure‐ and temperature‐dependent. A fundamental description of pressure and temperature effects on hydrogen bonding is presented for a well‐defined case, the formation of a complex between a donor and acceptor in an inert solvent, where no self‐association is present. The partial molar enthalpy and volume change on complexation both become pronounced near the critical point, where the density is highly variable with temperature and pressure.
A coupled knowledge based system using fuzzy optimization for advisory control
Authors: Petti Thomas F. , Dhurjati Prasad S. 
Published: June 2004

AbstractA knowledge based system is described that is designed to generate on‐line advice for operators regarding the proper distribution of hydrogen resources in a refinery. The system uses a coupled architecture incorporating numerical computing in a knowledge based system environment. This arrangement allows for powerful and flexible problem solving. One portion of the coupled system formulates an optimization problem that is subsequently solved by an external routine. This application is particularly concerned with uncertainty that is present in some of the constraints. To deal with this uncertainty, a fuzzy approach to the optimization is taken. A method is presented that solves the fuzzy optimization problem using standard mathematical programming techniques. The results of the fuzzy optimization allow the crisp solution to be expanded into a neighborhood of solutions that is considered acceptable. Although this work examines a specific problem, the concepts presented are general.
Fire and explosion hazards induced by repressurization of air driers
Authors: Schoofs Gregory R. 
Published: June 2004

AbstractAdsorbers used to dry or purify air typically contain 4A or 13X molecular sieves which are intermittently reactivated by thermal regeneration. This article shows that nitrogen adsorbs preferentially relative to oxygen in freshly reactivated 4A, 5A and 13X molecular sieves during the repressurization step. This produces an oxygen‐enriched, high‐pressure gas within the adsorber vessel which emerges immediately after the air‐drier is brought on‐line. The enriched oxygen concentration widens the flammability range of hydrocarbons, markedly diminishes the minimum autoignition temperature of hydrocarbons, and produces both a higher explosion pressure and a higher rate of explosion pressure rise relative to air at standard temperature and pressure. Thus, the oxygen‐enriched, high‐pressure gas can lead to fires, explosions, and other deleterious effects in and downstream of thermally regenerated air driers which contain large pore molecular sieves. Substituting 3A molecular sieve provides a simple, safe and inexpensive way to prevent transient oxygen enrichment and the problems associated with it. Because activated aluminas and silica gels can also enhance fire and explosion hazards, type 3A molecular sieve becomes the adsorbent of choice for air drying applications.
Accelerated disturbance damping of an unknown distributed system by nonlinear feedback
Authors: Chen Chien‐Chong , Chang Hsueh‐Chia 
Published: June 2004

AbstractWe propose a new control design methodology for distributed systems with unknown nonlinear dynamics. The approach is appropriate for systems whose linearized differential operator possesses an eigenspectrum that can be partitioned into a low‐dimensional slow spectrum and an infinite‐dimensional fast complement. This separation of time scales allows us to utilize center manifold and normal form techniques of modern geometric theories for dynamical systems. It is shown that the convergence to an asymptotically stable equilibrium point after a small‐amplitude transient disturbance quickly (exponentially fast) approaches an invariant manifold W which is locally tangent to the eigenspace of the slow modes and is hence of the same dimension. The nonlinear dynamics on this invariant manifold is much slower than the fast approach and is dominated by the slow modes with the fast modes coupled “adiabatically” to them. The convergence can hence be best accelerated using a slow control with smooth nonlinear feedback involving only the slow modes. Nonlinear feedback is shown to drastically improve the performance of linear feedback. The only required information about the system in our approach is the slow adjoint eigenfunctions which can be easily estimated with a Karhunen‐Loeve scheme for distributed systems. This identification scheme is quite robust to changes in process dynamics and can hence be carried out on‐line in parallel with feedback control. The overall approach is verified by numerical experiments.