bluuebunny/crossref_metadata_2025_split huggingface dataset:
Engineering design methods for cavitation reactors II: Hydrodynamic cavitation
Authors: Gogate Parag R. , Pandit Aniruddha B. 
Published: April 2004

AbstractThe bubble behavior and hence the pressure generated at the collapse of the cavity for hydrodynamic cavitation depends on the operating conditions and geometry of the mechanical constriction generating cavitation. The effect of operating parameters such as inlet pressure through the system's orifice, initial cavity size, and the indirect effect of the hole diameter (it affects the frequency of turbulence in the vicinity of the orifice) on the bubble behavior was numerically studied. The bubble dynamics were simulated in two stages considering: Rayleigh‐Plesset equation up to the point of bubble wall velocity = 1,500 m/s; then the compressibility of the medium using the equation of Tomita and Shima. An empirical correlation was developed to predict the collapse pressure generated as a function of just mentioned parameters. The trends in the magnitudes of collapse pressure match the observed experimental trends for cavitation‐induced reactions. The work is an extension of the earlier analysis done for the sonochemical reactors. Some recommendations are also suggested for the design of hydrodynamic cavitation reactors based on the simulations.
Global optimization of mixed‐integer nonlinear problems
Authors: Adjiman C. S. , Androulakis I. P. , Floudas C. A. 
Published: April 2004

AbstractTwo novel deterministic global optimization algorithms for nonconvex mixed‐integer problems (MINLPs) are proposed, using the advances of the αBB algorithm for nonconvex NLPs of Adjiman et al. The special structure mixed‐integer αBB algorithm (SMIN‐αBB) addresses problems with nonconvexities in the continuous variables and linear and mixed‐bilinear participation of the binary variables. The general structure mixed‐integer αBB algorithm (GMIN‐αBB) is applicable to a very general class of problems for which the continuous relaxation is twice continuously differentiable. Both algorithms are developed using the concepts of branch‐and‐bound, but they differ in their approach to each of the required steps. The SMIN‐αBB algorithm is based on the convex underestimation of the continuous functions, while the GMIN‐αBB algorithm is centered around the convex relaxation of the entire problem. Both algorithms rely on optimization or interval‐based variable‐bound updates to enhance efficiency. A series of medium‐size engineering applications demonstrates the performance of the algorithms. Finally, a comparison of the two algorithms on the same problems highlights the value of algorithms that can handle binary or integer variables without reformulation.
Generation of microparticles using CO2 and CO2‐philic antisolvents
Authors: Sarkari Marazban , Darrat Inaas , Knutson Barbara L. 
Published: April 2004

AbstractPrecipitation using a compressed antisolvent (PCA) is a demonstrated technology for generation of monodisperse ultrafine particles. Microparticle precipitation using CO2‐philic antisolvents was studied with the ultimate goal of developing fundamental approaches to tailor microparticle generation. The ability to micronize small solutes and polymeric systems using CO2‐philic liquid antisolvents is compared to precipitation with compressed CO2 and traditional antisolvents. Analogies are made between PCA and CO2‐philic antisolvent precipitation based on thermodynamic driving forces and the dynamics of the spray process. Analysis of the interfacial gradient energies of the miscible solvent–antisolvent systems indicates that the spray process is dominated by turbulent mixing and not atomization. The similar microparticle morphologies of amorphous and semicrystalline poly(lactic acid) (PLA) obtained using liquid CO2‐philic antisolvents and compressed CO2 suggest that a similar demixing mechanism dominates microparticle formation at these operating conditions.
Glycosaminoglycan deposition in engineered cartilage: Experiments and mathematical model
Authors: Obradovic Bojana , Meldon Jerry H. , Freed Lisa E. , Vunjak‐Novakovic Gordana 
Published: April 2004

AbstractFunctional cartilaginous constructs for scientific research and eventual tissue repair were cultivated in bioreactors starting from chondrocytes immobilized on polymeric scaffolds. The scaffolds gradually degraded as the cells regenerated tissue matrix consisting of glycosaminoglycan (GAG) and type II collagen. To facilitate data interpretation and optimize cultivation conditions, a mathematical model was developed which yields the concentrations of oxygen and GAG as functions of time and position in growing tissue. Calculated GAG concentrations were qualitatively and quantitatively consistent with profiles measured via high‐resolution image processing of tissue samples cultured at two different oxygen tensions for various periods of time.
Bubble‐column and airlift photobioreactors for algal culture
Authors: Sánchez Mirón Asterio , García Camacho Francisco , Contreras Gómez Antonio , Grima Emilio Molina , Chisti Yusuf 
Published: April 2004

AbstractBubble columns and airlift photobioreactors can be useful for culturing phototrophic organisms requiring light as a nutrient. Light availability in bubble columns and airlift devices is influenced by aeration rate, gas holdup, and the liquid velocity (mixing and turbulence). The photosynthetically generated oxygen also needs to be removed, as excessive dissolved oxygen suppresses photosynthesis. Oxygen removal capacity is governed by the magnitude of the overall gas–liquid mass‐transfer coefficient, kLaL. This work characterizes the relevant hydrodynamic and mass‐transfer parameters in three air‐agitated reactors: bubble column, split‐cylinder airlift device and concentric draft‐tube sparged airlift vessel. The reactors are then evaluated for culture of the microalga Phaeodactylum tricornutum. All reactors were about 0.06 m3 in working volume, and the working aspect ratio was about 10. Data were obtained in tap water for a base‐line comparison and in Mediterranean seawater, as a potential medium for algal culture. A theoretical relationship was developed and proved between kLaL and the aeration rate. In addition, a method based on mechanistic relationships was proved for predicting the liquid circulation velocity and kLaL in airlift reactors. Existing correlations applied satisfactorily to gas holdup and kLaL data obtained in the bubble column. Aqueous solution of sodium chloride (0.15 M) closely resembled seawater in terms of its hydrodynamics and oxygen transfer behavior. Under the conditions tested, all three reactors attained a biomass concentration of about 4 kg·m−3 after ∼260 h. The mean maximum specific growth rate was 0.022 h−1 in all cases at a power input of 109 W·m−3.
Patterns of sedimentation from surface currents generated by turbulent plumes
Authors: Zarrebini Mehran , Cardoso Silvana S. S. 
Published: April 2004

AbstractA theoretical model was developed for the dynamics and deposition pattern from gravity currents generated by axisymmetric particle‐laden plumes. This model incorporates the interaction between the particles in the environment and the continuing plume. This interaction plays a central role in the evolution of the behavior of the plume and on the sedimentation patterns on the surrounding floor. Theoretical predictions for the deposition patterns were successfully compared with data from laboratory experiments for environments of both infinite and finite lateral extent. The evolution of the particle concentration in the environment and in the surface current until steady state is attained was also examined. A simple analytical expression is proposed for the sedimentation rate on the ground in the case of dilute plumes. The application of these new results to estimate the patterns of sedimentation from industrial chimney emissions is also discussed.
Estimation of transport parameters of RO membranes for seawater desalination
Authors: Taniguchi Masahide , Kimura Shoji 
Published: April 2004

AbstractMembrane transport parameters from a running plant data were studied to understand their changes with time, as well as the causes of membrane fouling under various running conditions. First, the mass‐transfer coefficient of a spiral‐type reverse osmosis (RO) element was measured using a polyamide membrane, designated UTC‐80, and an appropriate correlation equation was obtained. Then, a computer program was developed to obtain membrane transport parameters from flux and rejection data of an actual RO plant. When it became apparent that the temperature corrections should be applied, laboratory experiments were used to determine them. Thus, the time course change of both solution and salt permeabilities and the relation between them could be followed. The permeability of each ion or solute can be obtained by the same method when their analytical data are available.
Two‐step procedure for data‐based modeling for inferential control applications
Authors: Amirthalingam Raja , Sung Su Whan , Lee Jay H. 
Published: April 2004

AbstractA two‐step procedure for building an inferential control model, which uses both historical operation data and plant test data, is proposed. Motivation for using the two types of data is given, and a systematic way to combine them in the model‐identification step is proposed. Some potential problems associated with the procedure in practice and their solutions are discussed. The efficacy of the procedure is demonstrated in a case study involving a multicomponent distillation column simulated in HYSYS.
Construction and optimization of complex surface‐reaction mechanisms
Authors: Aghalayam Preeti , Park Young K. , Vlachos Dionisios G. 
Published: April 2004

AbstractA multistep methodology for the quantitative determination of rate constants of a detailed surface‐reaction mechanism is proposed. As a starting point, thermodynamically consistent, coverage‐dependent activation energies and heats of reactions were derived from the application of the unity bond index–quadratic exponential potential formulation, and initial estimates of the preexpontentials were obtained from transition‐state theory or available experiments. Important feature identification analysis was performed to determine key kinetic parameters for various experiments. Model responses were parameterized in terms of these important parameters by polynomials and factorial design techniques, and these parameterized responses were subsequently used in simultaneous optimization through simulated annealing against different sets of experimental data to obtain a quantitative reaction mechanism that is valid over a wide range of operating conditions. The technique was successfully applied to the development of a comprehensive reaction mechanism for H2/air mixtures on polycrystalline Pt.
Dynamic and steady‐state features of a cooled countercurrent flow reactor
Authors: Garg Rohit , Luss Dan , Khinast Johannes G. 
Published: April 2004

AbstractA countercurrent flow reactor (CFR) is an autothermal reactor, in which the reactants flow countercurrently at equal velocities and flow rates through two compartments, with negligible heat‐transfer resistance between the two sections. Two‐reactor configurations can be used: a “regular” one, in which the two components are fed by two separate feeds; a “folded” configuration, in which a single feed flows first through one compartment and then reverses its direction and flows countercurrently in the second. Temperature and concentration profiles in the regular CFR configuration usually have mirror symmetry around its center. Under cooling, however, asymmetric steady‐state profiles may form. The interaction between the heat removed by the effluents and by cooling through the wall may generate complex periodic or even chaotic states. The temperature and concentration profiles in a folded CFR are the same as those attained in a regular CFR, which are symmetric around the reactor center. The imposed symmetry causes the steady‐state and dynamic features of the folded CFR to be less complicated than those of the regular CFR and is less likely to cause operational problems. Boundaries of parameter regions with qualitatively different features for both CFR configurations were constructed by the method of Khinast et al. (1998a). The analysis of the CFR enhances the understanding of similar dynamics observed in a reverse‐flow reactor.
Engineering approximations for activation energies in hydrogen transfer reactions
Authors: Blowers Paul , Masel Rich 
Published: April 2004

AbstractPrevious investigators have often used the Polanyi relationship, extensions due to Seminov, or the BOC‐MP/UBI‐QEP relationship to estimate activation barriers in complex reaction networks. However, these relationships are not accurate for many reactions. In this article, a new engineering approximation for the estimate of activation barriers is presented. The approximation allows one to estimate barriers analytically, using known heats of reaction and one adjustable parameter, the intrinsic barrier. The equation was fit to the recommended values of activation energies for all 151 independent hydrogen transfer reactions in the NIST tables. All but nine of the reactions are fit within ±4 kcal/mol. Of the nine failures, seven of the data points came from previous estimates, and may not be accurate. By comparison, Seminov's relationship fails for 47 of the reactions even though the Seminov relationship has three adjustable parameters compared to one in our approximation. The BOC‐MP/UBI‐QEP method gives errors of more than 10 kcal/mol for all 151 reactions and errors of more than 30 kcal/mol for many of the reactions. These results show that the new approximation is a significant improvement over the approximations that are currently in use.
High‐resolution adsorption isotherms of supercritical carbon dioxide on activated carbon
Authors: Humayun Raashina , Tomasko David L. 
Published: April 2004

AbstractSupercritical fluids are attractive solvents for heterogeneous processes, including catalysis and adsorptive separation. However, adsorption processes in the near‐critical region are poorly understood and exhibit unique behavior where the adsorption of the supercritical solvent plays an important role in the solute adsorption. The behavior of supercritical fluids in confined pores has been studied theoretically, but there are few experimental data on their behavior in industrially important microporous materials. The adsorption of carbon dioxide on Calgon F400 activated carbon over a wide range of pressures (0–20 MPa) at temperatures near the critical point of carbon dioxide (30 to 45°C) was studied. Near‐continuous adsorption and desorption isotherms were measured with a new flow gravimetric apparatus with precise control over pressure and temperature. As pressure is increased, the excess adsorption increases sharply at low pressures; then a broad maximum is observed. At temperatures greater than the critical temperature, there is a sharp drop in excess adsorption near the critical region where the density of the bulk fluid increases sharply. A crossover is observed near the critical region where, below a certain pressure, the excess adsorption decreases with temperature, while above the crossover point the trend is reversed. When analyzed as a function of solvent density, the crossover disappears, revealing an anomalous maximum in total adsorption near the critical point similar to the enhanced local density or “charisma” observed in binary solute–supercritical fluid systems. A 2‐D EOS model using the 2‐D Peng‐Robinson EOS was able to qualitatively describe the adsorption behavior over the entire pressure range, but the quantitative agreement was poor in the near‐critical region.
Equilibrium and diffusion of methanol and water in a nafion 117 membrane
Authors: Gates Craig M. , Newman John 
Published: April 2004

AbstractThe uptake concentrations of methanol and water in a Nafion membrane are measured as a function of methanol mol fraction from a liquid methanol–water mixture. The results are fitted by a thermodynamically consistent equation, derived from an expression of the Gibbs energy. The uptake of pure methanol and pure water from the vapor phase is measured as a function of vapor pressure. A discontinuity, known in the literature as Schroeder's paradox, between membrane uptakes of pure methanol and pure water from the liquid and vapor phases is noted. Regions of unconditional instability are enveloped by spinodal loci for the ternary mixture in the membrane when equilibrated with liquid mixtures. The effective diffusion coefficient is measured at 60°C for diffusion from a vapor into a saturated Nafion membrane. The effective diffusion coefficients are found to be on the order of 10−11 m2/s, which is comparable to other measurements made for diffusion of a vapor through the membrane.
Early warning of agglomeration in fluidized beds by attractor comparison
Authors: van Ommen J. Ruud , Coppens Marc‐Olivier , van den Bleek Cor M. , Schouten Jaap C. 
Published: April 2004

AbstractAn enhanced monitoring method, based on pressure fluctuation measurements, for observing nonstationarities in fluidized‐bed hydrodynamics is presented. Experiments show that it can detect small changes in the particle‐size distribution. Such a monitoring method is useful to give an early warning of the onset of agglomeration in a fluidized bed. In contrast to earlier methods, this method is insensitive to small changes in superficial gas velocity and can handle multiple signals, making it relevant to industrial application. By carefully choosing the measurement position, the method becomes also insensitive to small bed mass variations. It uses the attractor reconstructed from a measured pressure signal, which is a “fingerprint” of the hydrodynamics of the fluidized bed for a certain set of conditions. Using this method statistically the reconstructed attractor of a reference time series of pressure fluctuations (representing the desired fluidization behavior) is compared with that of successive time series measured during the bed operation.
Predicting LLE in mixed‐solvent electrolyte systems by an electrolyte EOS
Authors: Zuo Julian Youxiang , Zhang Dan , Fürst Walter 
Published: April 2004

AbstractThis work extends the previously published aqueous electrolyte equation of state (AEEOS) to predict liquid–liquid equilibria (LLE) of mixed‐solvent electrolyte systems. Interaction parameters between ions and organic solvents, and cations and anions were determined by fitting the experimental vapor‐pressure data of binary methanol + halide electrolyte mixtures, and then correlated to the cationic Stokes and anionic Pauling diameters. The focus is on the ionic standard/reference state and the standard Gibbs energy for transferring salts from one solvent to another. The methods applied to predict LLE of several ternary water + organic solvent + salt system are to select: 1. the hypothetical ideal gas at unit mol fraction, the system temperature, and 1 bar as the ionic standard state; 2. the infinite dilution in the solvent mixture as the ionic reference state, whose activity coefficients were converted to those at the infinite dilution in pure water by the ionic standard Gibbs energy of transfer. The predicted LLE results agree well with the measured data without any adjusted parameters in fitting the ternary experimental data. The extended AEEOS is comparable to the model of Zerres and Prausnitz, but the latter requires two adjusted parameters in fitting the ternary experimental data for each ternary system.
Ligand diffusion, receptor binding, and internalization: Zeroth‐order kinetics
Authors: Strieder William 
Published: April 2004

AbstractThe exact, analytical solution for steady‐state diffusion and zeroth‐order surface reaction at a cell‐wall chemoreceptor site is presented. Following Berg (1993), and others, the receptor is modeled as a chemically active circular site on an impermeable, inert cell wall. Explicit values of the dimensionless site‐specific rate constant mark the regions of chemical‐, transitional‐ and diffusion‐controlled kinetics. Particularly when the Michaelis‐Menten constant is small relative to the ligand bulk concentration, this simple form of the receptor‐site reaction current should provide a useful model for cell growth‐factor internalization, nutrient uptake, and certain cellular signaling behaviors. Various biophysical conditions that cause site mass‐transport resistance in cellular site‐reaction kinetic processes are discussed.
Mass‐transfer calculation methods for transient diffusion within particles
Authors: Alopaeus Ville 
Published: April 2004

AbstractModeling of diffusion within spherical particles is often an important part of modeling of many processes relevant to chemical engineering such as adsorption. The accurate solution of the differential equations describing diffusion is quite a complicated task involving calculation of infinite series. A rational approximation to the diffusion equation is presented in this article leading to a solution that is both very easy to use and very accurate. The present method was compared to the exact solution for diffusion and adsorption in spheres, and it was found that the present solution is practically indistinguishable from the exact solution. This method is also applicable to multicomponent systems in a straightforward manner.
Influence of impeller type on the flow structure in a stirred reactor
Authors: Revstedt Johan , Fuchs Laszlo , Kovács Tamas , Trägårdh Christian 
Published: April 2004

AbstractLarge eddy simulations (LES) of a stirred reactor with a liquid volume of 0.64 m3 were performed. The tank was stirred by either two standard Rushton impellers or two Scaba 6SRGT impellers. The LES can provide details of the flow field that cannot be obtained with so‐called Reynolds‐averaged equations and the corresponding models. The unsteady spatially filtered incompressible Navier‐Stokes equations were solved together with a transport equation for the concentration of an inert additive using a multigrid finite difference code with a staggered grid. The unresolved turbulent scales were modeled using a scale similarity model. The aim of this investigation has been to study the influence of impeller type on the flow structure and scalar transport. The results show that, compared at equal power input, the center plane velocities and the volume flow in the impeller stream do not differ much for the impeller types. Also, for the 6SRGT the periodic fluctuations associated with the blade passing is less pronounced.
Representation of high‐dimensional, molecular solid‐liquid phase diagrams
Authors: Samant Ketan D. , Berry David A. , Ng Ka M. 
Published: April 2004

AbstractA generic framework for the representation of multicomponent molecular solid‐liquid phase diagrams in the form of digraphs is presented. Pure components, eutectic points, and saturation points in the solid‐liquid composition space are represented as vertices of the digraph. These vertices are connected to form edges on the basis of the adjacency matrix, which is constructed by following a set of generic rules derived from the Gibbs phase rule. These edges form the boundaries of high‐dimensional saturation varieties. Included in the framework is a procedure for plotting high‐dimensional isobaric and isothermal isobaric phase behavior in the form of projections and cuts. With this framework, solid‐liquid phase behavior of multicomponent systems can be easily represented and studied. Applications include facilitation of experimental development of high‐dimensional phase diagrams and synthesis of crystallization‐based separation processes. The latter is illustrated with the separation of a quinary mixture.