bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bubble‐Size distributions and flow fields in bubble columns
Authors: Lehr F. , Millies M. , Mewes D. 
Published: April 2004

AbstractBubble‐size distributions and flow fields in bubble columns are calculated numerically. The population balance is simplified and reduced to a balance equation for the average bubble volume. Models developed predict the rate of bubble breakup and coalescence based on physical principles. The flow fields are numerically calculated for bubble columns with cylindrical cross sections using the Euler‐Euler method. The newly derived balance equations for the average bubble volumes are implemented into a commercial CFD code. The solutions of the balance equation for high superficial gas velocities result mainly in two fractions: one for the fraction with small and the other for the fraction with large bubble diameters. Both are considered pseudocontinuous phases, in addition to the liquid phase. The calculated flow fields are characterized by several large‐scale vortices. The local volume fractions of gas and liquid are locally inhomogeneous and highly time‐dependent. The time‐averaged flow field is axisymmetric and stationary. The calculated volume fractions, velocities, and bubble‐size distributions agree well with existing and previously published experimental results for bubble columns up to 0.3 m in diameter.
Non‐Fickian nonisothermal model for drying of polymer coatings
Authors: Vinjamur Madhu , Cairncross Richard A. 
Published: April 2004

AbstractAs a sequel to our study on experimental measurements of trapping skinning in a poly(methyl methacrylate)/acetone coating, a mathematical model of non‐Fickian diffusion that predicts trapping skinning is reported here including solvent transport due to a stress gradient that develops because of coating shrinkage. The predicted solvent concentration profile shows a sigmoidal shape and a front that moves into the coating. In the nearly constant rate period, the stress relaxes near the coating surface due to short relaxation times at high coating temperature. The stress relaxation causes negative non‐Fickian flux. At higher gas flow rates, the negative non‐Fickian flux causes the development of a thinner layer of low solvent concentration near the coating surface and a thicker layer of high solvent concentration inside the coating. Thus, more solvent remains in the coating dried at higher flows and trapping skinning occurs.
Modeling hydrodynamics of trickle‐bed reactors at high pressure
Authors: Narasimhan C. S. L. , Verma R. P. , Kundu Arunabha , Nigam K. D. P. 
Published: April 2004

AbstractA phenomenological hydrodynamic model of a trickle‐bed reactor developed predicts pressure gradient and liquid holdup at high pressures. The model consists of 1‐D force balance equations incorporating particle–gas drag, particle–liquid drag and gas–liquid interactions. The deviation between the measured and theoretical pressure drop is explained in terms of tortuosity and axial dispersion effects. Tortuosity encountered by the flowing liquid and gas phases has two components: (1) tortuosity angle (θ), the measure of the tortuous path the fluid would take; (2) an excess friction factor, which would approximate for resulting excess drag while the tortuous path is taken. These parameters were observed to play a major role in modeling the hydrodynamics in the trickle‐bed reactor. The model takes into account the tortousity effects in a unique way. The axial dispersion effect comes into the picture due to the back‐mixing, modeled in terms of the Peclet number (Pe) in a novel way. The overall model was tested with major experimental data for the high‐pressure concerning various types of gas–liquid systems, including hydrocarbons, aqueous solutions, coalescence inhibiting liquids, and so on, that are available in the literature, and the prediction has been found to be excellent.
Neural network particle sizing in slurries by reflectance spectroscopy
Authors: Li Mingzhong , Wilkinson Derek , Schrödl Markus 
Published: April 2004

AbstractMeasuring concentration and size of solids in suspension is important in many industries. Even though techniques based on optical transmission measurements have been well developed, they are not always successful in practical applications because low concentration suspensions are needed. A method developed determines particle‐size distribution and concentration from reflection measurements in concentrated suspensions using neural networks with particle concentrations up to 10% volume fraction. Based on measured optical reflectance spectra of suspensions with known particle‐size distributions and concentrations, a neural network was trained to identify particle‐size distribution and volume fraction of suspensions. Training is a time‐consuming process requiring presentation of many spectra and their corresponding particle‐size distributions and volume fractions to the neural network, but once concluded satisfactorily, the neural network can be used to predict the particle‐size distribution and volume fraction of high concentration suspensions rapidly in‐situ.
Dynamic measurement for the stiffness of loosely packed powder beds
Authors: Yanagida T. , Matchett A. J. , Coulthard J. M. , Asmar B. N. , Langston P. A. , Walters J. K. 
Published: April 2004

AbstractAn experimental methodology to measure the stiffness of loosely packed powder beds was developed, which had not been possible using previous methods. Experiments were performed on a range of sample powders including polyethylene, rubber, glass, sand, and clay powders. Powders were placed in a vertical, open, cylindrical vessel, and subject to sweep vibration at low accelerations. Base force and acceleration were measured using an impedance head and accelerometer. Apparent mass, defined as a ratio of base force to base acceleration, measured showed a significant peak frequency. The longitudinal elastic modulus of the bed was calculated from the data. For shallow beds in which the wall friction is negligible, the peak frequency is independent of the cross‐sectional area of the bed and sweep rate, but dependent on the bed height and acceleration. Data generated by the top‐cap method agreed reasonably for cases in which the packing state was not sensitive to external force. A substantial change in elasticity was detected with changes of packing states. Furthermore, the elasticity of packed beds conforms to Kendall's fourth‐order relationship with solid volume fraction over a range of packing conditions.
Novel pervaporation technology using absorption refrigeration for vapor removal
Authors: Fahmy Alaa , Mewes Dieter , Ohlrogge Klaus 
Published: April 2004

AbstractA novel process configuration for pervaporation and vapor permeation realizes the permeation driving force by absorbing the permeate vapor into a suitable solution with a very low vapor pressure. Although the suggested process design lacks an experimental demonstration, by using two well‐established technologies—the separation by pervaporation and the absorption refrigeration—it can achieve technical and economic advantages over the conventional condensation technology. Vacuum pressures as low as 8 mbar can be obtained at ambient temperatures without refrigeration, as well as low vacuum ranges that are not possible by condensation without freezing. Process simulations and feasibility investigations for the suggested process are discussed.
Combinatorial framework for effective scheduling of multipurpose batch plants
Authors: Sanmartí E. , Puigjaner L. , Holczinger T. , Friedler F. 
Published: April 2004

AbstractThe production scheduling of multipurpose batch plants is considered. A novel graph representation that looks at the specific characteristics of production scheduling in chemical processes is proposed. In these graphs, the nodes represent the production tasks, the arcs of the precedence relationships among them. The representation is flexible enough to consider a wide variety of production structures, including complex recipes. Both nonintermediate storage (NIS) and unlimited intermediate storage (UIS) transfer policies can be considered simply by choosing the appropriate precedence relationships. This representation provides the opportunity of incorporating highly efficient graph algorithms together with an appropriate branch‐and‐bound algorithm for solving multipurpose scheduling problems. The efficiency of the proposed method is established by solving examples and a complex case study.
Two‐mode models for describing mixing effects in homogeneous reactors
Authors: Chakraborty Saikat , Balakotaiah Vemuri 
Published: April 2004

AbstractThe Liapunov–Schmidt technique of bifurcation theory is used to spatially average the convection–diffusion–reaction equation over smaller time/length scales to obtain two‐mode models (TMMs) for describing mixing effects in homogeneous tubular, loop/recycle and tank reactors. For the isothermal case, these TMMs are described by a pair of coupled balance equations involving the mixing‐cup (Cm) and the spatially averaged (〈C〉) concentrations. One equation traces the evolution of Cm with (residence) time, while the other is a local equation that describes mixing resulting from coupling between diffusion, velocity gradients, and reaction at the local scales, in terms of an exchange between the two modes, Cm and 〈C〉. The TMMs have many similarities with the two‐phase models of catalytic reactors, with concept of transfer between phases being replaced by that of exchange between the two modes. Examples are presented to illustrate the usefulness of these TMMs in predicting micromixing effects on homogeneous reactions.
Measuring asphaltenes and resins, and dipole moment in petroleum fluids
Authors: Goual Lamia , Firoozabadi Abbas 
Published: April 2004

AbstractA petroleum fluid can be divided into three types of species: asphaltenes, resins, and oils. Asphaltenes and resins are polar, while the rest of the so‐called oils are either nonpolar or mildly polar. The interaction among these species strongly affect asphaltene precipitation from petroleum fluids. Different measuring methods for asphaltenes in a petroleum fluid give similar results, but different results for the resin content of a petroleum fluid. In addition to the amount affecting precipitation, the polarity of asphaltenes and resins affects precipitation strongly. The Onsager formulation of dipolar moments was used to measure the dipole moment of asphaltenes, resins and the oil species from eight different petroleum fluids from various parts of the world. The dipole moment, a measure of polarity, for resins was measured in this work for the first time. Results showed that resin separated from a petroleum fluid by propane is part of the total resin. Adsorption methods, however, give the total amount of resins. For a given petroleum fluid, asphaltenes had a higher dipole moment than resins. However, resins from one petroleum fluid can have a higher dipole moment than asphaltenes from another petroleum fluid.
Modeling of heavy metal salt solubility using the extended UNIQUAC model
Authors: Iliuta Maria C. , Thomsen Kaj , Rasmussen Peter 
Published: April 2004

AbstractSolid–liquid equilibria in complex aqueous systems involving a heavy metal cation (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, or Zn2+) and one or more ions for which Extended UNIQUAC parameters have been published previously are modeled using the Extended UNIQUAC model. Model parameters are determined on the basis of a data bank with more than 4,000 experimental data points for binary and ternary aqueous systems. The parameters are generally valid in the temperature range from the freezing point to the boiling point of the respective solutions.
Model for the gas evolution in a porous medium driven by solute diffusion
Authors: Tsimpanogiannis Ioannis N. , Yortsos Yannis C. 
Published: April 2004

AbstractAn effective continuum model is derived to describe the nucleation and subsequent growth of a gas phase from a supersaturated, slightly compressible binary liquid in a porous medium, driven by solute diffusion. The evolution of the gas results from reducing the system pressure at a constant rate or withdrawing the liquid at a constant rate. The model addresses two stages before the onset of bulk gas flow, nucleation and gas‐phase growth. Negligible gradients due to gravity or viscous forces are assumed, so the critical gas saturation signaling the onset of bulk gas flow is only a function of the nucleation fraction. Important quantities characterizing the process, such as the pore number fraction hosting activated sites, deviation from thermodynamic equilibrium, maximum supersaturation, and critical gas saturation, depend crucially on the nucleation characteristics of the medium. Heterogeneous nucleation models using preexisting gas trapped in hydrophobic cavities or in terms of a rate‐dependent nucleation are used to investigate the nucleation behavior. Using a simpler analytical model the relevant quantities during nucleation can be expressed in terms of a simple combination of dimensionless parameters. The theory predicts that the maximum supersaturation is a weakly increasing function of rate, which in the region of typical experimental parameters can be approximated as a power law. It depends sensitively on the probability density function of nucleation cavity sizes. The final nucleation fraction (thus, the critical gas saturation) is predicted to be a power law of the decline rate. The theoretical exponents agree well with experimental data. The subsequent evolution of the gas phase and the approach to the critical gas saturation is also described.
Feasibility and synthesis of hybrid reactive distillation systems
Authors: Chadda Nitin , Malone Michael F. , Doherty Michael F. 
Published: April 2004

AbstractA systematic method to synthesize hybrid reactive distillation configurations described here uses three building blocks. These building blocks are a cocurrent rectifying cascade, a cocurrent stripping cascade, and a countercurrent cascade. A feasibility diagram and a product purity diagram provide a global view of the “direct” and “indirect” sharp split products that can be obtained as a function of the reaction rate from single–feed and double–feed hybrid columns, respectively. These diagrams are used as a basis for quickly and systematically generating feasible column configurations (if any) that produce the desired product. Three esterification examples are used to illustrate the method. In spite of the fact that the examples form a homologous series, the feasible designs are quite different. The results compare well with column simulations.
Multiobjective optimization of SMB and varicol process for chiral separation
Authors: Zhang Ziyang , Hidajat K. , Ray Ajay K. , Morbidelli M. 
Published: April 2004

AbstractThe multiobjective optimization of continuous countercurrent chromatography separation units, such as simulated moving bed (SMB) and Varicol, is considered. The Varicol system is based on a nonsynchronous shift of the inlet and outlet ports instead of the synchronous one used in the SMB technology. The optimization problem is complicated by the relative large number of decision variables, including continuous variables, such as flow rates and lengths, as well as discontinuous ones, such as column number and configuration. It is also important to reformulate the optimization problem as multiobjective, since the factors affecting the cost of a given separation process are multiple and often in conflict with each other. A typical example is simultaneous maximization of the productivity of the process and the purity of the corresponding products. A new optimization procedure based on a genetic algorithm allows handling these complex optimization problems. An existing literature chiral separation model was used to illustrate the potential of this optimization procedure. This work also offered a unique opportunity to compare the optimal separation performance achievable with the SMB and Varicol technologies.
Simulation of five‐step one‐bed sorption‐enhanced reaction process
Authors: Xiu Guo‐hua , Soares Jose Luciano , Li Ping , Rodrigues Alirio E. 
Published: April 2004

AbstractA five‐step, one‐bed, sorption‐enhanced reaction process proposed by Carvill et al. in 1996 for hydrogen production by steam–methane reforming was analyzed. For the simulated results of the first step, data from Hufton et al. (1999) and Ding and Alpay (2000) for a fixed‐bed column of an admixture of a catalyst and a sorbent that selectively removes CO2 from the reaction zone were used. The sorbent is periodically regenerated by using the principles of pressure‐swing adsorption. The process steps allow direct production of hydrogen with high purity and high methane conversion. A model considering multicomponent and overall mass balance, Ergun relation for pressure drop, energy balance for the bed‐volume element, and nonlinear adsorption equilibrium isotherm coupled with three main reactions was derived to describe the sorption‐enhanced reaction cyclic process. Two different isotherms were used under wet and dry conditions. The LDF model adopted describes the mass‐transfer rate of CO2 in the adsorbent. Numerical solution of model equations for the cyclic process was obtained by the orthogonal collocation method. The operating conditions allow the combination of a sufficiently high purity of hydrogen (average purity over 80%) with traces of CO and CO2, high methane conversion, fast adsorbent regeneration, and cyclic steady‐state operation. The model predictions agree reasonably with the literature data. The package is suitable for the design and analysis of sorption‐enhanced reaction process.
Surface modification of polyvinylidene fluoride pervaporation membranes
Authors: Khayet Mohamed , Chowdhury Geeta , Matsuura Takeshi 
Published: April 2004

AbstractPolyvinylidene fluoride (PVDF) membranes were surface‐modified using fluorinated surface‐modifying macromolecules (SMMs) additives. The membranes were prepared using the phase‐inversion method. Two novel SMM formulations were used. The effect of some relevant parameters, such as the solvent evaporation time, evaporation temperature, and concentration of SMM in the PVDF casting solution, was considered. The prepared membranes were characterized in terms of the contact angle analysis, the liquid entry pressure of water measurements, and the scanning electron microscopy. Pervaporation experiments were conducted for dilute chloroform/water binary mixtures. Based on the contact angle analysis, the incorporation of SMM into the PVDF casting solution produced membranes with higher surface hydrophobicity. The pervaporative performance of the prepared membranes was investigated, and the relationship between the surface characteristics of the modified PVDF membranes and the chloroform separation discussed.
Flexibility analysis and design using a parametric programming framework
Authors: Bansal Vikrant , Perkins John D. , Pistikopoulos Efstratios N. 
Published: April 2004

AbstractThis article presents a new framework, based on parametric programming, that unifies the solution of the various flexibility analysis and design optimization problems that arise for linear, convex, and nonconvex, nonlinear systems with deterministic or stochastic uncertainties. This approach generalizes earlier work by Bansal et al. It allows (1) explicit information to be obtained on the dependence of the flexibility characteristics of a nonlinear system on the values of the uncertain parameters and design variables; (2) the critical uncertain parameter points to be identified a priori so that design optimization problems that do not require iteration between a design step and a flexibility analysis step can be solved; and (3) the nonlinearity to be removed from the optimization subproblems that need to be solved when evaluating the flexibility of systems with stochastic uncertainties.
Determination of operability limits using simplicial approximation
Authors: Goyal Vishal , Ierapetritou Marianthi G. 
Published: April 2004

AbstractDetermining the boundaries of any process/design where feasible and safe operation is guaranteed has long been recognized as a major concern in process industries. Of additional value is identifying the range of operating conditions where the design is most profitable. Although there is a lot of discussion in the open literature regarding design feasibility in terms of uncertainty of process variables, these techniques are rather limited due to the underestimation of the feasible space. A new approach is presented based on the ideas of inner and outer approximation of the feasible region to identify the operating envelopes where process operation is feasible, safe, and profitable. A number of example problems are presented including two case studies to illustrate the applicability of this approach.
CFD simulation of reactive flows: Catalytic combustion in a monolith
Authors: Canu P. , Vecchi S. 
Published: April 2004

AbstractCatalytic combustion in a structured catalyst was used to test advantages of computational fluid dynamics (CFD) codes with respect to simpler approaches to simulation of actual data and kinetic studies. Published experimental data on square channels and segmented monoliths were compared and used as a basis for parametric studies. The relevance of temperature‐dependent transport properties was quantified. A comparison of 2‐D approximations with a full 3‐D model, which predicts a different ignition behavior, shows that the latter is needed to properly describe actual data. The segmentation of the monolith shows some influence on the overall combustion rate. The sensitivity analysis of the importance of chemical kinetics relative to mass transport suggests a need for a better description of surface mechanism, even if the simulated data are not uniquely under chemical control. A parameter‐fitting procedure for kinetic studies based on the detailed 3‐D, segmented CFD model was developed and successfully tested for modeling inhibition by water. Results show that more detailed surface and gas‐phase reactions mechanisms must be included, but only after developing and validating a comparably detailed model of the momentum and heat transport in the actual geometry of the real process.
Group contribution method for Henry's Law constant of aqueous hydrocarbons
Authors: Sedlbauer Josef , Bergin Gaëtan , Majer Vladimir 
Published: April 2004

AbstractA functional group contribution scheme based on a hydration model predicts Henry's Law constant of aqueous hydrocarbons as a function of temperature and pressure. It uses the direct link of Henry's Law constant with the Gibbs free energy of hydration, as well as its temperature and pressure derivatives accessible from calorimetric and volumetric data. A semitheoretic model inspired by the fluctuation solution theory with five adjustable parameters was used for expressing the temperature and pressure dependence of ten functional contributions. A consistent group contribution scheme for hydration properties at 298 K and 0.1 MPa was taken from literature to constrain the model at reference conditions. Parameters for hydrocarbon functional groups were adjusted by simultaneous correlation of over 1,000 data points on Henry's Law constant and about 550 values on derivative hydration properties (enthalpy, heat capacity, and volume) available in a wide range of temperature and pressure. The resulting group additivity scheme can be used for predicting Henry's Law constant for alkanes, alkenes, alkylcycloalkanes, and alkylbenzenes up to 570 K and up to 100 MPa. Average accuracy of the predictions varies from 20 to 40% at ambient to high temperatures, respectively, and semiquantitative estimates are possible up to the critical point of water.