bluuebunny/crossref_metadata_2025_split huggingface dataset:
Falling film absorption on a cylindrical tube
Authors: Conlisk A. T. 
Published: June 2004

AbstractThe falling liquid film has become a popular means of transferring heat and mass from a vapor to a binary liquid film; applications include heat pump systems, desalination, and gas‐liquid contactors. In the heat pump application, in particular, the length of the liquid film is a crucial factor because of size and weight limitations. Consequently, it is desirable to be able to predict the amount of mass absorbed in a given length of tube. In this work the absorption of water vapor into a Lithium‐Bromide Water mixture is considered. It is shown that mass transfer takes place in a thin layer of fluid near the liquid‐vapor interface which is indicative of a very high level of liquid‐side mass‐transfer resistance. Closed form solutions for the velocity field may be used to derive a simple closed form solution for the mass fraction. For very thin films the temperature distribution may be obtained analytically in Laplace transform space; however, due to the complexity of the solution, numerical techniques are employed to obtain quantitative results. For thicker films a closed form solution for the temperature may be obtained as well. The principal objective of this work is to develop a design procedure not requiring a significant amount of numerical work whereby the absorption capacity of a given tube may be predicted as a function of the governing geometrical and physical parameters. The analytical/numerical results are presented for parameters corresponding to those of recent experiments and the agreement between theory and experiment is good.
Mass/heat‐exchange network representation of distillation networks
Authors: Bagajewicz Miguel J. , Manousiouthakis Vasilios 
Published: June 2004

AbstractThis article introduces the “state space” conceptual framework to process synthesis, which is used to provide a novel representation of a distillation network as a composite heat‐ and mass‐exchange network. This representation suggests that distillation network synthesis may best be viewed as an interacting heat‐ and mass‐exchange network synthesis problem. In that regard, familiar tools (such as pinch diagrams) from both heat‐exchange network (HEN) and mass‐exchange network (MEN) synthesis are shown to be of use in arriving at energy‐efficient distillation network designs. Examples of propylene‐propane and solvent‐water separations are used to illustrate the proposed conceptual framework.
Steric mass‐action ion exchange: Displacement profiles and induced salt gradients
Authors: Brooks Clayton A. , Cramer Steven M. 
Published: June 2004

AbstractThe study of nonlinear competitive equilibrium is of fundamental importance in understanding the behavior of proteins in preparative ion‐exchange chromatographic separations. In this work we present a steric mass‐action (SMA) ion‐exchange equilibrium formalism, which explicitly accounts for the steric hindrance of salt counterions upon protein binding in multicomponent equilibria. An analytical solution has been derived for the calculation of isotachic effluent profiles of displaced proteins and induced salt gradients under ideal chromatographic conditions. A stability analysis has been employed to establish the order of the feed components in the displacement train. Theoretical predictions are compared to experimental results for the separation of proteins by cation‐exchange displacement chromatography. These results demonstrate the efficacy of the SMA formalism in predicting complex behavior present in ion‐exchange displacement systems. Furthermore, the analytical solution of ideal isotachic displacement profiles with the SMA formalism enables rapid methods development and optimization of ion‐exchange displacement separations.
Depostition of submicron aerosol particles in turbulent and transitional flow
Authors: Shimada Manabu , Okuyama Kikuo , Asai Masahito 
Published: June 2004

AbstractBrownian and turbulent diffusive deposition of submicron aerosol particles from pipe flow is studied experimentally and theoretically. A theoretical model for evaluating the turbulent diffusive deposition is presented in which a turbulent flow in a circular pipe is numerically calculated based on the k‐ϵ turbulent flow model and deposition velocities are derived by solving the convection‐diffusion equation. Deposition velocities of monodisperse aerosol particles, 0.01–0.04 μm in diameter, are obtained experimentally by measuring the decrease in the particle number concentration of an aerosol at two cross‐sections of a circular test pipe through which the aerosol is flowing. The deposition velocities obtained when Re is larger than about 3,000 agree well with those predicted by the present analysis which are proportional to the 0.92nd power of Reynolds number and the 0.33rd power of Schmidt number. The particle deposition rates are measured when 1, 000 ≲ Re ≲ 2,000 suggest a transitional state for particle deposition which cannot be explained by the present analysis nor by the laminar pipe flow deposition theory.
Wave‐net: a multiresolution, hierarchical neural network with localized learning
Authors: Bakshi Bhavik R. , Stephanopoulos George 
Published: June 2004

AbstractA Wave‐Net is an artificial neural network with one hidden layer of nodes, whose basis functions are drawn from a family of orthonormal wavelets. The good localization characteristics of the basis functions, both in the input and frequency domains, allow hierarchical, multiresolution learning of input‐output maps from experimental data. Furthermore, Wave‐Nets allow explicit estimation for global and local prediction error‐bounds, and thus lend themselves to a rigorous and explicit design of the network. This article presents the mathematical framework for the development of Wave‐Nets and discusses the various aspects of their practical implementation. Computational complexity arguments prove that the training and adaptation efficiency of Wave‐Nets is at least an order of magnitude better than other networks. In addition, it presents two examples on the application of Wave‐Nets; (a) the prediction of a chaotic time‐series, representing population dynamics, and (b) the classification of experimental data for process fault diagnosis.
Model identification of a spatiotemporally varying catalytic reaction
Authors: Krischer K. , Rico‐Martínez R. , Kevrekidis I. G. , Rotermund H. H. , Ertl G. , Hudson J. L. 
Published: June 2004

AbstractThe occurrence of instabilities in chemically reacting systems, resulting in unsteady and spatially inhomogeneous reaction rates, is a widespread phenomenon. In this article, we use nonlinear signal processing techniques to extract a simple, but accurate, dynamic model from experimental data of a system with spatiotemporal variations. The approach consists of a combination of two steps. The proper orthogonal decomposition [POD or Karhunen‐Loève (KL) expansion] allows us to determine active degrees of freedom (important spatial structures) of the system. Projection onto these “modes” reduces the data to a small number of time series. Processing these time series through an artificial neural network (ANN) results in a low‐dimensional, nonlinear dynamic model with almost quantitative predictive capabilities.This approach is demonstrated using spatiotemporal data from CO oxidation on a Pt (110) crystal surface. In this special case, the dynamics of the two‐dimensional reaction profile can be successfully described by four modes; the ANN‐based model not only correctly predicts the spatiotemporal short‐term behavior, but also accurately captures the long‐term dynamics (the attractor). While this approach does not substitute for fundamental modeling, it provides a systematic framework for processing experimental data from a wide variety of spatiotemporally varying reaction engineering processes.
Experimental validation of a mathematical model for fixed‐bed desulfurization
Authors: Efthimiadis Evangelos A. , Sotirchos Stratis V. 
Published: June 2004

AbstractPorous particles of two commercially available ZnO sorbents differing in porosity, surface area, and pore‐size distribution were reacted with H2S at 500 and 600°C in a fixed‐bed reactor. Concentration breakthrough curves were determined by analyzing the effluent of the reactor using a gas chromotograph equipped with thermal conductivity and flame photometric detectors. The pore structure of samples collected from different positions in the reactor was analyzed by mercury porosimetry and gas adsorption to determine the variation of the average structural properties of the sorbent with the length of the reactor. The obtained experimental data were used to validate a fixed‐bed desulfurization model, which employs detailed submodels for diffusion, reaction, and structure evolution in the porous sorbent particles. With the various parameters appearing in the submodels determined from independent thermogravimetric reactivity evolution experiments, the fixed‐bed desulfurization model was found to be capable of providing an excellent description of the behavior of the desulfurization sorbents in a fixed‐bed reactor.
A kinetic model for olefin polymerization in high‐pressure autoclave reactors
Authors: Chan Wai‐Man , Gloor Paul E. , Hamielec Archie E. 
Published: June 2004

AbstractFree radical copolymerization in high‐pressure autoclave reactors is studied by developing a mathematical model. Kinetic mechanisms to describe the polymerization rate, molecular weight averages, branching frequencies, as well as copolymer composition are presented. Two phase kinetics due to polymer‐monomer solubilities in the reaction mixture are taken into account. Gel formation from cross‐linking reactions is also analyzed. A mixing model is developed to represent the stirring effect inside the reactor. The mathematical model is implemented as a computer program to simulate commercial autoclave reactors. PID control equations are used to maintain operation at the unstable steady state. A sensitivity study is performed on the mixing model parameters and on some of the kinetic parameters and the model is compared to rate data from commercial reactors.
Fibroblast‐populated collagen microsphere assay of cell traction force: Part 1. Continuum model
Authors: Moon Alice G. , Tranquillo Robert T. 
Published: June 2004

AbstractThe most popular in vitro assay currently used to characterize cell traction forces exerted on extracellular matrix (ECM) fibers is the fibroblast‐populated collagen lattice (FPCL) assay. The compaction of a disk of cell‐populated collagen gel, in terms of rate or extent of diameter reduction, is typically reported as the measure of cell traction. This measure, however, depends on assay properties incidental to the intrinsic traction, such as the initial cell concentration, the initial collagen concentration, and the geometry of the gel. Thus, there is a clear need to identify and measure an objective index of cell traction. Here, we propose as such an index a traction parameter (reflective of the cell‐fiber mechanical interaction) defined in a continuum theory in which the interactive processes of cell motility and ECM deformation are modeled by expressions for cell and ECM conservation coupled to the mechanical force balance for the cell‐ECM composite. The equations are formulated and solved for our adaptation of the FPCL assay in which cells are initially dispersed in a collagen gel microsphere, conferring several experimental and theoretical advantages over the popular disk geometry. The solution of the nonlinear system of partial differential equations (parameterized on the traction parameter) is then compared to compaction data for the fibroblast‐populated collagen microspheres (FPCM). We show that the model predictions are consistent with the data when the initial cell concentration and the initial FPCM diameter are varied. In Part 2, we show how these results, along with the determination of the growth parameters of the cells and the viscoelastic parameters of the gel, have allowed us to estimate the magnitude of the traction parameter, which is a direct measure of the traction exerted by fibroblasts in a physiologically relevant collagen gel.
Rheological properties of Hydroxypropyl Guar (HPG) slurries
Authors: Shah Subhash N. 
Published: June 2004

AbstractRheological behavior of moderately concentrated (up to 35 vol. %) suspensions or slurries prepared with non‐Newtonian carrier fluids is investigated. Extensive experimental data on the Poiseuille slit flow of suspensions of sand in Hydroxypropyl Guar (HPG) solutions are presented. Flow data are gathered by pumping various non‐Newtonian slurries into a unique, 8 ft (2.4 m) tall vertical apparatus, with great care taken to calibrate the instrument and to avoid settling difficulties. Investigated are the effects of polymer concentration, solids concentration, test temperature, and shear rate on the rheological properties of slurries. The rheological behavior of HPG solutions and HPG suspensions is characterized by a pseudoplastic power law non‐Newtonian fluid model over a shear rate range of 30 to 500 s−1. The correlations for predicting the relative slurry viscosity for HPG fluids are presented. Substantial increase in viscosity of these non‐Newtonian fluids is observed, and they are found to be a strong function of polymer concentration, shear rate, test temperature, and particle concentration. Results of this investigation are also compared with those available for Newtonian and non‐Newtonian suspensions.
Dynamics of shell‐and‐tube heat exchangers to arbitrary temperature and step flow variations
Authors: Xuan Y. , Roetzel W. 
Published: June 2004

AbstractA versatile and efficient method is developed for predicting dynamic performances of parallel and counterflow heat exchangers subject to arbitrary temperature variations and step flow disturbances, including the effect of flow maldistribution and the influence of heat capacities of both fluids, shell wall and tube bank as well as nonzero initial temperatures. Two algorithms of numerical inversion of the Laplace transform are introduced to determine the final temperature profiles in the realtime domain and some examples are calculated with nonuniform initial conditions. The accuracy of the proposed method is demonstrated with the calculated results at new steady states. Experiments are carried out on a labor‐sized heat exchanger to further examine the feasibility of this method and the comparison between calculated and measured temperature profiles is illustrated and discussed.
Control of nonlinear systems using polynomial ARMA models
Authors: Hernández Evelio , Arkun Yaman 
Published: June 2004

AbstractMost of the advanced nonlinear control algorithms require a model of the system to be controlled. Unfortunately, most of the processes in the chemical industry are nonlinear, and fundamental models describing them are lacking. Thus there is a need for the identification and control of nonlinear systems through available inputoutput data. In this article, we briefly introduce the input‐output model used (polynomial ARMA models), and analyze its stability and invertibility. This paves the way to the development of a nonlinear‐model‐predictive controller. Implementation issues such as modeling of disturbance, state and parameter estimation are discussed. The theory presented is illustrated through examples.
Kinetics of carbothermal reduction synthesis of beta silicon carbide
Authors: Weimer Alan W. , Nilsen Kevin J. , Cochran Gene A. , Roach Raymond P. 
Published: June 2004

AbstractCarbothermal reduction kinetics to synthesize SiC is studied under conditions of high carbon/silica precursor heating rates (105 K/s) and minimized reaction times (s) over a wide temperature range (1,848⩽T⩽2,273 K). The reaction mechanism includes rapid formation of a gaseous SiO intermediate. Further carbon reduction of the SiO to SiC is reaction‐rate‐controlling. Carbon crystallite diameter, d, has a substantial influence on the rate of reaction and the size of synthesized SiC. Fractional oxide conversion, X, can be described by a contracting volume shrinking core model:

where k0 = 27.4 m/s and E = 382±34 kJ/mol.
Developing flow of a gas‐particle mixture in a vertical riser
Authors: Pita Jorge A. , Sundaresan Sankaran 
Published: June 2004

AbstractA computational study of steady, developing flow of gas‐particle suspensions in a vertical riser has been carried out, using a model based on kinetic theory of granular materials, to understand the role of inlet configuration on the pattern of flow development. Three inlet configurations—uniform inlet, core‐annulus flow at the inlet and circumferential injection of secondary gas—were examined. It is found that the inlet configuration can have a profound impact on the rate of segregation of particles to the wall and the internal recirculation. Circumferential injection of gas has a favorable effect on the flow in the sense that it can decrease the extent of internal recirculation.
Application of flexible recipes for model building, batch process optimization and control
Authors: Keesman Karel J. 
Published: June 2004

AbstractUnlike the traditionally fixed recipes in batch process operation, flexible recipes allow the adjustment of some of its relevant recipe items. These adjustments can either be predefined in cases of planned experimentation, or suggested by a formal process optimization or control algorithm on the basis of actual information. In both the response surface methodology and the simplex evolutionary operation (EVOP), some well‐known methods for empirical model building and process optimization, flexible recipes are involved. Another application of flexible recipes arises in a feedforward quality control strategy of batch processes when variations in market or process conditions are known a priori. The experimental results of these strategies are presented for the batchwise production of benzylalcohol on a pilotplant scale. Experiments have been performed to obtain a reliable model of the yield. On the basis of this model, better process conditions have been suggested, which substantially deviate from the final simplex resulted from experiments within simplex EVOP. Finally, an adaptive feedforward control strategy has been applied for a priori known disturbances in the process inputs.
Nonlinear predictive control of periodically forced chemical reactors
Authors: Özgülşen Fatih , Kendra Scott J. , Çinar Ali 
Published: June 2004

AbstractA nonlinear model‐predictive control strategy is developed to maintain the superior‐to‐steady‐state performance of a periodically forced chemical reactor. The performance of the predictive controller is investigated in the presence of measurement disturbances and parametric uncertainty. It is also shown that statistically inferred input‐output models can be a substitute whenever detailed fundamental models are not available. A nonlinear autoregressive polynomial model based on observed plant data is built and incorporated into the control scheme. The catalytic oxidation of ethylene in a periodically‐forced, continuous stirred‐tank reactor is considered as the test case.
Membrane elasticity effects on permeability measurements in vesicles
Authors: Chiruvolu Shivkumar , Zasadzinski Joseph A. N. 
Published: June 2004

AbstractTypical experiments to measure permeability in biologically relevant cell membranes utilize vesicles, single bilayer membrane capsules, as idealized cells. The permeation of solute through the vesicle membrane is analyzed with the assumption that the vesicle volume and membrane area are fixed during the experiment. In response to the excess solute concentration internal to the vesicle, however, an osmotic stress is set up that acts to stretch the vesicle membrane, resulting in an initial dilution of the vesicle contents, followed by a continued elastic response of the vesicle membrane as the experiment proceeds and the internal and external concentrations equilibrate. We derive a simple analytic theory of this process that couples the mass‐transfer process with the area elasticity of the vesicle membrane. If dilution of the exterior solution is used to initiate the permeation, significant effects on measured permeabilities are predicted for membranes with a low elastic modulus, when large concentration differences are imposed or vesicles are greater than 0.1 micron in diameter. In practice, this leads to an underestimate of the permeability of membranes composed of polyunsaturated lipids or lipids in contact with alcohols or alkanes. It could also lead to the erroneous conclusion that the permeability is concentration‐dependent. The effects of elasticity, however, are minor, if dialysis is used to continually remove any exterior solute or if saturated phospholipid membranes with a large elastic modulus or vesicles of less than 0.1 micron diameter are used.
Visualization of flow characteristics in a 2‐D bubble column and three‐phase fluidized bed
Authors: Tzeng J.‐W. , Chen R. C. , Fan L.‐S. 
Published: June 2004

AbstractMacroscopic flow structures of gas‐liquid and gas‐liquid‐solid fluidization systems are studied through flow visualization using a two‐dimensional column under various operating conditions. The gas distributor in the column comprises multiple injectors which are individually regulated to generate desired gas flow rates, bubble injection frequencies, and bubble sizes. Colored bed particles and neutrally buoyant particles as solid and liquid tracers, respectively, are used for flow visualization through video photography. In a gas‐liquid system operated under liquid‐batch conditions, bubble streams injected near both sidewalls are observed to migrate toward bed vertical axis, and vortices appear along the sidewalls when gas velocity exceeds 4–6 mm/s. A considerable amount of liquid descends along the sidewalls in a vortical flow pattern. The gross circulation pattern occurring at high gas velocities is associated closely with induced liquid or liquid‐solid flows resulting from rising bubbles and bubble wakes. When the gross circulation occurs, four flow regions can be distinguished. The formation of and mechanism for gross circulations can be interpreted in part based on two simplified flow conditions involving single bubbles rising in a stationary liquid and single chains of bubbles injected in a batch liquid. The effects of particle size, inlet liquid velocity and gas flow distribution on the macroscopic flow structure are also examined.
A simple model and experiments for adsorption‐desorption hysteresis: Water vapor on silica gel
Authors: Rajniak Pavol , Yang Ralph T. 
Published: June 2004

AbstractA simple model is proposed for the evaluation of the primary and secondary adsorption and desorption processes for hysteresis‐dependent sorption systems. The model is based on the use of pore blocking interpretation of hysteresis in an interconnected network of pores. The model is simple to use and requires only the primary adsorption and primary desorption isotherms to predict all secondary desorption and adsorption isotherms. A complete set of equilibrium adsorption‐desorption curves covering the hysteresis loop (appearing in the range of relative pressure 0.3–0.7) was measured for water vapor on silica gel at 25° C. The usefulness of the model is supported by its agreement with experimental data.
Polydisperse tube diameters compromise multiple open tubular chromatographyw
Authors: Schisla D. K. , Ding Hongbing , Carr P. W. , Cussler E. L. 
Published: June 2004

AbstractThis article demonstrates that even 1% polydispersity in hollow‐fiber diameters can increase plate heights by as much as an order of magnitude. The demonstration includes an analytical extension of the Taylor‐Aris and the Golay dispersion theories, a numerical solution using the measured polydisperity, and successful predictions of the performance of different hollow‐fiber systems over a range of flow rates. All these results show that the effect of polydispersity can dominate column performance, especially in the region where the column efficiency is optimal.