bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling capillary condensation hysteresis cycles in reconstructed porous media
Authors: Štěpánek František , Marek Miloš , Adler Pierre M.
Published: April 2004

A computational algorithm for tracking liquid–vapor interfaces moving with curvature‐dependent velocity, based on the Gibbs energy formulation and the level‐set approach, is described. The algorithm is used for finding equilibrium distributions of condensate in several samples of 3‐D reconstructed porous media under varying relative saturation of the surrounding atmosphere. Primary and higher‐order hysteresis cycles are calculated and their dependence on various physico‐chemical parameters (temperature, wetting angle) as well as on geometrical properties of the porous medium is investigated. An explanation of the influence of the morphology of a porous medium on the character of corresponding hysteresis loops is provided.
Viscosity effects on Dean vortex membrane microfiltration
Authors: Kluge Tanja , Kalra Amrit , Belfort Georges
Published: April 2004

The influence of changing viscosity by adding polyethylene glycol (PEG) during microfiltration of silica suspensions in the presence and absence of Dean vortices was determined. A new microfiltration membrane module design containing helically wound hollow fibers (with Dean vortices) was compared with a standard commercial cross‐flow module (without Dean vortices) containing linear hollow fibers during filtration of poly(ethylene) glycol solutions and silica suspensions. The influence of solution viscosity on permeation flux behavior was evident through two separate effects. First, increased viscosity effected the formation and stability of vortices and, hence, wall shear rate and convective back‐flow. Second, permeation flux was reduced with increasing fluid viscosity. Flux improvements (linear vs. helical membranes) of up to 45% were observed for all value of the silica suspensions with and without PEG. The energy required to obtain these improvements, however, was considerable. Flux advantages of the helical design decreased and eventually disappeared as the viscosity of the solution increased up to 12 times that of water at 27°C. New mass‐transfer correlations for microfiltration of poly(ethylene) glycol solutions containing silica concentrations for laminar flow in a helical and a linear module were obtained with respect to the solution viscosity, for a silica particle concentration of 0.1 wt. %.
Design and upgrade of nonredundant and redundant linear sensor networks
Authors: Bagajewicz Miguel J. , Sánchez Mabel C.
Published: April 2004

The design of sensor networks featuring minimum cost, while satisfying constraints of redundancy only, is examined. For this purpose, the concept of degree of redundancy for measurements and degree of observability for unmeasured variables are merged into one single property, the degree of estimability of a variable. In addition, the concept of estimation efficiency is introduced. Based on these concepts, mathematical programming procedures are presented that allow the design of sensor networks for different degrees of estimability of key variables.
Detection, identification, and reconstruction of faulty sensors with maximized sensitivity
Authors: Qin S. Joe , Li Weihua
Published: April 2004

A new method proposed here detects, reconstructs, and identifies faulty sensors using a normal process model, which can be built from first principles or statistical methods such as partial least squares or principal component analysis. The model residual is used to detect sensor faults that demonstrate a deviation from the normal process model. To identify which sensor is faulty, a structured residual approach with maximized sensitivity is proposed to make one residual insensitive to one subset of faults but most sensitive to other faults. The structured residuals are subject to exponentially weighted moving average filtering to reduce the effect of noise and dynamic transients. The confidence limits for these filtered structured residuals are determined using statistical inferential techniques. In addition, other indices including generalized likelihood ratio test, cumulative sum, and cumulative variance of the structured residuals are compared to identify faulty sensors. The fault magnitude is then estimated based on the model and faulty data. Four types of sensor faults, including bias, precision degradation, drifting and complete failure, are simulated to test this method. Data from an industrial boiler process are used to test its effectiveness. Both single faults and simultaneous double faults are detected and uniquely identified with the method.
Scoping and screening complex reaction networks using stochastic optimization
Authors: Marcoulaki E. C. , Kokossis A. C.
Published: April 2004

A systematic methodology to target the performance of chemical reactors with the use of stochastic optimization is presented. The approach employs a two‐level strategy where targets are followed by the proposition of reactor configurations that match or are near the desired performance. The targets can be used for synthesis and retrofit problems, as they can provide the incentives to modify the operation, and ideas in developing the reactor design. The application of stochastic optimization enables confidence in the optimization results, can afford particularly nonlinear reactor models, and is not restricted by the dimensionality or the size of the problem.
Formation of microgel beads by electric dispersion of polymer solutions
Authors: Poncelet D. , Neufeld R. J. , Goosen M. F. A. , Burgarski B. , Babak V.
Published: April 2004

Microcapsules are produced by a dropwise addition of one solution into a solidifying bath. By applying an electrostatic potential between the droplet formation device and the collecting solution, it is possible to obtain smaller droplets which are desirable for many applications. Droplet formation may be divided into two phases. Under a certain critical value of the electric potential Uc, liquid exits the nozzle as droplets. The surface tension decreases with increasing electric potential resulting in a reduction of droplet diameter to approximately 200 μm. At higher electric potential, liquid exits the nozzle as a jet which subsequently breaks into droplets, which are smaller than 200 μm. In this case, droplet size is mainly determined by the jet instability (theory of Rayleigh).
Vapor‐liquid and chemical equilibria of formaldehyde‐water mixtures
Authors: Albert Michael , García Baudilio Coto , Kreiter Cornelius , Maurer Gerd
Published: April 2004

A physicochemical model of the thermodynamic properties of formaldehyde‐containing mixtures was revised and extended using new experimental data for vapor–liquid and chemical equilibria. The new vapor–liquid equilibrium data of the formaldehyde–water system were taken for very diluted (formaldehyde concentrations as low as 0.07 mass %) and very concentrated (up to 71 mass %) formaldehyde solutions at temperatures between 363 and 423 K and pressures up to about 650 kPa. The new chemical equilibrium data were obtained applying 13 C‐NMR spectroscopy to the same system at temperatures between 338 and 383 K at formaldehyde concentrations of up to about 62 mass %. Results from both investigations were used simultaneously—together with data from the literature—to improve a physicochemical model of the thermodynamic properties of aqueous solutions of formaldehyde.
Intermolecular forces in phase‐change heat transfer: 1998 Kern award review
Authors: Wayner Peter C.
Published: April 2004

The variation of long‐range intermolecular forces near interfaces profoundly affects the performance of change‐of‐phase heat exchangers. Starting with the fundamental electromagnetic force between molecules (dielectric properties), the effects of shape (Kelvin effect), temperature (Clapeyron effect) and concentration on the heat‐transfer characteristics of thin films and larger systems are reviewed and connected. A judicious selection of literature gives a consistent set of models of particular use in heat transfer. Examples of experimental verification of these interfacial models in this rapidly developing field are also presented.
Mass‐transfer enhancement in single‐drop extraction experiments
Authors: Henschke Martin , Pfennig Andreas
Published: April 2004

To reduce costs, engineers in the industry wish to substitute laboratory‐scale experiments for pilot‐scale investigations. Thus mass‐transfer experiments with single drops seem to be a first step toward the design of liquid–liquid extraction columns, along with other experiments needed, for example, for the estimation of coalescence parameters. In this article it is shown that it is possible to describe nonstationary mass transfer between single drops and a continuous phase with a single parameter, the instability constant CIP. The instability constant is independent of both drop diameter and contact time between drop and continuous phase. Thus in principle a single laboratory experiment allows the determination of CIP for a given combination of components. When mass transfer in an extraction column is calculated using the estimated value of CIP, an increase in mass transfer due to the concentration gradient in the continuous phase of the column has to be accounted for appropriately.
Characterizing growth‐rate dispersion of NaNO3 secondary nuclei
Authors: Jones Christopher M. , Larson Maurice A.
Published: April 2004

Previous work on growth‐rate dispersion has shown how to calculate crystal‐size distributions when the growth‐rate distribution is known and how to calculate the growth rate distribution when the crystal‐size distribution is known. There is a significant lack of information, however, on how growth‐rate dispersion is affected by changes in system conditions like supersaturation, stirring speed, slurry density, or temperature. In this work, the growth‐rate distributions of sodium nitrate secondary nuclei are characterized as a function of the nucleation and growing supersaturations. Growth‐rate dispersion is characterized by analyzing the mean, spread, and shape of the growth‐rate distribution. This provides a means of determining the factors that cause and control growth‐rate dispersion. The analysis of this experimental work provides valuable insight into the relationships among supersaturation conditions, strain, and dislocation density. The average growth rates of secondary nuclei are dislocation controlled at low growing supersaturations and strain controlled at high growing supersaturations, where increasing the nucleation supersaturation causes an increase in both dislocation density and strain. Increasing strain by itself will decrease growth rates, while increasing dislocation density by itself will increase growth rates. This work also suggests that harsh system conditions can affect growth rates adversely.
Modeling Au(CN) extraction by mixtures of primene JMT and cyanex 925 reagents
Authors: Alguacil Francisco José
Published: April 2004

A chemically based thermodynamic model to predict the distribution coefficient has been developed for the Au(CN)‐Primene JMT‐Cyanex 925 system. The predictive model makes use of the extraction mechanism, speciation in the organic phase, and the equilibrium constant for the extraction reaction. The distribution coefficient of gold can be predicted by the equation DAu = K′[H+], where K′ is an effective extraction constant and [H+] is the proton concentration of the aqueous phase at equilibrium. Excellent agreement between the experimental data and the predicted value was obtained. Furthermore, for the present extraction system, the equilibrium isotherm was determined at 20°C.
Air separation by integrally asymmetric hollow‐fiber membranes
Authors: Feng Xianshe , Ivory John , Rajan Varagur S. V.
Published: April 2004

Integrally asymmetric hollow‐fiber membranes each with an outer skin layer and a porous substrate were studied for air separation to produce nitrogen and oxygen enriched air. The test on both bore‐side feed and shell‐side feed with cocurrent and countercurrent flow arrangements for a wide range of stage cuts shows that the bore‐side feed countercurrent flow was the most advantageous configuration in the permeator design. When operated in the bore‐side feed countercurrent configuration, the permeator performance compared favorably with the commercial systems available for nitrogen production. A mathematical model was developed for this configuration. Since the concentration polarization in the substrate was a major concern for the bore‐side feed configuration, especially for high stage‐cut operations, a theoretical approach was pursued to formulate the concentration polarization. This allows for the diagnosis of the significance of concentration polarization in a specific permeation process, although it is difficult to predict concentration polarization accurately due to limited knowledge of the detailed membrane structure.
Geographic and process information for chemical plant layout problems
Authors: Özyurt Derya B. , Realff Matthew J.
Published: April 2004

Geographic information systems (GIS) introduced here offer a source of information for problems with a geographic dimension, such as layout and environmental decision making. A mixed‐integer linear‐programming formulation of a chemical‐plant layout problem was developed, and is presented along with an existing formulation. The effectiveness of these formulations is highly problem‐ and data‐specific, and a combination of the two formulations can be derived that is more effective on certain problems than either formulation alone. The formulations are ineffective for some problems due to the highly redundant search space engendered by symmetries in the layout—symmetries that can be eliminated by a more careful analysis of the situation using location‐specific information such as existing units and facilities, geographic constraints, wind, elevation, and soil conditions. Different classes of such information can be captured from a GIS and represented within the mixed‐integer linear‐programming formulation. Two cases studies presented illustrate the formulations and the use of geographic information for chemical‐plant layout.
New analysis and design tool for achieving low variability process designs
Authors: Tseng J. L. , Cluett W. R. , Bialkowski W. L.
Published: April 2004

A new process analysis and design tool was developed. The analysis tool consists of a systematic algorithm for analyzing a block diagram representation of a process flowsheet and identifying different paths between a given input and output variable. Transfer function representations of different paths are calculated to determine the contribution of each path to the overall attenuation characteristics of the process. To improve these attenuation characteristics, the paths that contribute the most to the overall variability must be identified and addressed. The design tool consists of a set of guidelines that the engineer can use to develop alternate process designs or control strategies to eliminate these identified paths, reduce their contribution to overall variability, or negate their effects by adding new paths. Although the ingenuity of the design engineer is critical, this tool provides the engineer with a means to identify problems in a process design, to help develop design alternatives, and a quantitative basis for comparing and evaluating these alternatives. This new tool was applied to a standard design for a stock preparation system in a pulp and paper mill.
Impinging jets confined by a conical wall: Laminar flow predictions
Authors: Miranda João M. , Campos João B. L. M.
Published: April 2004

A laminar jet flow confined by a conical wall and an impinging plate was investigated. The Navier‐Stokes equations were numerically solved by a finite difference technique and the results compared with laser Doppler anemometry data, the latter also covering the transition and turbulent flow regimes. Transition was found to start in the impingement region at a jet Reynolds number of around 1,600. The investigation concentrated on assessing the effects of nozzle‐to‐plate distance (always less than one nozzle diameter), jet Reynolds number, and nozzle outlet conditions. The shape of the velocity profile at the nozzle outlet determines the entire cell flow field, whereas nozzle‐to‐plate distance affects the flow in the expansion region. Under certain flow and geometric conditions a recirculation zone appears in the expansion region, in the vicinity of the plate.
Settling of polydisperse particles with thin double layer at small péclet number
Authors: Wang H. , Wen C. S.
Published: April 2004

The special‐function expansion method is used to solve the sedimentation problem of polydisperse colloid particles with thin double layer. The pair‐distribution function is expanded into Legendre polynomials. The recurrence formulas for calculating the coefficients of the Legendre polynomials and the expressions for calculating the sedimentation coefficient are deduced analytically. Then, the sedimentation of polydisperse particles with thin double layer at small Péclet number is analyzed numerically by the perturbation method. Results indicate that the sedimentation of potential interacting particles is more complex than that of the hard spheres, and the existence of the thin double layer affects the particles settling heavily. Critical double‐layer thickness exists, without which a colloid system may change from a stable one into an unstable one and the hindered settling may change into accelerated settling.
Possible air separations with superconducting membranes
Authors: Gordon Ryan D. , Cussler E. L.
Published: April 2004

Permeabilities of oxygen, nitrogen and helium across porous, superconducting membranes with 5‐μm pores are consistent with those across nonsuperconducting membranes with well‐defined pores of similar sizes. This is true both at ambient and superconducting temperatures. Transport can occur by Knudsen diffusion, Poiseuille flow, capillary condensation, and turbulent flow. There is no evidence of surface diffusion. Theoretical considerations of superconducting membranes are consistent with these results, indicating when superconductivity might play a role. However, past reports concerning air separation with superconducting membranes with these micrometer‐sized pores are questionable.
Liquid‐phase sorption‐enhanced reaction process
Authors: Sircar S. , Rao M. B.
Published: April 2004

A process for carrying out simultaneous liquid‐phase reaction and separation of desired products is described. It uses a fixed packed column of an admixture of a catalyst and an adsorbent that selectively removes a reaction byproduct from the reaction zone. The adsorbent is periodically regenerated using the concepts of liquid‐phase concentration swing adsorption. The integrated process allows production of multiple products at high purity with high conversions. For an endothermic reaction, the process permits much higher conversions of reactants to products at a substantially lower temperature than would be necessary by a plug‐flow reactor using the catalyst alone. The concept is demonstrated for hydrolysis of methyl acetate to produce acetic acid and methanol.
Nonequilibrium cell model for multicomponent (reactive) separation processes
Authors: Higler Arnoud , Krishna R. , Taylor Ross
Published: April 2004

A generic nonequilibrium cell model for multicomponent separation processes, including liquid‐phase chemical reactions, was developed. Its important features include the use of Maxwell‐Stefan equations to describe interphase mass transfer and the use of a multiple cell per stage approach to consider various mixing characteristics of vapor and liquid phases. A finite difference approach was used for solving the diffusion‐reaction equations in each fluid phase to properly account for effects of reactions on mass transfer. The multiple cells per stage approach was adopted to take into account the effect of concentration and temperature profiles on a tray on the local reaction rates. The model was compared to several case studies by Kooijman (1995). Comparison of various flow models showed only minor differences between Kooijman's model and the nonequilibrium cell model. The differences were found only for cases in which the phases are assumed to be imperfectly mixed and to be caused by different ways of modeling the interface concentration profiles in various flow models. In addition, some calculations are described for reactive distillation operations described by Okasinski and Doherty (1998) and Marek (1956). These examples show that staging in both flow directions influences overall column performance considerably.
Effect of tube size and obstacles on explosion limits in flowing gases
Authors: Bolk Jeroen W. , Westerterp K. Roel
Published: April 2004

In a large pilot plant the upper explosion limit of ethene–air–nitrogen mixtures was experimented in 3.0‐m‐long and 21‐, 50‐, and 100‐mm‐dia. tubes at different flow rates, pressures, and temperatures. The upper explosion limit, influenced by the gas velocity, becomes smaller and shifts to higher oxygen concentrations for increasing flow rates. The results of these tubes could be correlated based on the tube Reynolds number. A cooling effect of the tube wall, which might influence the explosion region, was not observed. An increase in pressure lowers the critical oxygen content as does an increase in temperature, thus the explosion region becomes larger. Different obstacles were tested, which alter the hydrodynamics. Reaction fronts could only propagate for increased oxygen concentrations through a structured Sulzer laboratory gauze packing or a sudden reduction in diameter from 50 to 20 mm. In the experiment, where the tube was completely filled with glass spheres, propagation of reaction fronts through this packed bed was not possible, even at very low gas velocities and very high oxygen concentrations. In a deep dead zone connected to the tube, the gas was ignited and reacted without igniting the gas outside the dead zone. After some time the reaction stopped because of oxygen starvation. However, dead zones with another geometry, where renewal of the combustible gas can occur, still may be dangerous.
Laser‐induced fluorescence technique for the quantification of mixing in impinging jets
Authors: Unger David R. , Muzzio Fernando J.
Published: April 2004

A laser‐induced fluorescence (LIF) technique is implemented to measure concentration profiles and mixing performance in two impinging jet geometries. Experimental results are reported for steady and unsteady (transitional) mixing of initially segregated miscible fluids. Flow structures are visualized by imaging concentration distributions at five vertical planes throughout the mixers. Mixing is quantified for each Reynolds number examined by calculating the overall intensity of segregation. Mixing performance varies substantially as a function of Reynolds number. Optimum operating conditions are identified for both impinging jet geometries. The results demonstrate the ability of laser‐induced fluorescence to quantitatively capture small‐ and large‐scale flow structures and accurately and reproducibly quantify mixing performance in real time for industrially‐relevant mixing devices. The LIF technique proves to be an accurate and versatile method to quantify mixing performance of miscible fluids.
Variation of gravure coating thickness during early stages of doctor blade wear
Authors: Hanumanthu R.
Published: April 2004

With all operating parameters fixed, the mean coated thickness in gravure coating should ideally be a constant fraction of the volume factor of the engraving, and, hence, invariant over coated distance. Experimental data presented, however, reveal an unexpected variation of gravure coating thickness over the first few thousand meters of coated web. The observed variation is attributed to wear of the blade tip. The lubrication approximation is invoked to model a series of steady‐state flows between blade tips of various profiles and a smooth surface at a fixed gap away from them. The blade tip profiles are chosen to simulate those of a continously wearing blade tip. The resulting four‐parameter model is used to “fit” experimental data of gravure coating thickness variation. Then, the model is used to predict the effects of various operating parameters, including coating liquid properties, blade thickness, blade setup, and web speed, on this phenomenon.
Mass transfer and dispersion around active sphere buried in a packed bed
Authors: de Carvalho João R. F. Guedes , Alves Manuel A. M.
Published: April 2004

Mass transfer around single spheres in granular beds of inerts (packed or fluidized) was analyzed for transport by advection and diffusion/dispersion. Fluid flow in the granular bed around the spheres was assumed to follow Darcy's law; at each point, dispersion of solute was assumed to be determined by the coefficients of transverse and longitudinal dispersion, respectively, in the cross‐stream and streamwise directions. The elliptic equation resulting from a differential mass balance was solved numerically over a wide range of the relevant parameters. Resulting values of the Sherwood number are represented accurately by the product of two terms: the solution for advection plus molecular diffusion, which depends only on the Peclet number relative to the active sphere; the enhancement brought about by convective dispersion, which depends only on the Peclet number relative to the inert particles.
Experimental and computational study of multiphase gas/particle flow in a CFB riser
Authors: Mathiesen Vidar , Solberg Tron , Arastoopour Hamid , Hjertager Bjørn H.
Published: April 2004

The flow behavior in the riser of a circulating fluidized‐bed reactor was studied experimentally and computationally. Laser Doppler anemometry was applied to measure the flow behavior of FCC catalysts. Particle diameter and mean and fluctuating velocity for different particle sizes were measured at different flow conditions. A typical core‐annulus flow with a relative velocity between particles of different sizes was obtained. A significant radial segregation of the mean diameter was measured in the riser. A multifluid computational fluid dynamics model was developed and verified against the experimental results. The flow model is based on a Eulerian description of the phases where the kinetic theory for granular flow forms the basis for the turbulence modeling in the solid phases. The model is generalized for one gas phase and N number of solids phases to enable a realistic description of the particle‐size distribution in gas/solid flow systems. Each solid phase is characterized by a diameter, form factor, density, and restitution coefficient. Simulations with one gas and two solid phases were conducted, and the computational results agreed generally well with the measurements.
Experimental and modeling study on tubular dense membranes for oxygen permeation
Authors: Xu Nanping , Li Shiguang , Jin Wanqin , Shi Jun , Lin Y. S.
Published: April 2004

Tubular La0.6Sr0.4Co0.2Fe0.8O3–δ perovskite‐type membranes were prepared by isostatic pressing. A mathematical model was developed to simulate the performance of the tubular perovskite‐type dense membranes for oxygen permeation. The experimental oxygen permeation fluxes of tubular La0.6Sr0.4Co0.2Fe0.8O3–δ perovskite‐type membrane increased with decreasing downstream oxygen partial pressure and increasing helium flow rate, which coincided with the results of the oxygen permeation modeling study. Parametric study indicated that air should be supplied sufficiently during the oxygen permeation operation. Modeling oxygen permeation fluxes as a function of the tubular membrane length and tubular membrane thickness are discussed in detail. The oxygen flux slightly decreased after long‐term operation over 110 h. EDS and XRD analysis indicated that SrSO4, CoSO4, SrO, Co2O3, and La2O3 were formed on the surfaces of the tubular membrane due to the interaction with trace SO2 in the air and the helium, and segregation of surface elements. The oxygen permeation of tubular La0.6Sr0.4Co0.2Fe0.8O3–δ membrane was stable after SO2
in the air and the helium has been removed.
Scaleup experiments on seeded batch cooling crystallization of potassium alum
Authors: Doki Norihito , Kubota Noriaki , Sato Akira , Yokota Masaaki , Hamada Osamu , Masumi Fumio
Published: April 2004

Potassium alum was crystallized by natural cooling in two well‐mixed laboratory‐scale (12.2 L) and pilot‐scale (600 L) crystallizers. When unimodal product crystals of grown seeds were used, no scaleup effect on product crystal‐size distribution (CSD) was observed if enough seeds were loaded over a critical seed concentration. Cooling rate, crystal yield (crystal suspension density), and stirring condition do not seriously affect the product CSD under such a seeding condition. Low supersaturation peak caused by the growth of enough seeds, the short period of nucleation, and the agglomeration of nuclei to the growing seed crystals are considered to be mechanisms working to produce unimodal product crystals of grown seeds. Simple design calculations are demonstrated to determine the amount of seed with the help of a critical seed concentration, which can be determined easily from laboratory‐scale experiments. Crystallizer volume was calculated simply from a mass balance.
Stochastic modeling of carbon oxidation
Authors: Chen Wei‐Yin , Kulkarni Advait , Milum Jeremy L. , Fan L. T.
Published: April 2004

Recent studies of carbon oxidation by scanning tunneling microscopy indicate that measured rates of carbon oxidation can be affected by randomly distributed defects in the carbon structure, which vary in size. Nevertheless, the impact of this observation on the analysis or modeling of the oxidation rate has not been critically assessed. This work focuses on the stochastic analysis of the dynamics of carbon clusters' conversions during the oxidation of a carbon sheet. According to the classic model of Nagle and Strickland‐Constable (NSC), two classes of carbon clusters are involved in three types of reactions: gasification of basal‐carbon clusters, gasification of edge‐carbon clusters, and conversion of the edge‐carbon clusters to the basal‐carbon clusters due to thermal annealing. To accommodate the dilution of basal clusters, however, the NSC model is modified for the later stage of oxidation in this work. Master equations governing the numbers of three classes of carbon clusters, basal, edge and gasified, are formulated from stochastic population balance. The stochastic pathways of the three different classes of carbon during oxidation, that is, their means and the fluctuations around these means, have been numerically simulated independently by the algorithm derived from the master equations, as well as by an event‐driven Monte Carlo algorithm. Both algorithms have given rise to identical results.
Wet oxidation of an azo dye: Lumped kinetics in batch and mixed flow reactors
Authors: Donlagic Jelka , Levec Janez
Published: April 2004

Oxidation of a dilute aqueous solution of a model azo dye pollutant (Orange II) was studied in batch and continuous well‐mixed (CSTR) reactors. Both reactors operate at 200–250°C, and total pressures up to 50 bar and at oxygen partial pressure from 10 to 30 bar. The model pollutant concentrations were in a range between 100 and 1,000 mg/L, which may be found in industrial wastewaters. The dye oxidation undergoes a parallel‐consecutive reaction pathways, in which it first decomposes thermally and oxidatively to aromatic intermediates and via organic acids to the final product carbon dioxide. To develop a kinetic equation capable of predicting organic carbon reduction, all organic species present in solution were lumped by total organic carbon (TOC). The lumped oxidation rate in batch reactor exhibited second‐order behavior, whereas in the CSTR it was found linearly proportional to its TOC concentration. The lump behavior in batch reactor was dominated by the refractory low molecular mass aliphatic acids formed during the oxidation.
Development of a metal hydride electrode waste treatment process
Authors: Bianco J. C. , Martin D. , Ansart F. , Castillo S.
Published: April 2004

Manufacturing residues of metal hydride electrodes for nickel–metal hydride batteries were chemically processed to recover the metal part and heat treated for the organic part. Chemical recovery yielded Ni‐Co alloy after electrolysis of the solution and hydroxides of other metals, mainly rare earths. The organic part, pyrolyzed at 700°C, led to separation between carbon and fluorinated matter. Infrared coupling at the output of the pyrolysis furnace was used to identify the pyrolysis gases.
Infinite dilution activity coefficients from ab initio solvation calculations
Authors: Lin Shiang‐Tai , Sandler Stanley I.
Published: April 2004

A Group Contribution Solvation (GCS) model was developed to calculate infinite dilution activity coefficients (γ∞) based on modern computational chemistry. The GCS model results in an average error of 7% in γ∞ for the limited number of data points among water, n‐hexane, acetonitrile and n‐octanol, whereas the errors are 47% and 52% with the UNIFAC model and the modified UNIFAC model, respectively. GCS was also used to calculate infinite dilution partition coefficients, which can be used to determine how a dilute solute partitions between two solvents. Solutes were examined in three different liquid‐liquid systems: water/n‐hexane, water/acetonitrile, and water/n‐octanol. With GCS, the average errors are 22% (for 18 solutes), 18% (for 14 solutes) and 14% (for 15 solutes) for these solvent systems, while comparable errors are 237%, 286% and 226% with UNIFAC; and 342%, 414% and 306% with modified UNIFAC. The GCS model is a powerful new tool to predict the octanol‐water partition coefficients.
Equation‐of‐state parameters for pure polymers by molecular dynamics simulations
Authors: Fermeglia Maurizio , Pricl Sabrina
Published: April 2004

Two new procedures, based on molecular mechanics and molecular dynamics computer simulations, are presented for estimating the PHSCT EOS and the LF EOS parameters of a set of four polymers of industrial relevance and to predict their PVT behavior. These new, original methods offer good results, are relatively inexpensive, are absolutely general, and can be applied in principle to any equation of state, provided the model parameters have a well‐defined physical meaning.
Estimation of cell traction and migration in an isometric cell traction assay
Authors: Knapp David M. , Tower Theodore T. , Tranquillo Robert T. , Barocas Victor H.
Published: April 2004

A quantitative analysis of data from an in vitro assay presented allows for simultaneous study of cell migration within as well as cell traction on tissue equivalents (collagen gels seeded with tissue cells to serve as model tissues). Using our anisotropic biphasic theory for modeling tissue equivalents, the ability of the model to simulate the data was validated by accurately predicting the alignment of fibroblasts and collagen fibrils in the compacting collagen gels and the effects of gel aspect ratio on gel compaction. The effects of migration and adhesion modulating factors (platelet‐derived growth factor‐BB and an anti‐β1 integrin antibody), as well as mechanical stress in the collagen network (attached vs. floating gels), on cell migration and traction during compaction were investigated. In all cases, cell migration was negatively correlated with cell traction. The relevance of the results to wound contraction is discussed.
Internal mass flux through frost
Authors: Fukada Satoshi , Inoue Kunihiro
Published: April 2004

An experimental method is developed for determining the internal mass flux through frost with a dendrite structure. The theory and experimental procedures of the measurements using water slightly concentrated with deuterium are described. The internal mass flux determined from variations in the deuterium concentration in frost with time shows an almost linear decrease in the frost depth direction from the surface. The profile of the local frost density is almost flat in the depth direction. The frost uniformity is kept independent of the cooled‐plate temperature and the total pressure in the container unless part of the frost melts. The cause for the uniformity of frost density is discussed in terms of the frost temperature profile and microscopic crystal growth.
Magnetic resonance imaging of the filtration process
Authors: Dirckx Conrad J. , Clark Simon A. , Hall Laurance D. , Antalek Brian , Tooma Joe , Hewitt J. Michael , Kawaoka Ken
Published: April 2004

This article demonstrates that 3‐D magnetic resonance imaging (MRI) provides sufficient spatial resolution to visualize accurately the internal architecture of a 10‐in. cartridge filter and housing. A paramagnetic material (<5‐μm iron‐oxide particles) used as the contaminant, together with a gradient‐echo imaging sequence, enables location of the areas on the filter surface where the particles are deposited, even at the earliest stages of blocking. The magnetic susceptibility contrast mechanism of MR imaging sequence and particulate matter produces a far larger volume reduction in MR signal than that generated by the actual displacement of fluid by the particles. Using this spatial amplification effect, the temporal performance of the filter was studied by imaging the deposition of 3.75 g of the particulate material at ten incremental stages of blocking. Blocking is heterogeneous initially, both longitudinally along the filter length and radially across the transverse sections, and continues to be heavier in the areas of initially greater deposition as more material is entrapped. The correlation between the areas of heavy blocking and the internal support structure of the filter cartridge is discussed, since those regions appear to be strongly related to the cartridge body design. In a separate set of experiments, the 3‐D flow field of a Newtonian fluid through the filter system was measured for an unblocked filter. These measurements also show some correlation between the spatial heterogeneity of particulate deposition and the heterogeneous flow paths of liquid through the filter.
Colloidal gas aphrons (CGA): Dispersion and structural features
Authors: Jauregi Paula , Mitchell Geoffrey R. , Varley Julie
Published: April 2004

Colloidal gas aphrons (CGA) have previously been defined as surfactant stabilized gas microbubbles and characterized for a number of surfactants in terms of stability, gas holdup and bubble size even though there is no conclusive evidence of their structure (that is, orientation of surfactant molecules at the gas–liquid interface, thickness of gas–liquid interface, and/or number of surfactant layers). Knowledge of the structure would enable us to use these dispersions more efficiently for their diverse applications (such as for removal of dyes, recovery of proteins, and enhancement of mass transfer in bioreactors). This study investigates dispersion and structural features of CGA utilizing a range of novel predictive (for prediction of aphron size and drainage rate) and experimental (electron microscopy and X‐ray diffraction) methods. Results indicate structural differences between foams and CGA, which may have been caused by a multilayer structure of the latter as suggested by the electron and X‐ray diffraction analysis.
Parameters affecting fluid dispersion in a continuous oscillatory baffled tube
Authors: Ni Xiongwei , Pereira Nitin E.
Published: April 2004

Experimental measurements on the axial dispersion of fluid in an oscillatory baffled tube that is operated continuously were studied. Two models, the continuous stirred tank with feedback and the plug flow with axial dispersion, were used to analyze the residence‐time distributions and determine the axial dispersion for this system. The effect of the density of tracer solution, the tracer injection position, and the tracer injection time on the axial dispersion was explored. It was found that the axial dispersion was sensitive to the changes in the density of tracer solution, but insensitive to the tracer injection position and injection time. A correlation linking the axial dispersion with the energy dissipation in the system both in the absence and presence of fluid oscillation was established. The Isotropic Turbulence Theory was applied, and for the first time the mixing length in the system was evaluated and compared with that of other devices.
On‐line data compression and error analysis using wavelet technology
Authors: Misra Manish , Qin S. Joe , Kumar Shailesh , Seemann Dick
Published: April 2004

Wavelet representation of a signal is efficient for process data compression. An on‐line compression algorithm based on Haar wavelets is proposed here. As a new data point arrives, the algorithm computes all the approximation coefficients and updates the multiresolution tree before it prepares to receive the next data point. An efficient bookkeeping and indexing scheme improves compression ratio more significantly than batch‐mode wavelet compression. Reconstruction algorithms and historian format for this bookkeeping are developed. Various analytical results on the bounds on compression ratio and sum of the square error that can be achieved using this algorithm are derived. Experimental evaluation over two sets of plant data shows that wavelet compression is superior to conventional interpolative methods (such as boxcar, backward slope, and SLIM3) in terms of quality of compression measured both in time and frequency domain and that the proposed on‐line wavelet compression algorithm performs better than the batch‐mode wavelet compression algorithm due to the efficient indexing and bookkeeping scheme. The on‐line algorithm combines the high quality of compression of wavelet‐based methods and on‐line implementation of interpolative compression algorithms at the same time.
Improving dual composition control in continuous distillation by a novel column design
Authors: Barolo Massimiliano , Papini Claudio A.
Published: April 2004

How a novel design of continuous distillation columns may impact the performance of conventional controllers when it is required to accurately control the purity of both products in a binary separation is analyzed. The proposed column layout is characterized by the presence of a middle vessel, to which two streams are fed: the liquid flow coming from the rectifying section and the feed to be separated. The actual liquid flow to the column is determined by the middle‐vessel level controller. For different control configurations and conventional proportional‐integral control, it is shown that using a middle‐vessel column provides a way to reduce the interaction between the composition loops, in such a way that the control performance of middle‐vessel columns may be made remarkably superior to that of the conventional columns. The results obtained are supported by a theoretical analysis based on the frequency‐dependent relative gain array tool.
Equations of state for the calculation of fluid‐phase equilibria
Authors: Wei Ya Song , Sadus Richard J.
Published: April 2004

Progress in developing equations of state for the calculation of fluid‐phase equilibria is reviewed. There are many alternative equations of state capable of calculating the phase equilibria of a diverse range of fluids. A wide range of equations of state from cubic equations for simple molecules to theoretically‐based equations for molecular chains is considered. An overview is also given of work on mixing rules that are used to apply equations of state to mixtures. Historically, the development of equations of state has been largely empirical. However, equations of state are being formulated increasingly with the benefit of greater theoretical insights. It is now quite common to use molecular simulation data to test the theoretical basis of equations of state. Many of these theoretically‐based equations are capable of providing reliable calculations, particularly for large molecules.
Molecular thermodynamics of asphaltene precipitation in reservoir fluids
Authors: Wu Jianzhong , Prausnitz John M. , Firoozabadi Abbas
Published: April 2004

A previously described molecular‐thermodynamic framework, based on colloid theory, is used to correlate experimental asphaltene‐precipitation data at high‐temperature and pressure conditions. In this framework, asphaltenes and resins are represented by pseudopure components, and all other components in a crude oil are presented by a continuous medium that affects van der Waals attractions among asphaltene and resin molecules. Model parameters are evaluated systematically from average properties of asphaltenes and resins in crude oils, and from dispersion‐force properties of the oil medium. Given the composition of the medium, and asphaltene and resin concentrations, the molecular‐thermodynamic model described here can be used to identify the onset of asphaltene precipitation, and the total amount of precipitation at the given operation conditions. Calculated results for the effects of oil composition and pressure on asphaltene precipitation are in good agreement with at least some experimental measurements for four reservoir fluids, including Texaco, Shell, Weyburn, and North‐Sea crude oils.
Characterization of differential ebulliometers for measuring activity coefficients
Authors: Raal J. David
Published: April 2004

Differential ebulliometry is a powerful and rapid procedure for obtaining infinitely dilute activity coefficients with potentially very good accuracy. Tedious degassing procedures are not necessary, as in a static method, and from only a few measurements full system phase behavior can be evaluated. The principal problem, precise evaluation of the equilibrium liquid composition from the known composition of a prepared solution charged to the apparatus, is well known but has so far defied adequate resolution. A system of exact self‐consistent equations was developed for the characterization of an ebulliometer through a dimensionless ebulliometer constant. Evaluation of this constant from typical data and its subsequent use are illustrated for a system of known phase equilibrium behavior. Remarkably, the equations permit evaluation of the effective “static” holdups in various parts of the equipment without any volume measurements. Since one equation is redundant to the main purpose, it can be used for a consistency check of measured and calculated data. The equations also furnish a guide for the operation of ebulliometers.
Coalescence in polymer blends during shearing
Authors: Lyu Su‐Ping , Bates Frank S. , Macosko Christopher W.
Published: April 2004

Control of coalescence is a critical factor in preparing polymer blends with specific morphologies. Coalescence was studied as a function of shear rate, volume fraction, viscosity ratio, and amount of block copolymer in a model system comprising polystyrene (PS) and high density polyethylene (HDPE). Small drops of HDPE (∼2 μm) were initially developed by shearing at 10 s−1 in a cup‐cone shear cell for 20 min. The shear rate γ˙ was then decreased to between 0.1 and 2.5 s−1, and the state of coalescence was determined after quenching samples following specified periods of steady shearing. The PS portions of quenched samples were dissolved in chloroform, and the HDPE particles filtered from the suspension. These particles were imaged by scanning electron microscopy, which showed a sharp increase in the volume‐average particle diameter at specific times that depend on shear rate volume fraction, and viscosity ratio. Little change was observed in the number average diameter (Dn) at low shear rates up to a total strain of 360. At higher shear rates, however, Dn significantly increased. Interestingly, adding small amounts of block copolymer to the blends significantly suppressed coalescence. These results are discussed in terms of particle trajectory and deformation during flow.