bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fluid flow in compressible porous media: II: Dynamic behavior
Authors: Jönsson K. Ann‐Sofi , Jönsson Bengt T. L. 
Published: June 2004

AbstractThis article deals with the dynamic behavior during filtration and wet pressing of compressible porous media. An equation is developed which permits the derivation of the time dependency of porosity and flow at varying locations in a medium subjected to hydraulic pressure and/or mechanical load. Furthermore, a numerical solution that allows the equation to be solved rapidly and with high accuracy on a common PC is presented. The computer program developed in conjunction with this work has been used to illustrate the dynamics of fluid flow in some industrially important applications, such as wet pressing of paper pulp and flow in chromatography columns. The program has also been used to calculate the flow and concentration variations during mechanical impulse loading (that is, a press pulse).
High‐temperature oxidation resistance of SiO2‐coated polyimide composite
Authors: Neogi Sudarsan , Gulino Daniel A. 
Published: June 2004

AbstractSilicon dioxide films (500–5,000 Å‐thick) were deposited on silicon wafers and polyimide composite surfaces by plasma‐enhanced chemical vapor deposition. The chemical reaction takes place on the surface and depends on substrate conditions and process parameters. In the present study, SiO2 films were deposited from tetraethylorthosilicate (TEOS) in the 275–400°C temperature range under the influence of a radio frequency discharge (13.56 MHz). The properties of the deposited films, such as refractive index, density, stoichiometry, and adhesion, were obtained. The deposition characteristics of the films were studied as a function of process parameters including temperature, pressure, and RF power level. Finally these TEOS‐SiO2 films were found to be effective in the protection of polyimide‐based composites for higher‐temperature (350–400°C) applications.
Use of dielectric loss to determine blend time for organic polymer solutions
Authors: Shervin Carl R. , Studeny Joseph E. , Romaszewski Raymond A. 
Published: June 2004

AbstractWhen scaling up mixing applications, it is often important to measure blend time. In our application, we need to measure blend time in nonaqueous solutions of organic polymers in pilot‐ and plant‐scale steel tanks. Techniques employing visual observations can be used in small‐scale glass or Plexiglas tanks, but these methods are not applicable to large‐scale operations. Another standard technique is to measure conductivity of a tracer material, which is useful particularly for aqueous systems, but does not provide an adequate response for our system.A new technique that we established involves the measurement of the dielectric loss of a tracer material added to an acrylic polymer solution in mineral oil. It is demonstrated that the addition of N,N‐dimethylformamide (DMF) results in mixing curves that give blend times equivalent to those measured by visual methods. Our preliminary studies were performed in a 2‐L vessel over a temperature range of 30–120°C. The magnitude of the dielectric loss measurement is shown to depend on the scanning frequency of the measurement and the temperature of the polymer solution. The variation over a small temperature range is slight and will not interfere with the measurements.
Imaging velocity profiles: Flow through an abrupt contraction and expansion
Authors: Xia Yang , Callaghan Paul T. , Jeffrey Kenneth R. 
Published: June 2004

AbstractDynamic nuclear magnetic resonance (NMR) microscopy has been used to study the laminar flow of water through cylindrical tubes in the vicinity of both an abrupt expansion and an abrupt contraction. Radial profiles of the velocity have been obtained, at a spatial resolution on the order of 20 μm, for the velocity components in the axial and transverse directions, both at the junction and at different axial displacements on either side of the junction. The data have been compared with solutions of the Navier‐Stokes equations obtained by finite difference numerical methods using a Macintosh personal computer. Excellent agreement is apparent without the need for any adjustable parameters, the numerical solutions depending only on the Reynolds number determined from inlet flow conditions. This study demonstrates the usefulness of dynamic NMR microscopy for the study of the flow of Newtonian fluids in complex geometries. The method can also be applied to the flow of non‐Newtonian fluids.
Transport phenomena during freezing of isolated hepatocytes
Authors: Toner Mehmet , Tompkins Ronald G. , Cravalho Ernest G. , Yarmush Martin L. 
Published: June 2004

AbstractThe cellular response of isolated rat hepatocytes to freezing stress under various chemical and physical conditions was investigated using cryomicroscopic observations and a theoretical transport model. Cryomicroscopy was used to determine the cellular dehydration during freezing at different cooling rates. Using these results, water permeability parameters were also obtained. In addition, intracellular ice formation (IIF) parameters were obtained from rapid freezing experiments at a cooling rate of 400°C/min to decouple the effects of dehydration from IIF. The water permeability and IIF parameters were then used in a transport model to predict the probability of IIF under a wide range of chemical and physical conditions observed during cell freezing. In order to verify the model predictions, experiments were performed under similar conditions and compared to the theoretical predictions. The results suggest that slowly cooled cells (< 80°C/min) dehydrate excessively and escape IIF. On the other hand rapidly cooled cells (> 120°C/min) contain enough undercooled cellular water which undergoes IIF between −5 and −12°C.
Two‐dimensional finite element analysis of microwave heating
Authors: Ayappa K. G. , Davis H. T. , Davis E. A. , Gordon J. 
Published: June 2004

AbstractTransient temperature profiles for long rods of lossy dielectric materials with thermally‐dependent dielectric properties exposed to uniform plane waves are obtained. Maxwell's equation and the heat equation are simultaneously solved using the finite element method to predict the power absorbed and the resulting temperature rise in samples of square and circular cross‐section. Following the method introduced recently, we derive an exact radiation boundary condition which is independent of the rod cross‐section. For a cylindrical sample, the boundary condition is imposed on the cylinder itself. For a square rod, the boundary condition is imposed on a cylinder containing the rod. The temperature dependence of dielectric properties and sample dimensions appreciably influence heating patterns. For square samples, the edges focus radiation, causing preferential heating at the edges. This effect is pronounced for larger samples. In addition, the incident wave polarization influences the heating of the rod. For waves where the electric field is polarized along the long axis of the sample (TMz polarization) the power absorbed is higher than when the electric field is perpendicular to the axis (TEz polarization). A case involving runaway heating is also investigated.
Wrong‐way behavior of packed‐bed reactors: Influence of reactant adsorption on support
Authors: Il'in Andrew , Luss Dan 
Published: June 2004

AbstractWrong‐way behavior refers to a large transient temperature increase caused by a sudden reduction in the feed temperature or increase in the feed rate to a packed‐bed reactor operating at an intermediate or high level of conversion. This dynamic temperature rise may be affected by reactant adsorption on the inert catalyst support. The wrong‐way behavior usually leads to formation of a downstream‐moving temperature front. In such cases, reactant adsorption tends to moderate and decrease the maximal transient temperature of these fronts. However, when the wrong‐way behavior generates an upstream‐moving temperature front, reactant adsorption may substantially increase the temperature rise over that attained in its absence and ignite the reactor. Reactant adsorption may also lead to surprising dynamic effects upon changes in feed velocity.
Sedimentation of monodisperse and bidisperse hard‐sphere colloidal suspensions
Authors: Al‐Naafa M. A. , Selim M. Sami 
Published: June 2004

AbstractThe effect of concentration on the sedimentation rate of uncharged rigid spheres was investigated. Three submicron sizes of silica spheres were prepared according to the method of Stöber (1968). The particles were sterically stabilized by chemisorption of stearyl alcohol at their surface by the method developed by van Helden (1981). The sterically stabilized silica particles dispersed in cyclohexane are known to behave as hard spheres. Monodisperse gravity sedimentation experiments were carried out for the various particle species over a wide concentration range of ϕ = 0.003 to ϕ = 0.37, where ϕ is the particle volume fraction in cyclohexane. The data for dilute suspensions (ϕ < 0.03) were found to be well described by Batchelor's equation: U/U0 = 1–6.55ϕ, where U is the sedimentation velocity and U0 is the Stokes velocity of a sphere in isolation. The data over the entire concentration range (0<ϕ<0.37) were found to be well described by the equation: U/U0 = (1–ϕ)6.55.Bidisperse sedimentation experiments were also carried out, and the dilute data were found to be well represented by Batchelor's 1982 theory for polydisperse suspensions. The high concentration data were analyzed in terms of a model that does not distinguish between interactions of like and unlike particles.
Supercritical phase fischer‐tropsch synthesis: Catalyst pore‐size effect
Authors: Fan Li , Yokota Kohshiroh , Fujimoto Kaoru 
Published: June 2004

AbstractThe Fischer‐Tropsch synthesis reaction was conducted in a supercritical fluid medium using a fixed‐bed reactor. Tailor‐made catalyst supports which had sharp pore diameter distributions were prepared by the pH swing method. The relationships between the catalyst pore structure and the catalytic activity or the product distribution were studied. The influence of the catalyst pore size on the mass transfer of reactants and products was also characterized. The catalyst pore size affected not only catalytic activity but also product selectivity. The diffusion of reactants inside the catalyst pellets in the supercritical fluid media was simulated and the effects of catalyst pore size and catalyst particle size on catalytic performances were consistent with simulation results.
Mixed‐gas adsorption dynamics of high‐concentration components in a particulate bed
Authors: Frey Douglas D. 
Published: June 2004

AbstractThe study of LeVan et al. (1988) concerning the dynamics of mixed‐gas adsorption of components having high concentrations is extended to the case of multicomponent isotherms determined from either ideal or nonideal adsorbed solution theory. A discussion is given of the effect of isotherm properties on the dynamics of isothermal, mixed‐gas adsorption when the adsorbate concentrations in the feed gas are large enough so that the interstitial fluid velocity varies significantly along the adsorption front.
Design considerations for tubular reactors with highly exothermic reactions
Authors: Shinnar Reuel , Doyle Francis J. , Budman Hector M. , Morari Manfred 
Published: June 2004

AbstractPractical guidelines are required for the design and operation of complicated catalytic packed‐bed reactors. Primary among design considerations is the avoidance of operating regions of high parametric sensitivity, in which small changes in operating conditions can lead to thermal runaway in the reactor. Existing criteria for predicting these regions rely on complex mathematical formulations for differential sensitivity between input and output variables. The present work centers on the development of practical design criteria for avoiding reactor instability and temperature sensitivity in multitubular packed‐bed reactors. A set of simple guidelines is proposed for the sizing of reactors and proper selection of operating conditions. The implications of these open‐loop sensitivities for a controlled reactor are investigated. It is shown through simulation studies that violation of the proposed criteria leads to control problems and difficulty in operating at the design point.
Comparative study of flow schemes for a simulated countercurrent adsorption separation process
Authors: Ching C. B. , Chu K. H. , Hidajat K. , Uddin M. S. 
Published: June 2004

AbstractContinuous separation of three carbohydrate mixtures [fructose‐dextran (M. W. ≈ 9,400), raffinose‐dextran (M. W. ≈ 6,000), and fructose‐raffinose] has been carried out using a simulated countercurrent process with silica gel as the sorbent and deionized water as the eluent. Experiments were conducted using the commercial four‐section arrangement and a modified three‐section flow scheme which does not recycle part of the eluent for reuse. Data for the four‐section flow scheme reflect a much higher product concentration in the raffinate and a substantially lower rate of fresh eluent consumption than for the three‐section scheme. It is concluded that when both the extract and raffinate products are desired, the four‐section scheme should be used for the separation of a mixture with a small separation factor which usually requires a large quantity of eluent to achieve an efficient separation. The behavior of the simulated countercurrent process was simulated theoretically by representing the process in terms of an equivalent true countercurrent system. A good fit to the experimental data was obtained when the process was configured in the four‐section mode. However, the same theoretical approach failed to provide a good representation of the behavior of the three‐section scheme in one respect: predicted concentrations of the raffinate product were about two times higher than experimental values. The discrepancy may be attributed to the periodic switching of fluid inlet and outlet points in the operation of the three‐section simulated countercurrent unit.
Predictive correlation for binary diffusion coefficients in dense carbon dioxide
Authors: Funazukuri Toshitaka , Ishiwata Yoshihisa , Wakao Noriaki 
Published: June 2004

AbstractBinary diffusion coefficients of some organic compounds in carbon dioxide at 313.2 K and 16.0/25.0 MPa were measured by using the Taylor‐Aris tracer response technique. We propose a new correlation of Schmidt numbers as a function of solvent molar volumes for predicting binary diffusion coefficients in dence CO2 and self‐diffusion coefficients of dense CO2. The correlation was also found to be valid for predicting self‐diffusion coefficients of dense CH4 at Fv/A* < 40 or v2/(ṽ2)0 > 1.62.
Dense, vertical gas‐solid flow in a pipe
Authors: Miller Aubrey , Gidaspow Dimitri 
Published: June 2004

AbstractThe hydrodynamics of gas‐solid flow, usually referred to as circulating fluidizedbed flow, was studied in a 7.5‐cm clear acrylic riser with 75‐μm FCC catalyst particles. Data were obtained for three central sections as a function of gas and solids flow rates. Fluxes were measured by means of an extraction probe. Particle concentrations were measured with an X‐ray densitometer. In agreement with previous investigators, these data showed the flow to be in the core‐annular regime, with a dilute rising core and a dense descending annular region. However, unlike the previous studies conducted worldwide, the data obtained in this investigation allowed us to determine the viscosity of the suspension. The viscosity was a linear function of the volume fraction of solids. It extrapolates to the high bubbling‐bed viscosities.
Bed expansion of liquid‐solid inverse fluidization
Authors: Karamanev D. G. , Nikolov L. N. 
Published: June 2004

AbstractThe bed expansion characteristics of two‐phase inverse fluidization were studied. Twelve different spheres with diameters from 1.31 to 7.24 mm and densities between 75 and 930 kg/m3 were fluidized with water. The experimental lne‐lnU curves were parallel to those predicted by the model of Richardson and Zaki and therefore the exponents n were similar. However, Ui, the liquid velocity at ε = 1 differed from that predicted from the standard drag curve for Ret > 130. This can be explained by the fact that the drag curve of a freely rising light sphere differs from that of a falling particle. The values of Ui calculated using this modified drag curve were in good agreement with the experimental results. The difference between experimental and calculated from the Ergun equation minimal fluidization velocities is explained by the difference in mechanical inertia of the light and heavy particles.
Discrete‐time nonlinear controller synthesis by input/output linearization
Authors: Soroush Masoud , Kravaris Costas 
Published: June 2004

AbstractThis work concerns the synthesis of discrete‐time nonlinear controllers for nonlinear processes that make the closed‐loop system linear in an input/output sense. The synthesis of state feedback controllers is studied first, followed by the synthesis of dynamic output feedback controllers. Both problems are solved within the globally linearizing control (GLC) framework. Precise theoretical connections between the derived controllers and model algorithmic control (MAC) are established. The theory is illustrated by a chemical reactor example.
An analysis of the statistical model adsorption isotherm
Authors: Kaminsky R. D. , Monson P. A. 
Published: June 2004

AbstractThe statistical model adsorption isotherm developed by Ruthven and coworkers and used in the prediction and correlation of adsorption in microporous materials especially zeolites is critically examined from the perspective of statistical mechanics. This is done by applying the method to a class of molecular models for which the statistical thermodynamics may be solved analytically without approximation. The models considered are finite length single component and binary one‐dimensional systems in which the molecules interact via square well potentials. These are among the simplest realistic yet analytically solvable molecular models of adsorption in porous materials. Our analysis clarifies the theoretical status of the Ruthven approach as well as revealing some of the weaknesses in it.
Thickening theories—an analysis
Authors: Fitch Bryant 
Published: June 2004

AbstractThere is as yet no theoretically sound and empirically proven procedure that is fully reliable for the design of thickeners. From a logical standpoint, a sound procedure is one correctly deduced from valid premises or assumptions. As noted in Fitch's earlier work(979), there is no reason to believe that existing mathematical models are based on uniformly valid assumptions. There is also much reason to believe that they are not. Therefore existing mathematical models or “theories” of thickening are analyzed for mathematical consistency, scientific credibility, and relevance to chemical engineering. Domains in which the models are useful approximations of reality and thus are relevant to chemical engineering practice are identified. Emendations or alternatives are suggested to bring the models more nearly into conformity with empirical results. Design procedures are suggested that, although involving assumptions that cannot be uniformly valid, would seem more reasonable than existing ones.
Drag relationships for liquid droplets settling in a continuous liquid
Authors: Greene G. A. , Irvine T. F. , Gyves T. , Smith T. 
Published: June 2004

AbstractExperiments are reported in which the drag of single liquid droplets settling in a tall column of another lighter immiscible liquid are measured. The experimental data for the eight pairs of liquids that were tested covered a range of droplet Reynolds numbers from 10−3 to 104. Two regimes of droplet settling were encountered. In the first regime, the droplets remained spherical, and the drag agreed very well with established solid sphere drag models. In the second regime, the droplets became deformed and oscillated; the drag was found to depart suddenly from predictions of spherical models and to increase with increasing Reynolds number. Empirical models for the point of departure from spherical drag and the coefficient of drag in the unstable regime are derived.
An approach to fault diagnosis of chemical processes via neural networks
Authors: Fan J. Y. , Nikolaou M. , White R. E. 
Published: June 2004

AbstractThis article presents an approach to fault diagnosis of chemical processes at steadystate operation by using artificial neural networks. The conventional back‐propagation network is enhanced by adding a number of functional units to the input layer. This technique considerably extends a network's capability for representing complex nonlinear relations and makes it possible to simultaneously diagnose multiple faults and their corresponding levels in a chemical process. A simulation study of a heptane‐to‐toluene process at steady‐state operation shows successful results for the proposed approach.
Cosolvent interactions in supercritical fluid solutions
Authors: Ekart Michael P. , Bennett Karen L. , Ekart Susan M. , Gurdial Gurdev S. , Liotta Charles L. , Eckert Charles A. 
Published: June 2004

AbstractThe addition of cosolvents to supercritical fluid (SCF) solvents can have large effects on solubilities, giving engineers the ability to tailor loadings and selectivities of solutes for difficult separations. It is necessary to have a better understanding of the special intermolecular interactions that occur in SCF solutions to predict the effects of cosolvents. We use a SCF chromatographic technique to acquire a database of cosolvent effects for a variety of cosolvents and solutes; examination of the cosolvent effects shows evidence of hydrogen bonding, charge transfer complex formation, and dipole‐dipole coupling between solute and cosolvent molecules. SCF solvents, carbon dioxide, ethane, and fluoroform, are compared, and then the use of the chromatograph to measure solubilities is discussed.