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Isothermal
Terms modified by Isothermal Selected AbstractsPressureless Sintering of 3Y-TZP/Stainless-Steel Composite LayersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008Mahdi Dourandish A pressureless sintering method was utilized to fabricate metal/ceramic joints out of yttria-stabilized zirconia (3Y-TZP) and stainless steels (SS). Ultrafine (150 nm) and nanoscale (75 nm) 3Y-TZP particles and micrometric 17-4PH, 316L, and 420 SS (<31 ,m) powders were tested. Isothermal and nonisothermal sintering behaviors of the powders and composite layers in hydrogen, argon, and vacuum atmospheres were examined. It was found that the mismatch strain between the zirconia ceramic and SS during cosintering is significant, which leads to bond cracking and joint failure. Nevertheless, interlayer diffusion of Zr, Fe, and Cr and the formation of a reaction zone, particularly during vacuum sintering, enables an accommodation of the residual stresses caused by the mismatch shrinkage upon cooling. The formation of a porous region close to the metal layer was observed. Sinter joining of zirconia to 420 SS is more successful compared with austenitic steel because of a lower difference in the coefficient of thermal expansion. [source] Monitoring the reaction progress of a high-performance phenylethynyl-terminated poly(etherimide).POLYMER ENGINEERING & SCIENCE, Issue 5 2002Part I: Cure kinetics modeling The cure kinetics of a phenylethynyl-terminated poly(etherimide) are examined via differential scanning calorimetry (DSC) measurements. Isothermal holds at temperatures ranging from 325°C to 360°C provided the necessary information to develop reaction kinetics models using both first-order reaction kinetics and combination reaction kinetics. The first-order reaction kinetics model works well for quick estimates of degree of cure versus time over the experimental temperature range. However, significantly more accurate predictions of degree of cure versus time were provided by the combination reaction kinetics model. The lack of accuracy in the first order model is due to the fact that the reaction cannot be described by a simple order. The experimental procedures followed to obtain the cure kinetics data and the construction of the models from this data are described; the predictions of these models are compared with the experimental results. [source] Generalized slit flow of an ellis fluidPOLYMER ENGINEERING & SCIENCE, Issue 11 2001Ryszard T. Steller Isothermal, steady-state and fully developed flows of Ellis fluids in planar and annular slits are discussed. The flow equations derived for Ellis fluids describe also the flows of Newtonian and power law fluids as specific cases. The most important flows resulting from thp general theory, i.e., the pressure flows in flat and annular slits for stationary channel walls and at transverse and longitudinal movements of a wall, are analyzed in detail. Numerical verification of the results leads to the conclusion that the planar and annular flows of Ellis and power law fluids are qualitatively similar The quantitative differences resulting from the slit curvature and the type of constitutive equation are relatively large only for flows of strongly non-New-tonian liquids. [source] On helical flows of polymer fluidsPOLYMER ENGINEERING & SCIENCE, Issue 6 2001Jae-Hyeuk Jeong Isothermal and non-isothermal steady helical flows are theoretically investigated under the assumption that the flow is fully developed in both the thermal and hydrodynamic senses. It is well known that the basic gross characteristics of steady isothermal helical flows of non-Newtonian liquids can be found relatively easily if the flow curve (or non-Newtonian viscosity) in simple shearing is known. Nevertheless, evaluation of more detailed viscoelastic properties in this type of flow is also sometimes desirable. These properties are shown to be exactly determined in both the isothermal and non-isothermal cases as soon as a nonlinear viscoelatic constitutive equation is specified. Shear thinning due to fluid rotation and strong temperature dependence of Newtonian viscosity highly increase dissipative heat. This can produce significant non-isothermal effects in intense helical flows, even when the wall temperature is kept uniform and constant. It is shown that the energy consumption in isothermal and non-isothermal helical flows is always higher than in respective annular flows with the same flow rate. Comparisons between our calculations and available experimental data are also discussed. [source] Isothermal and nonisothermal crystallization kinetics of nylon 10 12POLYMER ENGINEERING & SCIENCE, Issue 9 2000Yongjin Li This article studied the crystallization behaviors of a newly industrialized polyamide, Nylon 10 12, under isothermal and nonisothermal conditions from the melt. A differential scanning calorimeter (DSC) was used to monitor the energetics of the crystallization process. During isothermal crystallization, relative crystallinity develops in accordance with the time dependence described by the Avrami equation with the exponent n=2.0. For nonisothermal studies, several different analysis methods were used to describe the crystallization process. The experimental results show that the Ozawa approach cannot adequately describe the nonisothermal crystallization kinetics. However, Avrami treatment for nonisothermal crystallization is able to describe the system very well. The calculated activation energy is 264.4 KJ/mol for isothermal crystallization by Arrhenius form and 235.5 KJ/mol for nonisothermal crystallization by Kissinger method. [source] Kinetic studies on the influence of temperature and growth rate history on crystal growthCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2008P. M. Martins Abstract Crystallization experiments of sucrose were performed in a batch crystallizer to study the effect of temperature and growth rate history on the crystal growth kinetics. In one of the growth methods adopted, the isothermal volumetric growth rate (RV) is determined as a function of supersaturation (S) at 35, 40 and 45 ºC. In the other, crystals are allowed to grow at constant supersaturation by automatically controlling the solution temperature as the solute concentration decreased. Using the latter method RV is calculated as the solution is cooled. The obtained results are interpreted using empirical, engineering and fundamental perspectives of crystal growth. Firstly, the overall activation energy (EA) is determined from the empirical growth constants obtained in the isothermal method. The concept of falsified kinetics, widely used in chemical reaction engineering, is then extended to the crystal growth of sucrose in order to estimate the true activation energy (ET) from the diffusion-affected constant, EA. The differences found in the isothermal and constant supersaturation methods are explained from the viewpoint of the spiral nucleation mechanism, taking into account different crystal surface properties caused by the growth rate history in each method. Finally, the crystal growth curve obtained in the batch crystallizer at 40 ºC is compared with the one obtained in a fluidized bed crystallizer at the same temperature. Apparently divergent results are explained by the effects of crystal size, hydrodynamic conditions and growth rate history on the crystallization kinetics of sucrose. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High-Temperature Electrochemistry: A ReviewELECTROANALYSIS, Issue 6 2004Gregory Abstract High-temperature electrochemistry remains a relatively unexplored field of research, although in recent years significant developments have been made. This report details the main experimental methods and approaches to heating an electrochemical system under both isothermal and non-isothermal conditions and gives an insight into the experimental and electroanalytical results obtainable under such conditions. It has been shown that the promotion of mass transport at high-temperatures, through diffusion or convection, often results in increased current signals. This increase benefits electroanalytical measurements by lowering detection limits. High temperatures also usefully enhance the sensitivity of systems with sluggish kinetics. [source] Multiple displacement amplification as a pre-polymerase chain reaction (pre-PCR) to process difficult to amplify samples and low copy number sequences from natural environmentsENVIRONMENTAL MICROBIOLOGY, Issue 7 2005Juan M. Gonzalez Summary Microbial assessment of natural biodiversity is usually achieved through polymerase chain reaction (PCR) amplification. Deoxyribonucleic acid (DNA) sequences from natural samples are often difficult to amplify because of the presence of PCR inhibitors or to the low number of copies of specific sequences. In this study, we propose a non-specific preamplification procedure to overcome the presence of inhibitors and to increase the number of copies prior to carrying out standard amplification by PCR. The pre-PCR step is carried out through a multiple displacement amplification (MDA) technique using random hexamers as priming oligonucleotides and ,29 DNA polymerase in an isothermal, whole-genome amplification reaction. Polymerase chain reaction amplification using specific priming oligonucleotides allows the selection of the sequences of interest after a preamplification reaction from complex environmental samples. The procedure (MDA-PCR) has been tested on a natural microbial community from a hypogean environment and laboratory assemblages of known bacterial species, in both cases targeting the small subunit ribosomal RNA gene sequences. Results from the natural community showed successful amplifications using the two steps protocol proposed in this study while standard, direct PCR amplification resulted in no amplification product. Amplifications from a laboratory assemblage by the two-step proposed protocol were successful at bacterial concentrations ,,10-fold lower than standard PCR. Amplifications carried out in the presence of different concentrations of fulvic acids (a soil humic fraction) by the MDA-PCR protocol generated PCR products at concentrations of fulvic acids over 10-fold higher than standard PCR amplifications. The proposed procedure (MDA-PCR) opens the possibility of detecting sequences represented at very low copy numbers, to work with minute samples, as well as to reduce the negative effects on PCR amplifications of some inhibitory substances commonly found in environmental samples. [source] Low cycle thermo-mechanical fatigue: damage operator approachFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2010M. NAGODE ABSTRACT The strain-life approach is standardized and widely accepted for determining fatigue damage under strain-controlled low cycle fatigue (LCF) loading. It was first extended to non-isothermal cases by introducing an equivalent temperature approach (ETA). The paper presents its extension that is the damage operator approach (DOA) enabling online continuous damage calculation for isothermal and non-isothermal loading with mean stress correction. The cycle closure point, cycle equivalent temperature, threshold temperature and separate rainflow counting obligatory for the ETA are not necessary for the DOA any more. Both approaches are equivalent for the second and subsequent runs of block loading if temperature is constant. However, for non-isothermal cases, the DOA is within the worst and the best case scenarios of the ETA. The approaches are compared to the simple stress histories and several thermo-mechanical fatigue (TMF) cycle types. [source] A critical plane fatigue model with coupled meso-plasticity and damageFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2008N. HUYEN ABSTRACT The work proposed in this paper is a possible way of modelling some local observations at the surface of mild steel specimens submitted to uniaxial and multiaxial loads. It is clearly seen that local plasticity, controlled by local microstructural heterogeneities, plays a fundamental role in microcrack nucleation and damage orientation is closely related to the applied loading mode. The framework of irreversible thermodynamics with internal variables for time-independent, isothermal and small deformations has been used to build a critical plane damage model by assuming the existence of a link between mesoplasticity and mesodamage. Non-associated plasticity and damage rules allow the evolution of some plastic slip before any damage nucleation, as seen during the observations. A key feature of this proposal is the capacity to reflect nonlinear damage accumulation under variable amplitude loading. [source] An overview of the damage approach of durability modelling at elevated temperatureFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2001J.-L. Chaboche Lifetime prediction techniques for components working at elevated temperature are revisited. Two damage approaches in which time effects at high temperature are introduced in different ways are discussed in greater detail. First, a creep,fatigue damage model considers the interaction of the two processes during the whole life before macrocrack initiation; and second, a creep,fatigue,oxidation model separates the fatigue life into two periods: during initiation the environment-assisted processes interact with fatigue, although bulk creep damage only interacts during the micropropagation period. The second model is illustrated by its application to a coated single-crystal superalloy used in aerojet turbine blades. Its capabilities are illustrated in a number of isothermal and thermomechanical fatigue tests. Anisotropy effects are also briefly discussed and a special test, introducing cyclic thermal gradients through the wall thickness of a tubular component, demonstrates the predictive capabilities for actual engine conditions. [source] Modelling Approach for Planar Self-Breathing PEMFC and Comparison with Experimental Results,FUEL CELLS, Issue 4 2004A. Schmitz Abstract This paper presents a model-based analysis of a proton exchange membrane fuel cell,(PEMFC) with a planar design as the power supply for portable applications. The cell is operated with hydrogen and consists of an open cathode side allowing for passive, self-breathing, operation. This planar fuel cell is fabricated using printed circuit board,(PCB) technology. Long-term stability of this type of fuel cell has been demonstrated. A stationary, two-dimensional, isothermal, mathematical model of the planar fuel cell is developed. Fickian diffusion of the gaseous components,(O2, H2, H2O) in the gas diffusion layers and the catalyst layers is accounted for. The transport of water is considered in the gaseous phase only. The electrochemical reactions are described by the Tafel equation. The potential and current balance equations are solved separately for protons and electrons. The resulting system of partial differential equations is solved by a finite element method using FEMLAB,(COMSOL Inc.) software. Three different cathode opening ratios are realized and the corresponding polarization curves are measured. The measurements are compared to numerical simulation results. The model reproduces the shape of the measured polarization curves and comparable limiting current density values, due to mass transport limitation, are obtained. The simulated distribution of gaseous water shows that an increase of the water concentration under the rib occurs. It is concluded that liquid water may condense under the rib leading to a reduction of the open pore space accessible for gas transport. Thus, a broad rib not only hinders the oxygen supply itself, but may also cause additional mass transport problems due to the condensation of water. [source] Crystallization and Grain Growth Kinetics for Precipitation-Based Ceramics: A Case Study on Amorphous Ceria Thin Films from Spray PyrolysisADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Jennifer L. M. Rupp Abstract The introductory part reviews the impact of thin film fabrication, precipitation versus vacuum-based methods, on the initial defect state of the material and microstructure evolution to amorphous, biphasic amorphous-nanocrystalline, and fully nanocrystalline metal oxides. In this study, general rules for the kinetics of nucleation, crystallization, and grain growth of a pure single-phase metal oxide thin film made by a precipitation-based technique from a precursor with one single organic solvent are discussed. For this a complete case study on the isothermal and non-isothermal microstructure evolution of dense amorphous ceria thin films fabricated by spray pyrolysis is conducted. A general model is established and comparison of these thin film microstructure evolution to kinetics of classical glass-ceramics or metallic glasses is presented. Knowledge on thermal microstructure evolution of originally amorphous precipitation-based metal oxide thin films allows for their introduction and distinctive microstructure engineering in devices-based on microelectromechanical (MEMS) technology such as solar cells, capacitors, sensors, micro-solid oxide fuel cells, or oxygen separation membranes on Si-chips. [source] Comparative study of the continuous phase flow in a cyclone separator using different turbulence models,INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2005H. Shalaby Abstract Numerical calculations were carried out at the apex cone and various axial positions of a gas cyclone separator for industrial applications. Two different NS-solvers (a commercial one (CFX 4.4 ANSYS GmbH, Munich, Germany, CFX Solver Documentation, 1998), and a research code (Post-doctoral Thesis, Technical University of Chemnitz, Germany, September, 2002)) based on a pressure correction algorithm of the SIMPLE method have been applied to predict the flow behaviour. The flow was assumed as unsteady, incompressible and isothermal. A k,, turbulence model has been applied first using the commercial code to investigate the gas flow. Due to the nature of cyclone flows, which exhibit highly curved streamlines and anisotropic turbulence, advanced turbulence models such as Reynolds stress model (RSM) and large eddy simulation (LES) have been used as well. The RSM simulation was performed using the commercial package activating the Launder et al.'s (J. Fluid. Mech. 1975; 68(3):537,566) approach, while for the LES calculations the research code has been applied utilizing the Smagorinsky model. It was found that the k,, model cannot predict flow phenomena inside the cyclone properly due to the strong curvature of the streamlines. The RSM results are comparable with LES results in the area of the apex cone plane. However, the application of the LES reveals qualitative agreement with the experimental data, but requires higher computer capacity and longer running times than RSM. This paper is organized into five sections. The first section consists of an introduction and a summary of previous work. Section 2 deals with turbulence modelling including the governing equations and the three turbulence models used. In Section 3, computational parameters are discussed such as computational grids, boundary conditions and the solution algorithm with respect to the use of MISTRAL/PartFlow-3D. In Section 4, prediction profiles of the gas flow at axial and apex cone positions are presented and discussed. Section 5 summarizes and concludes the paper. Copyright © 2005 John Wiley & Sons, Ltd. [source] Anisotropic, isothermal, turbulent swirling flow in a complex combustor geometryINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10-11 2005L. N. Jones Abstract The performance of popular second moment closure (LRR, SSG) turbulence models is assessed and compared against experimental data for anisotropic swirling flow in a cylindrical combustion chamber. In contrast to previous studies, where the dissipation anisotropy is correlated with the stress anisotropy, the benefit of approximating the former for swirling flows in terms of the mean strain and vorticity is investigated. Second moment closure models are found to predict mean and turbulent flow quantities reasonably well everywhere except near the wall. The anisotropic dissipation model is found to improve prediction of mean flow quantities near the chamber axis and acts to preserve turbulence further downstream. Copyright © 2005 John Wiley & Sons, Ltd. [source] A segregated method for compressible flow computation Part I: isothermal compressible flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2005Guillermo Hauke Abstract Traditionally, coupled methods have been employed for the computation of compressible flows, whereas segregated methods have been preferred for the computation of incompressible flows. Compared to coupled methods, segregated solvers present the advantage of reduced computer memory and CPU time requirements, although at the cost of an inferior robustness. Therefore, in a series of papers we present unified computational techniques to compute compressible and incompressible flows with segregated stabilized methods. The proposed algorithms have an increased robustness compared to existing techniques, while possessing additional benefits such as employing standard pressure boundary conditions. In this first part, the thermodynamics of isothermal, thermally perfect compressible flows is set up in the framework of symmetric systems and the corresponding segregated algorithms are introduced. Copyright © 2005 John Wiley & Sons, Ltd. [source] Three-dimensional incompressible flow calculations using the characteristic based split (CBS) schemeINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2004P. Nithiarasu Abstract In this paper, the characteristic based split scheme is employed for the solution of three-dimensional incompressible viscous flow problems on unstructured meshes. Many algorithm related issues are discussed. Fully explicit and semiimplicit forms of the scheme are explained and employed in the calculation of both isothermal and nonisothermal incompressible flows simulation. The extension of the scheme to porous medium flows is also demonstrated with relevant examples. Copyright © 2004 John Wiley & Sons, Ltd. [source] A parametric study of multi-phase and multi-species transport in the cathode of PEM fuel cellsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2008Nada Zamel Abstract In this study, a mathematical model is developed for the cathode of PEM fuel cells, including multi-phase and multi-species transport and electrochemical reaction under the isothermal and steady-state conditions. The conservation equations for mass, momentum, species and charge are solved using the commercial software COMSOL Multiphysics. The catalyst layer is modeled as a finite domain and assumed to be composed of a uniform distribution of supported catalyst, liquid water, electrolyte and void space. The Stefan,Maxwell equation is used to model the multi-species diffusion in the gas diffusion and catalyst layers. Owing to the low relative species' velocity, Darcy's law is used to describe the transport of gas and liquid phases in the gas diffusion and catalyst layers. A serpentine flow field is considered to distribute the oxidant over the active cathode electrode surface, with pressure loss in the flow direction along the channel. The dependency of the capillary pressure on the saturation is modeled using the Leverette function and the Brooks and Corey relation. A parametric study is carried out to investigate the effects of pressure drop in the flow channel, permeability, inlet relative humidity and shoulder/channel width ratio on the performance of the cell and the transport of liquid water. An inlet relative humidity of 90 and 80% leads to the highest performance in the cathode. Owing to liquid water evaporation, the relative humidity in the catalyst layer reaches 100% with an inlet relative humidity of 90 and 80%, resulting in a high electrolyte conductivity. The electrolyte conductivity plays a significant role in determining the overall performance up to a point. Further, the catalyst layer is found to be important in controlling the water concentration in the cell. The cross-flow phenomenon is shown to enhance the removal of liquid water from the cell. Moreover, a shoulder/channel width ratio of 1:2 is found to be an optimal ratio. A decrease in the shoulder/channel ratio results in an increase in performance and an increase in cross flow. Finally, the Leverette function leads to lower liquid water saturations in the backing and catalyst layers than the Brooks and Corey relation. The overall trend, however, is similar for both functions. Copyright © 2007 John Wiley & Sons, Ltd. [source] Studies on pyrolysis of vegetable market wastes in presence of heat transfer resistance and deactivationINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 9 2005Ruby Ray Abstract In the present investigation, the pyrolysis of predried vegetable market waste (dp=5.03 mm) has been studied using a cylindrical pyrolyser having diameter of 250 mm under both isothermal and non-isothermal conditions within the temperature range of 523,923 K with an intention to investigate the effective contribution of different heat transfer controlling regime namely intra-particle, external along with kinetically control regime on the overall global rate of pyrolysis. Thermogravimetric method of analysis was utilized to obtain experimental data for both isothermal and non-isothermal cases by coupling a digital balance with the pyrolyser. The pyrolysis of vegetable market waste has been observed to exhibit deactivated concentration independent pyrolysis kinetics, analogous to catalytic poisoning, throughout the entire range of study. The deactivation is of 1st order up to 723 K and follows the 3rd order in the temperature range of 723 Effects of storage aging on the cure kinetics of bismaleimide prepregsADVANCES IN POLYMER TECHNOLOGY, Issue 4 2005M. Frigione The effects of room temperature aging on the subsequent polymerization kinetics of a bismaleimide (BMI) matrix prepreg, for high performance composites, have been characterized by different time and storage conditions. The study has focused on the stability of BMI matrix carbon fiber prepregs, when exposed to controlled environmental conditions before being used in composite manufacturing. The effects of aging on glass transition temperature, reactivity, and processability have been investigated by calorimetry through dynamic, isothermal, and cure-simulating tests. A theoretical kinetic model for epoxy matrix prepregs, developed in previous studies, has been applied to the polymerization of both aged and unaged BMI matrix. The model is able to satisfactorily describe the effect of processing variables such as temperature and degree of reaction during the curing of the composite under different conditions (curing temperature and heating rate). The effects of diffusion-controlled phenomena on the reaction kinetics, associated with changes in glass transition temperature as a function of the degree of polymerization and cross-linking, have been taken into account in the formulation of an nth-order kinetic model. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 253,265, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20048 [source] Improving mechanical performance of injection molded PLA by controlling crystallinityJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Angela M. Harris Abstract Currently, use of poly(lactic acid) (PLA) for injection molded articles is limited for commercial applications because PLA has a slow crystallization rate when compared with many other thermoplastics as well as standard injection molding cycle times. The overall crystallization rate and final crystallinity of PLA were controlled by the addition of physical nucleating agents as well as optimization of injection molding processing conditions. Talc and ethylene bis-stearamide (EBS) nucleating agents both showed dramatic increases in crystallization rate and final crystalline content as indicated by isothermal and nonisothermal crystallization measurements. Isothermal crystallization half-times were found to decrease nearly 65-fold by the addition of only 2% talc. Process changes also had a significant effect on the final crystallinity of molded neat PLA, which was shown to increase from 5 to 42%. The combination of nucleating agents and process optimization not only resulted in an increase in final injection molded crystallinity level, but also allowed for a decreased processing time. An increase of over 30°C in the heat distortion temperature and improved strength and modulus by upwards of 25% were achieved through these material and process changes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Study of operating variables in the transformation of aqueous ethanol into hydrocarbons on an HZSM-5 zeoliteJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2002Andres T Aguayo Abstract With the aim of determining the possibilities of directly upgrading the liquid obtained from carbohydrate fermentation, the effect of operating conditions (temperature, space time, water content in the feed) has been studied in the catalytic transformation of aqueous ethanol into hydrocarbons on an HZSM-5 zeolite in an isothermal fixed bed reactor. Special attention has been paid to the effect of water content on the yield, product distribution and catalyst deactivation. Although deactivation by coke decreases as the water content is increased, this content must be limited at 450,°C and higher temperatures in order to avoid irreversible deactivation of the catalyst by dealumination. © 2002 Society of Chemical Industry [source] IDEA: Interface dynamics and energetics algorithmJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2007D. Duca Abstract IDEA, interface dynamics and energetics algorithm, was implemented, in FORTRAN, under different operating systems to mimic dynamics and energetics of elementary events involved in interfacial processes. The code included a parallel elaboration scheme in which both the stochastic and the deterministic components, involved in the developed physical model, worked simultaneously. IDEA also embodied an optionally running VISUAL subroutine, showing the dynamic energy changes caused by the surface events, e.g., occurring at the gas-solid interface. Monte Carlo and ordinary differential equation system subroutines were employed in a synergistic way to drive the occurrence of the elementary events and to manage the implied energy flows, respectively. Biphase processes, namely isothermal and isobaric adsorption of carbon monoxide on nickel, palladium, and platinum surfaces, were first studied to test the capability of the code in modeling real frames. On the whole, the simulated results showed that IDEA could reproduce the inner characteristics of the studied systems and predict properties not yet experimentally investigated. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Fountain flow revisited: The effect of various fluid mechanics parametersAICHE JOURNAL, Issue 5 2010Evan Mitsoulis Abstract Numerical simulations have been undertaken for the benchmark problem of fountain flow present in injection-mold filling. The finite element method (FEM) is used to provide numerical results for both cases of planar and axisymmetric domains under laminar, isothermal, steady-state conditions for Newtonian fluids. The effects of inertia, gravity, surface tension, compressibility, slip at the wall, and pressure dependence of the viscosity are all considered individually in parametric studies covering a wide range of the relevant parameters. These results extend previous ones regarding the shape of the front, and in particular the centerline front position, as a function of the dimensionless parameters. The pressures from the simulations have been used to compute the excess pressure losses in the system (front pressure correction or exit correction). Inertia leads to highly extended front positions relative to the inertialess Newtonian values, which are 0.895 for the planar case and 0.835 for the axisymmetric one. Gravity acting in the direction of flow shows the same effect, while gravity opposing the flow gives a reduced bulge of the fountain. Surface tension, slip at the wall, and compressibility, all decrease the shape of the front. Pressure-dependence of the viscosity leads to increased front position as a corresponding dimensionless parameter goes from zero (no effect) to higher values of the pressure-shift factor. The exit correction increases monotonically with inertia, compressibility, and gravity, while it decreases monotonically with slip and pressure-dependence of the viscosity. Contour plots of the primary variables (velocity-pressure) show interesting trends compared with the base case (zero values of the dimensionless parameters and of surface tension). © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] In situ high temperature microscopy study of the surface oxidation and phase transformations in titanium alloysJOURNAL OF MICROSCOPY, Issue 3 2002S. Malinov Summary Two popular commercial titanium alloys, Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo-0.08Si, were used for in situ high temperature microscopy study. The experiments were performed on an optical microscope equipped with high temperature stage using both normal and florescence lights. Two kinds of experiments were performed, at continuous heating/cooling with different rates and in isothermal conditions at different temperatures. The changes taking place on the sample surface during the experiments were monitored. The morphology of the ,,,,, phase transformation was recorded at different heat treatment conditions using the effect of thermal etching. An effect of sample surface oxidation and deoxidation was observed during continuous heating. The appearance and disappearance of ordered titanium oxides Ti3O and Ti2O are discussed based on the phase equilibrium diagram. The kinetics of the surface oxidation was monitored in both isothermal and continuous cooling conditions. [source] Game theoretic approach to multiobjective designs: Focus on inherent safetyAICHE JOURNAL, Issue 1 2006Anjana Meel Abstract A method for designing processes that are inherently safer,with the primary focus on disturbances having the potential for unbounded hazardous responses,is introduced. In cases where safety is not threatened (as in isothermal fermentation reactors), but product quality can rapidly degrade, this method provides designs that ensure high product quality (as in pharmaceutical processes). Using game theory, the method accounts for the trade-offs in profitability, controllability, safety and/or product quality, and flexibility. For nonlinear processes that are hard to control; that is, have an unstable and/or nonminimum-phase steady state, over a wide range of operating conditions, extended bifurcation diagrams are introduced. When a steady state is nonminimum phase, the process may exhibit inverse response. The steady states of processes are classified on the basis of instability and nonminimum-phase behavior to segregate the operating regimes into distinct zones. Locally optimal designs, one corresponding to each zone, are obtained first. These are compared with other locally optimal designs at alternate operating conditions, and/or process reconfigurations, to obtain the globally optimal design using game theory. Four indices,profitability, controllability, safety and/or product quality, and flexibility,characterize the optimality of a design. A novel index for safe operation and/or product quality at a steady state is formulated as a function of the eigenvalues of the Jacobian of the process model and the Jacobian of the process zero dynamics, providing a quantitative measure of instability and nonminimum-phase behavior. The application of the proposed method to an isothermal, continuous stirred-tank reactor (CSTR) with van der Vusse reactions, an exothermic CSTR, and an anaerobic fermentor with substrate and product inhibition is presented. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source] Air drying of milk droplet under constant and time-dependent conditionsAICHE JOURNAL, Issue 6 2005Xiao Dong Chen Abstract Spray drying is the prime process for many years for manufacturing food powders. Dairy powders are one of the main products consumed worldwide. There has been a stream of studies published previously on both modeling the drying characteristics of a single milk droplet and the dryer wide simulations incorporating computational fluid dynamics (CFD). In CFD simulations, large numbers of particles of different sizes need be tracked to represent the size distribution; it is desirable to have an accurate yet simple model for drying of a single droplet, which does not require partial differential equation. Here for the first time, two such models are validated. One model is of the characteristic drying rate curve approach and the other (new) model is of the reaction engineering approach. The model predictions are compared against a very wide range of experimental results including isothermal and time-varying temperature conditions. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] Measuring velocity distributions of viscous fluids using positron emission particle tracking (PEPT)AICHE JOURNAL, Issue 7 2004S. Bakalis Abstract Positron emission particle tracking (PEPT) can be used to trace the path of a radioactive particle within opaque fluids in pilot-scale equipment; the method can track particles through several centimeters of metal. PEPT has been successfully used to follow isokinetic tracers in viscous fluids and thus to measure velocity distributions under both isothermal and nonisothermal conditions in pipe flow. The accuracy of the method decreased as the measured velocities increased; the faster the particle traveled, the less accurate its detection. For velocities of up to 0.5 m/s the accuracy of the method was acceptable. Agreement between experimentally measured and theoretical velocity distributions was very good, for a range of fluids and process conditions. As tracer particles are used, there were problems ensuring that all parts of the measurement volume were sampled. This is possible to overcome to an extent by adjusting particle size; 600-,m tracers did not pass within 1 mm from the tube wall, whereas 240-,m particles passed much closer to the boundaries of the flow. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1606,1613, 2004 [source] Online estimation and control of polymer quality in a copolymerization reactorAICHE JOURNAL, Issue 5 2002Myung-June Park The validity of an online state estimator for a semi-batch MMA/MA solution copolymerization reactor was established using online densitometer and viscometer. Using the conventional extended Kalman filter (EKF) as the state estimator, the experiment was conducted under both isothermal and nonisothermal conditions for application to the control of copolymer properties. Further analysis was made by using ofline measurement data for the mol fraction of MMA in the remaining monomers and the solid content. The EKF was found to provide a good estimate for the state of the copolymerization system. A model predictive controller was designed and implemented to obtain copolymers with uniform copolymer composition and the desired weight average molecular weight by adopting the feed flow rate of MMA and the reaction temperature as control inputs. The controller was proven effective with a satisfactory performance for the control of polymer properties in the semi-batch copolymerization reactor. [source] Crystallization Kinetics and Electrical Relaxation of BaO,0.5Li2O,4.5B2O3 GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2009Rahul Vaish Transparent glasses in the composition BaO,0.5Li2O,4.5B2O3 (BLBO) were fabricated via the conventional melt-quenching technique. X-ray powder diffraction combined with differential scanning calorimetric (DSC) studies carried out on the as-quenched samples confirmed their amorphous and glassy nature, respectively. The crystallization behavior of these glasses has been studied by isothermal and nonisothermal methods using DSC. Crystallization kinetic parameters were evaluated from the Johnson,Mehl,Avrami equation. The value of the Avrami exponent (n) was found to be 3.6±0.1, suggesting that the process involves three-dimensional bulk crystallization. The average value of activation energy associated with the crystallization of BLBO glasses was 317±10 kJ/mol. Transparent glass,ceramics were fabricated by controlled heat-treatment of the as-quenched glasses at 845 K/40 min. The dielectric constants for BLBO glasses and glass,ceramics in the 100 Hz,10 MHz frequency range were measured as a function of the temperature (300,925 K). The electrical relaxation and dc conductivity characteristics were rationalized using electric modulus formalism. The imaginary part of the electric modulus spectra was modeled using an approximate solution of the Kohlrausch,Williams,Watts relation. The temperature-dependent behavior of stretched exponent (,) was discussed for the as-quenched and heat-treated BLBO glasses. [source]
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