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Momentum Transfer (momentum + transfer)
Selected AbstractsExperimental Study and Modelling of Formation and Decay of Active Species in an Oxygen DischargeCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1 2005A.-M. Diamy Abstract A microwave (2.45 GHz) oxygen discharge (3 hPa, 150 W, 50 mL.min,1) is studied by optical emission spectroscopy of O(5P) (line 777.4 nm) and of the atmospheric system of O2(head-line 759.4 nm). Calibration of the spectral response of the optical setup is used to determine the concentrations of O(5P) and O2(b). The concentration of the O(5P) atoms is in the range 108,109 cm,3 and the concentration of the O2(b) molecules is in the range 1014 , 2 × 1014 cm,3 along the discharge tube. An attempt is made to simulate the experimental results by using coupling the Boltzmann equation, homogeneous energy transfer V-V and V-T, heterogeneous reactions on the walls (energy transfer and recombination of atoms) and a kinetic scheme (electronic transfer and chemical reactions). The Boltzmann equation includes momentum transfer, inelastic and superelastic processes and e-e collisions. V-V and V-T transfer equations are obtained from the SSH theory and the kinetic scheme includes 65 reactions with 17 species [electrons e, ions O, and O2,, fundamental electronic neutral species O(3P), O2, O2(X,v), O3 and excited neutral species O2(a), O2(b), O2(A), O(1D), O(1S), O(5P), O(4d 5Do), O(5s 5So), O(3d 5Do) and O(4s 5So)]. A fair agreement between experimental results and modelling is obtained with the following set of fitting values: , heterogeneous deactivation coefficient for O2(b) , = 2.6 × 10,2; , rate constant of reaction [O(1D) + O(3P) , 2 O(3P)] k34 = 1.4 × 10,11 cm3.s,1; , electron concentration in the range 1010 , 1011 cm,3. Modelling shows that the recombination coefficient for oxygen atoms on the silica wall (range 1.4 × 10,3 , 0.2 × 10,3) is of the same order as the values obtained in a previous paper and that the ratio ([O] / 2 [O2]initial) is about 33,50%. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Undulatory fish swimming: from muscles to flowFISH AND FISHERIES, Issue 2 2006Ulrike K. Müller Abstract Undulatory swimming is employed by many fish for routine swimming and extended sprints. In this biomechanical review, we address two questions: (i) how the fish's axial muscles power swimming; and (ii) how the fish's body and fins generate thrust. Fish have adapted the morphology of their axial musculature for high power output and efficiency. All but the superficial muscle fibres are arranged along curved trajectories, and the myomeres form nested cones. Two conflicting performance goals shape the fibre trajectories of the axial muscles. Maximum power output requires that all fibres contract uniformly. In a bending fish, uniform contraction in a single myomere can be ensured by curved fibre trajectories. However, uniform strain is only desirable if all muscle fibres have the same contractile properties. The fish needs several muscle-fibre types that generate maximum power at different contraction speeds to ensure effective muscle power generation across a range of swimming speeds. Consequently, these different muscle-fibre types are better served by non-uniform contractions. High power output at a range of swimming speeds requires that muscle fibres with the same contractile properties contract uniformly. The ensuing helical fibre trajectories require cone-shaped myomeres to reduce wasteful internal deformation of the entire muscle when it contracts. It can be shown that the cone-shaped myomeres of fish can be explained by two design criteria: uniform contraction (uniform strain hypothesis) and minimal internal deformation (mechanical stability hypothesis). So far, only the latter hypothesis has found strong support. The contracting muscle causes the fish body to undulate. These body undulations interact with the surrounding water to generate thrust. The resulting flow behind the swimming fish forms vortex rings, whose arrangement reflects the fish's swimming performance. Anguilliform swimmers shed individual vortex rings during steady swimming. Carangiform swimmers shed a connected chain of vortex rings. The currently available sections through the total flow fields are often not an honest representation of the total momentum in the water , the wake of carangiform swimmers shows a net backward momentum without the fish accelerating , suggesting that our current picture of the generated flow is incomplete. To accelerate, undulatory swimmers decrease the angle of the vortex rings with the mean path of motion, which is consistent with an increased rate of backward momentum transfer. Carangiform swimmers also enlarge their vortex rings to accelerate and to swim at a higher speed, while eel, which are anguilliform swimmers, shed stronger vortex rings. [source] Scaling laws in hadronic processes and string theoryFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 7-8 2003O. Andreev We briefly review a possible scheme for getting the known QCD scaling laws within string theory. In particular, we consider amplitudes for exclusive scattering of hadrons at large momentum transfer and hadronic form factors. [source] Optimal time integration parameters for elastodynamic contact problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 6 2001A. Czekanski Abstract In this paper, we employ the generalized- , time integration scheme for treating elastodynamic contact problems. The criteria invoked for the selection of the four time integration parameters are motivated by our desire to ensure that the solution is unconditionally stable, second-order accurate, provides optimal high-frequency dissipation and preserves the energy and momentum transfer in dynamic rigid impact problems. New closed-form expressions for the time integration parameters are determined in terms of user-specified high-frequency spectral radius. The selected parameters help in avoiding the spurious high-frequency modes, which are present in the traditional Newmark method. Copyright © 2001 John Wiley & Sons, Ltd. [source] Evaluation of electroosmotic drag coefficient of water in hydrated sodium perfluorosulfonate electrolyte polymerJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2009Liuming Yan Abstract The electroosmotic drag coefficient of water molecules in hydrated sodium perfluorosulfonate electrolyte polymer is evaluated on the basis of the velocity distribution functions of the sodium cations and water molecules with an electric field applied using molecular dynamics simulations. The simulation results indicate that both velocity distribution functions of water molecules and of sodium cations agree well with the classic Maxwellian velocity distribution functions when there is no electric field applied. If an electric field is applied, the distribution functions of velocity component in directions perpendicular to the applied electric field still agree with the Maxwellian velocity distribution functions but with different temperature parameters. In the direction of the applied electric field, the electric drag causes the velocity distribution function to deviate from the Maxwellian velocity distribution function; however, to obey the peak shifted Maxwellian distribution function. The peak shifting velocities coincide with the average transport velocities induced by the electric field, and could be applied to the evaluation of the electroosmotic drag coefficient of water. By evaluation of the transport velocities of water molecules in the first coordination shells of sodium cations, sulfonate anion groups, and in the bulk, it is clearly shown that the water molecules in the first coordination shell of sodium cations are the major contribution to the electroosmotic drag and momentum transfer from water molecules within the first coordination shell to the other water molecules also contributes to the electroosmotic drag. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Multi-scale study on the secondary reactions of fluid catalytic cracking gasolineAICHE JOURNAL, Issue 8 2009Bo-lun Yang Abstract Multi-scale model considered the heat transfer, mass transfer, momentum transfer, fluid flow with reactions together at different spatiotemporal scales for the riser reactor of secondary reactions of fluid catalytic cracking gasoline (SRFCCG) process has been preformed in this work. Micro-scale of kinetics in catalyst particles, meso-scale of clusters, voids, dense phase, dilute phases, and heterogeneous structures in gas,solid flow, and the macro-scale of product distribution over riser reactor have been established using multi-scale modeling method and integrated by the multi-domain strategy. The proposed model was solved with the software of EQUATRAN-G. Good agreement between simulation results and the experimental data suggested that the proposed model was well constructed and simulation exercise was successful. The multi-scale model was capable of predicting heterogeneous structures of multi-phase flow, reactor temperature profile, and product distribution of SRFCCG process. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Fluid-particle drag in low-Reynolds-number polydisperse gas,solid suspensionsAICHE JOURNAL, Issue 6 2009Xiaolong Yin Abstract Lattice-Boltzmann simulations of low-Reynolds-number fluid flow in bidisperse fixed beds and suspensions with particle,particle relative motions have been performed. The particles are spherical and are intimately mixed. The total volume fraction of the suspension was varied between 0.1 and 0.4, the volume fraction ratio ,1/,2 from 1:1 to 1:6, and the particle size ratio d1/d2 from 1:1.5 to 1:4. A drag law with improved accuracy has been established for bidisperse fixed beds. For suspensions with particle,particle relative motions, the hydrodynamic particle,particle drag representing the momentum transfer between particle species through hydrodynamic interaction is found to be an important contribution to the net fluid-particle drag. It has a logarithmic dependence on the lubrication cutoff distance and can be fit as the harmonic mean of the drag forces in bidisperse fixed beds. The proposed drag laws for bidisperse fixed beds and suspensions are generalized to polydisperse suspensions with three or more particle species. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Two-phase flow in structured packings: Modeling and calculation on a macroscopic scaleAICHE JOURNAL, Issue 3 2008B. Mahr Abstract A model is presented that allows calculating the macroscopic flow field of counter-current two-phase flow in strongly anisotropic porous structures. It is applied to corrugated structured packings. All flow field variables and packing properties are averaged over the volume of an elementary cell. The anisotropic gas flow resistance is derived from measurements and from separate CFD calculations on 3D-X-ray CT scans. The liquid's flow resistance is calculated using an analytical model of liquid film flow on an inclined plate. Liquid flow along both preferential flow directions is represented by two separate phases, in order to consider horizontal forces despite their symmetry. Gas-liquid momentum transfer above the loading point is included. The macroscopic flow field is calculated for a 288 mm I.D. column containing four packing elements. Liquid spreading from a point source, for uniform irrigation, increased hold-up at the packing elements' joints and pressure drop are tested against experimental results. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] CFD modeling of flow patterns and hydraulics of commercial-scale sieve traysAICHE JOURNAL, Issue 4 2003Getye Gesit A computational fluid dynamics (CFD) model was used to predict the flow patterns and hydraulics of a commercial-scale sieve tray. The model considers the 3-D two-phase flow of gas and liquid in which each phase is treated as an interpenetrating continuum having separate transport equations. Interaction between the two phases occurs via an interphase momentum transfer. For the CFD analysis, the commercial packages CFX5.4 and CFX4.4 of AEA Technology were employed. Velocity distributions, clear liquid height, froth height, and liquid holdup fraction in froth were predicted for various combinations of gas and liquid flow rates. Tray geometry and operating conditions were based on the experimental work that Solari and Bell carried out in a 1.22-m diameter air,water simulator in 1986 at Fractionation Research Inc. Predicted results were found to be in good agreement with the experimental data of these authors. The objective of the work was studying the extent to which CFD can be used as a prediction and design tool for industrial trays. The simulation results are such that CFD can be used as an invaluable tool in tray design and analysis. [source] Temperature gradient analyzers for compact high-resolution X-ray spectrometersJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2010D. Ishikawa Compact high-resolution X-ray spectrometers with a one-dimensional temperature gradient at the analyzer crystal are considered. This gradient, combined with the use of a position-sensitive detector, makes it possible to relax the usual Rowland-circle condition, allowing increased space at the sample position for a given energy resolution or arm radius. Thus, for example, it is estimated that ,meV resolution is possible with a 3,m analyzer arm and 200,mm clearance between the sample and detector. Simple analytic formulae are provided, supported by excellent agreement with ray-tracing simulations. One variation of this method also allows the detector position sensitivity to be used to determine momentum transfer, effectively improving momentum resolution without reducing (slitting down) the analyzer size. Application to medium-resolution (,10,100,meV) inelastic X-ray scattering spectrometers with large angular acceptance is discussed, where this method also allows increased space at the sample. In some cases the application of a temperature gradient can improve the energy resolution even with a single-element detector. [source] Image contrast in X-ray reflection interface microscopy: comparison of data with model calculations and simulationsJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2008P. Fenter The contrast mechanism for imaging molecular-scale features on solid surfaces is described for X-ray reflection interface microscopy (XRIM) through comparison of experimental images with model calculations and simulated measurements. Images of elementary steps show that image contrast is controlled by changes in the incident angle of the X-ray beam with respect to the sample surface. Systematic changes in the magnitude and sign of image contrast are asymmetric for angular deviations of the sample from the specular reflection condition. No changes in image contrast are observed when defocusing the condenser or objective lenses. These data are explained with model structure-factor calculations that reproduce all of the qualitative features observed in the experimental data. These results provide new insights into the image contrast mechanism, including contrast reversal as a function of incident angle, the sensitivity of image contrast to step direction (i.e. up versus down), and the ability to maximize image contrast at almost any scattering condition defined by the vertical momentum transfer, Qz. The full surface topography can then, in principle, be recovered by a series of images as a function of incident angle at fixed momentum transfer. Inclusion of relevant experimental details shows that the image contrast magnitude is controlled by the intersection of the reciprocal-space resolution function (i.e. controlled by numerical aperture of the condenser and objective lenses) and the spatially resolved interfacial structure factor of the object being imaged. Together these factors reduce the nominal contrast for a step near the specular reflection condition to a value similar to that observed experimentally. This formalism demonstrates that the XRIM images derive from limited aperture contrast, and explains how non-zero image contrast can be obtained when imaging a pure phase object corresponding to the interfacial topography. [source] Analysis of fluid-structure interaction in low pressure MEMS by Integral EquationsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Attilio FrangiArticle first published online: 25 FEB 200 The evaluation of gas dissipation occurring in inertial polysilicon MEMS is addressed focusing the attention on the free,molecule flow. In this regime, which is very often of interest for industrial applications, collisions between molecules can be neglected and the momentum transfer to the moving shuttle can be easily computed. Since the surfaces of silicon MEMS are generally very rough, a complete diffusion model is adopted to describe the wall,molecule interaction. A Boundary Integral Equation approach is proposed and it is shown that the introduction of the key assumption of small perturbations is crucial in the development of a robust and fast numerical tool. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Detection and characterization of ultra-thin films with neutron reflectometryACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2009Z. Tun Specular reflectometry, being a technique based on interference between coherent X-ray or neutron beams, is considered to have a fundamental limit in sensing the presence of films that are too thin for the maximum momentum transfer, Qmax, to which reflectivity has been measured. However, it is known both experimentally and from simulations that an ultra-thin film, with thickness t << 2,/Qmax, can be detected if it exists sandwiched between two contrast-matched media. This possibility is qualitatively explained using phase-vector diagrams. The diagrams also show that the detection is through unmistakable shifts of the interference maxima and minima, and that the scattering-length density of the ultra-thin film determined by least-squares analysis is unique. [source] Time-of-flight studies of secondary ions produced by 400,eV He+ ion impact on Ar, Kr, and Xe thin films at 8 KRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2002Kenzo Hiraoka Secondary ions produced by 400,eV He+ ion impact on Ar, Kr, and Xe thin films deposited on a silicon substrate at 8,K were measured as a function of film thickness using a time-of-flight secondary-ion mass spectrometer. For Ar, the cluster ions Arn+ up to n,=,4 as well as the monomer ion (n,=,1) were observed and they showed characteristic film-thickness dependence with increase of the film thickness up to ,200 monolayers. This is due to the momentum transfer in the elastic collision between the incident He+ ion and the matrix Ar atoms and also to the relaxation of electronic excitations (e.g., holes and excitons) to phonons resulting in the film erosion. In contrast, neither dimer nor cluster ions were detected for solid Kr and Xe films. This is due to the less efficient momentum transfer in the elastic collision between He+ and Rg's (Rg,=,Kr and Xe) and also to the efficient electronic energy migration in solid Kr and Xe. The ions originating from the silicon substrate such as Si+, SiCH3+, SiOH+, and C+ were found to be sensitized by the deposition of Xe film in the range of 0,40 monolayers. The penetration depths of the primary ion He+ through the rare gas films increase in the order Ar,<,Kr,<,Xe. Copyright © 2002 John Wiley & Sons, Ltd. [source] CFD simulation of gas,solid bubbling fluidized bed: A new method for adjusting drag lawTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009Farshid Vejahati Abstract In computational fluid dynamics modelling of gas,solid two phase flow, drag force is one of the dominant mechanisms for interphase momentum transfer. Despite the profusion of drag models, none of the available drag functions gives accurate results in their own original form. In this work the drag correlations of Syamlal and O'Brien (Syamlal and O'Brien, Int. J. Multiphase Flow. 1988; 14(4):473,481), Gidaspow (Gidaspow, Appl. Mech. Rev. 1986; 39:1,23), Wen and Yu (Wen and Yu, Chem. Eng. Prog. Symp. Ser. 1966; 62(2):100,111), Arastoopour et al. (Arastoopour et al., Powder Technol. 1990; 62(2): 163,170), Gibilaro et al. (Gibilaro et al., Chem. Eng. Sci. 1985; 40:1817,1823), Di Felice (Di Felice, Int. J. Multiphase Flow. 1994; 20(1):153,159), Zhang-Reese (Zhang and Reese, Chem. Eng. Sci. 2003; 58(8):1641,1644) and Hill et al. (Hill et al., J. Fluid Mech. 2001; 448:243,278) are reviewed using a multi-fluid model of FLUENT V6.3.26 (FLUENT, 2007. Fluent 6.3 User's Guide, 23.5 Eulerian Model, Fluent, Inc.) software with the resulting hydrodynamics parameters being compared with experimental data. The main contribution of this work is to propose an easy to implement and efficient method for adjustment of Di Felice drag law which is more efficient compared to the one proposed by Syamlal-O'Brien. The new method adopted in this work showed a quantitative improvement compared to the adjusted drag model of Syamlal-O'Brien. Prediction of bed expansion and pressure drop showed excellent agreement with results of experiments conducted in a Plexiglas fluidized bed. A mesh size sensitivity analysis with varied interval spacing showed that mesh interval spacing with 18 times the particle diameter and using higher order discretization methods produces acceptable results. Dans la modélisation par la dynamique des fluides par ordinateur de l'écoulement diphasique gaz-solide, la force de traînée est l'un des mécanismes dominants dans le transfert de quantité de mouvement interphase. Malgré la profusion des modèles de traînée, aucune des fonctions de traînée disponibles ne donnent de résultats précis dans leur forme originale. Dans cet article, les corrélations de traînée de Syamlal and O'Brien (Syamlal and O'Brien, Int. J. Multiphase Flow. 1988; 14(4):473,481), Gidaspow (Gidaspow, Appl. Mech. Rev. 1986; 39:1,23), Wen and Yu (Wen and Yu, Chem. Eng. Prog. Symp. Ser. 1966; 62(2):100,111), Arastoopour et al. (Arastoopour et al., Powder Technol. 1990; 62(2):163,170), Gibilaro et al. (Gibilaro et al., Chem. Eng. Sci. 1985; 40:1817,1823), Di Felice (Di Felice, Int. J. Multiphase Flow. 1994; 20(1):153,159), Zhang-Reese (Zhang and Reese, Chem. Eng. Sci. 2003; 58(8):1641,1644) et Hill et al. (Hill et al., J. Fluid Mech. 2001; 448:243,278) sont examinées à l'aide du modèle multi-fluides du logiciel FLUENT V6.3.26 (FLUENT, 2007. Fluent 6.3 User's Guide, 23.5 Eulerian Model, Fluent, Inc.), les paramètres hydrodynamiques résultants étant comparés aux données expérimentales. La principale contribution de ce travail est de proposer une méthode efficace et facile à mettre en ,uvre pour l'ajustement de la loi de traînée de Di Felice qui est plus efficace comparativement à celle proposée par Syamlal-O'Brien. La nouvelle méthode adoptée dans ce travail montre une amélioration quantitative par rapport au modèle de traînée ajusté de Syamlal-O'Brien. La prédiction de l'expansion de lit et de la perte de charge montre un excellent accord avec les résultats des expériences menées dans un lit fluidisé en plexiglass. Une analyse de sensibilité de la taille des mailles avec des mailles de taille variable variés montre qu'une taille de maille égale à 18 fois le diamètre des particules et l'utilisation de méthodes de discrétisation d'ordre supérieur donnent des résultats acceptables. [source] Using a New Interfacial Area Transport Equation to Predict Interfacial Area in Co-current Jet MixersTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2002Stephen L. Yarbro Abstract In multiphase operations, such as liquid-liquid or gas-liquid systems, the interfacial area affects the interfluid heat, mass and momentum transfer and ultimately, the overall equipment performance. To better understand the mixing process, we developed a multi-fluid model that predicts interfacial area for kerosene-water mixtures in co-current jet mixers. The model has ensemble-averaged conservation equations for each fluid and includes a transport equation, derived from an overall energy balance, for the interfacial area concentration. In the model, the mechanical energy of the continuous phase creates interfacial area. Comparing the final, one-dimensional model to experimental data proved the model is accurate. Over 93% of the calculated and experimental data obtained from 0.027 inch and 0.041 inch diameter co-current jet mixers compared within 15%. Dans les opérations polyphasiques, comme les systèmes liquide-liquide ou gaz-liquide, la surface interfaciale influe sur les transferts inter-fluides de chaleur, de matière et de quantité de mouvement et donc sur la performance globale des équipements. Pour mieux comprendre le procédé de mélange, nous avons mis au point un modèle multifluide qui prédit la surface interfaciale pour des mélanges kérosène-eau dans des mélangeurs cocourants à jets. Le modèle comprend des équations de conservation globalement moyennées pour chaque fluide ainsi qu'une équation de transport, établie à partir d'un bilan énergétique global, pour la concentration de la surface interfaciale. Dans ce modèle, l'énergie mécanique de la phase continue crée la surface interfaciale. La comparaison entre le modèle unidimensionnel final et les données expérimentales démontre la bonne précision du modèle. Plus de 93 % des données calculées et expérimentales obtenues pour des mélangeurs cocourants à jets de 0,027 à 0,041 pouces de diamètre sont comparables à 15 % près. [source] CFD modeling of subcooling process for beer fermentation liquidASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009Yuejin Yuan Abstract A model of subcooling process for beer fermentation liquid was established at the base of a computational fluid dynamics (CFD) technique which assumed that all the biochemical reactions were suppressed to a lower extent by the cryogenic condition and their influences on heat and momentum transfer of liquid could be ignored. The subcooling process of fermentation liquid in a cooling tank was simulated, where the temperature was from 10 to , 1 °C. The transient temperature and velocity distributions of the fermentation liquid were obtained by the simulation. The results indicated that the temperature delamination was distinct in the direction of the tank axis, while the temperature gradient was inconspicuous along the radial direction. The fermentation liquid showed a complicated movement including numerous local small circumfluences, which was different from our conventional knowledge. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Temporal behaviour of global perturbations in compressible axisymmetric flows with free boundariesASTRONOMISCHE NACHRICHTEN, Issue 1 2009V.V. Zhuravlev Abstract The dynamics of small global perturbations in the form of a linear combination of a finite number of non-axisymmetric eigenmodes is studied in the two-dimensional approximation. The background flow is assumed to be an axisymmetric perfect fluid with adiabatic index , = 5/3 rotating with a power law angular velocity distribution , , r,q, 1.5 < q < 2.0, confined by free boundaries in the radial direction. The substantial transient growth of acoustic energy of optimized perturbations is discovered. An optimal energy growth G is calculated numerically for a variety of parameters. Its value depends essentially on the perturbation azimuthal wavenumber m and increases for higher values of m. The closer the rotation profile to the Keplerian law, the larger growth factors can be obtained but over a longer time. The highest acoustic energy increase found numerically is of order ,102 over ,6 typical Keplerian periods. Slow neutral eigenmodes with corotation radius beyond the outer boundary mostly contribute to the transient growth. The revealed linear temporal behaviour of perturbations may play an important role in angular momentum transfer in toroidal flows near compact relativistic objects (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation of the Development of Conflagration of Solid Material via Analysis of Coupled Heat, Mass and Momentum TransportCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2009U. Krause Abstract A mathematical model is presented for the transport of heat, mass and momentum transfer through a porous medium to simulate the chain of events from self-heating, subsequent self-ignition to smouldering fire propagation and burn-out of combustible fractions. The model comprises both diffusive and convective transport. The chemical reaction sub-model includes solid fuel decomposition and the combustion of char, carbon monoxide and hydrogen. Furthermore, biological processes, which may be a precursor of self-heating and vaporization/condensation of moisture, are also included into the model. All input data necessary for implementing the model have been determined experimentally. The model has been validated against laboratory scale self-ignition and smouldering propagation experiments and then applied to predictions of different fire scenarios during storage of bulk materials. [source] Reactive magnetron sputtering of highly (001)-textured WS2,x films: Influence of Ne+, Ar+ and Xe+ ion bombardment on the film growthPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2006K. Ellmer Abstract Layer-type van der Waals semiconductor WS2,x films were grown by radio frequency reactive magnetron sputtering from a metallic tungsten target onto oxidized silicon substrates. The sputtering atmosphere consisted of 75% hydrogen sulfide and 25% neon, argon or xenon. The substrate voltage and hence the energy of the ions bombarding the growing film, was varied from about 20 V (floating potential) to ,80 V. By in situ energy-dispersive X-ray diffraction the growth of the films was monitored and by elastic recoil detection analysis the film composition was measured. It was found that with xenon in the sputtering atmosphere a substrate voltage of ,20 V is sufficient to suppress the crystalline film growth, while for argon as the sputtering rare gas this occurs only at ,80 V. The disturbed film growth is accompanied by a sulfur loss of the growing WS2,x films down to x = 1.1 for sputtering in Ar + H2S at a substrate potential of ,60 V. The results are tentatively explained by the different momentum transfers to sulfur atoms, which is highest for argon ions. It has also to be taken into account that the low-energy xenon bombardment is a many-body cascade process with a much higher local energy density compared to argon and neon bombardment and leading to a higher defect density and a supression of the crystalline growth. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Study on Evaporating Characteristics of a Coaxial Two Impinging-Stream ConcentratorCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2006J. Yan Abstract Based on the coaxial two impinging-streams principle, a new device for solution concentration was built and studied theoretically and experimentally. The experimental study focused on the effects of inlet air temperature, inlet air flow rate, and accelerating pipe length on the volumetric evaporative coefficient of the impinging-stream concentrator (ISC). The results show that the ISC has a relatively high volumetric evaporative coefficient, which increases with higher inlet air flow rates and higher inlet air temperature, and the ISC with a shorter accelerating pipe is more efficient. A theoretical model was suggested based on the consideration of mass, heat, and momentum transfers between liquid droplets and hot air. The concentration process of a sucrose solution in the ISC was simulated using the model and the results were compared with the experimental results, which indicated that the suggested model is reliable with a maximum relative error of less than 6.6,%. 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