Academic literature on the topic 'Kinetic modelisation of the homogeneous phase'
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Journal articles on the topic "Kinetic modelisation of the homogeneous phase"
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Gast, Sebastian, Ute S. Tuttlies, and Ulrich Nieken. "Kinetic study of the toluene oxidation in homogeneous liquid phase." Chemical Engineering Science 217 (May 2020): 115500. http://dx.doi.org/10.1016/j.ces.2020.115500.
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Bostan, Mihaï, and José Antonio Carrillo. "Fluid models with phase transition for kinetic equations in swarming." Mathematical Models and Methods in Applied Sciences 30, no. 10 (August 7, 2020): 2023–65. http://dx.doi.org/10.1142/s0218202520400163.
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We concentrate on kinetic models for swarming with individuals interacting through self-propelling and friction forces, alignment and noise. We assume that the velocity of each individual relaxes to the mean velocity. In our present case, the equilibria depend on the density and the orientation of the mean velocity, whereas the mean speed is not anymore a free parameter and a phase transition occurs in the homogeneous kinetic equation. We analyze the profile of equilibria for general potentials identifying a family of potentials leading to phase transitions. Finally, we derive the fluid equations when the interaction frequency becomes very large.
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Hwang, Bing Joe, and Tse Chuan Chou. "Heterogenizing homogeneous catalyst. 2. Effect of particle size and two-phase mixed kinetic model." Industrial & Engineering Chemistry Research 26, no. 6 (June 1987): 1132–40. http://dx.doi.org/10.1021/ie00066a013.
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Davari, Seyyed Ali, and Dibyendu Mukherjee. "Kinetic Monte Carlo simulation for homogeneous nucleation of metal nanoparticles during vapor phase synthesis." AIChE Journal 64, no. 1 (August 12, 2017): 18–28. http://dx.doi.org/10.1002/aic.15887.
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Erdös, Emerich, Petr Voňka, Josef Stejskal, and Přemysl Klíma. "An homogeneous growth model of gallium arsenide epitaxial layers from the gas phase." Collection of Czechoslovak Chemical Communications 54, no. 11 (1989): 2933–50. http://dx.doi.org/10.1135/cccc19892933.
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This paper represents a continuation and ending of the kinetic study of the gallium arsenide formation, where a so-called inhomogeneous model is proposed and quantitatively formulated in five variants, in which two kinds of active centres appear. This model is compared both with the experimental data and with the previous sequence of homogeneous models.
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MASHAYEK, FARZAD. "Droplet–turbulence interactions in low-Mach-number homogeneous shear two-phase flows." Journal of Fluid Mechanics 367 (July 25, 1998): 163–203. http://dx.doi.org/10.1017/s0022112098001414.
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Several important issues pertaining to dispersion and polydispersity of droplets in turbulent flows are investigated via direct numerical simulation (DNS). The carrier phase is considered in the Eulerian context, the dispersed phase is tracked in the Lagrangian frame and the interactions between the phases are taken into account in a realistic two-way (coupled) formulation. The resulting scheme is applied for extensive DNS of low-Mach-number, homogeneous shear turbulent flows laden with droplets. Several cases with one- and two-way couplings are considered for both non-evaporating and evaporating droplets. The effects of the mass loading ratio, the droplet time constant, and thermodynamic parameters, such as the droplet specific heat, the droplet latent heat of evaporation, and the boiling temperature, on the turbulence and the droplets are investigated. The effects of the initial droplet temperature and the initial vapour mass fraction in the carrier phase are also studied. The gravity effects are not considered as the numerical methodology is only applicable in the absence of gravity. The evolution of the turbulence kinetic energy and the mean internal energy of both phases is studied by analysing various terms in their transport equations. The results for the non-evaporating droplets show that the presence of the droplets decreases the turbulence kinetic energy of the carrier phase while increasing the level of anisotropy of the flow. The droplet streamwise velocity variance is larger than that of the fluid, and the ratio of the two increases with the increase of the droplet time constant. Evaporation increases both the turbulence kinetic energy and the mean internal energy of the carrier phase by mass transfer. In general, evaporation is controlled by the vapour mass fraction gradient around the droplet when the initial temperature difference between the phases is negligible. In cases with small initial droplet temperature, on the other hand, the convective heat transfer is more important in the evaporation process. At long times, the evaporation rate approaches asymptotic values depending on the values of various parameters. It is shown that the evaporation rate is larger for droplets residing in high-strain-rate regions of the flow, mainly due to larger droplet Reynolds numbers in these regions. For both the evaporating and the non-evaporating droplets, the root mean square (r.m.s.) of the temperature fluctuations of both phases becomes independent of the initial droplet temperature at long times. Some issues relevant to modelling of turbulent flows laden with droplets are also discussed.
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Slavinskaya, N. A., U. Riedel, V. E. Messerle, and A. B. Ustimenko. "Chemical Kinetic Modeling in Coal Gasification Processes: an Overview." Eurasian Chemico-Technological Journal 15, no. 1 (December 24, 2012): 1. http://dx.doi.org/10.18321/ectj134.
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<p>Coal is the fuel most able to cover world deficiencies in oil and natural gas. This motivates the development of new and more effective technologies for coal conversion into other fuels. Such technologies are focused on coal gasification with production of syngas or gaseous hydrocarbon fuels, as well as on direct coal liquefaction with production of liquid fuels. The benefits of plasma application in these technologies is based on the high selectivity of the plasma chemical processes, the high efficiency of conversion of different types of coal including those of low quality, relative simplicity of the process control, and significant reduction in the production of ashes, sulphur, and nitrogen oxides. In the coal gasifier, two-phase turbulent flow is coupled with heating and evaporation of coal particles, devolatilization of volatile material, the char combustion (heterogeneous/porous oxidation) or gasification, the gas phase reaction/oxidation (homogeneous oxidation) of gaseous products from coal particles. The present work reviews literature data concerning reaction kinetic modelling in coal gasification. Current state of related kinetic models for heterogeneous/homogeneous oxidation of coal particles, included plasma assisted, is reviewed.</p>
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Rosti, Marco E., Zhouyang Ge, Suhas S. Jain, Michael S. Dodd, and Luca Brandt. "Droplets in homogeneous shear turbulence." Journal of Fluid Mechanics 876 (August 9, 2019): 962–84. http://dx.doi.org/10.1017/jfm.2019.581.
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We simulate the flow of two immiscible and incompressible fluids separated by an interface in a homogeneous turbulent shear flow at a shear Reynolds number equal to 15 200. The viscosity and density of the two fluids are equal, and various surface tensions and initial droplet diameters are considered in the present study. We show that the two-phase flow reaches a statistically stationary turbulent state sustained by a non-zero mean turbulent production rate due to the presence of the mean shear. Compared to single-phase flow, we find that the resulting steady-state conditions exhibit reduced Taylor-microscale Reynolds numbers owing to the presence of the dispersed phase, which acts as a sink of turbulent kinetic energy for the carrier fluid. At steady state, the mean power of surface tension is zero and the turbulent production rate is in balance with the turbulent dissipation rate, with their values being larger than in the reference single-phase case. The interface modifies the energy spectrum by introducing energy at small scales, with the difference from the single-phase case reducing as the Weber number increases. This is caused by both the number of droplets in the domain and the total surface area increasing monotonically with the Weber number. This reflects also in the droplet size distribution, which changes with the Weber number, with the peak of the distribution moving to smaller sizes as the Weber number increases. We show that the Hinze estimate for the maximum droplet size, obtained considering break-up in homogeneous isotropic turbulence, provides an excellent estimate notwithstanding the action of significant coalescence and the presence of a mean shear.
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Roscoe, John M. "The kinetics of gas phase reactions studied in a "homogeneous reactor"." Canadian Journal of Chemistry 66, no. 9 (September 1, 1988): 2325–34. http://dx.doi.org/10.1139/v88-368.
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The use of a "well-stirred" or "homogeneous" reactor in kinetic studies of gas phase reactions has been examined to assess the sensitivity of the method to the criteria upon which its use is based. The effects of heterogeneous and homogeneous secondary reactions are considered and the validity of the assumption of homogeneity has been examined experimentally for conditions similar to those which have been used elsewhere. The atom sink presented by the excess reagent under pseudo first order conditions results in failure of the homogeneity assumption. However, it is found that homogeneity is not required for successful use of the method provided the analytical measurements have good spatial resolution and the reaction volume is well-defined. The method is illustrated by using it to study some reactions of O(3P).
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Gast, Sebastian, Jörn H. Matthies, Ute S. Tuttlies, and Ulrich Nieken. "A Novel Experimental Setup for Kinetic Studies of Toluene Oxidation in the Homogeneous Liquid Phase." Chemical Engineering & Technology 40, no. 8 (June 28, 2017): 1445–52. http://dx.doi.org/10.1002/ceat.201700045.
Full textDissertations / Theses on the topic "Kinetic modelisation of the homogeneous phase"
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Laduye, Guillaume. "CVD du carbure de silicium à partir du système SiHxCl4-x/CyHz/H2 : étude expérimentale et modélisation." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0116/document.
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Le carbure de silicium est un matériau souvent employé comme matrice dans les composites thermostructuraux. Le précurseur classiquement utilisé pour son élaboration par dépôt/infiltration par voie gazeuse est CH3SiCl3. La thèse vise à évaluer le remplacement de ce précurseur par des précurseurs gazeux bi-sourcés de SiC où carbone et silicium sont apportés séparément.A partir du système SiHCl3/C3H8/H2, l’influence du débit total, de la température, de la pression totale et de (C/Si)gaz sont évaluées et comparées aux résultats obtenus avec le système CH3SiCl3/H2. La mesure in situ de la vitesse de dépôt permet de définir des lois cinétiques apparentes. L’analyse IRTF de la phase gazeuse indique que les évolutions des pressions partielles des différents produits stables sont corrélées avec les transitions cinétiques et les changements de composition du solide. Les simulations numériques de l’évolution de la phase gazeuse montrent une bonne corrélation avec les résultats expérimentaux et permettent de proposer des mécanismes homogènes et hétérogènes qui pourraient expliquer les écarts à la stoechiométrie du dépôt.L’étude de six précurseurs supplémentaires permet de mieux identifier le rôle des principales espèces en phase homogène et hétérogène, et notamment les précurseurs effectifs de dépôt. Enfin, l’étude de l’infiltration de matériaux poreux modèles révèle des améliorations significatives en termes d’homogénéité de vitesse de dépôt.Ainsi, des conditions propices à l’infiltration de carbure de silicium peuvent être obtenues en adaptant la réactivité de la phase gazeuse par la sélection de précurseurs initiaux et des chemins réactionnels qui en découlentSilicon carbide (SiC) is material of choice for the matrix of Ceramic Matrix Composites (CMC).CH3SiCl3/H2 mixtures are currently used as gas precursor for the synthesis of the CVI-SiC matrices.The present work considers the dual-source approach with two separate carbon and silicon precursorsmolecules.In the case of SiHCl3/C3H8/H2 mixture, systematic studies of total flow rate, temperature, total pressureand C/Si ratio of initial gaseous phase are realized. Kinetics obtained with growth rate measurements and solid composition are compared with results from CH3SiCl3/H2 mixture. On the basis of the apparent reaction orders and activation energies, experimental kinetic laws are derived. Through IRTF analysis of the gas phase, the partial pressures of the different stable products are correlated with deposition kinetic and solid composition. Results obtained in gas-phase kinetic simulation show a good correlation with the experimental results and a mechanism of homogeneous decomposition is proposed. A better understanding of the role of the principal species in homogenous and heterogeneous phase is obtained through the study of six other gas systems and the roles of some effective precursors are discussed. Finally, infiltration results of porous material models with different precursor systems reveal significant improvements as homogeneity of kinetic deposit.Hence, favourable conditions to silicon carbide infiltration can be obtained by adapting the reactivity of the gas phase, with the choice of initial precursors and homogeneous chemistry associated. Asystematic study of the process evidences promising working windows for the infiltration of pure SiCin porous performs
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Coille, Ingrid. "Thermodynamic and kinetic characterisation of antibody / hapten pairs and optimisation of an immunoassay of fluorescence in homogeneous phase." [S.l. : s.n.], 2001. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9609571.
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Piaud, Benjamin. "Modélisation mésoscopique des écoulements avec changement de phase à partir de l'équation de Boltzmann-Enskog : introduction des effets thermiques." Phd thesis, Toulouse 3, 2007. http://tel.archives-ouvertes.fr/tel-00931543.
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Ce travail de thèse concerne la modélisation et la simulation des écoulements diphasiques avec changement de phase par des équations cinétiques de type Boltzmann. Ce travail est motivé par deux applications distinctes pour lesquelles la compréhension et l'analyse fine des mécanismes et des dynamiques de changement de phase sont nécessaires. Le premier thème concerne la mise au point de dispositifs passifs de refroidissement diphasiques pour la micro-électronique. Le seconde thématique concerne la formation de dépôts de filtration résultant de l'agrégation de particules colloïdales à la surface d'une membrane dans des procédés de filtration membranaire. Pour les applications de type colloïdal, un modèle à deux fluides est proposé en adaptant des méthodes Boltzmann-sur-Réseau de la littérature pour la résolution de l'écoulement. Enfin, dans une partie plus exploratoire, un méthode de résolution originale de l'équation de Boltzmann-Enskog est proposée afin de traiter des écoulements avec changement de phase en incluant les effets thermiques.
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Coille, Ingrid [Verfasser]. "Thermodynamic and kinetic characterisation of antibody hapten pairs and optimisation of an immunoassay of fluorescence in homogeneous phase = Thermodynamische und kinetische Charakterisierung von Antikörper-Hapten-Paaren und Optimierung von einem Fluoreszenzimmunoassay in homogener Phase / vorgelegt von Ingrid Coille." 2001. http://d-nb.info/963166549/34.
Full textBook chapters on the topic "Kinetic modelisation of the homogeneous phase"
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Gasanova, L. M. "Mental-Computing Based Investigation of Kinetic and Mechanisms of Homogeneous Gas-Phase Oxidation of Methane by Hydrogen Peroxide." In Advances in Intelligent Systems and Computing, 377–84. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-68004-6_49.
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Jordan, Robert B. "Kinetics in Heterogeneous Systems." In Reaction Mechanisms of Inorganic and Organometallic Systems. Oxford University Press, 2007. http://dx.doi.org/10.1093/oso/9780195301007.003.0011.
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In this Chapter, a heterogeneous system is one in which the reactants are present in at least two phases. The discussion will concentrate on two such conditions, two-phase gas/liquid systems and three-phase gas/liquid/solid systems. Chemists tend to favor homogeneous conditions, with the reactants all in one phase, because they provide more controlled and reproducible conditions. However, heterogeneous conditions are often preferred in industrial processes because of the ease of separating the catalyst from the products. In many mechanistic studies, heterogeneity adds a complicating feature to be avoided, but there are times when this cannot be done, or when it happens unexpectedly. In gas/liquid systems, the gas often has limited solubility in the liquid which contains the other reagents. As a consequence, there can be problems of mass transport of the gaseous reactant from the gas to the liquid phase. Mass transport can limit the concentration of the gas in the liquid and/or become a rate-limiting feature of the system. These features can confuse interpretations of product distributions and rate laws. The gas/liquid/solid systems generally involve reactants in the gas and liquid phases and a catalyst as the solid phase. In some cases, the solid may be produced from initially homogeneous conditions, and a question arises as to whether the real catalyst is the original species added or the solid product formed under the reaction conditions. There are further questions about the factors that may control the rate of the catalytic process. In the chemistry laboratory, these systems are most often encountered with the gases H2 or CO reacting with substrate and possibly a catalyst in the liquid phase. For the mechanistic interpretation of kinetic observations, an important factor is the rate of mass transfer of the gas to the liquid phase. The rate of gas absorption into the liquid is typically represented as a first order process, driven by the difference between the saturated gas concentration [G(I)]f and the concentration at any time [G(I)], as given by where kLA is an effective first-order rate constant. This constant is taken as a product of an inherent absorption rate constant, kL, and something related to the surface area of the liquid phase, A.
Conference papers on the topic "Kinetic modelisation of the homogeneous phase"
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Slavinskaya, N. A. "Chemical Kinetic Modeling in Coal Gasification Processes: An Overview." In ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-23362.
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Coal is the fuel most able to cover world deficiencies in oil and natural gas. This motivates the development of new and more effective technologies for coal conversion into other fuels. Such technologies are focused on coal gasification with production of syngas or gaseous hydrocarbon fuels, as well as on direct coal liquefaction with production of liquid fuels. The benefits of plasma application in these technologies is based on the high selectivity of the plasma chemical processes, the high efficiency of conversion of different types of coal including those of low quality, relative simplicity of the process control, and significant reduction in the production of ashes, sulphur, and nitrogen oxides. In the coal gasifier, two-phase turbulent flow is coupled with heating and evaporation of coal particles, devolatilization of volatile material, the char combustion (heterogeneous/porous oxidation) or gasification, the gas phase reaction/oxidation (homogeneous oxidation) of gaseous products from coal particles. The present work reviews literature data concerning modelling of coal gasification. Current state of related kinetic models for coal particle gasification, plasma chemistry and CFD tools is reviewed.
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Field, Brandon S., and Pega Hrnjak. "Adiabatic Two-Phase Pressure Drop of Refrigerants in Small Channels." In ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2006. http://dx.doi.org/10.1115/icnmm2006-96200.
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The adiabatic pressure drop of two-phase refrigerant flow in small channels has been investigated. A rectangular channel with dh = 148.0 μm has been tested with four refrigerants: R134a, R410A, Propane (R290) and Ammonia (R717). This data has been combined with data taken from five different channels, with dh varying from 70 μm to 305 μm, of R134a. The measured pressure drops are compared to many published separated-flow and homogeneous pressure drop models. A new correlation for C, the Chisholm parameter, has been developed based on Reynolds number of the vapor phase (which contains the majority of the kinetic energy) and the dimensionless grouping ψ — a dimensionless ratio of viscous to surface tension effects taken from the analysis of capillary flow performed by Sou and Griffith (1964). This allows the new correlation to account for the varying fluid properties (including surface tension) that are found in the different refrigerants. The new correlation takes flow regime into account by means of a Weber number based flow transition criteria, following the flow map of Akbar et al. [10].
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Uykur, Cüneyt, Andrew L. Zuccato, Graham T. Reader, and David S. K. Ting. "Hydrogen Peroxide Effect on HCCI Performance." In ASME 2001 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/2001-ice-417.
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Abstract Methane fueled Homogeneous Charged Compression Ignition (HCCI) combustion is investigated using detailed kinetic modeling. Control of heat release rate is identified as the biggest challenge against HCCI operation. A new control strategy, hydrogen peroxide (H2O2) addition, along with intake mixture preheating, is proposed to resolve this problem. A single-zone perfectly stirred reactor type formulation is employed with detailed chemical kinetic mechanism to predict homogeneous gas-phase chemical kinetics. The effects of H2O2 addition on the performance parameters of a methane-fueled HCCI engine are simulated. The results show that HCCI performance can be improved radically by the addition of H2O2 since it lowers the ignition delay time substantially. The resulting NOx concentration in high IMEP operating conditions is significantly less than that emitted from conventional internal combustion engines. Possibility of increasing NOx emissions with increasing initial temperature has been shown. Reduction in carbon monoxide emission is predicted with the addition of H2O2 via the increased hydroxyl chemistry. More flexible control of HCCI operation is possible by regulating the amount of H2O2 added.
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Schwarzkopf, J. D., C. T. Crowe, and P. Dutta. "A k-ε Model for Particle-Laden Turbulent Flows." In ASME 2009 Fluids Engineering Division Summer Meeting. ASMEDC, 2009. http://dx.doi.org/10.1115/fedsm2009-78385.
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A dissipation transport equation for the carrier phase of particle-laden turbulent flows was recently developed. This equation shows a new production of dissipation term due to the presence of particles that is related to the velocity difference between the particle and the surrounding fluid. In the development, it was assumed that each coefficient was the sum of the coefficient for single phase flow and a coefficient quantifying the contribution of the particulate phase. The coefficient for the new production term (due to the presence of particles) was found from homogeneous turbulence generation by particles and the coefficient for the dissipation of dissipation term was analyzed using DNS. A numerical model was developed and applied to particles falling in a channel of downward turbulent air flow. Boundary conditions were also developed to ensure that the production of turbulent kinetic energy due to mean velocity gradients and particle surfaces balanced with the turbulent dissipation near the wall. The turbulent kinetic energy is compared with experimental data. The results show attenuation of turbulent kinetic energy with increased particle loading; however the model does under predict the turbulent kinetic energy near the center of the channel. To understand the effect of this additional production of dissipation term (due to particles), the coefficients associated with the production of dissipation due to mean velocity gradients and particle surfaces are varied to assess the effects of the dispersed phase on the carrier phase turbulent kinetic energy across the channel. The results show that this additional term plays a significant role in predicting the turbulent kinetic energy and a reason for under predicting the turbulent kinetic energy near the center of the channel is discussed. It is concluded that the dissipation coefficients play a critical role in predicting the turbulent kinetic energy in particle-laden turbulent flows.
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Diounou, E., P. Fede, R. Fournier, S. Blanco, and O. Simonin. "Kinetic Approach for Solid Inertial Particle Deposition in Turbulent Near-Wall Region Flow Lattice Boltzmann Based Numerical Resolution." In ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-12021.
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The purpose of the paper is the deposition on the wall of inertial solid particles suspended in turbulent flow. The modeling of such a system is based on a statistical description using a Probability Density Function. In the PDF transport equation, an original model proposed Aguinaga et al. (2009) is used to close the term representing the fluid-particle interactions. The resulting kinetic equation may be difficult to solve especially in the case of the particle response time is smaller than the integral time scale of the turbulence. In the present paper, the Lattice Boltzmann Method is used in order to overcome such numerical problems. The accuracy of the method and its ability to solve the two-phase kinetic equation is analyzed in the simple case of inertial particles in homogeneous isotropic turbulence for which Lagrangian random walk simulation results are available. The results from LBM are in accordance with the random walk simulations.
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Bhopatkar, Neelesh S., Heng Ban, and Thomas K. Gale. "Prediction of Mercury Speciation in Coal-Combustion Systems." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-15502.
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This study is a part of a comprehensive investigation, to conduct bench-, pilot-, and full-scale experiments and theoretical studies to elucidate the fundamental mechanisms associated with mercury oxidation and capture in coal-fired power plants. The objective was to quantitatively describe the mechanisms governing adsorption, desorption, and oxidation of mercury in coal-fired flue gas carbon, and establish reaction-rate constants based on experimental data. A chemical-kinetic model was developed which consists of homogeneous mercury oxidation reactions as well as heterogeneous mercury adsorption reactions on carbon surfaces. The homogeneous mercury oxidation mechanism has eight reactions for mercury oxidation. The homogeneous mercury oxidation mechanism quantitatively predicts the extent of mercury oxidation for some of datasets obtained from synthetic flue gases. However, the homogeneous mechanism alone consistently under predicts the extent of mercury oxidation in full scale and pilot scale units containing actual flue gas. Heterogeneous reaction mechanisms describe how unburned carbon or activated carbon can effectively remove mercury by adsorbing hydrochloric acid (HCI) to form chlorinated carbon sites, releasing the hydrogen. The elemental mercury may react with chlorinated carbon sites to form sorbed HgCl. Thus mercury is removed from the gas-phase and stays adsorbed on the carbon surface. Predictions using this model have very good agreement with experimental results.
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Corre, Cedric, Jean-Luc Estivalezes, Stephane Vincent, and Olivier Simonin. "Direct Numerical Simulation of the Motion of Particles Larger Than the Kolmogorov Scale in a Homogeneous Isotropic Turbulence." In ASME 2008 Fluids Engineering Division Summer Meeting collocated with the Heat Transfer, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/fedsm2008-55156.
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Predicting interactions between particles and a surrounding viscous fluid is the concern of many environmental and industrial applications. A Direct Numerical Simulation (DNS) of dilute isotropic turbulent particulate flow has been conducted in a periodic box, with 1283 grid points. The objective is to understand the modification of isotropic turbulence due to dispersed solid particles by analyzing the DNS results. Previous numerical simulations have been, for the most part, limited to the point-particle regime. On the opposite, in these simulations, the diameter of the particles is larger than the Kolmogorov length scale. In order to maintain a constant turbulent kinetic energy, a physical forcing scheme is implemented. Thereby, statistics on the characteristics of the particles are more reliable. Furthermore, interactions between particles are treated via a repulsing force, consequently, simulations are four-way coupling. Simulations are performed with a fictitious domain approach and with the penalty method. For solving the velocity-pressure coupling, an augmented Lagrangian optimization algorithm is used. Results present the influence of the particle phase on the turbulence spectrum. Moreover, the comparison with particle-free case is particularly interesting notably about the anisotropy of the flow caused by the presence of the particles.
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Villedieu, Philippe, and Olivier Simonin. "Kinetic Modeling and Monte-Carlo Simulations of Droplet Coalescence in a Turbulent Gas Flow." In ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/fedsm2002-31385.
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Two-phase gas-droplet flows are involved in a lot of industrial applications, especially in the combustion field (Diesel engine, turbomachinery, rocket engine,…). Among all the characteristics of the spray, the droplet size distribution generally has a major influence on the global performances of the system and must be accurately taken into account in a numerical simulation code. This is a difficult task because the carrier gas flow is very often turbulent. Hence, droplets located in the vicinity of the same point may have different velocities and coalesce, leading at the end to a strong modification of the initial droplet size distribution. The first part of our contribution will be devoted to the presentation of a new kinetic model for droplet coalescence in turbulent gas flows. This model is an extension, to the case of sprays, of the ideas introduced by Simonin, Deutsch and Lavie´ville in [1]. The key ingredient is the use of the “joint density function”, fgp (t, x, r, v, u), representing the density of droplets at time t, located at point x, with radius r and velocity v and “viewing” an instantaneous turbulent gas velocity u. The great advantage of using fgp (t, x, r, v, u) instead of the usual density function fp (t, x, r, v) is the possibility to close the collision operator, in the governing kinetic equation, with less restrictive assumptions on the velocity correlations of two colliding droplets. The link between this model and the usual one (relying on the so-called “chaos assumption”) will be discussed. In the second part of our contribution, we shall present a new Monte-Carlo algorithm derived from our kinetic model. Numerical simulation results, for some academic test cases (homogeneous isotropic turbulence), will be shown and compared to the results obtained with a classical algorithm for droplet collision, based on the chaos assumption (see for example [2] or [3]). The figure 1 below shows a comparison between the temporal evolution of the mass mean radius computed by a classical collision model (neglecting the influence of gas and droplet velocity correlation) and by the “joint-pdf” based model. In the first case, the growth rate of the droplet, due to coalescence phenomena, is overestimated. Moreover, figure 2 shows that the droplet kinetic energy, induced by the turbulent gas motion, decays rapidly with the chaos assumption based model, as already noticed by Lavie´ville et al [1] in the case of solid particle collisions.
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Agranat, Vladimir M., Sergei V. Zhubrin, and Igor Pioro. "Multi-Group Two-Phase Flow Model of Drift Drop Plume." In 2014 22nd International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icone22-30010.
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A homogeneous two-phase multi-group model of drift drop plumes emerging from natural draft cooling towers has been developed and validated using the experimental data obtained in the 1977 Chalk Point Dye Tracer Experiment (CPDTE). The conservation equations for mass fractions of water droplets having different sizes are solved in addition to the standard conservation equations for mixture mass, momentum, energy, water vapor mass fraction and turbulent quantities (turbulent kinetic energy and its dissipation rate). Extra terms are provided to the conservation equations for mass fractions of liquid water to account for the drift of water drops due to their gravitational settling. Various formulations for drift velocity and terminal velocity have been tested and compared. The phase change effects (condensation, evaporation, solidification and melting) are assumed to be negligible due to specific conditions of the experiment. The droplet-size distribution available at the cooling tower exit and containing the 25 groups of drops is simplified to 11 groups. Also, the 3-group and 1-group options are considered for comparison. The individual drop deposition fluxes and the total deposition flux are calculated and compared with the experimental data available at the sensors located on the 35° arcs at 500 and 1000 m from the cooling tower centerline. The total deposition flux is calculated as a sum of products of individual group mass concentrations of water drops and corresponding terminal velocities. The model has been incorporated into the commercial general-purpose Computational Fluid Dynamics (CFD) code, PHOENICS. The study has demonstrated a good agreement between the CFD predictions and the experimental data on the water vapor plume rise and the total drift deposition fluxes. In particular, the plume rise predictions agree well with experimental values (the errors are from 4% to 34% at different distances from the tower centerline). The predicted deposition fluxes are in agreement with the experimental values within a factor of 1.5, which is well within the industry acceptable error limits (a factor of 3). The model developed is recommended for analyzing the drift drop plumes under the conditions similar to CPDTE conditions of small Stokes numbers. It is easier to use and not less accurate than the multiphase Eulerian-Lagrangian CFD models used recently by various researchers for modeling CPDTE plume. The model has a potential to supplant or complement the latter in the computational analyses of gravitational phenomena in complex two-phase flows in engineering equipment and its environment.
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Koncˇar, Bosˇtjan, Ivo Kljenak, and Borut Mavko. "Nucleate Boiling Flow Simulation With Coupling of Eulerian and Lagrangian Methods." In ASME 2005 Summer Heat Transfer Conference collocated with the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems. ASMEDC, 2005. http://dx.doi.org/10.1115/ht2005-72297.
Full textAbstract:
Subcooled boiling flow was simulated by combining the two-fluid model of the CFX-4.4 code and a Lagrangian bubble-tracking model. At present, both models are coupled “off-line” via the local bubble Sauter diameter. The two-fluid model simulation with the CFX-4.4 code provides local values of turbulent kinetic energy field of the liquid phase, which is used as an input for the bubble-tracking model. In the bubble-tracking model, vapour is distributed in the liquid in the form of individually tracked bubbles. The result of the Lagrangian simulation is a non-homogeneous distribution of local Sauter diameter, which is used in the two-fluid model to predict the interfacial forces and interfacial transfer rates of mass and heat transfer. The coupled approach requires a few iterations to obtain a converged solution. The results of the proposed approach were validated against boiling flow experiments from the literature. A good agreement between measured and calculated radial profiles of void fraction and bubble diameter was obtained.