Journal articles: '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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9

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.

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BUNNER, BERNARD, and GRÉTAR TRYGGVASON. "Dynamics of homogeneous bubbly flows Part 2. Velocity fluctuations." Journal of Fluid Mechanics 466 (September 10, 2002): 53–84. http://dx.doi.org/10.1017/s0022112002001180.

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Direct numerical simulations of the motion of up to 216 three-dimensional buoyant bubbles in periodic domains are presented. The bubbles are nearly spherical and have a rise Reynolds number of about 20. The void fraction ranges from 2% to 24%. Part 1 analysed the rise velocity and the microstructure of the bubbles. This paper examines the fluctuation velocities and the dispersion of the bubbles and the ‘pseudo-turbulence’ of the liquid phase induced by the motion of the bubbles. It is found that the turbulent kinetic energy increases with void fraction and scales with the void fraction multiplied by the square of the average rise velocity of the bubbles. The vertical Reynolds stress is greater than the horizontal Reynolds stress, but the anisotropy decreases when the void fraction increases. The kinetic energy spectrum follows a power law with a slope of approximately −3.6 at high wavenumbers.

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Carrillo, José Antonio, and Mattia Zanella. "Monte Carlo gPC Methods for Diffusive Kinetic Flocking Models with Uncertainties." Vietnam Journal of Mathematics 47, no. 4 (November 5, 2019): 931–54. http://dx.doi.org/10.1007/s10013-019-00374-2.

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Abstract In this paper we introduce and discuss numerical schemes for the approximation of kinetic equations for flocking behavior with phase transitions that incorporate uncertain quantities. This class of schemes here considered make use of a Monte Carlo approach in the phase space coupled with a stochastic Galerkin expansion in the random space. The proposed methods naturally preserve the positivity of the statistical moments of the solution and are capable to achieve high accuracy in the random space. Several tests on a kinetic alignment model with self propulsion validate the proposed methods both in the homogeneous and inhomogeneous setting, shading light on the influence of uncertainties in phase transition phenomena driven by noise such as their smoothing and confidence band.

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Qu, Xiaohui, Hui Wang, Qingzhu Zhang, Xiangyan Shi, Fei Xu, and Wenxing Wang. "Mechanistic and Kinetic Studies on the Homogeneous Gas-Phase Formation of PCDD/Fs from 2,4,5-Trichlorophenol." Environmental Science & Technology 43, no. 11 (June 2009): 4068–75. http://dx.doi.org/10.1021/es802835e.

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Chabán, Omar Y., Rosa M. Domínguez, Armando Herize, María Tosta, Angela Cuenca, and Gabriel Chuchani. "Kinetic and mechanism of the homogeneous, unimolecular elimination ofα,β-unsaturated aldehydes in the gas phase." Journal of Physical Organic Chemistry 20, no. 5 (2007): 307–12. http://dx.doi.org/10.1002/poc.1140.

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15

Geerts, J. W. M. H., Q. Chen, J. M. N. van Kasteren, and K. van der Wiele. "Thermodynamics and kinetic modeling of the homogeneous gas phase reactions of the oxidative coupling of methane." Catalysis Today 6, no. 4 (February 1990): 519–26. http://dx.doi.org/10.1016/0920-5861(90)85047-r.

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PANDYA, R. V. R., and F. MASHAYEK. "Non-isothermal dispersed phase of particles in turbulent flow." Journal of Fluid Mechanics 475 (January 25, 2003): 205–45. http://dx.doi.org/10.1017/s0022112002002781.

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In this paper we consider, for modelling and simulation, a non-isothermal turbulent flow laden with non-evaporating spherical particles which exchange heat with the surrounding fluid and do not collide with each other during the course of their journey under the influence of the stochastic fluid drag force. In the modelling part of this study, a closed kinetic or probability density function (p.d.f.) equation is derived which describes the distribution of position x, velocity v, and temperature θ of the particles in the flow domain at time t. The p.d.f. equation represents the transport of the ensemble-average (denoted by 〈〉) phase-space density 〈W(x, v, θ, t)〉. The process of ensemble averaging generates unknown terms, namely the phase-space diffusion current j = βv〈u′W〉 and the phase-space heat current h = βθ〈t′W〉, which pose closure problems in the kinetic equation. Here, u′ and t′ are the fluctuating parts of the velocity and temperature, respectively, of the fluid in the vicinity of the particle, and βv and βθ are inverse of the time constants for the particle velocity and temperature, respectively. The closure problems are first solved for the case of homogeneous turbulence with uniform mean velocity and temperature for the fluid phase by using Kraichnan’s Lagrangian history direct interaction (LHDI) approximation method and then the method is generalized to the case of inhomogeneous flows. Another method, which is due to Van Kampen, is used to solve the closure problems, resulting in a closed kinetic equation identical to the equation obtained by the LHDI method. Then, the closed equation is shown to be compatible with the transformation constraint that is proposed by extending the concept of random Galilean transformation invariance to non-isothermal flows and is referred to as the ‘extended random Galilean transformation’ (ERGT). The macroscopic equations for the particle phase describing the time evolution of statistical properties related to particle velocity and temperature are derived by taking various moments of the closed kinetic equation. These equations are in the form of transport equations in the Eulerian framework, and are computed for the case of two-phase homogeneous shear turbulent flows with uniform temperature gradients. The predictions are compared with the direct numerical simulation (DNS) data which are generated as another part of this study. The predictions for the particle phase require statistical properties of the fluid phase which are taken from the DNS data. In DNS, the continuity, Navier–Stokes, and energy equations are solved for homogeneous turbulent flows with uniform mean velocity and temperature gradients. For the mean velocity gradient along the x2- (cross-stream) axis, three different cases in which the mean temperature gradient is along the x1-, x2-, and x3-axes, respectively, are simulated. The statistical properties related to the particle phase are obtained by computing the velocity and temperature of a large number of particles along their Lagrangian trajectories and then averaging over these trajectories. The comparisons between the model predictions and DNS results show very encouraging agreement.

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Mahajan, Devinder, Viwat Krisdhasima, and Robert D. Sproull. "Kinetic modeling of homogeneous methanol synthesis catalyzed by base-promoted nickel complexes." Canadian Journal of Chemistry 79, no. 5-6 (May 1, 2001): 848–53. http://dx.doi.org/10.1139/v01-032.

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Nickel complexes promoted by alkoxide bases can affect facile conversion of synthesis gas into methanol under thermodynamically favorable temperatures. At 100°C, syngas conversion of 99% with turnover frequency of 66 h-1 is reported. The reaction is truly catalytic in Ni as well as in base. A kinetic study of the Ni(CO)4-KOMe catalyst system in 1,2-bis(2-methoxy ethoxy)ethane (triglyme)-MeOH solvent mixture is presented. The kinetic expression includes terms of zero-order in H2 and first-order in CO with syngas of H2-CO stoichiometry of ~2:1 and less than first-order in Ni (0.03-0.10 M), ~third-order in base (2.0-4.75 M), and an exponential dependence on methanol concentration (13.0-23.7 M at 2.0 M base; 15.8-22.6 M at 3.0 M base). The activation energy of 42.2 kJ mol-1 was estimated from the Arrhenius plot of the data between 374 and 393 K. Gas phase IR spectrum at the end of each run showed an intense signature peak at 2060 cm-1 for Ni(CO)4. Process uncertainties to commercialization of this versatile homogenous catalyst system for CO hydrogenation to methanol are discussed.Key words: homogeneous catalysis, syngas conversion, methanol synthesis, alkoxides, carbonyls of nickel.

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Pascal, V., Y. Gorsse, N. Alpy, K. Ammar, M. Anderhuber, AM Baudron, G. Campioni, et al. "MULTIPHYSICS MODELISATION OF AN UNPROTECTED LOSS OF FLOW TRANSIENT IN A SODIUM COOLED FAST REACTORS USING A NEUTRONIC-THERMAL-HYDRAULIC COUPLING SCHEME." EPJ Web of Conferences 247 (2021): 07001. http://dx.doi.org/10.1051/epjconf/202124707001.

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Sodium cooled fast neutron reactors (SFR) are one of the selected reactor concepts in the framework of the Generation IV International Forum. In this concept, unprotected loss of cooling flow transients (ULOF), for which the non-triggering of backup systems is postulated, are regarded as potential initiators of core melting accidents. During an ULOF transient, spatial distributions of fuel, structure and sodium temperatures are affected by the core cooling flow decrease, which will modify the spatial and energy distribution of neutron in the core due to the spatial competition of neutron feedback effects. As no backup systems are triggered, sodium may reach its boiling temperature at some point, leading to local sodium density variations and making the transient fluctuate in a two-phase flow physics where thermal-hydraulics and neutronics may interact with each other. The transient phenomenology involves several physic disciplines at different time and spatial scales, such as core neutronics, coolant thermal-hydraulics and fuel thermo-mechanics. This paper presents the results of thermal-hydraulic/neutronic coupled simulations of an ULOF transient on the SFR project ASTRID. These coupled calculations are based on the supervisor platform SALOME to link the neutron code APOLLO3® to the system thermal-hydraulic code CATHARE3. The physical approach used by the coupling to describe the neutron kinetic is a quasi-static adiabatic one, updating the normalized spatial power distribution periodically by performing static neutron calculations, while a point kinetic model associated to a neutron feedback model calculates the power amplitude variations.

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Canova-Davis, E., C. T. Redemann, Y. P. Vollmer, and V. T. Kung. "Use of a reversed-phase evaporation vesicle formulation for a homogeneous liposome immunoassay." Clinical Chemistry 32, no. 9 (September 1, 1986): 1687–91. http://dx.doi.org/10.1093/clinchem/32.9.1687.

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Abstract Complement-mediated release of enzyme molecules from reversed-phase evaporation vesicles serves as the basis of the sensitive homogeneous immunoassay reported here. We found it necessary to co-entrap the substrate glucose 6-phosphate with the bacterial enzyme glucose-6-phosphate dehydrogenase (EC 1.1.1.49) to protect enzyme activity during liposome preparation. Enzyme can be released specifically from these liposomes by incubation with antibody and complement. the enzyme is not merely available to substrate but is actually physically free of the liposomes. Inhibition of this complement-mediated lysis by theophylline is the basis for the homogeneous liposome immunoassay described. The assay results vary linearly with theophylline concentrations in plasma in the clinically relevant range, and serum components do not interfere. The reagents in the assay kit are stable for at least seven months when stored at 5 degrees C. No nontheophylline compounds reacted significantly with the antiserum used. The assay can be run in a kinetic format, with either ultraviolet or colorimetric detection.

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Lai, Chris C. K., and Scott A. Socolofsky. "The turbulent kinetic energy budget in a bubble plume." Journal of Fluid Mechanics 865 (March 1, 2019): 993–1041. http://dx.doi.org/10.1017/jfm.2019.66.

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We present the turbulent kinetic energy (t.k.e.) budget of a dilute bubble plume in its asymptotic state. The budget is derived from an experimental dataset of bubble plumes formed inside an unstratified water tank. The experiments cover both the adjustment phase and asymptotic state of the plume. The diameters $d$ of air bubbles are in the range 1–4 mm and the air void fraction $\unicode[STIX]{x1D6FC}_{g}$ is between 0.7 % and 1.8 %. We measured the three components of the instantaneous liquid velocity vector with a profiling acoustic Doppler velocimeter. From the experiments, we found the following inside the heterogeneous bubble core of the plume: (i) the probability density functions of the standardized liquid fluctuations are very similar to those of homogeneous bubble swarms rising with and without background liquid turbulence; (ii) the characteristic temporal frequency $f_{cwi}$ at which bubbles inject t.k.e. into the liquid agrees with the prediction $f_{cwi}=0.14u_{s}/d$ observed and theoretically derived for homogeneous bubble swarms ($u_{s}$ is the bubble slip velocity); (iii) the liquid turbulence is anisotropic with the ratio of turbulence intensities between the vertical and horizontal components in the range 1.9–2.1; (iv) the t.k.e. production by air bubbles is much larger than that by liquid mean shear; and (v) an increasing fraction of the available work done by bubbles is deposited into liquid turbulence as one moves away from the plume centreline. Together with the existing knowledge of homogeneous bubble swarms, our results of the heterogeneous bubble plume support the view that millimetre-sized bubbles create specific patterns of liquid fluctuations that are insensitive to flow conditions and can therefore be possibly modelled by a universal form.

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KOCH, DONALD L., and ASHOK S. SANGANI. "Particle pressure and marginal stability limits for a homogeneous monodisperse gas-fluidized bed: kinetic theory and numerical simulations." Journal of Fluid Mechanics 400 (December 10, 1999): 229–63. http://dx.doi.org/10.1017/s0022112099006485.

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A linear stability analysis is performed for the homogeneous state of a monodisperse gas-fluidized bed of spherical particles undergoing hydrodynamic interactions and solid-body collisions at small particle Reynolds number and finite Stokes number. A prerequisite for the stability analysis is the determination of the particle velocity variance which controls the particle-phase pressure. In the absence of an imposed shear, this velocity variance arises solely due to the hydrodynamic interactions among the particles. Since the uniform state of these suspensions is unstable over a wide range of values of particle volume fraction φ and Stokes number St, full dynamic simulations cannot be used in general to characterize the properties of the homogeneous state. Instead, we use an asymptotic analysis for large Stokes numbers together with numerical simulations of the hydrodynamic interactions among particles with specified velocities to determine the hydrodynamic sources and sinks of particle-phase energy. In this limit, the velocity distribution to leading order is Maxwellian and therefore standard kinetic theories for granular/hard-sphere molecular systems can be used to predict the particle-phase pressure and rheology of the bed once the velocity variance of the particles is determined. The analysis is then extended to moderately large Stokes numbers for which the anisotropy of the velocity distribution is considerable by using a kinetic theory which combines the theoretical analysis of Koch (1990) for dilute suspensions (φ [Lt ] 1) with numerical simulation results for non-dilute suspensions at large Stokes numbers. A linear stability analysis of the resulting equations of motion provides the first a priori predictions of the marginal stability limits for the homogeneous state of a gas-fluidized bed. Dynamical simulations following the detailed motions of the particles in small periodic unit cells confirm the theoretical predictions for the particle velocity variance. Simulations using larger unit cells exhibit an inhomogeneous structure consistent with the predicted instability of the homogeneous gas–solid suspension.

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Rosas, Felix, Rosa M. Domínguez, María Tosta, José R. Mora, Edgar Márquez, Tania Córdova, and Gabriel Chuchani. "The mechanism of the homogeneous, unimolecular gas-phase elimination kinetic of 1,1-dimethoxycyclohexane: experimental and theoretical studies." Journal of Physical Organic Chemistry 23, no. 8 (January 13, 2010): 743–50. http://dx.doi.org/10.1002/poc.1646.

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Díaz, José Antonio, Elżbieta Skrzyńska, Jean-Sébastien Girardon, Jamal Ftouni, Mickaël Capron, Franck Dumeignil, and Pascal Fongarland. "Kinetic modeling of the quasi-homogeneous oxidation of glycerol over unsupported gold particles in the liquid phase." European Journal of Lipid Science and Technology 118, no. 1 (October 15, 2015): 72–79. http://dx.doi.org/10.1002/ejlt.201500189.

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Tsai, Ching Yi, Seshu B. Desu, and Chien C. Chiu. "Kinetic study of silicon carbide deposited from methyltrichlorosilane precursor." Journal of Materials Research 9, no. 1 (January 1994): 104–11. http://dx.doi.org/10.1557/jmr.1994.0104.

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The kinetics of silicon carbide (SiC) deposition, in a hot-wall chemical vapor deposition (CVD) reactor, were modeled by analyzing our own deposition rate data as well as reported results. In contrast to the previous attempts which used only the first order lumped reaction scheme, the present model incorporates both homogeneous gas phase and heterogeneous surface reactions. The SiC deposition process was modeled using the following reactions: (i) gas phase decomposition of methyltrichlorosilane (MTS) molecules into two major intermediates, one containing silicon and the other containing carbon, (ii) adsorption of the intermediates onto the surface sites of the growing film, and (iii) reaction of the adsorbed intermediates to form silicon carbide. The equilibrium constant for the gas phase decomposition process was divided into the forward and backward reaction constants as 2.0 × 1025 exp[(448.2 kJ/mol)/RT] and 1.1 × 1032 exp[(-416.2 kJ/mol)/RT], respectively. Equilibrium constants for the surface adsorption reactions of silicon-carrying and carbon-carrying intermediates are 0.5 × 1011 exp[(-21.6 kJ/mol)/RT] and 7.1 × 109 exp[(-33.1 kJ/mol)/RT], while the rate constant for the surface reaction of the intermediates is 4.6 × 105 exp[(-265.1 kJ/mol)/RT].

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Xie, Hui, Gen Cang Yang, Lei Jia, and Zhen Lin Lu. "A Homogeneous Solidification Criterion for Undercooled Ni-20at%Pb Hypermonotectic Melts." Materials Science Forum 695 (July 2011): 340–43. http://dx.doi.org/10.4028/www.scientific.net/msf.695.340.

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The kinetic process of liquid-liquid phase separation in the undercooled Ni-20at%Pb hypermonotectic alloy melts was analyzed theoretically. The results showed that liquid-liquid separation could not be inhibited due to smaller nucleation barrier and bigger nucleation rate of Pb-rich droplets. In the course of liquid-liquid phase separation, the volume fraction of Pb-rich droplets was thought as a function of time or temperature. At a certain cooling rate, the volume fraction was mainly controlled by the undercooling of Ni-Pb hypermonotectic melts. Based on the above results, a homogeneous solidification criterion for the undercooled Ni-20at%Pb hypermonotectic alloy melts was developed. Such a criterion predicted that the homogeneous microstructure could be obtained at the undercooling 263K, and the experimental results accorded with the predicting ones on the whole.

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Garrett, A. J. M. "Multi-species kinetic generalization of the Appleton–Hartree dispersion formula." Journal of Plasma Physics 33, no. 2 (April 1985): 265–84. http://dx.doi.org/10.1017/s0022377800002506.

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This paper calculates, on a kinetic basis, the dispersion relation and field polarization for waves propagating linearly through a homogeneous magnetoplasma when thermal velocities are far less than the phase velocity. Approximations are brought in only as necessary and their physical significance explained. The result is an improved derivation of the Sen–Wyller generalization of the Appleton–Hartree formula for velocity-dependent collision frequency. Further generalization to several charged species is made, and the dispersion relation is also considered in terms of the angle between the ambient magnetic field and the group (rather than phase) propagation direction. Special case reduction to the Appleton-Hartree formula is confirmed. Complications concerning the limit of weak spatial dispersion are discussed. The analysis is restricted to weakly ionized plasmas in which the charge to neutral particle mass ratios are small, collisions are weak, and the wave vector is predominantly real.

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Mehrabadi, M., S. Tenneti, R. Garg, and S. Subramaniam. "Pseudo-turbulent gas-phase velocity fluctuations in homogeneous gas–solid flow: fixed particle assemblies and freely evolving suspensions." Journal of Fluid Mechanics 770 (March 31, 2015): 210–46. http://dx.doi.org/10.1017/jfm.2015.146.

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Gas-phase velocity fluctuations due to mean slip velocity between the gas and solid phases are quantified using particle-resolved direct numerical simulation. These fluctuations are termed pseudo-turbulent because they arise from the interaction of particles with the mean slip even in ‘laminar’ gas–solid flows. The contribution of turbulent and pseudo-turbulent fluctuations to the level of gas-phase velocity fluctuations is quantified in initially ‘laminar’ and turbulent flow past fixed random particle assemblies of monodisperse spheres. The pseudo-turbulent kinetic energy $k^{(f)}$ in steady flow is then characterized as a function of solid volume fraction ${\it\phi}$ and the Reynolds number based on the mean slip velocity $\mathit{Re}_{m}$. Anisotropy in the Reynolds stress is quantified by decomposing it into isotropic and deviatoric parts, and its dependence on ${\it\phi}$ and $Re_{m}$ is explained. An algebraic stress model is proposed that captures the dependence of the Reynolds stress on ${\it\phi}$ and $Re_{m}$. Gas-phase velocity fluctuations in freely evolving suspensions undergoing elastic and inelastic particle collisions are also quantified. The flow corresponds to homogeneous gas–solid systems, with high solid-to-gas density ratio and particle diameter greater than dissipative length scales. It is found that for the parameter values considered here, the level of pseudo-turbulence differs by only 15 % from the values for equivalent fixed beds. The principle of conservation of interphase turbulent kinetic energy transfer is validated by quantifying the interphase transfer terms in the evolution equations of kinetic energy for the gas-phase and solid-phase fluctuating velocity. It is found that the collisional dissipation is negligible compared with the viscous dissipation for the cases considered in this study where the freely evolving suspensions attain a steady state starting from an initial condition where the particles are at rest.

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Xu, Fei, Ruiming Zhang, Yunfeng Li, Qingzhu Zhang, and Wenxing Wang. "Theoretical Mechanistic and Kinetic Studies on Homogeneous Gas-Phase Formation of Polychlorinated Naphthalene from 2-Chlorophenol as Forerunner." International Journal of Molecular Sciences 16, no. 10 (October 26, 2015): 25641–56. http://dx.doi.org/10.3390/ijms161025641.

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Lezama, Jesus, and Gabriel Chuchani. "Kinetic and Mechanisms of the Homogeneous, Unimolecular Elimination of Phenyl Chloroformate andp-Tolyl Chloroformate in the Gas Phase." International Journal of Chemical Kinetics 47, no. 10 (August 24, 2015): 664–70. http://dx.doi.org/10.1002/kin.20939.

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Ferreira, Arthur Batista, Abiney Lemos Cardoso, and Márcio José da Silva. "Tin-Catalyzed Esterification and Transesterification Reactions: A Review." ISRN Renewable Energy 2012 (November 21, 2012): 1–13. http://dx.doi.org/10.5402/2012/142857.

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The recent increase in the world biofuels demand, along with the need to reduce costs while improving the environmental sustainability of the biodiesel production, have led to the search for catalysts that should be economically viable, efficient, and environmentally friendly. This paper reviews recent research and development of organic and inorganic tin catalysts; focusing on kinetic properties and catalytic activity in two key reactions for biodiesel production: free fatty acids (FFA) esterification and triglycerides (TG) transesterification. First the basic knowledge of homogeneous tin catalysts in esterification reactions of different carboxylic acids is provided. Second, main advances obtained in the study of FFA esterification reactions catalyzed by tin chloride are covered. The effect of the principal parameters of reaction on the yield and rate of alkyl esters production is described. Kinetic measurements allowed the determination of the activation energy (46.79 kJ mol−1) and a first-order dependence in relation to both FFA and tin chloride catalyst concentration. Aspects related to recycling of the tin chloride catalyst in phase homogeneous are discussed. Third the advances obtained in the development of homogeneous catalysts based on tin complexes in transesterification reactions are summarized. Finally, results obtained from the use of tin organometallics compounds in reactions of vegetable oils transesterification reactions are concisely presented. The optimization of processes catalytic homogeneous utilized in the transesterification reactions can contribute to the improvement of the technology biodiesel production.

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31

Xuezhi, Dai. "Study on Hydrolysis Reaction Rate of Several Chemical Warfare Agents." E3S Web of Conferences 290 (2021): 01009. http://dx.doi.org/10.1051/e3sconf/202129001009.

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According to the first-order kinetic reaction equation, the hydrolysis rate constants of homogeneous and heterogeneous phase of eight poisons under different conditions were calculated, and the relationship between hydrolysis rate constants and temperature was obtained according to the arrhenius formula, and the activation energy of hydrolysis reaction of some poisons was calculated. The evolution curve of homogeneous hydrolysis rate of 0.5 g/L HD with time was collected by T-135 method, and the hydrolysis rate was 0.1 min-1 and the half-life was 7 min. Poison concentration, pH of system, environmental temperature and structural composition of soil all affect the hydrolysis rate of Chemical Warfare Agents.

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32

Jordan, Aszetta, Zhentong Liu, and Oswald N. C. Uwakweh. "Mechanical alloying studies in the Γ(Fe3Zn10) and Γ1(Fe5Zn21) single and mixed phase compositions." Journal of Materials Research 13, no. 5 (May 1998): 1177–85. http://dx.doi.org/10.1557/jmr.1998.0168.

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Homogeneous or uniform crystalline materials are obtained following the ball milling of pure elemental powders of Fe and Zn in proportions to yield single phases Γ(Fe3Zn10), Γ1(Fe5Zn21), and Γ + Γ1 mixed phase (Fe25Zn75). Differential scanning calorimetry (DSC) measurements of the as-milled materials show characteristic stages in the temperature range of 50–600 °C prior to establishing stable equilibrium. The activation energies determined from kinetic analyses range from 49 to 189 kJ/mole in these materials. A characteristic stage at 130 °C marking the distinct evolution of the Γ and Γ1 phases from the intermediate or mixed phase composition is identified from XRD measurements. The identification of a unique Fe site with a quadrupole splitting (QS) of 1.5 mm/s in corroboration with x-ray diffraction (XRD) shows that this stage marks the onset of an in situ transformation prior to the distinct evolution of the homogeneous phases. The Mössbauer effect measurement of the as-milled materials are resolved in terms of four unique Fe sites with QS of 1.1, 0.241, 0.073, and 0.0772 mm/s.

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33

Pai, Madhusudan G., and Shankar Subramaniam. "Two-way coupled stochastic model for dispersion of inertial particles in turbulence." Journal of Fluid Mechanics 700 (April 18, 2012): 29–62. http://dx.doi.org/10.1017/jfm.2012.89.

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AbstractTurbulent two-phase flows are characterized by the presence of multiple time and length scales. Of particular interest in flows with non-negligible interphase momentum coupling are the time scales associated with interphase turbulent kinetic energy transfer (TKE) and inertial particle dispersion. Point-particle direct numerical simulations (DNS) of homogeneous turbulent flows laden with sub-Kolmogorov size particles report that the time scale associated with the interphase TKE transfer behaves differently with Stokes number than the time scale associated with particle dispersion. Here, the Stokes number is defined as the ratio of the particle momentum response time scale to the Kolmogorov time scale of turbulence. In this study, we propose a two-way coupled stochastic model (CSM), which is a system of two coupled Langevin equations for the fluctuating velocities in each phase. The basis for the model is the Eulerian–Eulerian probability density function formalism for two-phase flows that was established in Pai & Subramaniam (J. Fluid Mech., vol. 628, 2009, pp. 181–228). This new model possesses the unique capability ofsimultaneouslycapturing the disparate dependence of the time scales associated with interphase TKE transfer and particle dispersion on Stokes number. This is ascertained by comparing predicted trends of statistics of turbulent kinetic energy and particle dispersion in both phases from CSM, for varying Stokes number and mass loading, with point-particle DNS datasets of homogeneous particle-laden flows.

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34

Nikitopoulos, D. E. "Mach Number Scaling of Single-Component, Two-Phase Flow." Journal of Fluids Engineering 115, no. 4 (December 1, 1993): 772–77. http://dx.doi.org/10.1115/1.2910211.

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A simple two-fluid formulation is used to investigate compressibility effects and Mach number scaling for equilibrium, evaporating two-phase flow. The definition of the local two-phase Mach number emerges from a critical flow analysis. Comparisons of the theoretical critical mass flux with existing experimental data obtained in steam-water flows show very good agreement for moderate and high qualities over a wide critical pressure range. Within this quality range the predicted critical mass flux is quite insensitive to the velocity ratio. The analysis confirms previous observations, based on homogeneous flow models, indicating that in variable area ducts the critical state does not occur at a geometrical throat. Results of existing critical flow experiments in slowly diverging ducts are discussed in the light of this conclusion. A way from the neighborhood of the flash horizon, pressure-drop and kinetic energy changes are shown to scale with similar local Mach functions as those of single-phase compressible flow. Existing experimental data from vertical-upwards and horizontal two-phase flows in pipes indicate that the Mach number calculated on the basis of the local homogeneous state provides the optimum scaling performance. Scaling of the same experimental data using a Mach number based on the local nonhomogeneous state provides results that are in reasonably good agreement with the theoretical scaling guidelines and predictions, but is handicapped by considerable scatter in the scaled experimental variables.

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35

Yen, Fu Su, Pei Ling Chang, Pei Ching Yu, and Rong Jeh Yang. "Characterization on Microstructure Homogeneity of θ-Al2O3 Powder Systems During Phase Transformation." Key Engineering Materials 351 (October 2007): 81–87. http://dx.doi.org/10.4028/www.scientific.net/kem.351.81.

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The traditional differential thermal analysis (DTA) techniques are employed to evaluate the kinetic behavior induced by the inter-particle relationships in a nano-particle θ-Al2O3 powder system during θ- to α- phase transformation. Discrepancies in homogeneity and inter-particle distance of the powder system may result in the diagnostic DTA profiles which can be use to evaluate the characteristics of the powder system as well as the formed α-Al2O3 particles. Based on the acknowledgement, a quasi-homogeneous transformation shows that a duration of 90 seconds is needed for one θ-crystallite to transform into one α-nucleus with a heating rate of 10 oC min-1 and fabrication of the high phase-pure and mono-sized α-Al2O3 powders is obtained.

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36

Xu, Fei, Xiangli Shi, Yunfeng Li, and Qingzhu Zhang. "Mechanistic and Kinetic Studies on the Homogeneous Gas-Phase Formation of PCTA/DTs from 2,4-Dichlorothiophenol and 2,4,6-Trichlorothiophenol." International Journal of Molecular Sciences 16, no. 9 (August 28, 2015): 20449–67. http://dx.doi.org/10.3390/ijms160920449.

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37

Li, Meng, Fenghui Niu, Daryle H. Busch, and Bala Subramaniam. "Kinetic Investigations ofp-Xylene Oxidation to Terephthalic Acid with a Co/Mn/Br Catalyst in a Homogeneous Liquid Phase." Industrial & Engineering Chemistry Research 53, no. 22 (December 26, 2013): 9017–26. http://dx.doi.org/10.1021/ie403446b.

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38

Faravelli, Tiziano, Alessio Frassoldati, Eliseo Ranzi, Miccio Francesco, and Miccio Michele. "Modeling Homogeneous Combustion in Bubbling Beds Burning Liquid Fuels." Journal of Energy Resources Technology 129, no. 1 (February 21, 2006): 33–41. http://dx.doi.org/10.1115/1.2424957.

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This paper introduces a model for the description of the homogeneous combustion of various fuels in fluidized bed combustors (FBC) at temperatures lower than the classical value for solid fuels, i.e., 850°C. The model construction is based on a key bubbling fluidized bed feature: A fuel-rich (endogenous) bubble is generated at the fuel injection point, travels inside the bed at constant pressure, and undergoes chemical conversion in the presence of mass transfer with the emulsion phase and of coalescence with air (exogenous) bubbles formed at the distributor and, possibly, with other endogenous bubbles. The model couples a fluid-dynamic submodel based on two-phase fluidization theory with a submodel of gas phase oxidation. To this end, the model development takes full advantage of a detailed chemical kinetic scheme, which includes both the low and high temperature mechanisms of hydrocarbon oxidation, and accounts for about 200 molecular and radical species involved in more than 5000 reactions. Simple hypotheses are made to set up and close mass balances for the various species as well as enthalpy balances in the bed. First, the conversion and oxidation of gaseous fuels (e.g., methane) were calculated as a test case for the model; then, n-dodecane was taken into consideration to give a simple representation of diesel fuel using a pure hydrocarbon. The model predictions qualitatively agree with some of the evidence from the experimental data reported in the literature. The fate of hydrocarbon species is extremely sensitive to temperature change and oxygen availability in the rising bubble. A preliminary model validation was attempted with results of experiments carried out on a prepilot, bubbling combustor fired by underbed injection of a diesel fuel. Specifically, the model results confirm that heat release both in the bed and in the freeboard is a function of bed temperature. At lower emulsion phase temperatures many combustible species leave the bed unburned, while post-combustion occurs after the bed and freeboard temperature considerably increases. This is a well-recognized undesirable feature from the viewpoint of practical application and emission control.

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39

Ali, A. A., E. A. Ogryzlo, Y. Q. Shen, and P. T. Wassell. "The formation of O2(a1Δg) in homogeneous and heterogeneous atom recombination." Canadian Journal of Physics 64, no. 12 (December 1, 1986): 1614–20. http://dx.doi.org/10.1139/p86-285.

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The recombination of oxygen atoms has been studied in a discharge flow system at room temperature. The yield of O2(a1Δg) in the recombination on Pyrex has been found to be 0.08 (±0.02). In the gas phase, O2(a) was found to be formed in a process that is second order in [O] and first order in [N2]. The rate constant for this third-order reaction was found to be 3.4 (±0.4) × 10−34 cm6∙molecule−2∙s−1, representing a yield of 0.07 (±0.02). In the presence of molecular oxygen, the rate of production of O2(a) was found to increase. A kinetic study of this effect led to the conclusion that collisions of molecular oxygen with an unidentified precursor can produce O2(a) with high efficiency.

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40

Thomas, Colin A., R. Jason Bonilla, Yong Huang, and Philip G. Jessop. "Hydrogenation of carbon dioxide catalyzed by ruthenium trimethylphosphine complexes Effect of gas pressure and additives on rate in the liquid phase." Canadian Journal of Chemistry 79, no. 5-6 (May 1, 2001): 719–24. http://dx.doi.org/10.1139/v00-200.

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Kinetic and mechanistic studies of CO2 hydrogenation were performed in liquid triethylamine and at subcritical CO2 pressures to avoid complications from phase behaviour that are observed under supercritical conditions. Kinetic measurements of the hydrogenation of CO2 to formic acid, catalyzed by RuCl(O2CMe)(PMe3)4, support a CO2 insertion mechanism. The reaction is first-order in both H2 and CO2 under most conditions. The rate is strongly dependent on the choice of additive, with methanol giving the greatest rates. Because only trace amounts of methanol are needed, the effect of the additive is believed to involve direct interactions with the catalyst rather than changes in the physical properties of the reaction medium. The optimized rates exceed 3500 h1. Addition of an inert gas affects the rate of the reaction, probably via the phenomenon of gas expansion of the liquid phase.Key words: carbon dioxide, homogeneous catalysis, hydrogenation, formic acid, expanded liquids.

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41

Fan, Kai, Guoqing Zhou, Jinjin Zhang, Haijun Yang, Jun Hu, and Zhengchi Hou. "pH-sensitive microfiltration membrane prepared from polyethersulfone grafted with poly(itaconic acid) synthesized by simultaneous irradiation in homogeneous phase." Water Science and Technology 78, no. 3 (August 1, 2018): 602–10. http://dx.doi.org/10.2166/wst.2018.330.

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Abstract Poly(itaconic acid) (PIA) was grafted onto polyethersulfone (PES) by homogeneously phased γ-ray irradiation. Kinetic polymerization observed was studied by analyzing the effect of irradiation dosages and monomer concentrations. Then, a pH-sensitive microfiltration (MF) membrane was prepared from these PES-g-PIA polymers with different degrees of grafting under phase inversion method. Finally, the contact angles, morphologies, pore sizes, deionized water permeability and filtration performance for aqueous polyethylene glycols solution of the MF membranes were studied. The results show that grafting PIA groups onto PES molecular chains endowed the MF membranes with effective pH-sensitive properties.

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42

BRILLIANTOV, NIKOLAI V., JÜRGEN SCHMIDT, and FRANK SPAHN. "NUCLEATION AND GROWTH OF A SOLID PHASE IN A GAS EXPANDING INTO VACUUM." International Journal of Modern Physics C 18, no. 04 (April 2007): 676–84. http://dx.doi.org/10.1142/s0129183107010930.

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We study kinetics of homogeneous nucleation in over-saturated vapor expanding from a reservoir through a long channel into vacuum. Assuming adiabatic conditions for the gas, we derive an equation of state which accounts for the phase transformation of vapor into the condensed phase. To describe the growth rate of particles of the new phase gas kinetic theory is employed. We find the size-distribution of these particles, the temperature and flux velocity along the channel. Calculations are performed for the particular case of water vapor expanding to vacuum from its equilibrium state at the triple point. These conditions correspond presumably to the formation of the gas-dust plume, recently detected at Enceladus – the icy moon of Saturn. Our results, therefore, shed some light on this interesting astrophysical phenomenon.

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43

Dagaut, P., M. Cathonnet, J. P. Rouan, R. Foulatier, A. Quilgars, J. C. Boettner, F. Gaillard, and H. James. "A jet-stirred reactor for kinetic studies of homogeneous gas-phase reactions at pressures up to ten atmospheres (≈1 MPa)." Journal of Physics E: Scientific Instruments 19, no. 3 (March 1986): 207–9. http://dx.doi.org/10.1088/0022-3735/19/3/009.

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44

Burlot, A., B. J. Gréa, F. S. Godeferd, C. Cambon, and J. Griffond. "Spectral modelling of high Reynolds number unstably stratified homogeneous turbulence." Journal of Fluid Mechanics 765 (January 15, 2015): 17–44. http://dx.doi.org/10.1017/jfm.2014.726.

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AbstractWe study unconfined homogeneous turbulence with a destabilizing background density gradient in the Boussinesq approximation. Starting from initial isotropic turbulence, the buoyancy force induces a transient phase toward a self-similar regime accompanied by a rapid growth of kinetic energy and Reynolds number, along with the development of anisotropic structures in the flow in the direction of gravity. We model this with a two-point statistical approach using an axisymmetric eddy-damped quasi-normal Markovian (EDQNM) closure that includes buoyancy production. The model is able to match direct numerical simulations (DNS) in a parametric study showing the effect of initial Froude number and mixing intensity on the development of the flow. We further improve the model by including the stratification timescale in the characteristic relaxation time for triple correlations in the closure. It permits the computation of the long-term evolution of unstably stratified turbulence at high Reynolds number. This agrees with recent theoretical predictions concerning the self-similar dynamics and brings new insight into the spectral energy distribution and anisotropy of the flow.

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45

Frolova, L. A., A. V. Derimova, T. E. Butyrina, and M. O. Savchenko. "An Investigation of the Mechanism Magnetite Precipitation Using Ammonium Carbonate." Eurasian Chemico-Technological Journal 20, no. 3 (September 28, 2018): 223. http://dx.doi.org/10.18321/ectj725.

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The purpose of this study is to determine the phase composition of iron oxide compounds formed during precipitation by ammonium carbonate hydrolysis products, to establish the magnetite formation regions and the kinetic characteristics of the reaction formation Fe3O4. Characterization by X-ray diffraction (XRD) indicated that magnetite is formed in a solution of ferrous sulphate during the hydrolysis of ammonium carbonate. It has a homogeneous phase composition and a cubic crystal structure. Phase diagrams of the formation of the crystalline phase of magnetite, goethite and ferric hydroxide have been determined. It has been established that magnetite with a spinel structure is formed under controlled slow precipitation from ferrous sulphate with an ammonium carbonate solution. The calculation of the kinetic characteristics of the reactions of solid phase precipitation (a rate constant at different initial concentrations of ferrous sulphate, the order of the reaction) has shown that the process proceeds in two stages with the formation of an intermediate compound and its further oxidation. Moreover, the rate constant of oxidation is 0.654 L/min mol, and the rate constant of the first reaction is much higher – 1.645 L/min mol.

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46

Parthasarathy, R. N., and G. M. Faeth. "Turbulent dispersion of particles in self-generated homogeneous turbulence." Journal of Fluid Mechanics 220 (November 1990): 515–37. http://dx.doi.org/10.1017/s0022112090003366.

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Turbulent dispersion of particles in their self-generated homogeneous turbulent field was studied both experimentally and theoretically. Measurements involved nearly monodisperse spherical glass particles (nominal diameters of 0.5, 1.0 and 2.0 mm) falling with uniform particle number fluxes in a nearly stagnant water bath. Particle Reynolds numbers based on terminal velocities were 38, 156, and 545 for the three particle sizes. The flows were dilute with particle volume fractions less than 0.01%. Measurements included particle motion calibrations, using motion-picture shadowgraphs; and streamwise and cross-stream mean and fluctuating particle velocities, using a phase-discriminating laser velocimeter. Liquid-phase properties were known from earlier work. Particle properties were predicted based on random-walk calculations using statistical time-series methods to simulate liquid velocities along the particle path.Calibrations showed that particle drag properties were within 14% of estimates based on the standard drag correlation for spheres, however, the particles (particularly the 1.0 and 2.0 mm diameter particles) exhibited self-induced lateral motion even in motionless liquid due to eddy-shedding and irregularities of shape. Particle velocity fluctuations were primarily a function of the rate of dissipation of kinetic energy in the liquid since this variable controls liquid velocity fluctuations. Streamwise particle velocity fluctuations were much larger than cross-stream particle velocity fluctuations (2–5:1) largely due to varying terminal velocities caused by particle size variations. Cross-stream particle and liquid velocity fluctuations were comparable owing to the combined effects of turbulent dispersion and self-induced motion. Predicted mean and fluctuating particle velocities were in reasonably good agreement with the measurements after accounting for effects of particle size variations and self-induced motion. However, the theory must be extended to treat self-induced motion and to account for observations that this motion was affected by the turbulent environment.

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Costa, Lino, Rui Vilar, and Tamás Réti. "Laser Powder Deposition of Tool Steels: Strategies Leading to Homogeneous Parts." Materials Science Forum 514-516 (May 2006): 739–43. http://dx.doi.org/10.4028/www.scientific.net/msf.514-516.739.

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The microstructure and properties of tool steel parts built by laser powder deposition (LPD) depend considerably on the build-up strategy and on the processing parameters used. This dependence can lead to inconsistent results which may limit the widespread acceptance of LPD. There is, thus, a need for efficient process optimisation tools that take into consideration the complex phase transformations that may occur during the part build-up process and their effect on final properties. A model coupling finite element heat transfer calculations with transformation kinetic theory has been developed, which allows the microstructure and property distributions in parts produced by LPD to be predicted. Application of this model to the deposition of tool steels not only explains the origin of the heterogeneous distribution of properties usually mentioned in the literature but also allows designing build-up strategies that consistently lead to homogeneous, high quality parts. Its application to the study of the influence of substrate pre-heating and idle time between the deposition of consecutive layers is illustrated in the present paper.

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Radhakrishnan, K. "New Integration Techniques for Chemical Kinetic Rate Equations: Part II—Accuracy Comparison." Journal of Engineering for Gas Turbines and Power 108, no. 2 (April 1, 1986): 348–53. http://dx.doi.org/10.1115/1.3239910.

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A comparison of the accuracy of several techniques recently developed for solving stiff differential equations is presented. The techniques examined include two general-purpose codes EPISODE and LSODE developed for an arbitrary system of ordinary differential equations, and three specialized codes CHEMEQ, CREK1D, and GCKP84 developed specifically to solve chemical kinetic rate equations. The accuracy comparisons are made by applying these solution procedures to two practical combustion kinetics problems. Both problems describe adiabatic, homogeneous, gas-phase chemical reactions at constant pressure, and include all three combustion regimes: induction, heat release, and equilibration. The comparisons show that LSODE is the most efficient code—in the sense that it requires the least computational work to attain a specified accuracy level—currently available for chemical kinetic rate equations. An important finding is that an iterative solution of the algebraic enthalpy conservation equation for the temperature can be more accurate and efficient than computing the temperature by integrating its time derivative.

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49

Do, Tuan Q., and Sonnet Hung Q. Nguyen. "Anisotropic power-law inflation in a two-scalar-field model with a mixed kinetic term." International Journal of Modern Physics D 26, no. 07 (February 2017): 1750072. http://dx.doi.org/10.1142/s0218271817500729.

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We examine whether an extended scenario of a two-scalar-field model, in which a mixed kinetic term of canonical and phantom scalar fields is involved, admits the Bianchi type I metric, which is homogeneous but anisotropic spacetime, as its power-law solutions. Then, we analyze the stability of the anisotropic power-law solutions to see whether these solutions respect the cosmic no-hair conjecture or not during the inflationary phase. In addition, we will also investigate a special scenario, where the pure kinetic terms of canonical and phantom fields disappear altogether in field equations, to test again the validity of cosmic no-hair conjecture. As a result, the cosmic no-hair conjecture always holds in both these scenarios due to the instability of the corresponding anisotropic inflationary solutions.

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Aguilera, Miguel. "Scaling Behaviour and Critical Phase Transitions in Integrated Information Theory." Entropy 21, no. 12 (December 5, 2019): 1198. http://dx.doi.org/10.3390/e21121198.

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Integrated Information Theory proposes a measure of conscious activity ( Φ ), characterised as the irreducibility of a dynamical system to the sum of its components. Due to its computational cost, current versions of the theory (IIT 3.0) are difficult to apply to systems larger than a dozen units, and, in general, it is not well known how integrated information scales as systems grow larger in size. In this article, we propose to study the scaling behaviour of integrated information in a simple model of a critical phase transition: an infinite-range kinetic Ising model. In this model, we assume a homogeneous distribution of couplings to simplify the computation of integrated information. This simplified model allows us to critically review some of the design assumptions behind the measure and connect its properties with well-known phenomena in phase transitions in statistical mechanics. As a result, we point to some aspects of the mathematical definitions of IIT that 3.0 fail to capture critical phase transitions and propose a reformulation of the assumptions made by integrated information measures.

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Journal articles on the topic 'Kinetic modelisation of the homogeneous phase'

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