The Experts below are selected from a list of 228 Experts worldwide ranked by ideXlab platform
Xi Chen - One of the best experts on this subject based on the ideXlab platform.
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Thermophoretic Velocity of a Small Nonevaporating or Evaporating Particle in a High-Temperature Diatomic Gas
Journal of colloid and interface science, 1999Co-Authors: Xi ChenAbstract:Abstract Kinetic-theory analytical results concerning the thermophoretic velocity of a spherical nonevaporating or evaporating particle suspended in a high-temperature Diatomic Gas with appreciable dissociation degree (e.g., for oxygen with temperatures greater than 3000 K or for nitrogen with temperatures greater than 5500 K) are presented for the free-molecule regime. Molecular dissociation in the bulk Gas and atomic recombination at the surface of the cold particle are included in the analysis. It is shown that the thermophoretic velocity of the suspended particle is directly proportional to the temperature gradient and approximately inversely proportional to the Gas pressure. The thermophoretic velocities of both nonevaporating and evaporating particles are independent of the particle radius and increase slightly with increase in the specular-reflection fraction. For a nonevaporating particle, the thermophoretic velocity almost does not depend on the recombination fraction of atoms at the particle surface. For an intensely evaporating particle, the thermophoretic velocity (UTV) increases with increasing thermal accommodation factor (a) and decreases with increasing atomic recombination fraction (α) at high Gas temperatures with appreciable molecular dissociation, whileUTValmost does not depend onaand α at low Gas temperatures.
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the drag force acting on a small evaporating particle exposed to a high temperature Diatomic Gas flow
Journal of Colloid and Interface Science, 1998Co-Authors: Xi ChenAbstract:Kinetic-theory analytical results are presented concerning the effect of intense evaporation on the drag force acting on a spherical particle exposed to a high-temperature Diatomic Gas for the case of a free-molecule regime. Molecule dissociation and atom recombination are included in the analysis. It has been shown that evaporation may substantially enhance the drag force acting on a particle, especially for the case of the particle materials with low-evaporation latent heat and small molecular mass at high Gas temperatures. The values of the recombination fraction of atoms at the particle surface and of the fraction of the specularly reflected molecules or atoms significantly affect the drag force acting on a particle. Neglecting Gas dissociation may appreciably overestimate the drag force acting on a nonevaporating or evaporating particle at high Gas temperatures.
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thermophoresis of a small evaporating particle in a high temperature Diatomic Gas
Journal of Colloid and Interface Science, 1997Co-Authors: Xi ChenAbstract:Kinetic-theory analytical results are presented concerning the effect of intense evaporation on the thermophoretic force acting on a spherical particle suspended in a high-temperature Diatomic Gas for the case of free-molecule regime. Molecule dissociation and atom recombination are included in the analysis. It has been shown that evaporation may substantially enhance the thermophoretic force acting on a particle, especially for the case of the particle materials with low evaporation latent heat and small molecular weight and at high Gas temperatures. The values of the effective atomic and molecular thermal-accommodation factors do not affect the thermophoretic force acting on a nonevaporating particle, but they affect significantly the evaporation-added thermophoretic force. It has been shown that the recombination fraction of atoms at the particle surface does not influence the thermophoresis.
Chengwen Zhong - One of the best experts on this subject based on the ideXlab platform.
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a conservative implicit scheme for steady state solutions of Diatomic Gas flow in all flow regimes
Computer Physics Communications, 2020Co-Authors: Ruifeng Yuan, Chengwen ZhongAbstract:Abstract An implicit scheme for steady state solutions of Diatomic Gas flow is presented. The Rykov model equation is solved in the finite volume discrete velocity method framework, in which the translational and rotational degrees of freedom are taken into account. At the cell interface, a difference scheme of the model equation is used to construct a multiscale flux (similar to discrete unified Gas-kinetic scheme), so that the cell size is not constrained by the cell Knudsen number. The physical local time step is implemented to preserve the multiscale property in the nonuniform-mesh case. The implicit macroscopic prediction technique is adopted to find a predicted equilibrium state at each time step, making the scheme highly efficient in all flow regimes. Furthermore, an integral error compensation technique with negligible computational cost is proposed, which makes the scheme conservative and allows more flexible discretization for particle velocity space. With the compensation technique, the unstructured velocity-space mesh is used in the test cases, which reduces the velocity mesh number significantly. The present method is proved to be efficient and accurate.
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a conservative implicit scheme for steady state solutions of Diatomic Gas flow in all flow regimes
arXiv: Computational Physics, 2018Co-Authors: Ruifeng Yuan, Chengwen ZhongAbstract:An implicit scheme for steady state solutions of Diatomic Gas flow is presented. The method solves the Rykov model equation in the finite volume discrete velocity method (DVM) framework, in which the translational and rotational degrees of freedom are taken into account. At the cell interface, a difference scheme of the model equation is used to construct a multiscale flux (similar to discrete unified Gas-kinetic scheme (DUGKS)), so that the cell size is not constrained by the cell Knudsen (Kn) number. The physical local time step is implemented to preserve the multiscale property in the nonuniform-mesh case. The implicit macroscopic prediction technique is adopted to find a predicted equilibrium state at each time level and the implicit macroscopic governing equation is solved along with the implicit microscopic system. Furthermore, an efficient integral error compensation technique is applied, which makes the scheme conservative and allows more flexible discretization for particle velocity space. In the test cases, the unstructured velocity-space mesh is used, the present method is proved to be efficient and accurate.
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unified Gas kinetic scheme for Diatomic molecular simulations in all flow regimes
Journal of Computational Physics, 2014Co-Authors: Pubing Yu, Kun Xu, Chengwen ZhongAbstract:A unified Gas-kinetic scheme (UGKS) is constructed for both continuum and rarefied flow computations. The underlying principle for the development of UGKS is the direct modeling for the Gas evolution process from the kinetic to the hydrodynamic scale, which is used in the flux construction across a cell interface. More specifically, the physical process from the kinetic particle free transport to the hydrodynamic pressure wave propagation is recovered in the flux function. In the previous study, the UGKS has been developed mainly for monatomic Gas with particle translational motion only. The construction of time evolution solution is based on the BGK, Shakhov, and ES-BGK models. The UGKS has been validated through extensive numerical tests. In this paper, a UGKS for Diatomic Gas will be constructed, where the Gas-kinetic Rykov model with a Landau-Teller-Jeans-type rotational energy relaxation is used in the numerical scheme. The new scheme will be tested in many cases, such as homogeneous flow relaxation, shock structure calculations, hypersonic flow passing a flat plate, and the flow around a blunt circular cylinder. The analytic, DSMC, and experimental measurements will be used for validating the solutions of UGKS.
V A Rykov - One of the best experts on this subject based on the ideXlab platform.
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numerical study of unsteady rarefied Diatomic Gas flows in a plane microchannel
Computational Mathematics and Mathematical Physics, 2014Co-Authors: I N Larina, V A RykovAbstract:The numerical solution of a kinetic equation for a Diatomic Gas (nitrogen) is used to study two-dimensional unsteady Gas flows in a plane microchannel caused by discontinuous in the initial distributions of macroscopic Gas parameters. The plane discontinuity fronts are perpendicular to the walls of the channel. The arising flows are model ones for Gas flows in a shock tube and a microchannel. The reflection of an incident shock wave from a flat end face is studied. It is found that the Gas piles up at the cold wall, which slows down the shock wave detachment. The numerical results are in qualitative agreement with experimental data.
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numerical investigation of rarefied Diatomic Gas flows through a plane channel into a vacuum
Fluid Dynamics, 2013Co-Authors: I N Larina, V A RykovAbstract:Rarefied flows through a plane microchannel into a vacuum are numerically investigated on the basis of the model kinetic equation for a diatonic Gas (nitrogen). The dependence of the Gas flow rate through the channel on the Knudsen number, the wall temperature, and the channel length is determined. The energy flux transferred to the cold Diatomic Gas from the hot channel walls is calculated. The results for Diatomic and monatomic Gases are compared.
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computation of rarefied Diatomic Gas flows through a plane microchannel
Computational Mathematics and Mathematical Physics, 2012Co-Authors: I N Larina, V A RykovAbstract:A numerical method based on a model kinetic equation was developed for computing Diatomic rarefied Gas flows in two dimensions. Nitrogen flows through a plane microchannel were computed, and the Gas flow rate was constructed as a function of the Knudsen number for various channel lengths.
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kinetic model of the boltzmann equation for a Diatomic Gas with rotational degrees of freedom
Computational Mathematics and Mathematical Physics, 2010Co-Authors: I N Larina, V A RykovAbstract:A system of model kinetic equations is proposed to describe flows of a Diatomic rarefied Gas (nitrogen). A conservative numerical method is developed for its solution. A shock wave structure in nitrogen is computed, and the results are compared with experimental data in a wide range of Mach numbers. The system of model kinetic equations is intended to compute complex-geometry three-dimensional flows of a Diatomic Gas with rotational degrees of freedom.
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shock wave structure in a Diatomic Gas based on a kinetic model
Fluid Dynamics, 2008Co-Authors: V A Rykov, V A Titarev, E M ShakhovAbstract:The structure of a normal (direct) shock in a Gas for the parameters corresponding to nitrogen is investigated with allowance for the rotational degrees of freedom on the basis of a model kinetic equation. For various Mach numbers the structure is compared with both the known experimental results and the solutions of the Navier-Stokes approximation within the framework of two-temperature hydrodynamics. The possibility of assuming the constancy of the fraction of excited rotational degrees of freedom is studied.
R. S. Myong - One of the best experts on this subject based on the ideXlab platform.
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a generalized hydrodynamic computational model for rarefied and microscale Diatomic Gas flows
Journal of Computational Physics, 2004Co-Authors: R. S. MyongAbstract:On the basis of Eu's generalized hydrodynamics, a computational model is developed for the numerical simulation of rarefied and microscale Diatomic Gas flows. The rotational nonequllibrium effect is taken into account by introducing excess normal stress associated with the bulk viscosity of the Gas. The computational model for Diatomic Gases reduces to the model for monatomic Gases in the limit of vanishing bulk viscosity. The thermodynamically consistent computational model is applied to the one-dimensional shock wave structure and the two-dimensional hypersonic rarefied flow around a blunt body in order to demonstrate its capability and validate the numerical results. The general properties of the constitutive equations are also presented through a simple analysis. The numerical results show that the new generalized hydrodynamic computational model yields the solutions in qualitative agreement with experimental data and DSMC results in the case of the problems studied.
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Numerical Computations of Nonequilibrium Diatomic Gas Flows Using Eu’s Generalized Hydrodynamic Equations
AIP Conference Proceedings, 2003Co-Authors: R. S. MyongAbstract:The generalized hydrodynamic computational models for Diatomic Gas flows are developed. The rotational nonequilibrium effect is included by introducing excess normal stress associated with the bulk viscosity of the Gas. The new models are applied to study the one‐dimensional shock structure and the multi‐dimensional rarefied hypersonic flow about a blunt body. The general properties of the constitutive equations are also presented through a simple analysis. An excellent agreement with experiment is observed for the inverse shock density thickness.
G Spiga - One of the best experts on this subject based on the ideXlab platform.
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Diatomic Gas diffusing in a background medium kinetic approach and reaction diffusion equations
Communications in Mathematical Sciences, 2006Co-Authors: Marzia Bisi, G SpigaAbstract:The problem of a Diatomic Gas made up by atoms and molecules undergoing reactions of dissociation and recombination through a transition state is addressed. The Gas is difiusing in a scattering and dissociating background medium. Extended Boltzmann-like kinetic equations for the relevant distribution functions and exact balance equations for mass, momentum, and energy are derived and discussed. It is shown that, in the asymptotic limit of small Knudsen numbers, a suitable scaling leads to a consistent formal derivation of hydrodynamic equations of reaction{difiusion type for number densities of atoms and molecules.
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singular perturbation techniques in the study of a Diatomic Gas with reactions of dissociation and recombination
Applied Mathematics and Computation, 2003Co-Authors: M Galli, Maria Groppi, Riccardo Riganti, G SpigaAbstract:Model equations for the description of chemical reactions of dissociation and recombination through a transition state constitute necessarily singular perturbation problems because of the very short lifetime of the excited molecules, compared to all other characteristic times. Asymptotic solutions are derived and tested versus an accurate numerical solution by resorting to different expansion algorithms, taking initial layer corrections into account. Since the singular problem turns out to be also singularly perturbed, techniques like Hilbert and Chapman-Enskog expansions, typical of the Boltzmann equation for Gas kinetic theory, have been considered. The simple stationary state approximation, very popular in chemistry, is shown to provide very good results out of the initial layer if equipped with the proper initial conditions, as obtained from the present analysis.
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kinetic theory of a Diatomic Gas with reactions of dissociation and recombination through a transition state
Journal of Physics A, 2000Co-Authors: Maria Groppi, Alberto Rossani, G SpigaAbstract:Extended kinetic equations, according to the scattering kernel formulation of the Boltzmann equation, are derived for a chemical reaction of dissociation and recombination in the frame of the transition-state theory. Conservation laws and moment equations are discussed, and, in the spontaneous asymptotic limit induced by the transition species, collision equilibria are determined to leading order. In the spirit of the stationary-state approximation, a closed set of fluid-dynamic equations of the Euler type are then obtained for the main macroscopic fields. Preliminary numerical results are finally presented and briefly commented on.