摘要:

Kinetic theory gave new possibilities for the investigation of processes in gases. Some processes found or explained since the Boltzmann equation’s publication, which are outside the frames of classical macroscopic gas dynamics, will be considered. The main aim is to emphasize the kinetic nature of the phenomena. The strong theoretical results and computational methods of solution of the Boltzmann equation will be mentioned only in connection with this main aim. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581517

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Most of the cutting‐edge research on molecule‐surface interactions has been taken over by molecular‐beam experiments. Even so, work on transport properties—much in the spirit of Lloyd Thomas—has been yielding subtle information on the role of the internal state that is difficult to obtain by other methods. Two such transport experiments are highlighted. One is the influence of an external magnetic field on a Knudsen flow. It gives information on nonequilibrium angular momentum polarizations produced by nonspherical molecule‐surface interactions. The other is Surface Light‐Induced Drift. It gives information on the rotational and vibrational‐state dependence of accommodation coefficients. This includes the role of the direction of the angular momentum with respect to the surface (“helicopter” vs. “cartwheel”). © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581518

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The Boltzmann equation for molecules of the Maxwell class (cross section inversely proportional to the relative speed) is shown to possess solutions with infinite energy. The same result is conjectured for power law potentials, but only for Maxwell molecules these solutions are eternal. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581520

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

On the basis of a recently discovered collision group, the Boltzmann collision integral is exactly rewritten in two parts. The first part describes the scattering of particles with small angles. In this part theinfinitydue to the infinite cross sections is extracted from the Boltzmann collision integral. Moreover, the Boltzmann collision integral is exactly represented as a divergence of the flow in velocity space. Owing to this, the role of collisions in the kinetic equation can be interpreted in terms of the non‐local friction force that depends on the distribution function. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581521

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In this work, we evaluate analytically the collision integrals for the nonlinear isotropic Boltzmann equation for the hard spheres for several initial distribution functions. The initial distribution functions include combinations of Maxwellians with different temperatures and delta‐functions. We do not find any preferential scattering into the high energy tail in the case when the initial distribution function is a sum of two Maxwellians with different temperatures. Our results may be used to devise a new method for the numerical integration of the nonlinear Boltzmann equation which avoids an approximate numerical evaluation of the collision integrals. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581522

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A multigroup approximation to the Boltzmann equation with an arbitrary partition of the speed variable combined with a spherical harmonics expansion of the directional dependence of the distribution function is presented. Based on the method of weighted residuals, weight functions assure the exact conservation of particle density, momentum and energy density. A numerical example shows the applicability of this very flexible method to study the relaxation of a homogeneous gas far from equilibrium. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581523

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

This paper considers the stationary linear, space‐dependent Boltzmann equation in the case of an interior source term together with an absorption term and general boundary reflections. First, mildL1‐solutions are constructed as limits of iterate functions. Then anH‐theorem on a relative entropy function of two different solutions is studied. Finally a generalized inequality (of Dorrozes‐Guiraud type) for the boundary terms in theH‐theorem is proved. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581524

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Low speed neutral particle transport, in long mean free path (LMFP) environments, presents challenges for well‐established techniques, such as the direct simulation Monte Carlo (DSMC) method. In particular, at low flow velocities, statistical methods suffer from noise that may render them impractical in LMFP environments [1]. We describe a non‐statistical (no random numbers are used) kinetic model for particle transport [2, 3, 4]. The behavior of particles is handled in two stages, Ballistic and Collisional. The ballistic operator tracks the location of the particles across a phase space mesh until the particles undergo a collision. The collision operator redistributes the particles in direction and energy in such a way as to conserve momentum and energy at each spatial location of the phase space mesh. In the past, the method has been applied to heat transport in LMFP environments [4]. The current application centers on flow past a micro air foil. We focus on the method and its extension to handle directional flows. Some typical results for high Knudsen number,(Kn = &lgr;L), flows past a flat plate are presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581526

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

One‐dimensional problems for a binary gas mixture are studied on the basis of numerical solution of the complete kinetic Boltzmann equation. The collision integral is evaluated by conservative discrete ordinate method. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581527

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Non‐equilibrium vibration‐dissociation kinetics, transport properties and dissociation rate coefficients in expanding flows are studied on the basis of different kinetic theory approaches: state‐to‐state, multi‐temperature and one‐temperature ones. The limits of validity of more simple models are discussed, the influence of non‐equilibrium vibrational distributions, initial conditions, nozzle profile on the macroscopic parameters, heat transfer and reaction rates is investigated. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1581528

出版商:AIP    

年代:1903

数据来源: AIP