Study on characteristic motions of small particles in a gas mixture

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1.Study of fundamental properties of the Boltzmann equation for a binary gas mixtureThe collision term of the Boltzmann equation for a simple gas is simplified from a fivefold into a threefold integral for a hard-sphere molecular gas. We carried out the corresponding simplification of the collision terms for a binary gas mixture to make it possible to construct numerical kernel of them and clarified the properties of the solution for a gas with a uniform temperature or density gradient, which playd a fundamental role to analyze the thermophoresis or diffusophoresis problem in a gas mixture. Based on the above results, we developed a set of fluid dynamic type equations and their associated boundary conditions to describe the behavior of a gas mixture for small Knudsen numbers, a part of which will be presented in the near future.2.Stydy of new types of rarefied gas flow induced by a temperature fieldWe showed a new type of rarefied gas flow induced rather strongly near the edges of a heated or cooled body numerically by the direct simulation Monte Carlo (DSMC) method and clarified the physical mechanism of it, which should be taken into account in considering the motion of slender particles. In addition, we pointed out that, for the case of intermediate or large Knudsen numbers, a flow was induced by the direct effect of the geometry of bodies or their surrounding boundaries and presented an example of the flow, which was also a new type of rarefied gas flow.3.Study of the drag and thermal force on a sphere in a simple gasWe reviewed the existing works on the drag and thermal force on a sphere in a simple gas and summarized our group works based on the rigorous analysis or numerical analysis of the Boltzmann equation in a useful form for a wide range of researchers.