Topic
Knudsen number
About: Knudsen number is a research topic. Over the lifetime, 5052 publications have been published within this topic receiving 104278 citations.
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TL;DR: In this article, the behavior of the rarefied gas between two concentric circular cylinders consisting of the condensed phase of the gas, where evaporation or condensation occurs, is considered on the basis of kinetic theory.
Abstract: Cylindrical Couette flows of a rarefied gas between two concentric circular cylinders consisting of the condensed phase of the gas, where evaporation or condensation occurs, are considered on the basis of kinetic theory, with interest in the behavior of the gas in the continuum limit. The limiting solution is obtained by asymptotic analysis of the Boltzmann equation. In some range of the parameters of the problem, neither evaporation nor condensation occurs. The limiting solution in this case is different from the continuum solution (the conventional Couette flow without evaporation and condensation on the cylinders) and is subject to the effect of the flow that is induced if the effect of gas rarefaction is taken into account. This paradoxical result is confirmed by investigating the behavior of the numerical solution of the kinetic equation as the Knudsen number approaches zero.
30 citations
30 citations
TL;DR: It is shown that, by using appropriate operator splitting methods for the time discretization, one obtains stability properties which are only mildly dependent on the Knudsen number and essentially independent of the size of the electric field.
Abstract: The approximate solution of the Boltzmann transport equation via Galerkin-type series expansion methods leads to a system of first order differential equations in space and time for the expansion coefficients. This system is extremely stiff close to the fluid dynamical regime (for small Knudsen numbers), and exhibits a mildly dispersive behavior, due to the acceleration of waves by the external force (the electric field). In this paper a class of difference methods is presented and analyzed which represent a generalization of the well-known Scharfetter--Gummel exponential fitting approach for the drift-diffusion equations. It is shown that, by using appropriate operator splitting methods for the time discretization, one obtains stability properties which are only mildly dependent on the Knudsen number and essentially independent of the size of the electric field.
30 citations
TL;DR: In this paper, a model bridging between molecular and continuous heat and mass transfer processes is formulated on the basis of the well-known three-layer concept (droplet-collision-free zonecontinuum).
30 citations
TL;DR: In this article, the pore geometry in the catalyst layer was simplified into a bundle of tubes whose diameters can be derived from pore-size distribution of the focused ion beam (FIB) images.
30 citations