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, a new analytical model is presented and solved for gas diffusion in fuel cell porous media based on fractal geometry, and an expression for the effective gas diffusivity of multi-scale porous media is derived, expressed in terms of bulk diffusion, pore structure as well as the Knudsen number.
53 citations
TL;DR: In this paper, a first-order model is used for slip and jump boundary conditions and an analytical solution for the fully developed flow is also given, where the wall temperature profiles along the wall present the highest increases for asymmetric heating and the highest considered Kn value.
53 citations
TL;DR: In this article, the problem of temperature distribution in liquid-vapor phase change between plane liquid surfaces is considered both analytically and experimentally, and temperature distributions were measured using Chromel-Alumel thermocouples.
Abstract: The problem of temperature distribution in liquid‐vapor phase change between plane liquid surfaces is considered both analytically and experimentally. Classical kinetic theory calculations indicate that for a monatomic vapor, large temperature jumps exist at the interfaces, large enough possibly to cause the temperature distribution to be anomalous. Surprisingly, no experimental results have been reported so far. A continuum analysis, with special consideration of the Knudsen layers, clearly establishes the adverse roles played by polyatomic molecules and the presence of a contaminant gas. The need to work with monatomic vapors under low levels of contamination is clearly indicated. An experimental setup was constructed to measure temperature distributions in the vapor between an evaporating liquid surface and a cooler condensing surface. Temperature distributions were measured using Chromel–Alumel thermocouples. Measurements were made in water, Freon 113, and mercury. The temperature profiles obtained in mercury, over a wide range of temperatures, clearly show large temperature jumps at the interfaces, as large as almost 50% of the applied temperature difference. These results appear to be the first to confirm this important phenomenon.
53 citations
TL;DR: Bird's direct simulation Monte Carlo method is used to compute the molecular velocity distribution of a gas with heat flow, finding the Sonine-polynomial coefficients away from walls agree with theory.
Abstract: Bird's direct simulation Monte Carlo method is used to compute the molecular velocity distribution of a gas with heat flow. At continuum nonequilibrium conditions (small heat flux), Chapman-Enskog behavior is obtained for inverse-power-law molecules (hard-sphere through Maxwell): the Sonine-polynomial coefficients away from walls (i.e., the normal solution) agree with theory. At noncontinuum nonequilibrium conditions (large heat flux), these coefficients differ systematically from their continuum values as the local Knudsen number (nondimensional heat flux) is increased.
53 citations
53 citations