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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 paper, an experimental investigation of the interdiffusion behavior of gases in a low permeability graphite was performed by sweeping the opposite faces of a graphite septum with helium and argon at uniform pressure and measuring the diffusive flux of both gases.
Abstract: An experimental investigation of the interdiffusion behavior of gases in a low permeability graphite was performed by sweeping the opposite faces of a graphite septum with helium and argon at uniform pressure and measuring the diffusive flux of both gases. The objectives were to ascertain the diffusion mechanism, to verify the applicable equations and associated theories, and to determine the parameters required to use these equations. At all experimental pressures, contributions of both normal and Knudsen diffusion effects were detectable via the pressure dependence of the diffusion fluxes. It was found that a previously proposed dusty‐gas model formed an excellent basis for correlating the results. The dusty‐gas model yields flux equations which predict the diffusion behavior over a wide range of pressures for particular gas concentrations at the boundaries. Only two experimentally determined parameters (characteristic of the gases and graphite) are required. These are: an effective normal‐diffusion coefficient obtained through interdiffusion experiments and a Knudsen coefficient obtained through single‐gas (permeability) experiments. The procedures used to evaluate these parameters in terms of the experimental data are described in detail.

43 citations

Journal ArticleDOI
TL;DR: In this paper, a new slip model is proposed for slip flows and an analytical approach is developed for collisionless steady-state heat conduction inside a fully diffuse enclosure for non-continuum gas phase conduction encountered in micro/nano devices.
Abstract: This article presents a comprehensive study of various modeling techniques for noncontinuum gas-phase heat conduction encountered in micro/nano devices over a broad range of Knudsen number. A new slip model is proposed for slip flows and an analytical approach is developed for collisionless steady-state heat conduction inside a fully diffuse enclosure. Excellent agreements with direct simulation Monte Carlo (DSMC) simulations have been achieved for both of them. For problems in the transition regime and/or with partially thermal accommodated walls, the DSMC method is employed. Some noncontinuum phenomena such as the steady gas flows induced by the nonuniform temperature field are observed.

43 citations

Posted Content
TL;DR: In this article, the authors investigated the applicability of fluid dynamics in ultrarelativistic heavy ion (AA) collisions and high multiplicity proton nucleus (pA) collisions.
Abstract: We investigate the applicability of fluid dynamics in ultrarelativistic heavy ion (AA) collisions and high multiplicity proton nucleus (pA) collisions. In order for fluid dynamics to be applicable the microscopic and macroscopic distance/time scales of the system have to be sufficiently separated. The degree of separation is quantified by the ratio between these scales, usually referred to as the Knudsen number. In this work, we calculate the Knudsen numbers reached in fluid dynamical simulations of AA and pA collisions at RHIC and LHC energies. For this purpose, we consider different choices of shear viscosity parametrizations, initial states and initialization times. We then estimate the values of shear viscosity for which the fluid dynamical description of ultrarelativistic AA and pA collisions breaks down. In particular, we study how such values depend on the centrality, in the case of AA collision, and multiplicity, in the case of pA collision. We found that the maximum viscosity in AA collisions is of the order $\eta/s \sim 0.1 \ldots 0.2$, which is similar in magnitude to the viscosities currently employed in simulations of heavy ion collisions. For pA collisions, we found that such limit is significantly lower, being less than $\eta/s=0.08$

43 citations

Journal ArticleDOI
TL;DR: In this paper, a molecular sensor known as pressure sensitive paint (PSP) was used to obtain detailed pressure data inside the microchannel and at the channel entrance, and the achievable spatial resolution of the acquired pressure map can be as high as 5 mum.
Abstract: Fluid mechanics on the microscale is an important subject for researchers who are interested in studying microdevices since physical phenomena change from macroscale to microscale. Channel flow is a fundamental topic for fluid mechanics. By using a molecular sensor known as pressure-sensitive paint (PSP), detailed pressure data can be obtained inside the microchannel and at the channel entrance. The achievable spatial resolution of the acquired pressure map can be as high as 5 mum. PSP measurements are obtained for various pressure ratios from 1.76 to 20, with Knudsen number (K n) varying from 0.003 to 0.4. Compressibility and rarefaction effects can be seen in the pressure data inside the microchannel and at the channel entrance.

43 citations

Journal ArticleDOI
D. K. Bhattacharya1, George C. Lie1
TL;DR: It is shown that the viscosity of a very dilute gas decreases monotonically with the decreasing density, and it is predicted that at higher Kn, the slip coefficient is predicted to depend on the Knudsen number.
Abstract: Molecular-dynamics simulations were used to study the heat and momentum transport phenomena in very dilute gases flowing through a two-dimensional channel. Aside from pronounced slips in velocity and temperature at the wall, Navier-Stokes equations seem to be valid up to the maximum Knudsen number (Kn), 0.27, studied. It is further shown that the viscosity of a very dilute gas decreases monotonically with the decreasing density. For Kn less than \ensuremath{\sim}0.05, the slip coefficient, 1.16, calculated from the simulation is in good agreement with theoretical results, ranging from 1.134 to 1.230. However, at higher Kn, the slip coefficient is predicted to depend on the Knudsen number.

43 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023112
2022236
2021168
2020163
2019190
2018172