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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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Journal ArticleDOI
TL;DR: The tangential momentum accommodation coefficient (TMAC) as discussed by the authors is the boundary condition for flow of gases in the slip and transition flow regimes, and its precise determination is important for several other applications as well.
Abstract: The value of tangential momentum accommodation coefficient (TMAC) is required while prescribing the boundary condition for flow of gases in the slip and transition flow regimes. The precise determination of its value is important for several other applications as well. This article reviews the experimental techniques employed by researchers over the decades to measure this coefficient and the values reported in the literature, with relevance to calculation of the slip velocity. The review shows that the value of TMAC is dependent on a number of parameters including nature of the gas, pressure of the gas, material of the surface, surface cleanliness and roughness, and surface temperature. For monatomic gases, the TMAC at about 0.93 is almost constant with respect to the Knudsen number, and this value can be employed for most commonly available surface materials. However, for nonmonatomic gases, TMAC decreases with an increase in Knudsen number; a correlation of TMAC with Knudsen number for this class of ga...

201 citations

Journal ArticleDOI
TL;DR: In this paper, a Knudsen layer theory for lattice gases with arbitrary boundary conditions is presented, which allows a more accurate localization of the obstacle with respect to the lattice nodes.

196 citations

Journal ArticleDOI
TL;DR: In this paper, the theory of regularized moment equations is extended to 26 moment equations for planar Couette and Poiseuille flows, which can correctly predict the Knudsen layer, the velocity profile and the mass flow rate of pressure-driven PoISEUille flow up to 1.0 and capture the bimodal temperature profile.
Abstract: The method of moments is employed to extend the validity of continuum-hydrodynamic models into the transition-flow regime. An evaluation of the regularized 13 moment equations for two confined flow problems, planar Couette and Poiseuille flows, indicates some important limitations. For planar Couette flow at a Knudsen number of 0.25, they fail to reproduce the Knudsen-layer velocity profile observed using a direct simulation Monte Carlo approach, and the higher-order moments are not captured particularly well. Moreover, for Poiseuille flow, this system of equations creates a large slip velocity leading to significant overprediction of the mass flow rate for Knudsen numbers above 0.4. To overcome some of these difficulties, the theory of regularized moment equations is extended to 26 moment equations. This new set of equations highlights the importance of both gradient and non-gradient transport mechanisms and is shown to overcome many of the limitations observed in the regularized 13 moment equations. In particular, for planar Couette flow, they can successfully capture the observed Knudsen-layer velocity profile well into the transition regime. Moreover, this new set of equations can correctly predict the Knudsen layer, the velocity profile and the mass flow rate of pressure-driven Poiseuille flow for Knudsen numbers up to 1.0 and captures the bimodal temperature profile in force-driven Poiseuille flow. Above this value, the 26 moment equations are not able to accurately capture the velocity profile in the centre of the channel. However, they are able to capture the basic trends and successfully predict a Knudsen minimum at the correct value of the Knudsen number.

194 citations

Journal ArticleDOI
TL;DR: In this article, a model for simultaneous heat and mass transfer in a thin packed bed of desiccant particles was proposed, which accounts for diffusion of moisture into the particles by both Knudsen and surface diffusions.

193 citations

Journal ArticleDOI
TL;DR: In this article, the lattice Boltzmann equation (LBE) with multiple relaxation times (MRTs) was applied to simulate the Poiseuille flow in the slip flow regime.
Abstract: In this work, we apply the lattice Boltzmann equation (LBE) with multiple relaxation times (MRTs) to simulate the Poiseuille flow in the slip flow regime We analyse in detail the discrete diffusive and combined bounce-back-specular-reflection boundary conditions for the LBE, the discrete effects at the boundary, and determinations of the relaxation times for the Poiseuille flow in the slip flow regime In particular, we implement second-order slip boundary conditions with the MRT-LBE model and validate our numerical results for the slip Poiseuille flow with the Knudsen number Kn ≤ 02 by using the analytic solution Our analysis shows that the lattice Bhatnagar-Gross-Krook (BGK) model cannot yield correct results for the Poiseuille flow in the slip-flow regime We also discuss the possibilities of extending the LBE for the Knudsen layer in micro flows

192 citations


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