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 paper, the physical description of the electric arc in volume with chemical and thermal non-equilibrium conditions is given: two-temperature model, ionization-neutralization process and arc-gas interactions are discussed.
Abstract: The modelling of a dc plasma source operating at low power and at low mass flow rate is presented. The physical description of the electric arc in volume with chemical and thermal non-equilibrium conditions is given: two-temperature model, ionization–neutralization process and arc–gas interactions are discussed. The modelling assumptions are justified by the local non-dimensional numbers characterizing the system (Damkholer, Reynolds and Knudsen numbers). Special attention is focused on the influence of the arc power on the thermal non-equilibrium between electrons and heavy particles and the resulting ionization rate. The kinetic thermal non-equilibrium is shown as a decreasing function of the arc discharge current and it is established that the electron density never reaches equilibrium conditions, even at the throat exit. Calculations have been performed for a stationary arc confined to the throat. The gas is argon and the flow is axisymmetric and stationary.
29 citations
Journal Article•
TL;DR: In this article, a domain decomposition problem for Boltzmann- and Euler equations is considered, and the correct coupling conditions and the validity of the obtained coupled solution are proved.
Abstract: A nonequilibrium situation governed by kinetic equations with strongly contrasted Knudsen numbers in different subdomains is discussed We consider a domain decomposition problem for Boltzmann- and Euler equations, establish the correct coupling conditions and prove the validity of the obtained coupled solution Moreover numerical examples comparing different types of coupling conditions are presented
29 citations
TL;DR: In this paper, a computational method based on a kinetic model Boltzmann equation has been developed for microscale low speed flows, which is compared with those of the direct simulation Monte Carlo method and experiments for supersonic flows.
29 citations
TL;DR: The relations between the propelling force and the top wall moving velocity are obtained by solving the Boltzmann equation with the Shakhov model deterministically in a wide range of Knudsen numbers.
Abstract: The nonequilibrium gas flow in a two-dimensional microchannel with a ratchet surface and a moving wall is investigated numerically with a kinetic method [Guo et al., Phys. Rev. E 91, 033313 (2015)]. The presence of periodic asymmetrical ratchet structures on the bottom wall of the channel and the temperature difference between the walls of the channel result in a thermally induced flow, and hence a tangential propelling force on the wall. Such thermally induced propelling mechanism can be utilized as a model heat engine. In this article, the relations between the propelling force and the top wall moving velocity are obtained by solving the Boltzmann equation with the Shakhov model deterministically in a wide range of Knudsen numbers. The flow fields at both the static wall state and the critical state at which the thermally induced force cancels the drag force due to the active motion of the top wall are analyzed. A counterintuitive relation between the flow direction and the shear force is observed in the highly rarefied condition. The output power and thermal efficiency of the system working as a model heat engine are analyzed based on the momentum and energy transfer between the walls. The effects of Knudsen number, temperature difference, and geometric configurations are investigated. Guidance for improving the mechanical performance is discussed.
29 citations
TL;DR: In this paper, flux-corrected transport (FCT) is used as a filter to extract the solution from the noisy DSMC calculation for low-velocity flows, where the fluid velocity is much smaller than the mean molecular velocity.
Abstract: Gaseous flows in microfluidic devices are often characterized by relatively high Knudsen numbers. For such flows, the continuum approximation is not valid, and direct simulation Monte Carlo (DSMC) may be used to find an appropriate solution. For low-velocity flows, where the fluid velocity is much smaller than the mean molecular velocity, large statistical fluctuations in the solution mean that the features of the flow may be obscured by noise in the solution. The use of a high-order, nonlinear monotone convection algorithm, flux-corrected transport (FCT), as a filter to extract the solution from the noisy DSMC calculation is described. The diffusion, antidiffusion, and flux-limiting properties of FCT are discussed in terms of their filtering properties. The effects of filtering with FCT are demonstrated for a series of test problems, including a square wave with superimposed random noise, and low-and high-velocity and low- and high-Knudsen-number microchannel flows
29 citations