Rarefied gas flow into vacuum through a channel with sudden contraction or expansion
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RESEARCH PAPER
Rarefied gas flow into vacuum through a channel with sudden contraction or expansion O. Sazhin1 Received: 1 June 2020 / Accepted: 27 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Based on the direct simulation Monte Carlo method, we have simulated a flow of rarefied gas into vacuum through a channel with sudden contraction or expansion in cross section. The nonequilibrium effects at the input and output of the channel have been taken into account by including certain pre- and post-channel regions into the geometry under consideration. In a wide range of gas rarefaction, the mass flow rate through the channel and the flow field both inside the channel and in the upstream and downstream regions have been calculated. The results have been compared with the characteristics of a channel with the constant cross section. A significant effect of the channel geometry has been established. The Knudsen minimum has been found in the mass flow rate as a function of gas rarefaction, while a compression zone and a circulation zone have been discovered in the flow field. Keywords Rarefied gas · Channel flow · Gas flow rate · Direct simulation Monte Carlo method
1 Introduction A fair amount of theoretical and experimental research has been devoted to the rarefied gas flow through channels with a constant cross section (straight channels) (Sharipov and Seleznev 1998). Indeed, this type of channels is a widespread configuration of gas-driven micro- and nanosystems, vacuum technology and aerospace applications (Jousten 2016). In practice, however, more common are devices with curved channels or channels with a non-constant cross-section, such as micro-turbines, micro- and nano-separators, Knudsen pumps, micro-pumps, micro-gyroscopes, thermal flow micro-sensors, micro-heat pipes, micro-total analysis systems (or lab-on-a-chip systems), etc. (Li 2008). In these channels, changes in the cross-sectional area may be gradual or sudden, while the flow characteristics differ significantly from those in straight channels. This problem requires individual analysis, such as a numerical study of the rarefied gas outflow into vacuum through a cylindrical channel (pipe) with sudden contraction or expansion, based on the S-model kinetic equation * O. Sazhin [email protected] 1
Ural Federal University, Lenin av. 51, Yekaterinburg 620000, Russia
(Titarev and Shakhov 2014). The results were compared to the constant cross-sectional case and a significant effect of the channel geometry on the gas flow and the flow field was established. In particular, the gas flow in a channel with sudden expansion is essentially nonlinear and includes zones of the flow rapid expansion, pipe surface reflection and return flow. The authors claim with larger values of rarefaction in a wider section of reasonably long pipe, a Mach disk occurs. Based the linearized S-model kinetic equation computationally investigate and parameterize thermal transpiration pumping in single and multistage assemblies consisting of
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