Sudden contraction effects in nanochannel cross section on the rarefied gas flow characteristics: LBM analysis
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Sudden contraction effects in nanochannel cross section on the rarefied gas flow characteristics: LBM analysis Ehsan Kamali Ahangar, Javad Abolfazli Esfahania
, Mohammad Bagher Ayani
Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad 91775-1111, Iran Received: 2 September 2020 / Accepted: 5 October 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This mesoscopic investigation aims to study the rarefied gas flow inside a contracting nanochannel in the slip and transitional regimes by two relaxation time lattice Boltzmann method. Bosanquet-type effective viscosity and distribution functions correction at the corner points are used to enhance the precision of slippage velocity on the walls. The boundary conditions at the entrance and exit sections of the nanochannel are assumed nonequilibriumequilibrium distribution functions. The bounce back-specular reflection boundary conditions are considered for the wall exteriors. It is found that both momentum and rarefaction play essential roles concerning the separation phenomena in nanochannel flow. The higher outlet Knudsen number possesses the higher effective viscosity and shear stress, while the vortices become smaller and tend to disappear at higher Knudsen numbers. The results of the direct simulation Monte Carlo method have been utilized to validate the present numerical prediction, and an outstanding agreement between the results is shown.
1 Introduction One of the significant applications of rarefied gas flow is in the microfluidic-nanofluidic devices. Due to different operations of rarefied gas flows, the rarefaction characteristic is an important issue, and the Knudsen number shows it. The gaseous stream is apportioned into four customary regimes based on the Knudsen number including continuous regime (Kn< 0.001), slip regime (0.001 < Kn< 0.1), transition regime (0.1 < Kn< 10), and free molecular regime (Kn> 10) [1, 2]. Most pioneering research has focused on simulations of micronano channels with uniform cross-sections. Researchers have simulated the impact of surface harshness for gaseous flow inside the microchannel using different methods. These included molecular dynamics [3], molecular dynamics-continuum hybrid method for micro/nanoscale flow with constant wall temperatures [4], diluted microscale flow using mesoscopic scheme [5], and analytical solutions for gas stream in the microchannel at a broad range of Knudsen numbers [6]. The lattice Boltzmann method (LBM) is successful in rarefied gas dynamics because of its ability to simulate complex geometries with low computational cost in comparison to the other existing methods such as direct simulation Monte Carlo (DSMC). Arkilic et al. [7] used perturbation expansion of the Navier–Stokes equations with a firstorder adjustment to the velocity slippage. They forecast the mass flow rate in the slip regime
a e-mail: [email protected] (corresponding author)
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