In this study, we use direct simulation Monte Carlo method to simulate subsonic flow in nanochannels and micro/nanoscale backward-facing (BF) step considering a wide range of Knudsen number regimes. The nanochannel flow simulation indicates that the nanoscale flow through the nanochannel resembles unique features such as encountering negative pressure deviation behavior and observing flat velocity profiles at higher Knudsen number regimes. On the other hand, the micro/nano BF step flow simulations demonstrate that the length of separation region considerably decreases as the flow becomes more rarefied and approaches the transition regime. Meanwhile, the variations in the flow properties are much slower in the mid-transition and free-molecular regimes compared with the slip and early transition regime cases.

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