m Namvar-Mahboub - Department of Chemical Engineering, Isfahan University of Technology, Isfahan, ۸۴۱۵۶-۸۳۱۱۱, Iran
k Shams - Department of Chemical Engineering, Isfahan University of Technology, Isfahan, ۸۴۱۵۶-۸۳۱۱۱, Iran
M. R. Omidkhah - Department of Chemical Engineering, Tarbiat Modarres University, Tehran, Iran

Flow of rarefied gases through suddenly expanded/contracted channels are considered in nano and micro scales. The Direct Simulation Monte Carlo (DSMC) method is applied to predict the flowstructure and the Knudsen number effect. The system under consideration was studied for a relatively wide range of Knudsen numbers from 0.043 to 44. The simulations results reveal that no separation occurs for gas flow through the micro and nano scale channels with contraction evenfor small Knudsen numbers; however, there exist critical Knudsen numbers for both nano and microchannels with sudden expansion at which separation and secondary flows are observed. Furthermore, temperature, pressure and velocity distributions for both systems demonstrate similarbehaviors. The DSMC simulations results were qualitatively validated by comparing some of theresults with the existing simulation results using Lattice Boltzmann Method (LBM).

Rarefied gas; Nanochannel; Microchannel; MEMS; DSMC; Gas flow