  Gas separation of a binary gaseous mixture is one of characteristic phenomena
in the micro-scale flows that differ from the conventional size flows. In this
work, the separation in a binary gas mixture flows through a microchannel is
investigated by the lattice Boltzmann method with a diffuse-bounce-back (DBB)
boundary condition. The separation degree and rate are measured in the He--Ar
and Ne--Ar systems for different mole fractions, pressure ratios, and Knudsen
numbers. The results show that the separation phenomenon in the He--Ar mixture
is more obvious than that in the Ne--Ar mixture at the same mole fraction owing
to the larger molecular mass ratio. In addition, the increase in the pressure
ratio reduces the difference in the molecular velocities between the two
species, and the separation phenomenon becomes weaker. However, the gas
separation is enhanced with an increase in the Knudsen number. This is because
the resulting rarefaction effect reduces the interactions between the gas
molecules of the two species, and thus increases the difference in the
molecular velocity.
