A modified treatment for pressure boundary conditions in DSMC is shown, The microscale backward-facing gas flow is computed by a partitioned domain DSMC method and a general flow construction is obtained. It is shown that the recirculating flow region attached to the backward-facing step exists in the microscale flow with proper conditions while the region of separation on upper side does not. A discussion about the effect of flow parameters is given and a relationship between reattachment length and Reynolds number is obtained.

Gas flows driven by pressure in a microchannel are computed with the direct simulation Monte Carlo (DSMC) method. The rarefied effect is observed and slip velocity exists at solid boundaries. Temperature is almost constant in the whole flow field. The Mach number of the flow is very low. Density and pressure vary significantly along the channel while they are nearly invariant transversely. Nonlinearity of pressure distribution along the channel due to compressibility is found and reduces as the Knudsen number increases.