  Gaseous thermal transpiration flows through a rectangular micro-channel are
simulated by the direct simulation BGK (DSBGK) method. These flows are
rarefied, within the slip and transitional flow regimes, which are beyond many
traditional computational fluid dynamic simulation schemes, such as those based
on the continuum flow assumption. The flows are very slow and thus many
traditional particle simulation methods suffer large statistical noises. The
adopted method is a combination of particle and gas kinetic methods and it can
simulate micro-flows properly. The simulation results of mass flow rates have
excellent agreement with experimental measurements. In another case of 2D
channel, the DSBGK comparisons with the DSMC result and the solution of Shakhov
equation are also in very good agreement. Another finding from this study is
that numerical simulations by including two reservoirs at the channel ends lead
to appreciable differences in simulation results of velocity and pressure
distributions within the micro-channel. This is due to the inhaling and
exhaling effects of reservoirs at the channel ends. Even though excluding those
reservoirs may accelerate the simulations significantly by using a single
channel in simulations, special attentions are needed because this treatment
may over-simplify the problem, and some procedures and results may be
questionable. One example is to determine the surface momentum accommodation
coefficient by using analytical solution of the mass flow rate obtained in a
single-channel problem without the confinement effect of reservoirs at the two
ends.
