Rarefied gas flows in rotating helical channels

Numerical and experimental investigations are performed for the rarefied ga s flows in pumping channels of a helical-type drag pump. Modern turbomolecu lar pumps include a drag stage in the discharge side, operating roughly in the pressure range of 0.01 similar to 10 Torr. The flow occurring in the pu mping channel develops from the molecular transition to slip flow traveling downstream. Two different numerical methods are used in this analysis: the first one is continuum approach using the Navier-Stokes equations with sli p boundary condition, and the second one is stochastic particle approach th rough the use of the direct simulation Monte Carlo (DSMC) method. The main difficulty in modeling three-dimensional flows in the rotating helical chan nels comes from the rotating frame of reference. In the present DSMC method , trajectories of particles are calculated by integrating a system of diffe rential equations including the Coriolis and centrifugal forces.