Rarefied Gas Flows in Rotating Helical Channels

Numerical and experimental investigations are performed for the rarefied gas flows in pumping channels of a helical-type drag pump. Modern turbomolecular pumps include a drag stage in the discharge side, operating roughly in the pressure range of 0.01〜10 Torr. The flow occurring in the pumping 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 slip boundary condition, and the second one is stochatic particle approach through the use of the direct simulation Monte Carlo (DSMC) method. The main difficulty in modeling three-dimensional flows in the rotating helical channels comes from the rotating frame of reference. In the present DSMC method, trajectories of particles are calculated by integrating a system of differential equations including the Coriolis and centrifugal forces.