The rotor-stator performance of a turbomolecular pump with a real topology

Free molecular flow within rotor and stator rows of a turbomolecular pump is simulated using test-particle Monte Carlo method. The solution is performed in an inertial reference frame where molecular paths are straight lines. The following of molecule paths in both rotor and stator is done in a similar system of coordinates. The real 3-dimensional (3D) topology of the blade rows including blade thickness, clearance between blade tip wall and casing, and the gap between rotor and stator is considered. Good agreement between numerical results of several rotor-stator combinations and known experimental data confirms the validation of presented algorithm. This algorithm is readily extended to multi-rows turbomolecular pump and obtained results agrees with existing data of a trial machine. The parametric study of rotor-stator shows that maximum compression ratio is achieved using large number of blades with low height and small angles, while for the blades with high height and large angle the pumping speed increases. Also effect of the gap between rotor and stator is significant for small blade angle and it is negligible for the blades with large angle. (author)