Accurate simulation of turbomolecular pumps with modified algorithm by 3D direct simulation Monte Carlo method

• Real 3D model is more accurate than 2D or ideal 3D ones for DSMC simulation of TMP.
• A modified algorithm of real 3D model of single-stage TMP is developed.
• This algorithm can be used for multistage TMP without restrictions.
• Two added areas are included in calculation domain to obtain accurate results.
• Present results are better than those of previous studies compared with experiment.

The Monte Carlo method is suitable to use for the problems of turbomolecular pumps (TMPs). This method has three calculation models, namely, the 2D, ideal 3D, and real 3D models. Theoretically, real 3D models demonstrate the real geometry of TMP and should be more accurate than 2D and ideal 3D models. In this study, a simple modified algorithm of a real 3D model based on that of Amoli et al. is used to calculate the maximum compression ratio Kmax of a single-stage TMP in both the free molecular and transitional flow regimes. When the upstream and downstream areas are added to the calculation domain and are sufficiently large to ensure that the velocity distribution of incident molecules near the inlet and outlet of the blade area is close to the real condition, calculation results are quite accurate compared with the experiment data reported by Sawada and are much better than those reported by other previous studies.