DSMC calculations of blade rows of a turbomolecular pump in the molecular and transition flow regions

The performance of a turbomolecular pump (TMP) in both molecular and transi tion flow regions is predicted by the numerical solutions of the Boltzmann equation obtained by the direct simulation Monte Carlo method. The pumping characteristics of the TMP are investigated for a wide range of the Knudsen number. The maximum values of compression ratio and pumping speed strongly depend on the Knudsen number in transition region, while they depend weakl y on the Knudsen number in free molecular flow region. The present numerica l results show good agreement with the previously known experimental data. Finally, the results of the single blade row in both molecular and transiti on regions are used to predict the overall performance of a TMP, which has three kinds of blades with 24 rows. (C) 2000 Elsevier Science Ltd. All righ ts reserved.