High-fidelity modeling and performance analysis of the Holweck stage of hybrid molecular pump under transitional flow

This study establishes a validated performance prediction model for a Holweck stage composite molecular pump operating under transition flow conditions. Utilizing direct simulation Monte Carlo simulations and experimental validation, the research confirmed the robustness of a single-channel model, which significantly enhanced computational efficiency. The model's predictive accuracy was verified against experimental data, with acceptable errors for engineering applications. Findings reveal a nonlinear inverse relationship between pumping speed and compression ratio and demonstrate a significant degradation in performance as the flow transitions from the molecular to the viscous regime. The study quantifies the nonlinear impact of four key geometric parameters—radial clearance, helical angle, inlet groove depth, and pump height—providing critical insights for design optimization. Most notably, the research identifies a fundamental physical limitation: the Holweck stage is unable to effectively pump light gases, such as hydrogen, due to insufficient traction to overcome backflow, thereby highlighting the necessity of integrating complementary technologies in ultra-high vacuum systems.