[1Ia01-07] Vacuum Science Technology (VST)

[1Ia07] Improvement of Modified Knudsen Equation and Application to the Pump-Down Time Calculations

*Hajime Yoshida¹ (1. AIST, NMIJ)

In recent, the author and coworkers have developed the modified Knudsen equation (MK equation) by combining equations of each gas flow, which is applicable to the whole flow regime for arbitrary length of the tubes [1,2]. Comparing the calculations of MK equation with 82 literatures, it is found that the differences can be reduced mostly to below 20 % by introducing the effective length of turbulent flow into the MK equation. On the other hand, it is also found that considerable differences from 30 % to 70 % arise for the gas flow through an orifice when the pressure ratio of downstream to upstream is close to 1 and high-Re flow in short tubes. Also, as an application of the MK equation, the pump-down time of vacuum chamber is tried to calculate by using the MK equation.
[1] H. Yoshida, Y. Takei and K. Arai, Vacuum and Surface Science 63 (2020) 373.
[2] H. Yoshida, M. Hirata, T. Hara, Y. Higuchi, Packag Technol Sci. 34 (2021) 557.