Mathematical modeling non-contact external compression pumps with different molecular weights gases

Abstract

A distinctive feature of Roots type vacuum pumps is the selective of pumping, which is due to the dependence of reverse flows on the type of gas. To study this phenomenon, a mathematical model of the work process is used, based on solving differential equations of a system with variable mass. Comparisons of the experimental and calculated values of pumping speed and pressure increase for helium, argon and air show a discrepancy of no more than 10 %. Calculations have shown that under viscous flow conditions, switching from pumping argon to helium reduces pumping speed by more than 10 % and pressure increase by 50 %.