Numerical modeling of the Holweck pump

Abstract

A numerical model of the Holweck pump based on the kinetic equation is proposed. The modeling is realized in two stages. The first one consists of calculations of gas flows along and across a groove due to longitudinal and transversal pressure gradients, respectively. Analogous gas flows caused by longitudinal and transversal surface motions are calculated. These four solutions are determined by geometrical parameters of grooves. In the second stage, the pumping speed and the torque of the rotating cylinder are calculated as a linear superposition of the four solutions. The proposed methodology allows us easily to vary many parameters such as height and radius of the pump, angular velocity of the rotating cylinder, inclination of grooves, species, and temperature of the gas. A comparison of the numerical results with experimental data confirms that the groove curvature is not a predominant factor, while the gas rarefaction significantly affects the main characteristics of the pump.