Kinetic modeling of a tapered Holweck pump
The Holweck pump is a device widely used in many pumping systems. It can be a self-standing device or part of a multi-stage system, usually combined with a turbo-molecular pump (TMP). In the present work, an existing methodology [Sharipov et al., 2006] for the simulation of a Holweck pump with channels of constant cross sections, is extended and becomes more general by including pumps with tapered channels. The implemented procedure is based on the kinetic approach, is applicable in the whole range of the Knudsen number and is divided into two steps. First the flow through a tapered channel of a T-shape cross section is decomposed in four simple two-dimensional flows and a database for the dimensionless flow rate in terms of the reference gas rarefaction and the channel geometrical data is built based on linear kinetic theory. Then, using the mass conservation principal and the kinetic database, an ordinary differential equation is solved to yield the pressure evolution along the pump and the pump characteristic quantities of practical interest. Comparison of simulation results with existing experimental data has shown good agreement, proving the validity of the method and its capability of simulating the flow in a Holweck pump with small computational effort. In addition, the great advantage of the method for fast and easy-to-go parametric and sensitivity analysis concerning various operational and geometrical characteristics of the pump is demonstrated. (C) 2014 Elsevier Ltd. All rights reserved.