Flow characteristics of Roots pumps with multistage designs by CFD investigation

Department of Mechanical and Computer-Aided Engineering, National Formosa University, 64 Wunhua Road, Huwei, Yunlin, Taiwan, R.O.C.

^a Corresponding author: cfhsieh@nfu.edu.tw

Received: 8 January 2014
Accepted: 31 March 2015

Abstract

This study conducts a fluid analysis of multistage designs for a Roots pump, a type of positive displacement pump applied in blower and vacuum pumps. After a rotor profile is generated based on a mathematical model of a rotor, a three-dimensional numerical approach is developed using computational fluid dynamics (CFD) and applied to investigate the effect of multistage pump design on flow characteristics. The effects of serial versus parallel designs on fluid are illustrated using a two-lobed rotor. The fluid analysis, which pays particular attention to favorable stages, shows that in both serial and parallel connection designs, having more than three stages improves flow characteristics but to a relatively small degree because of increased leakage. It identifies the three-stage design as offering the greatest economy for pumping performance enhancement. A similar analysis is then performed on a three-lobed rotor design using the same three-stage design. A comparison of the flow characteristics of the two- versus three-lobed rotors based on serial versus parallel design and identical chamber volume identifies specific variations in flow rate, pressure, and pulsation.