Design methodology and performance analysis of conical rotors for dry screw vacuum pumps

The conical rotor, as an alternative internal compression structure, has shown the potential to enhance the performance of screw vacuum pumps further. In view of no available literature examining the design of them, to fill this gap, mathematical models for the generation and analysis of conical rotors were established in this paper. The generation process was based on a design implementing a rotor profile cluster and a conical helix. The analysis model reflected the geometric characteristics and thermodynamic performance of conical rotors. The effect of key parameters in conical rotors was investigated, and the difference between conical rotors and variable-pitch rotors was revealed. Results showed that with the increase in the conical angle the internal volume index enlarged while both the specific power and pumping speed decreased. To achieve greater internal compression, more rotor stages were needed. The rotor performance could be improved by changing the distribution of the tooth width angle for the rotor profile cluster at a certain inlet pressure. In comparison with the variable-pitch rotor, the specific power was lower for the conical rotor at a close pumping speed.