Design Method and Performance Analysis of the Variable-Radius and Variable-Pitch Rotor for Screw Vacuum Pumps

Variable cross-section rotors demonstrate significant potential for enhancing screw vacuum pump performance. This study proposes a variable-radius and variable-pitch screw rotor with a seven-segment fully smooth profile, accompanied by its parametric design methodology. Corresponding clearance design methods are provided, resulting in optimized clearance distribution. A thermodynamic model incorporating four leakage channels was developed. This model effectively simulates screw vacuum pump performance and has been experimentally validated. Systematic analysis was conducted on the effects of key parameters on pump geometric characteristics and performance, with comparative studies against two traditional constant cross-section rotors. Results demonstrate that the proposed design method enables rapid and precise generation of new 3D rotor models. The clearance optimization results validate the design expectations. The variable-radius design achieves cross-sectional variation, and its combination with variable pitch produces a dual internal compression effect, to which the variable radius contributes more significantly. With an increasing cone angle, the internal volume ratio rises significantly. Compared with conventional constant cross-section rotors, the rotor demonstrates superior performance in internal volume ratio, sealing characteristics, and structural integrity, notably cutting shaft power by 52.9% versus equal-pitch rotors. These findings provide an effective solution for developing high-performance screw vacuum pumps.