The effects of design parameters on performance of a novel roots profile

Abstract

The rotor profile is a key factor for improving the performance of Roots pumps. The geometric constraints of a novel Roots profile are derived and discussed in this paper. The available range of four independent design parameters, including lobe number n, ratio R of the center distance to the rotor diameter, base circle coefficient ε1, and contact ratio ε2 of the involute segment, were determined according to the design constraints. The area utilization efficiency ηA was defined to evaluate the theoretical working capacity of the Roots pump. From the perspective of geometry, the internal leakages due to the radial and meshing gaps were assessed using the tip concentric arc angle α1 and the geometric leakage index ηC derived from carryovers between the two intermeshing rotors. The results of the design domain indicated that more lobes produced a larger design domain and reduced the maximum available area utilization efficiency. The variations in the three performance indices within the feasible design domain reflected three optimizing directions: a larger α1, a higher ηA, and a lower ηC. The goal of area utilization efficiency contradicts that of the geometric leakage index.