Mitigation of radial exciting force of rotary lobe pump by gradually varied gap

Abstract

This paper presents a new structure of a rotary lobe pump cavity with gradually varied gap to mitigate the magnitude and fluctuation of the radial exciting force on the rotor. The geometry of the rotary lobe pump cavity is specially designed, so that the gap between the rotor and cavity is gradually changed during the rotors’ engaging. The flow in this geometry is numerically studied, and its effect on the pressure pulsation and radial exciting force is analysed, based on the dynamic mesh and local mesh reconstruction. Also, the mechanism of the mitigation of radial exciting force is briefly discussed. The value of the gap is an addition of gradually varied gap r (0 ∼ r max ) and the base gap (original constant gap: 0.2 mm). As for the results, it is found that as the varied gap r max value increases, the intensity of the reverse rotating vortex at the outlet decreases, and the secondary flow pulsation of the outlet section is effectively weakened. When r max = 0.1 mm, the radial exciting force in the y-direction on the rotor is reduced by 12% comparing with the equal gap, and the radial exciting force pulsation coefficient is 0.31. Meanwhile, the radial exciting force in the x-direction is reduced by 19% accordingly. The gradually varied gap cavity can effectively reduce the peak value of the pressure pulsation at outlet, weakening the influence of the rapid change of the outlet pressure on the radial exciting force. It is found that an optimal r max of 0.1 ∼ 0.15 mm has a remarkable effect on the mitigation of pressure pulsation and radial exciting force.