Analysis of circumferential gas force on star-wheel in a single screw expander

Abstract

Service life of a star-wheel directly affects operation stability of a single screw expander. In addition, since star-wheel tooth of a single screw expander is prone to wear, circumferential force of the star-wheel rotor is investigated in this paper. Geometric gap models between the meshing pair with a single line envelope profile at different rotation angles are established and meshed section pressure fields and velocity fields of a referent tooth flank are simulated. Circumferential gas torque calculation model of a referent tooth and multi-tooth are established, and torque influencing factors are analyzed. Results indicate that the pressure difference between the expansion cavity and low-pressure cavity as well as gap geometry shape have a significant influence on the pressure field and velocity field. Both gas forces that act on the meshed section and the unmeshed section of the tooth have significant effects on the circumferential torque. Due to multi-tooth coupling, total gas torque periodically changes with the star-wheel rotation angle. Moreover, the negative values indicate that the gas torque on the left side of the star-wheel is greater than that on the right side. Unbalanced gas torque can cause star-wheel teeth deviation towards the side with less force. This consequently results in wear increase.