Research On The Performance Of The Novel Cross-axis Conical Screw Rotor For Twin-screw Expanders

Twin-screw expander is a type of positive displacement expander,which is widely used in low-temperature heat source recovery system,and its working performance has a vital influence on the performance of the system.The built-in volume ratio formed by the conventional parallel-axis screw rotor of the twin-screw expander is relatively small,and the axial force of the screw rotor is relatively large under the working condition of large pressure difference.Therefore,in this paper the author proposes a construction method of a cross-axis conical twinscrew rotor based on the plane meshing theory and the tapered cross-section profile.The meshing line of the plane profile of the screw rotor is converted to the spherical surface,and the spherical profiles of the screw rotor is solved in reverse.The correct meshing of the spherical section profile of the cross-axis conical screw rotor on the spherical surface is realized,and a new type of cross-axis conical screw rotor is constructed.Multiple pairs of cross-axis screw rotors are constructed by changing the angle of the rotation axis of the screw rotor.The effect of the angle of the rotation axis of the screw rotor on the performance of the twin-screw expander are analyzed,and the performance of the traditional parallel axis screw rotor is used for comparison analysis.Numerical simulation is used to study the internal flow field of the cross-axis screw expander,and the internal pressure distribution and leakage of the screw expander are analyzed.Based on the mass conservation equation and energy conservation equation,a mathematical model of the working process of the twin-screw expander is established.The influence of the angle of the rotating shaft,the rotating speed of the expander and the intake volume on the working process of the expander are analyzed.The mechanical properties of the cross-axis screw rotors and the parallel-axis screw rotors are compared and analyzed.The axial force of the two sets of screw rotors is calculated,and the influence of temperature load and pressure load on the stress and deformation of the screw rotor is analyzed.The research results show that the novel cross-axis conical screw rotor is more suitable for large expansion ratio conditions: Under the condition that the expander intake volume is equal,the cross-shaft screw rotor can significantly increase the exhaust volume,thereby effectively increase the expander built-in volume ratio.Under the same working conditions,the pressure in the exhaust chamber of the cross-axis screw expander is smaller,and the working fluid is fully expanded to do work.The conical structure of the novel screw rotor can make the expander’s leakage area near the inlet be smaller,which is helpful to reduce the leakage of the expander near the intake port.The cross-axis conical screw rotor has better stress and deformation performance near the intake port.Compared with the conventional male screw rotor,the axial force of the cross-axis male screw rotor is significantly reduced,which can effectively alleviate the axial force caused by the expander under the high pressure difference.The novel cross-axis conical screw rotor proposed in this paper increases the built-in volume ratio of the expander and relieves its own axial force.It is more suitable for working conditions with large expansion ratios,it has theoretical and engineering significance for improving the comprehensive performance of the twin-screw expander and energy recovery system..