Study On A Smooth Screw Rotor And Its Working Performances For Twin-Screw Liquid Pumps

The twin-screw pump is a positive displacement liquid pump and the screw rotor is the core component.The existing twin-screw pump of?-type screw rotor is the most widely used.However,there are several non-smooth connection points in its corss-section profile,and the screw rotor has non-smooth edges,which causes problems such as easy wear and poor sealing performance.In this paper,a new smooth screw rotor is proposed based on the meshing theory.The proposed corss-scetion profile of the smooth screw rotor consists of a head circular arc,a root circular arc,an equidistant curve of the epicycloid and correction arc.In the working process,the proposed screw rotor can mesh correctly.The construction method,meshing characteristics and the variation of the geometric parameters are studied and their influences on the working performance of the smooth screw rotor are also analyzed.The leakage model of screw rotor's clearances and the pressure distribution model inside the working chamber are established.The three-dimensional transient numerical simulation with the structured grids of the twin-screw pump is conducted.The inner flow fields in working chambers are presented.The influences on the working performance of proposed screw rotor with varying clearances are studied.The mechanical characteristics of proposed smooth screw rotor and existing?-type screw rotor under the same operating condition are compared.With the increase of correction arc radius r₁,the area efficiency?_s decreases firstly and then increases,and the length of action line L_a decreases.When the correction arc radius takes the maximum value,the length of action line is the shortest,which is reduced by 70.725%compared with the?-type screw rotor.As the spiral depth?increases,the head circular arc radius R₁ and the length of the meshing area of the equidistant curve of the epicycloid decreases,but the radius angle?increases.Additionally,the area efficiency?_s and the length of action line L_a linearly decreases.Compared with the?-type screw rotor,the proposed smooth screw rotor realizes the smooth connection of the rotor profile and improves the wear resistance of the screw rotor.Moreover,the proposed smooth screw rotor has shorter action lines,and the maximum stress and the maximum deformation are reduced by 12.877%and 47.619%,respectively.The sealing performance and mechanical characteristics of the proposed screw rotor are significantly improved.The pressure inside the twin screw pump working chamber is in a ladder-like distribution,and the pressure variation between adjacent working chambers is equal.The differences between the pressure of each working chamber from numerical simulation and the pressure from the theoretical model is less than 1%.And the leakage at the flank clearance is more serious than that at the circumferential clearance,which is the main leakage of the screw rotor.In conclusion,the research contents has enriched the type of the screw rotor,and has great significance on the study of the inner flow filed for twin-screw pump.