Numerical Simulation Of Flow Field In The Melt Conveying Section Of An Eccentric Rotor Extruder

An innovative eccentric rotor extruder invented by Jinping Qu,the professor of South China University of Technology,makes use of the periodic changes of the radial and the axial direction of the cavity volume during the rotation and reverse motion of its eccentric rotor to make materials flow and deform under elongation stress,thus avoiding the problems of long thermal mechanical process and high energy consumption in the process of plasticization and transportation of the traditional screw extruder based on shear rheology.Because of the complex spatial topological structure inside the extruder and the special motion law of the eccentric rotor,the numerical simulation method is suitable for the research of the melt flow characteristics in the melt conveying process and the research results have important reference value for the selection of the technological parameters and the optimization of the equipment structure of the eccentric rotor extruder.In this paper,the basic structure and the melt conveying mechanism of an eccentric rotor extruder were introduced briefly first,and then the motion law and the function equation of the melt transportation of the eccentric rotor were proposed.Second,the numerical model of melt flow flied in the melt conveying section was constructed on the basis of reasonable hypothesis,and the transient flow analysis was carried out by Polyflow software.Third,the flow field components,such as the velocity field,the pressure field,the shear rate field and instantaneous flow,were analyzed in detail,and on the basis of this,the influences of different process conditions or structure parameters on the distribution and variation of the flow field components were studied.Finally,the accuracy of numerical simulation was verified by comparing the theoretical,the actual and simulated extrusion flow under the same conditions.The simulation results show that most of the melt is subjected to the periodic variation of the cavity volume,which produces elongational flow under the function of volumetrical elongational deformation,and a little melt near the eccentric rotor wall appears reverse direction couette flow.The maximum and minimum region of the melt pressure in the cavity is distributed near the meshing gap which is biased toward the rotor axis,and is periodically interlaced with each other in the axial direction.The instantaneous flow change curve shows that the melt transport has high efficiency and stability.The melt instantaneous flow rate curve proves that the melt transport process is highly efficient and stable.By changing process conditions or structure parameters of the melt conveying section,the results show that the distribution of the flow field remains constant,but numerical values of the flow field component appear obvious changes.Improving the rotating speed has little effects on the flow pulsation rate,but is beneficial for the multiplied growth of the maximum melt flow velocity,extrusion flow and extrusion flow efficiency,meanwhile the melt pressure range would also increase in spite of the diminishing growth rate;Increasing the eccentricity or rotor pitch would similarly increase the maximum melt flow velocity,extrusion flow and extrusion flow efficiency but bring down the flow pulsation rate,while the melt pressure range presents a slowing downtrend;Enhancing the radius of the rotor contributes to the linear growth of the maximum melt flow velocity and extrusion flow,yet the melt pressure range and the flow pulsation rate would raise obviously likewise,meanwhile extrusion flow efficiency would decrease.