Numerical Simulation Of The Flow And Mixing Characteristics In Polymer Vane Extruder

Polymer vane extruder, whose plasticating and conveying theory is based onelongational rheology, is a significant development on plastic processing equipment. For thesake of its unique structure, it’s necessary to use numerical simulation to study it. The resultscan be useful to set process parameters and optimize its structure.In this paper, firstly, in order to simulate the flow in a vane unit of vane extruder, MST(Mesh Superposition Technology) and UDF (User-Defined Functions) of POLYFLOW wereused to prescribe the motion of the vanes. Then we calculate the mixing, and use the statisticspost-processing module, POLYSTAT, to analyze the mixing characteristics. It was shown inthe results that vane extruder can generate good stretching to promote dispersive mixing.In the vane unit, the velocity of the melts is decided by the impellers, the entrance andthe exit: annular flow was formed by the impellers and positive flow was formed by entranceand exit. The flow rate is in direct proportion to the rotational velocity of the rotor. The meltswere separated into4areas by4vanes, and were stretched and pressed by the vane unitrepeatedly, realizing elongational flow mainly based on normal stress. Most stretching existednear the vanes in the big volumes of vane unit. Melts were stretched adequately here topromote dispersive mixing, and shearing promote the blending distribute uniformly.For dispersive mixing, stretching is more efficient to break up drops into droplets thanshear. It was shown in the statistics analyze results that strong stretching existed in vaneextruder, demonstrating that vane extruder generates better stretching than traditional screwextruders. The material trajectories show that material points entered vane unit in the sametime would distribute uniformly after a rotational period, demonstrating that the dispersivemixing capability of vane extruder is good.The probability function of mixing efficiency show that the outflow, where the shape ofcross-section changes has a highest mixing efficiency, fulfilling the demand of complicatedgeometry. The more vane units that material cross, the better distributive mixing we obtain.During the processing, about10%of the mechanical energy was used to generate stretching, and the area of the stretching efficiency is much larger than traditional screw extruders, whichis useful to break the droplets into small ones.