双转子连续混炼机混炼段相似放大初探

Similar Scale-up of Mixing Section of a Two-rotor Continuous Mixer

基于几何相似准则,分别对3种混炼段构型进行了2倍和10倍放大,用Polyflow软件对放大前后的混炼段流场进行了模拟研究,以1个旋转周期内不同横截面上的平均压力和平均混合指数、物料在混炼段的停留时间分布、混炼段出口截面上的解聚功率密度和修正Lyapunov指数的累积概率函数、比能耗、扭矩和轴向力等为评价指标,分析了几何相似放大对流场特征、混合效果、能耗等的影响。结果表明,采用几何相似准则对不同构型的混炼段进行放大时,在转速不变的情况下,产量均可按几何放大倍数的3次方放大,而混炼段流场特征、混合效果及比能耗保持不变,混炼段转子所受的轴向力和扭矩分别按几何放大倍数的平方和立方增大;在进一步的放大设计中需兼顾热平衡相似,以便在高产量下保证塑化品质。

Three mixing section configurations, i.e. double-flight, hake, and triple-flight were magnified to two and ten times according to geometric similarity principle, respectively. Polyflow software was employed to simulate the flow field in different mixing sections. Mean pressure and mixing index of different channel cross-sections during one revolution period, residence time distribution, cumulative probability distribution of depolymerization power density, and modified Lyapunov index on the exit of mixing section, specific energy, torque, and axial force were used as evaluating index to analyze the effects of geometric similarity scale-up on mixing sectiorfs flow field feature, mixing quality, energy cost, etc. In these simulations, the rotational speed of rotors kept constant while the volume flow rate of mixing section inlet increased by the geometric scaleup ratio＇s cube. Simulation showed that after being magnified to different size according to geometric similarity principle, the primary features of flow field, mixing effect and specific energy of mixing section were similar to those of corresponding prototypes, while torque and axial force increased by the square and cube of the geometric scale-up ratio, respectively. In the further study, similarity of the heat equilibrium should be considered to guarantee the similar plasticization effect.