偏心双桨搅拌流场及效果分析

生产工艺中需要聚苯乙烯粒子在液相苯乙烯中均匀悬浮与混合,要求底部固相不堆积,固相浓度分布均匀。为了达到理想的搅拌效果,本文研究了双桨的偏心率及转速对搅拌混合效果的影响。以底部椭圆封头,无挡板的反应釜和双层6折叶的开启涡轮式搅拌器为研究对象,用Fluent软件对搅拌器偏心时水的搅拌流场及聚苯乙烯粒子-苯乙烯固液搅拌进行数值模拟。模拟了不同偏心率和转速对搅拌流型、聚苯乙烯粒子浓度分布及能耗的影响,并用粒子图像测速法(PIV)实验验证水的搅拌流场。结果表明,偏心搅拌可使流体速度得到增加,桨叶下方的搅拌死区得到有效抑制;偏心率增大导致两侧的速度偏差越来越大,能量分布不均匀;偏心搅拌的聚苯乙烯粒子浓度分布比对中搅拌的更为均匀,可改善粒子在苯乙烯中的悬浮效果;相同搅拌效果的情况下,偏心率为0.15的功率消耗是对中搅拌的85%;对该固液搅拌时的最佳偏心率和最佳转速分别为0.15和95 r/min,此时固液搅拌混合效果最好,固相浓度分布最为均匀,消耗功率相对较少。

Study on the Mixing Flow Field and Effect in Eccentrically Stirred Tank with Double Impellers

In the production process,polystyrene particles are required to be suspended and mixed evenly in the liquid styrene,and the solid phase concentration should also be uniform without solid deposited in the bottom.In order to achieve the desired mixing effect,the influence of eccentricity and speed on the mixing effect was studied.In this paper,the baffle-free reactor and the double-layer 6-turn open turbo agitator equipped with the elliptical head in the bottom was taken as the research object.The stirring flow field and the polystyrene particles-styrene solid-liquid stirring were numerically simulated by Fluent software.The effects of different eccentricity and rotational speed on the agglomeration flow pattern and the concentration distribution of polystyrene particles and energy consumption were simulated.The stirring flow field of water was verified by particle image velocity (PIV) experiment.The results showed that the eccentric stirring can increase the velocity of the fluid,and the stirring dead zone below the blade was effectively improved.The increase of eccentricity led to the increasing deviation of velocity on both sides and the uneven distribution of energy.The concentration distribution of polystyrene particles by eccentric agitation was more uniform than that by symmetry mixing,which can improve the suspension effect of the particles in the styrene;In the case of the same stirring effect,the power consumption with an eccentricity of 0.15 was 85％ of the mixing;The optimum eccentricity and the optimum rotational speed of the solid-liquid mixing were 0.15 and 95 r/min,respectively.At this time,the solid-liquid mixing effect appeared to be the best,the solid-phase concentration distribution was the most uniform and the power consumption was relatively small.