高固含量轻浮颗粒在粘稠体系下的搅拌混合研究

发布时间：2018-02-16 23:04

  本文关键词： 轻浮颗粒 粘稠体系 推进式轴流桨 临界下拉转速与功率 计算流体力学(CFD)　出处：《浙江大学》2015年硕士论文　论文类型：学位论文

【摘要】：搅拌操作在石油、化工、食品、医药、肥料、染料、冶金、造纸以及污水处理等过程工业中应用广泛,在匀化、乳化、聚合和发酵等场合中发挥着重要作用。轻浮颗粒固-液搅拌混合不同于沉积颗粒的混合,它是将漂浮在液面的颗粒下拉并分散至搅拌釜中。目前有关固-液两相流搅拌的研究大都针对沉积颗粒悬浮展开,而对于轻浮颗粒下拉分散的研究相对较少,轻浮颗粒固-液混合搅拌釜设计等往往缺少理论指导,而实践证明简单地照搬沉积颗粒固-液搅拌混合的设计经验是不合适的。本文采用实验研究和数值模拟的方法研究搅拌釜结构和物性参数对轻浮颗粒下拉分散的影响,得到了颗粒下拉分散的临界下拉转速、功率、流场和浓度场等相关参数,为工业的实际应用打下了基础。本文首先在体系液相粘度为75.3mPa-s的搅拌釜中研究六斜叶开启涡轮桨、六直叶圆盘涡轮桨和推进式轴流桨在不同的浸入深度、桨径比和挡板布置方式下轻浮颗粒的下拉分散情况。实验结果表明：上推式搅拌桨的临界下拉转速和功率要大于下压式搅拌桨。最适合于轻浮颗粒下拉分散的搅拌釜结构为：搅拌桨采用下压式轴流桨,浸入深度为S=0.25T,采用一个偏心布置的全深度挡板。基于优选的搅拌釜结构,研究了液相粘度、固含量和颗粒大小等条件对轻浮颗粒下拉分散影响。研究表明：随着体系液相粘度的增大,临界下拉转速和功率不断增大；随着固含量和颗粒的增大,临界下拉转速和功率也随之增大。本文最后用数值模拟的方法研究了三种搅拌桨的流场、浓度场和湍流强度分布。研究表明：当曳力模型采用Gidaspow模型时,模拟结果与实验结果吻合良好,Gidaspow曳力模型适合于轻浮颗粒固-液两相流的模拟；三种搅拌桨作用下液面湍流强度最大区域位置基本相同,位于流体运动方向距挡板位置约90°靠近搅拌轴处,该位置与表面偏心涡的形成位置相近；最优的下压式轴流桨的桨径比为D/T=0.5；固-液混合非稳态模拟结果表明不同监测点位置的混合时间不同,其时间的长短与监测点位置的流体速度有关。
[Abstract]:Mixing operations are widely used in petroleum, chemical, food, medicine, fertilizer, dyes, metallurgy, papermaking and sewage treatment, etc. They are widely used in levelling, emulsifying, and so on. It plays an important role in polymerization and fermentation. Solid liquid mixing of frivolous particles is different from the mixing of deposited particles. At present, most of the researches on solid-liquid two-phase flow agitation are focused on sediment particle suspension, but there is relatively little research on the dispersion of frigid particles. The design of frivolous particle solid-liquid mixing agitator often lacks theoretical guidance. It has been proved that it is not appropriate to simply copy the design experience of solid-liquid mixing of sedimentary particles. In this paper, the effects of the structure and physical properties of agitator on the pull-down dispersion of frivolous particles are studied by means of experimental study and numerical simulation. The critical pull-down speed, power, flow field and concentration field of particle pull-down and dispersion were obtained, which laid the foundation for industrial application. In this paper, the six oblique blade turbomachinery was first studied in a agitator with liquid viscosity of 75.3 mPa-s. The six straight blade disk turbine propeller and the propelling axial flow propeller are immersed at different depths, The experimental results show that the critical pull-down speed and power of the upward impeller are higher than those of the down-pressure impeller, which is the most suitable for the pull-down dispersion of the frivolous particles. The structure of the mixing kettle is as follows: the agitator adopts the downward pressure axial flow propeller, The immersion depth is 0.25T, and an eccentrically arranged full-depth baffle is used. The liquid viscosity is studied based on the structure of the optimized agitator. The results show that the critical pull-down speed and power increase with the increase of liquid viscosity, and increase with the increase of solid content and particle size. The critical pull-down speed and power also increase. Finally, the flow field, concentration field and turbulence intensity distribution of three kinds of impellers are studied by numerical simulation. The results show that when the drag model is Gidaspow model, The simulation results are in good agreement with the experimental results. The Gidaspow drag model is suitable for the simulation of frigid particle solid-liquid two-phase flow, and the maximum turbulent intensity of liquid surface under the action of three kinds of impellers is basically the same. The direction of fluid motion is about 90 掳from the baffle near the stirring axis, which is close to the formation position of the surface eccentricity vortex. The optimal downpressure axial propeller is D / T 0.5. The unsteady simulation results of solid-liquid mixing show that the mixing time of different monitoring points is different, and the length of the time is related to the fluid velocity at the monitoring point.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ027

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