搅拌槽内固体颗粒混合的数值模拟

发布时间：2018-01-06 02:06

本文关键词：搅拌槽内固体颗粒混合的数值模拟　出处：《北京化工大学》2016年硕士论文　论文类型：学位论文

【摘要】：颗粒作为生产原料或产品在化工、医药、冶金、矿石和材料等过程工业领域有着广泛的应用。颗粒的混合通常是相关生产工艺中的重要单元操作。在颗粒的混合过程中,混合效果以及过程中的动力消耗则是关注的焦点。离散元(Discrete Element Method, DEM)作为一种可用于分析颗粒受力的数值方法,以颗粒的相互接触为起点,通过契合颗粒接触和碰撞等行为时的受力模型,计算颗粒随时间变化的运动信息,成为研究颗粒在过程工业中的有效方法。本研究在直径为0.284 m的标准椭圆封底的搅拌槽内,对球形颗粒的混合行为进行了数值模拟。通过使用Hertz-Mindlin and Linear Spring模型对固体颗粒间作用力进行计算,计算得到粒径范围为4-5mm的颗粒和粒径范围为2-3mm的颗粒在不同的桨型组合、转速和加料量下的颗粒混合过程。在数值模拟的同时,采用相同物性及尺度分布的玻璃珠颗粒作为实验原料,通过改变搅拌桨组合方式、物料装填系数、转速等条件探究固体颗粒搅拌功率的变化规律和混合度的变化规律。搅拌转速在30rpm和60rpm时,各桨型组合的功率的模拟结果和实验计算结果基本吻合。在对不同桨型的混合度进行模拟时,双螺带和内外单螺带的宏观混合作用较强。同时,针对同一颗粒物系和同一桨型,从初始状态到混合稳定状态的转数一定。即10%的2-3mm颗粒含量下四种桨型从开始到稳态经历的桨叶转数分别是100转(双螺带),170转(Paravisc),60转(内外单螺带),190转(Paravisc加三叶后掠)。改变转速对双螺带的宏观混合影响较大,对其他三种桨型影响较小。在不同转速下,2-3mm颗粒在径向上的位置变化不大,其在r/R=0.25,0.45,0.65,0.85处的颗粒集合径向位置维持在0-20mm,轴向位置主要与桨叶对颗粒的带动作用有关,但大部分操作条件下,上述四个位置处的颗粒集合的轴向位置也会趋于200-250mm区域。模拟结果显示各个桨型在混合的各个阶段时的混合程度与实验结果基本吻合。同时,数值模拟不仅提供了功率、扭矩和混合度等宏观参数的变化规律,也给出了观察颗粒混合内部结构变化和其他实验所不能测定的数据信息。
[Abstract]:Particles are used as raw materials or products in chemical, pharmaceutical, and metallurgical industries. Ore and materials are widely used in process industry. Particle mixing is usually an important unit operation in related production process. The mixing effect and the power consumption in the process are the focus of attention. Discrete Element Method. Demm) as a numerical method which can be used to analyze the force of particles, based on the interaction of particles, the force model is adopted to fit the behavior of particle contact and collision. Calculating the movement information of particles with time is an effective method to study particles in the process industry. This study is in the stirring tank with a standard elliptical bottom of 0.284 m in diameter. The mixing behavior of spherical particles was numerically simulated and the interaction forces between solid particles were calculated by using Hertz-Mindlin and Linear Spring model. The mixing process of particles with 4-5mm particle size and 2-3mm particle size under different propeller combinations, rotational speed and feed volume was obtained. The numerical simulation was also carried out at the same time. The glass beads with the same physical properties and size distribution were used as experimental materials, and the material loading coefficient was changed by changing the impeller combination mode. The changing law of mixing power and mixing degree of solid particles was studied under the conditions of rotating speed and so on. The stirring speed was 30rpm and 60rpm. The simulation results of the power of each propeller combination are in good agreement with the experimental results. When the mixing degree of different propellers is simulated, the macroscopic mixing between the double screw belt and the inner and outer single screw belt is stronger. At the same time. For the same particle system and the same paddle type. The rotation number from the initial state to the mixed stable state is constant, that is, the rotor rotation number of the four propeller types from the beginning to the steady state under the 2-3mm particle content of 10% is 100rpm (double screw belt) respectively. (170) Paravis cor 60 rpm (internal and external single snail belt 190 rpm + trefoil swept back). The change of rotational speed has a great influence on the macroscopic mixing of double snails. It has little effect on the other three types of propeller. The position of 2-3mm particles in the radial direction has little change at different rotational speeds, and it is 0.65 at r / r ~ (0.25) ~ 0.45 ~ 0. 5%. The radial position of the particle set at 0.85 is maintained at 0-20 mm, and the axial position is mainly related to the impelling effect of the blade on the particle, but under most operating conditions. The axial position of the particle set at the above four positions will also tend to be 200-250 mm. The simulation results show that the mixing degree of each propeller at each stage of mixing is basically consistent with the experimental results. At the same time. The numerical simulation not only provides the variation law of macroscopic parameters such as power torque and mixing degree but also gives the data information which can not be measured by observing the internal structure change of particle mixing and other experiments.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TQ027.1

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