高速分散器内流体力学特性的数值模拟

发布时间：2018-05-25 18:47

本文选题：高速分散器 + VOF模型　；参考：《北京化工大学》2015年硕士论文

【摘要】：高速分散器作为一种气液传质设备,通过转子的高速旋转,使液体在强大的离心力、剪切力作用下被分散成液滴、液丝,大大增加气液相接触面积,且其转子结构简单,便于清洗维护,因而具有广阔的应用前景。本文采用Ansys Fluent软件对高速分散器内低粘及高粘体系的流体力学特性进行数值模拟研究,对后续传质研究及分散器结构设计提供理论及数据支持。本文所研究的高速分散器的转子(内径211 mm,外径219 mm)沿周向均匀分布180个格栅。分别采用流体体积分数模型(Volume of Fluid, VOF)及欧拉多相流模型对低粘体系(空气-水)(转速300～1000 rpm,液相进料量1.164～3.443 m3.h-1,距离转子外缘径向距离0-208mm)及高粘体系(空气-糖浆)(转速300～1500 rpm,液相进料量0.381 m3·h-1,径向位置0～300 mm)的流体力学特性进行二维数值模拟,重点研究空腔区域液相形态、液滴直径及直径分布、液相速度、液相平均停留时间随操作条件的变化趋势及原因。结果表明,高转速下液滴直径变小但分布趋向于不均匀,且平均停留时间变短,即转速对气液相传质的影响较为复杂；液相进料量变大时,液滴直径略微变大且分布变得不均匀,液相平均停留时间减小,在一定程度上减弱传质效果；距离转子较远时,液滴由于飞行过程中的碰撞聚并导致直径增大,在设计分散器直径时应考虑这一影响。同时,粘度是影响空腔区域液相形态及流场特性的关键因素,低粘物料被分散器转子分散成大量液滴而高粘物料则形成连续的液丝。本文还针对低粘体系速度场进行三维数值模拟,得到液相轴向速度随转速及液相进料量的增加而增大,随径向位置远离转子而减小；轴向位移随转速及液相进料量的增加而增大。将二维及三维模拟结果同实验结果对比,发现两种方法的相对误差均在15%以下。三维模拟的计算精度总体优于二维模拟,但其模型网格数比二维模型高1-2个数量级。应综合考虑计算精度及计算时间选择合适的模拟方法。
[Abstract]:As a kind of gas-liquid mass transfer equipment, the high-speed disperser makes the liquid dispersed into droplets and wires under the strong centrifugal force and shear force through the high-speed rotation of the rotor, which greatly increases the gas-liquid contact area, and its rotor structure is simple. It is convenient for cleaning and maintenance, so it has broad application prospect. In this paper, Ansys Fluent software is used to simulate the hydrodynamic characteristics of low viscosity and high viscosity systems in a high speed dispersion, which provides theoretical and data support for the subsequent mass transfer study and the structure design of the dispersion. In this paper, the rotor (211mm inside diameter and 219mm outer diameter) of the high speed disperser is uniformly distributed along the circumference of 180 gratings. The fluid volume of Fluid, VOF) and Euler multiphase flow models were used for the study of low viscosity systems (air-water (rotational speed 300 脳 1000rpm), liquid phase feed rate 1.164 ~ 3.443 m ~ (3.h-1), radial distance 0-208 mm to the outer edge of rotor) and high viscosity (air-syrup) system. The two dimensional numerical simulation is carried out on the hydrodynamic characteristics of the velocity 300,500rpm, the liquid feed rate of 0.381 m3 h-1, and the radial position of 300mm. The variation trend and reason of liquid morphology, droplet diameter and diameter distribution, liquid velocity and average residence time of liquid phase with operating conditions were studied. The results show that the droplet diameter becomes smaller but the distribution tends to be uneven at high rotational speed, and the average residence time becomes shorter. The droplet diameter is slightly larger and the distribution becomes uneven, the average residence time of liquid phase decreases, the mass transfer effect is weakened to a certain extent, and when the droplet is far from the rotor, the droplet diameter increases due to the collision and accumulation during the flight. This effect should be taken into account in the design of the diameter of the disperser. At the same time, viscosity is the key factor affecting the liquid morphology and flow field characteristics in the cavity region. The low viscosity material is dispersed into a large number of droplets by the rotor of the disperser, while the high viscosity material forms a continuous liquid wire. In this paper, the 3-D numerical simulation of the velocity field of low viscosity system shows that the axial velocity of liquid increases with the increase of rotational speed and the amount of liquid feed, and decreases with the radial position away from the rotor. The axial displacement increases with the increase of rotational speed and liquid phase feed. Compared with the experimental results, the relative errors of the two methods are below 15%. The accuracy of 3D simulation is better than that of 2D simulation, but the grid number of 3D model is 1-2 orders of magnitude higher than that of 2D model. The calculation accuracy and calculation time should be considered synthetically and the appropriate simulation method should be chosen.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.1

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