射频热等离子体反应器模拟及优化

发布时间：2018-03-16 11:11

本文选题：射频热等离子体　切入点：数值模拟　出处：《中国科学院大学(中国科学院过程工程研究所)》2017年硕士论文　论文类型：学位论文

【摘要】：射频热等离子体具有温度高、导热快、冷速大、气氛可控等优点,在粉体制备领域有着重要应用。本文基于Fluent软件,通过流体力学计算对热等离子体反应器进行模拟,以典型制备过程——熔融球化和气化冷凝过程为对象,研究热等离子体制备球形粉体和纳米粉体的具体过程,为优化反应器和制备工艺提供指导。主要内容如下:(1)基于实验室现有10kW射频热等离子体反应器,进行模型建立、网格划分、网格优化、边界设定等工作,从三维尺度上了表征反应器内温度分布和速度分布。研究了载气、中气、边气流率的变化对反应器内温度分布和速度分布的影响,获得了反应器内流场分布的调控规律,为研究粉体在热等离子体反应器中的运动和受热过程奠定基础。(2)针对小颗粒粉体难以球化问题,模拟了不同粒径钨粉在热等离子体反应器中的运动过程,考察了粒径对粉体球化过程的影响。发现小颗粒易受逆向速度和径向速度的影响,在反应器内表现为强扩散和返混运动,吸收热量降低,这是小颗粒粉体难以球化的主要原因。通过优化载气、中气、边气流率,降低了颗粒的扩散和返混,改善了小颗粒的球化效果。(3)为了考察粒径对颗粒气化过程的影响,模拟了硅粉在热等离子体反应器中的运动和传热过程。统计颗粒在反应器中的停留时间、初始气化时间和完全气化时间,对比得到了粒径和总气化率的关系。发现30kW热等离子体反应器中,30.0μm以内颗粒的气化率在99%以上,残留未气化颗粒对产物质量的影响可以忽略。此结果与实验结果相吻合,可用于指导选择原料颗粒的粒度。(4)为了研究加料量对颗粒气化过程的影响,模拟了硅粉在热等离子体反应器中的受热过程。基于对反应器内轴向速度和温度的模拟计算,获得了连续相的热流密度分布。统计了颗粒在径向的分布变化,与热流密度分布相对比得到了加料量与总气化率的关系,分析了加料量对总气化率的具体影响。发现30 kW热等离子体反应器的加料量低于9.63 g·min-1时,总气化率大于99.0%,残留未气化颗粒对产物质量的影响可以忽略,该结果可以指导确定进入反应器的颗粒流率。
[Abstract]:RF thermal plasma has many advantages, such as high temperature, fast heat conduction, large cooling rate, controllable atmosphere, etc. It has important application in powder preparation field. Based on Fluent software, the thermal plasma reactor is simulated by hydrodynamic calculation. Taking the typical preparation process-melting spheroidization and gasification condensation process as the object, the specific process of preparing spherical and nano-sized powders by hot plasma was studied. The main contents are as follows: 1) based on the existing 10kW RF thermal plasma reactor in the laboratory, modeling, mesh generation, mesh optimization, boundary setting, etc. The temperature distribution and velocity distribution in the reactor were characterized on a three dimensional scale. The effects of the change of carrier gas, medium gas and edge flow rate on the temperature distribution and velocity distribution in the reactor were studied, and the regulation of the flow field distribution in the reactor was obtained. In order to study the movement and heating process of powder in hot plasma reactor, the movement process of tungsten powder with different particle size in the thermal plasma reactor was simulated in view of the difficult spheroidization of small particle powder. The effect of particle size on the spheroidization process of the powder was investigated. It was found that the small particles were easily affected by reverse velocity and radial velocity, and showed strong diffusion and backmixing motion in the reactor, and the absorption of heat decreased. This is the main reason that small particle powder is difficult to spheroidize. By optimizing the rate of carrier gas, medium gas and edge flow, the diffusion and backmixing of particles are reduced, and the spheroidizing effect of small particle is improved. (3) in order to investigate the effect of particle size on the gasification process, The movement and heat transfer process of silica fume in the thermal plasma reactor were simulated. The residence time, initial gasification time and complete gasification time of the particles in the reactor were calculated. The relationship between the particle size and the total gasification rate is obtained. It is found that the gasification rate of the particles in the 30 kW hot plasma reactor is more than 99%, and the influence of the residual ungasified particles on the quality of the product can be neglected. The results are in agreement with the experimental results. In order to study the effect of feeding amount on particle gasification process, the heating process of silicon powder in hot plasma reactor was simulated. Based on the simulation of axial velocity and temperature in the reactor, The distribution of heat flux of continuous phase is obtained, and the variation of particle distribution in radial direction is calculated. Compared with the distribution of heat flux, the relation between the feeding amount and the total gasification rate is obtained. The specific effect of feed rate on the total gasification rate was analyzed. It was found that the total gasification rate was greater than 99.0 when the feeding amount of 30 kW hot plasma reactor was less than 9.63 g 路min-1, and the effect of residual ungasified particles on the quality of the product could be neglected. The results can guide the determination of particle flow rate into the reactor.
【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O53;TB383.3

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