浓相气固流化床流化特性及CPFD数值模拟

发布时间：2018-06-26 06:34

本文选题：床层密度 + 空间分布　；参考：《中国矿业大学》2017年硕士论文

【摘要】：空气重介质流化床分选技术的基础是阿基米德原理,没有一个在空间上密度均匀分布的流化环境,待分选物料就难以按密度分层,进一步的分选也无法实现;而若床层密度在时间范围上的密度波动较大,则已分层的物料也容易被破坏掉,同样对分选结果不利。考虑到空气重介质流化床用于物料持续性分选,因此需对不同参数水平下的床内加重质的流化状态以及局部床层密度在空间和时间上的分布进行研究。论文首先研究了初始床层高度、加重质粒径和流化数,对空气重介质流化床床层密度在时间和空间分布上的影响。研究认为:床层密度在宽度方向上,总体呈现中间低(1.72-1.82g/cm3)、两边高(1.80-1.88g/cm3);沿床高方向上,则是中部较高(1.75-1.84g/cm3),上下部相近但较中部略偏低0.01-0.03g/cm3。较高的初始床层有利于将整体床层密度维持在一个较窄的范围内。增加初始床层高度主要是使水平方向的分布更加均匀,从而使对整体床层密度的标准差减小。越处于靠近布风板的位置,局部床层密度在时域上越稳定。较高的初始床层高度使得密度在时域分布上倾向于向低密度偏移。接着通过高速摄像和数字图像处理的方法,分别研究了加重质粒径和流化数对二维空气重介质流化床内气泡数目、当量直径和宽高比的影响。结果显示气泡在床层最上层和最下层出现的次数明显较多。加重质粒径由74-125μm升高到200-425μm,最上部的气泡数目减少了 73%。较大的加重粒径(dp=200-425μm)使得各区域气泡直径的分布范围更宽,且在床层上部受到的影响更大。相较于中上部,在床层下部,气泡直径分布的更为均匀。最后利用计算颗粒流体力学(CPFD)模型对空气重介质流化床内的流态化行为进行数值模拟,并与被广泛应用的双流体模型(TFM)相比较。总结分析两者的特点,并结合试验数据,选定Wen-Yu曳力模型作为默认曳力模型,后根据CPFD模拟结果分别研究了颗粒相时均体积分数、时均轴向速度和返混情况。
[Abstract]:The separation technology of air heavy medium fluidized bed is based on Archimedes principle. Without a fluidized environment with uniform density distribution in space, it is difficult to separate the materials to be sorted according to the density, and the further separation can not be realized. If the density of the bed layer fluctuates in the time range, the layered material is easily destroyed, which is also unfavorable to the separation results. Considering the use of air-heavy medium fluidized bed for continuous separation of materials, it is necessary to study the fluidization state and the spatial and temporal distribution of the local bed density in the bed with different parameters. In this paper, the effects of initial bed height, aggravation particle size and fluidization number on the time and space distribution of fluidized bed density are studied. The results show that the bed density is low (1.72-1.82g/cm3) and high on both sides (1.80-1.88g/cm3) in the width direction, and higher in the middle (1.75-1.84g/cm3) in the direction of the bed height, but it is 0.01-0.03g / cm ~ (-3) lower in the upper and lower parts but slightly lower than that in the middle part. A higher initial bed is conducive to keeping the overall bed density within a narrow range. Increasing the initial bed height is mainly to make the distribution of the horizontal direction more uniform, thus reducing the standard deviation of the density of the whole bed. The local bed density is more stable in time domain as it is located near the wind plate. The higher initial bed height makes the density tend to shift to low density in time domain distribution. Then, the effects of aggravation particle size and fluidization number on the number of bubbles, equivalent diameter and ratio of width to height in a two-dimensional air heavy medium fluidized bed are studied by means of high-speed photography and digital image processing. The results show that the number of bubbles appearing in the top and bottom layers of the bed is obviously more. The aggravation particle size increased from 74-125 渭 m to 200-425 渭 m, and the number of upper bubbles decreased by 73 渭 m. The larger aggravation particle size (dp=200-425 渭 m) makes the distribution range of bubble diameter wider, and the influence on the upper part of the bed is greater. The bubble diameter distribution is more uniform in the lower part of the bed than in the middle and upper part. Finally, the computational particle hydrodynamics (CPFD) model is used to simulate the fluidization behavior in an air-heavy medium fluidized bed, and it is compared with the widely used two-fluid model (TFM). The Wen-Yu drag model was selected as the default drag model, and the average volume fraction of particle phase, time-averaged axial velocity and backmixing were studied according to the CPFD simulation results.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD922;TD94

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