鼓泡塔气液两相及气液固三相流实验研究及数值模拟

发布时间：2018-02-10 00:25

本文关键词： CFD 鼓泡塔两相流三相流数值模拟 PBM　出处：《天津大学》2015年硕士论文　论文类型：学位论文

【摘要】：鼓泡塔反应器具有传质效率高、耗能较低、结构简单等显著优点,广泛应用于石油化工、生物化工等众多领域。而迄今为止,人们对于鼓泡塔内流场的认识仍然有限,而计算流体动力学(Computational Fluid Dynamics,CFD)的快速发展,为鼓泡塔内流场的研究提供了一种新的途径。本文应用欧拉-欧拉模型,在ANSYS-Fluent软件平台,对鼓泡塔中气液两相和气液固三相流动进行了模拟计算。为节省计算时间,采用全塔径均匀进气的简化方案,减少了75%~80%的网格数,大大减轻了计算量。同时,比较了单一气泡尺寸模型和群体平衡模型(Population Balance Model,PBM)在此简化条件下的适用性,发现单一气泡尺寸模型不能准确预测塔内流动情况。而PBM模型所得的气含率径向分布与实验值吻合较好。在PBM模型的计算中,发现原用于颗粒聚并计算的Abrahamson模型,在合适的Hamaker数下,也可用于气泡聚并的计算。为了解决出口边界处液相逸出和自由区域内有漩涡形成的问题,本文采用了新的边界条件,对原有的出口边界中气相和液相速度进行了修正,改进后的边界条件可以使液面处的流场更加均匀稳定,计算更容易收敛。在此状态下,使用Schiller-Naumann、Grace和Tomiyama三种曳力模型分别进行气液两相流模拟。将模拟值与实验值比较后,发现使用Tomiyama曳力模型所得模拟值与实验值符合程度较高。开展实验研究了气液固三相流体中的相含率分布规律。设计并搭建了高1.5m的鼓泡塔和取样测量装置,在0.01354 m/s和0.01805 m/s两表观气速下,测量了5个轴向高度上气固含率分布,并对结果做误差分析。在气液固三相流动的计算中,以搭建实验装置为几何模型,在此前的气液两相模型设定中加入固相进行非稳态模拟,发现气含率分布与实验值可信范围较符合,再次验证了选用的气液间模型合理性。固含率模拟值趋势与实验结果相符,但数值偏大,这可能是因固液密度差较大,导致固相测量值偏小。
[Abstract]:Bubble column reactor has many advantages, such as high mass transfer efficiency, low energy consumption, simple structure and so on. It is widely used in many fields, such as petrochemical, biochemistry and so on. However, up to now, people's understanding of the flow field in bubble column is still limited. The rapid development of Computational Fluid Dynamics (CFDs) provides a new way for the study of flow field in bubbling column. In this paper, Euler-Euler model is used in ANSYS-Fluent software platform. The gas-liquid two-phase and gas-liquid-solid three-phase flow in bubbling column was simulated and calculated. In order to save calculation time, a simplified scheme of uniform air intake with whole tower diameter was adopted, which reduced the mesh number by 75% and greatly reduced the calculation amount. The applicability of single bubble size model and population Balance model is compared under this simplified condition. It is found that the single bubble size model can not accurately predict the flow in the tower, while the radial distribution of gas holdup obtained by PBM model is in good agreement with the experimental data. In the calculation of PBM model, the Abrahamson model used for particle aggregation calculation was found. In order to solve the problem of liquid-phase escape at the exit boundary and the formation of vortex in the free region, a new boundary condition is adopted in this paper. The velocity of gas phase and liquid phase in the original exit boundary is modified. The improved boundary condition can make the flow field at the liquid level more uniform and stable, and the calculation is easier to converge. Three drag models, Schiller-Naumanni Grace and Tomiyama, are used to simulate gas-liquid two-phase flow. It is found that the simulated values obtained by using the Tomiyama drag model are in good agreement with the experimental values. The phase holdup distribution in gas-liquid-solid three-phase fluids is studied experimentally. A 1.5m bubble tower and a sampling measuring device are designed and built. At the two apparent gas velocities of 0.01354 m / s and 0.01805 m / s, the distribution of gas-solid holdup at five axial heights was measured, and the error analysis was made. In the calculation of gas-liquid-solid three-phase flow, the experimental device was built as the geometric model. It is found that the distribution of gas holdup is in good agreement with the credible range of experimental values, and the rationality of the selected gas-liquid model is verified again, and the trend of simulation value of solid holdup is consistent with the experimental results. However, the value is larger, which may be due to the large solid-liquid density difference, resulting in a small solid-phase measurement value.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ053.5

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