Numerical Simulation of Gas-Liquid Two-Phase Flow at Various Inlet Positions in Bubble Column at Low Gas Velocity
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摘要: 为了研究不同入口下塔式曝气池气液两相流动规律，采用欧拉双流体模型耦合群体平衡模型（PBM，population balance model），在对计算域网格及气相分布与实验验证的基础上，研究了四种距离曝气池底部中心不同位置处的入口对曝气池内气液两相流动的影响，探讨了气含率、气泡数密度、液相水平速度等流体动力学性质，以期为塔式曝气池设计提供指导和依据.研究结果表明：欧拉双流体模型耦合PBM的模拟结果优于单一气泡尺寸的欧拉双流体模型；曝气池内气含率、气相分布、旋涡强度、液相水平速度均受入口位置影响；当入口位置逐渐远离曝气池中心时，气相分布逐渐呈之字形，旋涡强度增大，气含率及气泡羽流周期则先增大后减小；入口位置对气泡数密度无明显影响，气泡数密度在气泡直径5.95 mm下分布最多.Abstract: In order to examine the law of the gas-liquid two-phase flow at various inlet positions of a bubble column, an Euler-Euler two-fluid model coupled with the population balance model (PBM) was used to simulate the effects of four inlets at various positions in the middle of the bubble column bottom on gas-liquid two-phase flow in the bubble column. We verified the mesh of the computational domain and gas hold-up distribution by comparing with experimental data. This study also investigated dynamic behaviours of gas hold-up, bubble number density, liquid horizontal velocity, etc., which provide instructions and basis for the design of the bubble column. The simulated results using an Euler-Euler two-fluid model with PBM were found to be consistent with the experimental results and better than those calculated using an Euler-Euler two-fluid model with single bubble diameter. Furthermore, the dynamic behaviours of gas hold-up, liquid horizontal velocity, distribution of gas hold-up, and vortex strength were all affected by the inlet position. When the inlet was farther from the middle of the bottom of the bubble column, the gas hold-up had an S-shaped distribution and the vortex strength increased; the gas hold-up and bubble plume oscillation period initially increased and then decreased. The bubble number density was not significantly affected by the inlet positions in the bubble column. Moreover, the group with the bubble diameters of 5.95 mm had the largest bubble number density.
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图 2 瞬态气含率模拟与实验对比
Figure 2. Comparison between experimental and computational results of instantaneous gas hold-up
图 3 监测点瞬态水平方向液相速度
Figure 3. Instantaneous horizontal liquid velocity at observation points
图 5 监测点瞬态水平方向液相速度
Figure 5. Calculated instantaneous horizontal liquid velocity at observation point
表 1 气泡直径分组
Table 1. Bubble size group discretization
组号 1 2 3 4 5 6 7 8 9 10 尺寸/mm 1.45 2.35 3.25 4.15 5.05 5.95 6.85 7.75 8.65 9.55 
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表 2 网格及计算参数验证
Table 2. Verification of mesh and calculated parameters
网格单元数量 时间步/s 最大迭代步 气含率 5 763 0.010 0 30 0.006 70 7 353 0.010 0 30 0.006 64 10 050 0.010 0 30 0.006 92 14 400 0.010 0 30 0.006 83 22 725 0.010 0 30 0.006 64 10 050 0.002 5 30 0.006 92 10 050 0.005 0 30 0.006 92 10 050 0.020 0 30 0.006 95 10 050 0.010 0 10 0.006 93 注:实验气含率为0.006 90.
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