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CFD Simulations of an Air-Water Bubble Column: Effect of Luo Coalescence Parameter and Breakup Kernels

机译:气泡水柱的CFD模拟:罗凝聚参数和破碎核的影响

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摘要

In this work, CFD simulations of an air-water bubbling column were performed and validated with experimental data. The superficial gas velocities used for the experiments were 0.019 and 0.038 m/s and were considered as an homogeneous regime. The former involves simpler physics when compared to a heterogeneous regime where the superficial velocities are higher. In order to simulate the system, a population balance model (PBM) was solved numerically using a discrete method and a closure kernels involving the Luo coalescence model as well as two different breakup models: Luo's and Lehr's. For the multi-phase calculations, an eulerian framework was selected and the interphase momentum transfer included drag, lift, wall lubrication, and turbulent dispersion terms. A sensitivity analysis was performed on a Luo coalescence kernel by changing the coalescence parameter (c0) from 1.1 to 0.1 and results showed that the radial profiles of gas holdup and axial liquid velocity were significantly affected by such parameter. From the simulation results, the main conclusions were: (a) A combination of the Luo coalescence and Luo breakup kernels (Luo-Luo) combined with a decreasing value of c0 improves the gas holdup profiles as compared to empirical values. However, at the lowest value of c0 investigated in this work, the axial liquid velocity deteriorates with regards to experimental data when using a superficial gas velocity of 0.019 m/s. (b) A combination of the Luo coalescence and Lehr breakup models (Luo-Lehr) was shown to improve the gas holdup values with experimental data when compared to the Luo-Luo kernels. However, as c0 decreases, the Luo-Lehr models underestimate the axial liquid velocity profiles with regards to empirical values. (c) A first and second order numerical schemes allowed predicting similar radial profiles of gas holdup and axial liquid velocity. (d) The mesh sensitivity results show that a 3 mm mesh size can be considered as reasonable for simulating experimental data. (e) The inclusion of wall lubrication parameter was found to be significant, although only when using finer meshing. In addition, it allows an improvement of the axial liquid velocity at the core of the bubble column.
机译:在这项工作中,对空气-水鼓泡塔进行了CFD模拟,并用实验数据进行了验证。用于实验的表观气体速度分别为0.019和0.038 m / s,被认为是均匀状态。与表面速度较高的非均质体系相比,前者的物理原理更为简单。为了模拟该系统,使用离散方法和涉及Luo合并模型以及两个不同分解模型(Luo's和Lehr's)的封闭核对人口平衡模型(PBM)进行了数值求解。对于多相计算,选择了欧拉框架,并且相间动量传递包括阻力,升力,壁润滑和湍流弥散项。通过将合并参数(c0)从1.1更改为0.1,对Luo合并内核进行了敏感性分析,结果表明,该参数显着影响了气体滞留率的径向分布和轴向液体速度。从模拟结果可以得出以下主要结论:(a)将Luo聚结和Luo破碎核(Luo-Luo)与c0的降低值相结合,与经验值相比可改善气体滞留率曲线。但是,在这项工作中研究的最低c0值下,当使用0.019 m / s的表观气体速度时,轴向液体速度相对于实验数据会下降。 (b)与Luo-Luo核相比,结合实验数据显示了Luo聚结模型和Lehr分解模型(Luo-Lehr)的组合可以提高气体滞留率。但是,随着c0的减小,Luo-Lehr模型相对于经验值低估了轴向液体速度曲线。 (c)一阶和二阶数值方案可以预测气体滞留率和轴向液体速度的相似径向分布。 (d)网格灵敏度结果表明,对于模拟实验数据,可以认为3 mm的网格尺寸是合理的。 (e)发现壁润滑参数很重要,尽管仅在使用更精细的啮合时才如此。此外,它可以改善气泡塔中心处的轴向液体速度。

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