湍动浆态床流体力学研究(Ⅳ)带垂直列管束的浆态床流体力学模型与模拟

Hydrodynamics of turbulent slurry bubble column(Ⅳ) Modeling and simulation of bubble column with vertical pipe bundles

工业浆态床反应器一般都安装有密集的换热列管,列管束的存在使得速度和气含率的径向分布趋于陡峭,形成"烟囱效应",目前对此还缺乏合适的流体力学模型进行定量描述。本文提出两点新思路以解决列管束的模拟问题:一是将密集列管束的影响作为体积源项而不是边界条件来考虑,在标准k-ε方程中增加与列管阻力相关的动量源、湍动源、耗散源本构关系;二是采用气泡群的径向升力和湍流扩散力平衡方程确定气含率径向分布。新模型中引入的阻力系数由流体力学文献给出,只有两个径向力和耗散参数需实验确定。模型计算的气含率和液速分布在宽泛的条件下与实验测量值符合良好,能够定量描述"烟囱效应"以及内构件参数对流动的影响。

The commercial-scale slurry bubble column reactors are generally equipped with bundles of vertical heat-exchange pipes. Experimental results showed that existence of the pipe bundles led to steepening of liquid velocity and gas holdup distributions, the so-called ＂funneling effect＂ . At present, there is still lack of reliable CFD models which quantitatively describe the impact of vertical pipe bundles. In this work, a novel hydrodynamic model was developed, with two new ideas. The influence of pipe bundles was regarded as volumetric sources instead of rigid wall boundaries, thus actions of internals on the flow were transformed to additional constitutive equations for momentum source, turbulent energy source and energy dissipation source in standard k-ε equations. For the determination of radial gas holdup profiles, the lateral lift force and turbulent dispersion force imposed on bubble swarms were introduced into the radial momentum balance equation. The new introduced pipe resistance coefficients in the CFD model came from literatures, only two parameters involving radial force and turbulent energy dissipation were determined by fitting experimental data. Radial profiles of gas holdup and liquid velocity predicted by the CFD model showed good agreements with experimental data. The model presented in this paper provides an effective tool for simulating the ＂funnel effect＂ and impacts of the pipe bundles on bubbly flow.