鼓泡塔反应器内两相流动态模拟研究

Numerical Modelling of Bubbling Flow Dynamic Behaviour in a Bubble Column

采用双流体模型以及考虑气相影响的湍流模型,对矩形鼓泡反应器中气液两相流行为进行了两维和三维数值模拟.结果表明,两维模拟不能准确预测气液两相流动态行为,而三维数值模拟则能准确模拟两相流动态行为。通过比较湍流粘度,发现两维模拟所得湍流粘度要比三维模拟高一个数量级。比较了三维模拟中湍流模型对模拟结果的影响.发现 RNGκ-ε模型所模拟的气泡流摆动周期明显小于κ-ε模型的模拟结果,模拟结果更接近实验结果.考察了升力和虚拟质量力在多相流动态行为模拟中的作用,发现它们对模拟结果产生不同程度的影响,其中升力的影响比虚拟质量力的影响显著。

2D and 3D numerical simulations with two-fluid approach were conducted to investigate the gas-liquid flow dynamic behaviour in a rectangle bubble column. In the simulations, κ-ε and RNG κ-ε turbulent models, which account for the influence of the bubbles on liquid phase turbulence, were employed to study the effect of such models on predication of the dynamic behaviour of the bubble plume. In addition, the influence of different interracial force closures such as drag, lift and added mass forces were also assessed. The simulation results indicated that for the 2D cases, the use of κ-ε model could merely yield a steady flow pattern with one big liquid circulation, while the use of RNG κ-ε model could produce a steady flow pattern, characterised by the appearance of three large vortices. However, all the 3D simulations have captured the plume meandering behaviour. The results showed that the value of the turbulence eddy viscosity predicted with 3D simulation was one order smaller than that with 2D simulation. Particularly, the meandering period of the bubble plume predicted by RNG κ-ε model, was obviously smaller than that predicted using κ-ε model in 3D simulations. The former gave the average turbulence eddy viscosity to be almost one third of that predicted by the latter. The assessment of the use of different interracial force closures and their combinations showed that the lift force has a pronounced effect on the result of bubbly flow behaviour besides the drag force. It was found that the predicted meandering period was much greater than the experimental observations without the inclusion of the lift force, while the predicted period was consistent with the experimental result when the lift force was considered. Our simulations also revealed that the inclusion of the added mass force could notably improve the prediction results.