规整填料表面液膜流动特性的数值模拟

Numerical simulation on hydraulic characteristics of liquid film on structured packing surface

精馏过程气液两相流运动分布特征对分离效率具有重要影响。为研究规整填料表面液膜流体动力学特性建立了基于VOF方法的CFD分析模型,并基于文献试验结果进行了验证。对液膜随时间和空间的演化分布特征、速度场分布和液相流量影响进行了模拟分析。液膜在波纹顶部下沿聚集形成凸起状波峰,在波纹底部波峰消失,而到达下节波纹上沿时,波峰重新形成;瞬态液膜厚度随时间波动,且沿填料表面液膜平均厚度先减小后保持稳定;发现液相聚集及形成液滴坠落容易导致出现干板区。不同位置液膜速度分布存在明显差异,沿填料表面液膜平均速度先增后减或保持稳定;液膜绕过波纹顶部时会加速,在波纹底部和上沿处会减速。液相流量增大,液膜平均厚度和速度均有所增大。

The hydraulic characteristics of gas-liquid two-phase flow in distillation process are important factor for separation efficiency. With water and air as working medium, a CFD model based on Navier- Stokes equations, RGN k-ε turbulent model and two-phase model of volume of fluid is employed to analyze the hydraulic characteristics of liquid film flow on the structured packing surface at normal temperature and pressure. The model and simulation method are validated by experimental results in literature. The spatial and temporal evolution of liquid film, velocity fields and influences of liquid mass flow rate are simulated and analyzed. Liquid will accumulate below the peaks of corrugation, forming a drop. At valleys, the liquid drop spreads and the film thickness increases, and as it reaches the upper slope of the next corrugation, the drop appears again. The instantaneous liquid film thickness oscillates with time. Along the packing surface the volume-averaged film thickness decreases first, and then keeps stable. Liquid accumulation and dropping have an important effect on the form of dry batches. The velocity profile within the bulk of film varies significantly at different positions of corrugation, and along the packing surface, the average velocity of liquid film increases first, then decreases or keeps stable. The liquid film will accelerate at the convex of corrugation and decelerate at the concave. With the increment of liquid mass flow rate, the average film thickness and velocity increase.