逆向气流对规整填料表面液膜流体动力学特性的影响

为研究气相流量对规整填料内气液两相逆流流动情况下流场结构及界面行为的影响,建立了基于分离涡模拟(DES)方法与VOF模型相结合的CFD分析模型,VOF控制方程离散采用显示差分格式,体积分数离散采用界面重构方法。计算域整体采用结构化曲线网格(贴体网格)划分,并对局部进行了细化。结果表明,气相F因子较小时(F≤1.354 Pa^0.5),液膜自由表面及其纵向速度分量(v_y)均呈周期性规律分布,波动幅度基本一致,而v_y均为负值。F=3.386 Pa^0.5时,液膜自由表面波动出现紊乱,幅值差异明显增大,而界面液膜v_y值仍基本呈周期性规律分布,在液相波峰下沿出现v_y >0的情况。F=5.418 Pa^0.5时,出现液相返混,气相和液相内均出现大小不等的回流区并随液相返混过程发展演化,同时局部液膜出现整体向上流动特征。F≥6.772 Pa^0.5后,填料下部出现干板区,底部出口不再有液相流出。随气相F因子增大,持液量和有效界面传质面积均先增后减。

Influences of counter-current gas flow on hydrodynamics of liquid film over structured packing surface

In order to study the influence of gas flow rate on flow structure,interface motion of counter-current gas-liquid flow over structured packing surface,a CFD model based on detached eddy simulation(DES)and volume of fluid(VOF)method was developed.Explicit interpolation scheme was used for the VOF formulations,and the Geo-Reconstruct method was chosen as the volume fraction discretization scheme.Structured curvilinear grids were generated for the whole fluid domain and locally refined to ensure that at least 10 grid points were within the liquid film.When F factor was low(F≤1.354 Pa^0.5),the distribution of free-surface and its velocity component v_y were periodic,and the fluctuation amplitude was almost uniform.Along the free-surface all values of v_y were negative.As F=3.386 Pa^0.5,fluctuation of free-surface appeared to be disturbed,while the distribution of v_y kept periodic,and at the lower edge of liquid waves v_y>0.As F=5.418 Pa^0.5,back mixing of liquid phase appeared,recirculation regions were formed in both phases and evolved with the liquid back mixing process,and the liquid film could wholly move upward in some concaves of solid surface.As F≥6.772 Pa^0.5,dry patch was formed at the lower part of packing region and no liquid could flow out from the bottom outlet.With the increment of F factor,both liquid holdup and effective interfacial area increased first and then decreased.