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建立了竖直管中降膜流动的二维模型,液体在重力作用下沿着管壁流下,气体从相反方向进入,采用多相流VOF(Volume of Fluid)模型,在流体力学软件FLUENT求解器中数值求算,模拟其中的液膜流动情况。通过改变液体和气体雷诺数,对于液膜的流体力学特征,包括液膜流动形态、液膜厚度随时间变化、流动方向液膜变化以及液膜中的速度分布等进行了分析。结果发现液膜形成过程主要可分为入口区、发展区和稳定区3个部分,液体雷诺数一定时,逆流气流对液膜形成的影响主要集中在稳定区;气相雷诺数一定时,随着液体雷诺数增大,液膜流动入口区变长,成熟区复合波中光滑液膜所占比例增加。液膜中的速度分布呈半抛物线型,速度随距离壁面距离增加增大,但在接近气液界面处略微下降。根据模拟得到的不同雷诺数的平均液膜厚度,与Nusselt理论预测值进行了比较,发现吻合良好。
A two-dimensional model of falling film flow in a vertical tube was established. The liquid flowed down along the tube wall under gravity and the gas flowed from the opposite direction. Using the multiphase flow VOF (Volume of Fluid) model, the FLUENT solver The numerical calculation, simulation of the liquid film flow. By changing the Reynolds number of liquid and gas, the hydrodynamic characteristics of the liquid film, including the flow pattern of the liquid film, the change of the liquid film thickness with time, the change of the liquid film in the flow direction and the velocity distribution in the liquid film were analyzed. The results show that the formation process of liquid film can be divided into three parts: entrance zone, development zone and stable zone. When the Reynolds number of liquid is constant, the influence of countercurrent airflow on the liquid film mainly concentrates in the stable zone. When the Reynolds number is constant, The liquid Reynolds number increases, the entrance area of the liquid film becomes longer, and the proportion of the smooth liquid film in the complex area of the mature area increases. The velocity distribution in the liquid film is semi-parabolic, and the velocity increases with increasing distance from the wall, but slightly decreases near the gas-liquid interface. According to the simulation, the average liquid film thickness at different Reynolds numbers was compared with the predicted value of Nusselt theory and found to be in good agreement.