Annular two-phase flow in a small diameter tube: OpenFOAM simulations with turbulence damping vs optical measurements

Q1 Chemical Engineering International Journal of Thermofluids Pub Date : 2024-09-19 DOI:10.1016/j.ijft.2024.100871
Emanuele Zanetti , Arianna Berto , Stefano Bortolin , Mirco Magnini , Davide Del Col
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Abstract

In this work, numerical simulations are performed to predict two-phase annular flow of refrigerant R245fa inside a 3.4 mm diameter vertical channel. The VOF (Volume of Fluid) method implemented in an OpenFOAM solver is used to accurately track the vapor-liquid interface. A 2D axisymmetric domain is considered and the Adaptive Mesh Refinement (AMR) method is applied to the cells near the liquid/vapor interface. The Reynolds-Averaged Navier Stokes (RANS) equations are solved and the k-ω SST model is adopted for turbulence modelling in both the liquid and vapor phase. Simulations are used to calculate instantaneous and mean values of the liquid film thickness at mass flux G = 100 kg m-2 s-1 and vapor quality ranging between 0.2 and 0.85. Numerical results are compared against measurements of the liquid film thickness taken during vertical annular downflow. Previous works from the literature and the deviations observed between present numerical and experimental results suggest the need for turbulence damping at the vapor-liquid interface by adding a source term in the ω equation. The simulations show that a low value of the turbulence damping parameter (e.g. 1) causes the average liquid film thickness to increase by 25 %–52 % compared to the non-damped scenario. The interface presents large amplitude disturbance waves in the non-damped case, whereas small ripple waves are predicted when turbulence damping is introduced. Furthermore, the difference between the application of a symmetric and asymmetric treatment for the source term is analysed. From the comparison between experimental data and numerical simulations, it emerges that the value of the correct damping source term to be applied is strictly dependent on the vapor quality.
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小直径管中的环形两相流:带湍流阻尼的 OpenFOAM 模拟与光学测量结果对比
在这项工作中,对制冷剂 R245fa 在直径为 3.4 毫米的垂直通道内的两相环形流动进行了数值模拟预测。采用 OpenFOAM 求解器中的 VOF(流体体积)方法来精确跟踪汽液界面。考虑了一个二维轴对称域,并对液体/蒸汽界面附近的单元采用了自适应网格细化(AMR)方法。对雷诺平均纳维-斯托克斯(RANS)方程进行求解,并采用 k-ω SST 模型对液相和汽相进行湍流建模。模拟计算了在质量通量 G = 100 kg m-2 s-1 和蒸汽质量介于 0.2 和 0.85 之间时液膜厚度的瞬时值和平均值。数值结果与垂直环形下流过程中的液膜厚度测量值进行了比较。之前的文献研究以及目前的数值结果和实验结果之间的偏差表明,有必要通过在 ω 方程中添加一个源项来阻尼汽液界面上的湍流。模拟结果表明,与无阻尼情况相比,湍流阻尼参数的低值(如 1)会导致平均液膜厚度增加 25%-52%。在无阻尼情况下,界面会出现大振幅扰动波,而引入湍流阻尼后,则会出现小波纹。此外,还分析了源项采用对称和非对称处理方法的区别。通过对比实验数据和数值模拟结果,可以发现正确的阻尼源项值与水汽质量密切相关。
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来源期刊
International Journal of Thermofluids
International Journal of Thermofluids Engineering-Mechanical Engineering
CiteScore
10.10
自引率
0.00%
发文量
111
审稿时长
66 days
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