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Simultaneous laser-induced fluorescence and capacitance probe measurement of downwards annular gas-liquid flows
International Journal of Multiphase Flow ( IF 3.8 ) Pub Date : 2021-04-20 , DOI: 10.1016/j.ijmultiphaseflow.2021.103665
Victor Voulgaropoulos , Andrius Patapas , Steven Lecompte , Alexandros Charogiannis , Omar K. Matar , Michel De Paepe , Christos N. Markides

This study focuses on the characterisation of downwards annular gas-liquid (air-water) flows, by employing a combination of advanced laser-based and capacitance-based measurement methods. A variant of laser-induced fluorescence (LIF), referred to as structured-planar laser-induced fluorescence (S-PLIF), eliminates biases commonly encountered during film-thickness measurements of gas-liquid flows, due to refraction and reflection of the light at the interface. A bespoke capacitance probe is also assembled to enable temporally resolved film-thickness measurements with high temporal resolution along the circumferential perimeter of the pipe. We compare the film mean thickness, roughness, and probability density functions obtained with each method. We find that both methods are able to measure time-averaged film thickness to within <20% deviations from each other and from results obtained from the available literature. The resulting probe data suggest a biased (suppressed) standard deviation of the film thickness, which can be attributed to its working principle, i.e., measuring the film thickness averaged along the circumferential perimeter of the pipe. The autocorrelation functions of the time-traces provide an insight into the characteristic time-scales of the interfacial phenomena in these flows, which span a range from 10 ms for highly gas-sheared flows and increase to about 30 ms for the smoother falling films. The power spectral densities reveal modal frequencies that start from 2.5 Hz for falling films, and increase with the gas Reynolds number by almost an order of magnitude. The turbulent wave activity (slope in the power spectrum) reduces with a decrease in gas shear, and shows similarities to the decay of homogeneous and isotropic turbulence. The sizes of the bubbles entrained in the liquid film are measured from the S-PLIF images, and exhibit log-normal distribution that become flatter with a decrease in the gas Reynolds number. The normalised location of the bubbles (quantified as the relative entrainment depth, i.e., distance of the bubble from the wall over the local film thickness) follows a Gaussian distribution, with the peaks located between 0.5 and 0.6, indicating that the majority of the bubbles accumulate in the middle of the thin film.



中文翻译:

向下环形气液流动的同时激光诱导荧光和电容探针测量

本研究的重点是通过结合先进的基于激光和基于电容的测量方法来表征向下的环形气-液(空气-水)流动。激光诱导荧光 (LIF) 的一种变体,称为结构化平面激光诱导荧光 (S-PLIF),消除了在气液流动的膜厚测量过程中由于光的折射和反射而经常遇到的偏差在界面上。还组装了一个定制的电容探头,以实现沿管道圆周周长具有高时间分辨率的时间分辨薄膜厚度测量。我们比较了每种方法获得的薄膜平均厚度、粗糙度和概率密度函数。我们发现这两种方法都能够将时间平均薄膜厚度测量到<20%彼此之间的偏差以及从现有文献中获得的结果的偏差。所得探针数据表明膜厚存在偏差(被抑制)标准偏差,这可归因于其工作原理,即测量沿管周长的平均膜厚。时间轨迹的自相关函数提供了对这些流动中界面现象的特征时间尺度的洞察,其范围从10 ms 对于高度气体剪切流,对于更平滑的降膜,增加到大约 30 ms。功率谱密度揭示了降膜的模态频率从 2.5 Hz 开始,并随着气体雷诺数增加几乎一个数量级。湍流波活动(功率谱中的斜率)随着气体切变的减小而降低,并显示出与均匀和各向同性湍流衰减的相似性。夹带在液膜中的气泡的大小是从 S-PLIF 图像中测量出来的,并且表现出对数正态分布,随着气体雷诺数的减小,该分布变得更平坦。气泡的归一化位置(量化为相对夹带深度,即气泡与壁的距离超过局部膜厚)遵循高斯分布,峰值位于 0 之间。

更新日期:2021-06-14
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