In this work, we calculate contact angles in X-ray tomography images of two-phase flow in order to investigate the wettability. Triangulated surfaces, generated using the images, are smoothed to calculate the contact angles. As expected, the angles have a spread rather than being a constant value. We attempt to shed light on sources of the spread by addressing the overlooked mesh corrections prior to smoothing, poorly resolved image features, cluster-based analysis, and local variations of contact angles. We verify the smoothing algorithm by analytical examples with known contact angle and curvature. According to the analytical cases, point-wise and average contact angles, average mean curvature and surface area converge to the analytical values with increased voxel grid resolution. Analytical examples show that these parameters can reliably be calculated for fluid–fluid surfaces composed of roughly 3000 vertices or more equivalent to 1000 pixel2. In an experimental image, by looking into individual interfaces and clusters, we show that contact angles are underestimated for wetting fluid clusters where the fluid–fluid surface is resolved with less than roughly 500 vertices. However, for the fluid–fluid surfaces with at least a few thousand vertices, the mean and standard deviation of angles converge to similar values. Further investigation of local variations of angles along three-phase lines for large clusters revealed that a source of angle variations is anomalies in the solid surface. However, in the places least influenced by such noise, we observed that angles tend to be larger when the line is convex and smaller when the line is concave. We believe this pattern may indicate the significance of line energy in the free energy of the two-phase flow systems.

中文翻译：

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两相流图像中的接触角

在这项工作中，我们计算了两相流的 X 射线断层扫描图像中的接触角，以研究润湿性。使用图像生成的三角化表面被平滑以计算接触角。正如预期的那样，角度具有扩展性而不是恒定值。我们试图通过在平滑之前解决被忽视的网格校正、分辨率不佳的图像特征、基于聚类的分析和接触角的局部变化来阐明扩散的来源。我们通过具有已知接触角和曲率的分析示例来验证平滑算法。根据分析案例，逐点和平均接触角、平均平均曲率和表面积随着体素网格分辨率的增加而收敛到分析值。分析示例表明，对于由大约 3000 个或更多相当于 1000 个像素的顶点组成的流体-流体表面，可以可靠地计算这些参数。在实验图像中，通过查看单个界面和簇，我们表明接触角被低估了润湿流体簇的接触角，其中流体 - 流体表面被解析为少于大约 500 个顶点。然而，对于至少有几千个顶点的流体-流体表面，角度的平均值和标准偏差收敛到相似的值。对大型团簇沿三相线角度局部变化的进一步研究表明，角度变化的来源是固体表面的异常。然而，在受这种噪音影响最小的地方，我们观察到，当线条是凸的时，角度往往更大，而当线条是凹的时，角度往往更小。我们相信这种模式可能表明线能在两相流系统的自由能中的重要性。