Contact Angles in Two-Phase Flow Images

Abstract

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.

4D Imaging of Two‐Phase Flow in Porous Media Using Laboratory‐Based Micro‐Computed Tomography

“…Once trained, computational neural networks also have the advantage of delivering very fast non-iterative reconstructions. The possibility of extracting wetting angles from pore-scale views of the fluid transport in porous media has gathered much scientific attention because of its importance for understanding the local pore physiochemical conditions (AlRatrout et al, 2017;Blunt et al, 2019;Khanamiri et al, 2020;Mascini et al, 2020;C. Sun et al, 2020).…”

“…The possibility of extracting wetting angles from pore‐scale views of the fluid transport in porous media has gathered much scientific attention because of its importance for understanding the local pore physiochemical conditions (AlRatrout et al., 2017; Blunt et al., 2019; Khanamiri et al., 2020; Mascini et al., 2020; C. Sun et al., 2020). A targeted study toward the wetting angle dynamics would put stringent requirements on the spatial resolution in order to resolve the three‐phase contact line accurately.…”

4D microvelocimetry reveals multiphase flow field perturbations in porous media

“…1 C ). For the filter sample experiment, the surface areas and mean curvatures of fluid–fluid and fluid–solid interfaces are calculated using the open-source code developed by Khanamiri et al ( 80 ); after downsampling by a factor two to reduce the computational requirements. From this, the energy contributions in Fig.…”

Validating mechanistic models of fluid displacement during imbibition

“…Geometric contact angles were first measured on micro-CT data by Andrew et al 23 , where the angle between the fluid/fluid interface and the solid surface was measured manually in the plane perpendicular to the three-phase-contact-line. This method was then enhanced by automated algorithms which find the geometric contact angle at every point on the three-phase-contact-line in the entire pore space 24,31,32,47 . We used the code developed by AlRatrout et al 24 to calculate the conventional geometric contact angle distribution, which was determined from a single 3D image at the end of imbibition.…”