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New insights of foam flow dynamics in a high-complexity 2D micromodel

Yeates, Christopher, Youssef, Souhail, Lorenceau, Elise
Colloids and surfaces 2019 v.575 pp. 184-198
bubbles, foams, hydrodynamics, image analysis, models, porous media
In this work, we present direct observation of foam flow through a 2D porous microfluidic device. Through a specially designed image processing workflow, we perform individual bubble tracking and establish flow dynamics within the micromodel structure. In addition to our experimental data, we provide 2D and 3D numerical Newtonian flow simulations on equivalent digitized versions of the model, carried out using Lattice Boltzmann simulation codes for comparison. The results show that foam flow in our experimental conditions, low gas fraction and high injection velocity, demonstrate a high degree of similarity to the flow of a Newtonian fluid in both 2D and 3D simulations, in aspects of large-scale flow distribution homogeneity and specific flow passage activation. However, the foam data shows a larger spread of pore-scale flow velocities, spanning from blocked off areas of quasi-zero flow, to zones of high velocity, with velocities well above the Newtonian counterparts. For our model depth and characteristics, the 2D simulation demonstrates slightly more flow heterogeneity and is closer to the foam case. Detailed bubble tracking gives access to other characteristics of the foam flow inside the medium such as the dichotomy between the flow patterns of the smallest bubbles, typically dispersing and accessing most regions available, and the largest bubbles, which travel in long straight preferential paths exclusively. We show that intrinsically tied to these different flow patterns is the relationship between bubble velocity and bubble size, as we demonstrate distinct populations of trapped and flowing bubbles with distinct sizes. Finally, we explore the relationships between microstructural parameters and flow intensity and note a weak correlation to local structural parameters. Our study, which combines high spatial and time resolution, small network dimensions, high network complexity and efficient bubble tracking, therefore sheds new light on the study of foam flow in porous media.