Investigating liquid‐fronts during spontaneous imbibition of liquids in industrial wicks. Part II: Validation by DNS

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Abstract
To validate the experimental results of Part‐1, we conducted a two‐phase flow simulation of imbibition of a wetting liquid through 2D microstructures made of ellipses of varying aspect ratios. The flow simulation in the particulate microstructures, characterized by low (ellipse) aspect ratio, produced somewhat even micro‐fronts, thus replicating the sharp fronts at the visual (macroscopic) scale observed in Part‐1. Whereas simulations in the fibrous microstructures produced highly uneven micro‐fronts, suggesting the formation of semi‐sharp or diffuse visual fronts. Increasing the porosity from 50% to 70% resulted in solid‐phase clustering and led to further increase in the unevenness of micro‐fronts, pointing to purely diffuse visual fronts. The evolution of the saturation plots along the flow direction, obtained from area‐averaging of fluid‐distribution plots, pointed to diffusing of sharp fronts with time. The predictions matched our previous experimental and numerical observations, that is, the particulate media create sharp fronts while the fibrous media create semi‐sharp/diffuse fronts.

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