The Critical Role of the Intermittent Two‐Phase Flow Topology on the Solute Dispersion in Partially Saturated Porous Media

Abstract Intermittent flow is a widely recognized phenomenon across various fields, characterized by the spatial‐temporal fluctuations of the two‐phase topology. However, its implications for solute dispersion and mixing remain insufficiently understood. In this study, intermittent two‐phase flow is induced within microfluidics under varying aqueous‐phase saturations. The coherent dispersive behavior of a tracer plume within the aqueous phase is systematically investigated. The results indicate that fluctuations in aqueous‐phase saturation and the dispersion coefficient persist beyond breakthrough. Flow intermittency enhances solute dispersion by directing the solute plume along temporally varying preferential paths, resulting in sharper, finger‐like concentration fronts with more pronounced gradients. Consequently, anomalous solute dispersion phenomena, including asymmetric and multimodal concentration distributions as well as prolonged tailing, are observed. Furthermore, wavelet analysis reveals a strong coherence between the flow field topology and solute mixing. Fluctuations in the dilution index consistently lag those of the effective Okubo‐Weiss parameter, highlighting the dominant role of flow field topology in controlling solute mixing. While solute dispersion is primarily enhanced by the intermittent two‐phase flow, the degree of mixing can be either suppressed or promoted. These findings advance our understanding of solute transport dynamics in intermittently connected two‐phase systems, with implications for optimizing dispersion and storage security in environmental applications, such as geological carbon sequestration.