Pore-scale visualization and modeling of convective dissolution in a horizontal channel

• Micro-PIV experiments and 3D numerical simulations were combined to investigate the dissolution dynamics in a fracture channel. • The interplay among the dissolution morphology, natural convection, and forced convection was elucidated. • A scaling relationship between the modified dissolution rate (R∗) and the mixed convection intensity (Pe and Ra) is established. Solid-phase dissolution is a critical process in subsurface applications, including solution mining of salt caverns, dam foundation stability, and geological carbon sequestration in deep saline aquifers. Under mixed convection, where gravity-driven natural convection and external forced convection coexist, dissolution morphologies are governed by mass transfer at solid-fluid interfaces. However, how buoyancy and flow dynamics influence mass transfer is still not well understood. In this study, by combining micro-particle image velocimetry (micro-PIV) experiments with three-dimensional pore-scale simulations, we investigate the interplay among morphology evolution, velocity fields, and concentration fields in initially flat fracture channels under varying horizontal forced and vertical natural convection conditions. Our results reveal that enhanced forced convection leads to a transition from wedge-shaped to uniform dissolution patterns at the channel scale, while enhanced natural convection induces localized dissolution troughs on the upper surface. These trough-triggered surface roughness, coupled with buoyancy-induced convective rolls, generate eddies that destabilize the concentration boundary layer (CBL), thereby enhancing mass transfer between the troughs and main flow channels. Based on quantitative analysis of solid dissolution, we establish a scaling relationship between the dissolution rate and the mixed convection intensity. This study provides new insights into the complex dynamics of mixed convection-driven dissolution and offers a framework for predicting mineral dissolution rates in large-scale reactive transport modeling.