Diffusive and convective dissolution of carbon dioxide in a vertical cylindrical cel

The dissolution and subsequent mass transfer of carbon dioxide gas into liquid barriers plays a vital role in many environmental and industrial applications. In our work, we study the downward dissolution and propagation dynamics of CO₂ into a vertical water barrier confined to a narrow vertical glass cylinder, using both experiments and direct numerical simulations. Initially, the dissolution of CO₂ results in the formation of a CO₂-rich water layer, which is denser in comparison to pure water, at the top gas-liquid interface. Continued dissolution of CO₂ into the water barrier results in the layer becoming gravitationally unstable, leading to the onset of buoyancy driven convection and, consequently, the shedding of a buoyant plume. By adding sodium fluorescein, a pH-sensitive fluorophore, we directly visualise the dissolution and propagation of the CO₂ across the liquid barrier. Tracking the CO₂ front propagation in time results in the discovery of two distinct transport regimes, a purely diffusive regime and an enhanced diffusive regime. Using direct numerical simulations, we are able to successfully explain the propagation dynamics of these two transport regimes in this laterally strongly confined geometry, namely by disentangling the contributions of diffusion and convection to the propagation of the CO₂ front.