If carbon dioxide dissolves into a body of water, a ${\mathrm{CO}}_2$-rich boundary layer forms at the interface, which is denser in comparison to pure water. Continued dissolution of ${\mathrm{CO}}_2$ 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. In this work, we look at the influence of confinement on this process in two ways: In the first part we focus on expanding our understanding of the short-time, transient diffusion of ${\mathrm{CO}}_2$ into a vertical water barrier confined to a narrow cylindrical cell by varying the cylinder diameter and ${\mathrm{CO}}_2$ pressure. By adding sodium fluorescein, a pH-sensitive fluorophore, we directly visualize the dissolution and propagation of the ${\mathrm{CO}}_2$ across the liquid barrier. Combined with particle-tracking experiments we quantify the effects of the cylinder width and ${\mathrm{CO}}_2$ pressure on the initial diffusive behavior, the onset of convection, and the enhancement of the buoyancy driven convection of the subsequent transport. In the second part, we investigate the long-time, steady mass transfer dynamics in the liquid barrier by trapping a slug bubble underneath the liquid barrier and varying the barrier height and partial ${\mathrm{CO}}_2$ pressure. We find that initially the Sherwood number scales as Sh $\propto {\mathrm{Ra}}^{1/4}$ with the Rayleigh number Ra, but for a sufficiently large barrier the Sherwood number reaches a constant value. Building on the ideas of Ahlers et al. [Phys. Rev. Lett. 128, 084501 (2022)], rescaling the Rayleigh number with an aspect-ratio-dependent relevant length scale results in a universal Sh vs Ra dependence.

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• Convection
• Rayleigh-Bénard convection