Influence of confinement on the dissolution of carbon dioxide in a vertical cylindrical cell

If carbon dioxide dissolves into a body of water, a CO2-rich boundary layer forms at the interface, which is denser in comparison to pure water. 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. 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 CO2 into a vertical water barrier confined to a narrow cylindrical cell by varying the cylinder diameter and CO2 pressure. By adding sodium fluorescein, a pH-sensitive fluorophore, we directly visualize the dissolution and propagation of the CO2 across the liquid barrier. Combined with particle-tracking experiments we quantify the effects of the cylinder width and CO2 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 CO2 pressure. We find that initially the Sherwood number scales as Sh ∝Ra1/4 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)10.1103/PhysRevLett.128.084501], rescaling the Rayleigh number with an aspect-ratio-dependent relevant length scale results in a universal Sh vs Ra dependence.