On the choice of analogue fluids in CO₂ convective dissolution experiments

Mixtures of ethylene glycol and methanol (EG-MeOH) have been used as an analogue system (i.e., EG-MeOH/water) in recent experiments in the context of convective dissolution of CO₂ in deep saline aquifers. We have conducted a linear stability analysis of a gravitationally unstable diffusive boundary layer as well as direct numerical simulation of convective mixing involved in dissolution of EG-MeOH species in water. We provide new evidences that EG-MeOH does not resemble the dynamics of convective instabilities and subsequent mixing associated with dissolution of CO₂ in water. It is found that there are fundamental differences in the evolution of the buoyancy-driven instability and dynamics of convective mixing between CO₂/water and a typical EG-MeOH/water analogue system. Our results show that for a constant Rayleigh number, the onset of convective instabilities for EG-MeOH/water can be different by an order of magnitude as compared with CO₂/water. In addition, EG-MeOH/water system reveals different dynamics associated with the convective mixing as compared to CO₂/water system. This study improves our understanding of the instability behavior of analogue systems, their proper selection, and motivates further experiments.