Typical analog fluids such as mixtures of ethylene glycol and methanol (EG-MeOH) and propylene glycol (PPG) have recently been used as an analog system 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 these analog fluids in water. We provide new evidences that neither EG-MeOH nor PPG analog systems do 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 these analog systems. Our results show that for a constant Rayleigh number the onset of convective instabilities for these analog fluids can be different by an order of magnitude as compared with CO2/water. We have shown that the base state density behavior of analog systems has a significant effect on the stability characteristics of the diffusive boundary layer and convective mixing beyond the onset of instability. According to the results of this study, the choice of an analog system is critically important in correct representation of the onset of convective instabilities of CO2/water and design of experiments. This study improves our understanding of the instability behavior of analog systems, their proper selection, and motivates further experiments.
