(372l) Estimation of Supersaturation in Pressure-Driven Supersaturated Gas-Liquid Systems

A gas-liquid system is referred to as supersaturated when the concentration of the solute phase (gas) exceeds the equilibrium concentration in the solvent phase (liquid). A supersaturated solution can be achieved either by changing the temperature and/or pressure of the system. The gas from a supersaturated liquid escapes either through bubble nucleation that usually occurs on solid surface and/or gas diffusion through the gas-liquid interface. A pressure-driven bubble nucleation process requires a minimum threshold supersaturation to initiate the formation of gas bubble(s). In addition, a certain waiting time is required at each pressure reduction step to ensure either enough time is given for the bubbles to nucleate and grow, or to conclude that the supersaturation is not sufficient to initiate the bubble nucleation. When the supersaturation is not sufficient to cause bubble nucleation, some or all of the supersaturated gas may diffuse out from the liquid through the gas-liquid interface before the next pressure reduction step to further increase the supersaturation. In this study, a simple analytical method developed based on Fick’s second law of diffusion and Henry’s law to estimate the supersaturations generated in three gas-liquid systems (CO₂-water, CH₄-water, and N₂-water) with two step-down pressures (100 and 500 mbar) is presented. Characteristic times of the gas-liquid systems were estimated to validate whether the waiting times used in this study are in accordance with the semi-infinite diffusion model used to estimate the supersaturations generated. During the waiting time, some or all of the supersaturated gas may diffuse out before initiating the next step-down pressure. Therefore, it is important to know the actual supersaturation in the system as a function of time during the waiting time in order to quantify the actual supersaturation required to initiate the bubble nucleation. Therefore, in this study the influence of step-down pressure, and the waiting time between the pressure reduction steps on supersaturation is also investigated.