High-speed imaging of degassing kinetics of CO2–water mixtures

The exsolution of gas molecules from gas–liquid mixtures plays a significant role in a wide range of applications from industrial processes such as metal casting to subsurface flow of oil or geothermal waters. This study aims to improve the understanding of the conditions under which free gas bubbles start forming in CO2–water mixtures. The bubble point pressure was determined under various different conditions like the temperature and initial pressure of the mixture along with other parameters such as the bubble growth rate. A series of depressurization experiments at high pressure and temperature (up to 100 bar and 100 °C) is performed using a pressure cell that allows for visual monitoring of the degassing process. Bubble formation during the depressurization process is recorded using a high-speed camera paired with a uniform light source along with a pressure transducer and thermocouple. Image analysis allows for the determination of the bubble point pressure and rate of bubble formation. For CO2 in its gaseous state and at moderate temperatures, decent agreement between experimental results and the theoretical bubble point pressure is found, although significant deviations are observed at elevated temperatures. More pronounced differences in bubble point are observed for mixtures starting out at high pressures where CO2 is a supercritical fluid, which lead to lower than expected bubble point pressures.