The behavior of pressurized liquefied CO2 in a vertical tube after venting through the top

This study presents results from small-scale experiments on the rapid phase transition of pressurized liquefied carbon dioxide in a vertical tube. The main motivation for the study was to provide reference data for the source terms in 1-D phase transition models. In addition a phase transition rate estimate and an energy estimate is presented. To initiate the test runs, a diaphragm was ruptured which led to the expansion towards atmospheric pressure and rapid boiling of the superheated liquid. The main contributions were the calculated front velocities and bulk flow velocities. Evaporation waves were observed, propagating with a velocity of 30±0.5 m/s into the superheated liquid. The initial pre-rupture condition was saturated liquid at ambient temperatures (19-21C). The pressure reduction in the bottom during the boiling period was typically 8 bar (reduction from 56 to 48 barg). Due to the high pre-rupture pressure, the tube was made of polycarbonate. High speed images showed that the tube surface was not sufficiently smooth to suppress heterogeneous nucleation entirely. Consequently, the evaporation wave front was rather diffuse, mainly caused by upstream wall nucleation. This limited the degree of superheat, hence homogenous bulk nucleation was not observed. A contact surface between the vapor and vapor-liquid phases was observed, accelerating out of the tube with a velocity of 90±5 m/s. A liquid layer front propagated with a constant velocity of 8.0±0.1 m/s. Gas bubbles in the upstream liquid bulk moved with a constant velocity of about 5 m/s after passage of the rarefaction wave.