Description:
<jats:title>Abstract</jats:title><jats:p>In this study, CO<jats:sub>2</jats:sub> free expansion from high‐pressure tanks is studied in a transient state while considering the influence of different phenomena—that is, viscous heating, phase transition (solid/liquid/vapour phase), and the Joule–Thomson effect—in an initially supersonic flow. This investigation is performed using computational fluid dynamics (CFD) techniques, comparing the obtained results with some experimental data of the literature with a maximum discrepancy of around 8.5%. In particular, for the first time from the literature, it is observed that, according to the velocity evolution at the outlet, the discharge process is conveniently divided into three here‐defined stages: (1) shocking flow, where pressure abruptly decreases with time and flow becomes supersonic, this leading to the condensation of part of CO<jats:sub>2</jats:sub>; (2) transition flow, characterized by a sort of constant pressure time trend; and (3) flashing flow, where pressure decreases less abruptly following an asymptotic pattern up to the atmospheric one and flow becomes subsonic. Furthermore, non‐equilibrium condensation occurring in the tank, tube, and outlet is observed, finding that the minimum temperature reached by the fluid is around 235 K (−38°C). As well, the non‐equilibrium condensation is taken into account in order to give an indication of the amount of liquid CO<jats:sub>2</jats:sub> leaving the outlet in the form of high‐speed jet, which can be a serious danger for personnel and surrounding installations. Moreover, we observe an important effect of viscous heating in the early‐stage expansion for a relatively short time range, within which the temperature in the tube experiences an abrupt increase of around 210 K (from 170 to 380 K). The same effect in the external room creates a convection flow, pushing CO<jats:sub>2</jats:sub> towards the top. The results of the present work can be used for health, safety, and environment (HSE) management purposes and for a more precise process design related to CO<jats:sub>2</jats:sub> storage and sequestration.</jats:p>