A unified thermodynamic framework for LNG rapid phase transition on water

• All of thermo-fluid dynamic aspects of an LNG following a release have been systematically dealt with.
• LNG kinetic and thermodynamic limits have been analysed in the light of multi-component nucleation theory, together with the importance of the interface temperature.
• Influence of LNG composition and ageing on RTP has been investigated against experimental data.
• Bubble growth theory has been applied to identify the expansion rate of LNG spilled on the water.
• Droplet size, fragmentation and explosion escalation has been analysed in detail.
• A new rigorous method has been set up to calculate the RPT overpressure, on the basis of Lighthill's acoustic model.

Rapid phase transition (RPT) is a phenomenon which frequently occurs after an LNG release on water. Its effects are potentially hazardous mainly because of the very fast rate of high energy release, in addition to fire and explosion. A significant case history and various experimental campaigns provide evidence which has allowed assessing different aspects of this event. This paper aims at offering a unified thermodynamic analysis of RPT. The thermodynamic and the kinetic limits of liquid superheat have been fully reviewed and specifically applied to LNG, within the homogeneous nucleation theory for multi-component liquids. Thermal and thermo-mechanical interface properties, such as interface temperature, evaporation rate, surface properties and liquid fragmentation have also been investigated. The importance of LNG composition has been analysed with respect to the experimental data. Finally, on the basis of the well known Shepherd and Sturtevart test, bubble growth rate has been modelled according to Mikic, Rohsenow and Griffith (MRG) equation and a new rigorous method has been set up to predict RPT overpressure, in line with Lighthill's acoustic theory, which removes the existing uncertainty and some subjectivities of the available models and possibly increases the thermo-fluid dynamic understanding of the phenomenon.