Cryogenic jets atomisation
MODELLING THERMAL AND SPRAY CHARACTERISTICS
The prediction of the spray dynamics and dispersion is of critical importance to predict the behaviour of the vapour cloud that cryogenic liquids produce, and is now part of an upheaval in the global energy industries for generating numerical tools to model the process. Important features of pressurised jets of cryogenic liquids can be predicted using the capabilities of MPflow.
FLASH-BOILING AND CAVITATING JETS
Flashing jets occur when a high-pressure liquid flowing through a nozzle or an orifice is suddenly exposed to a low-pressure environment, becoming superheated if it is not already so. Flashing is characterised by a rapid phase change along the jet and bubble nucleation within the liquid core that influences the spray formation .
Flashing is very important in safety studies in cases of accidental releases of a liquefied flammable gas through a small crack in the pipeline system. In the aerosol industry it can be used to control nucleation having the advantage of producing sprays with very fine droplets within small domains. In its dense part, the two-phase jet might appear in different forms like bubbly, slug or annular and the nucleation is possible to start upstream of the orifice (a process generally termed internal flashing) or at some distance downstream of the orifice (external flashing). The geometry and the nozzle length-to-diameter ratio, the degree of superheat or sub-cooling, the storage and ambient conditions play a crucial role in the atomisation process. Flashing occurs either if a liquid follows an isothermal depressurisation or an isobaric heating. In both cases, the fluid fails to adjust to the local changes in pressure and temperature admitting a metastable state which makes the process more challenging to understand.