Dynamic behaviors of in-tank subcooled liquid with depressurization-induced phase change and the impact on primary breakup of flashing jet

Abstract

Accidental releases of superheated liquids, such as liquefied petroleum or natural gases, are featured by depressurization across the outlet leading to liquid flashing within the upstream container and the downstream jet. In this work, dynamic behaviors of in-tank liquid with phase change throughout depressurized releases and the influence on the primary breakup of flashing jet were studied with an experimental 20 L tank. In-tank parameters (pressure, temperature, and liquid mass) and downstream jet morphology were characterized. A new nondimensional number (ηp), the ratio between the superheat levels of the saturated states corresponding to liquid temperature and pressure, was developed to describe the liquid's thermodynamic state under both release and ambient conditions. A thermodynamics-determined release rate model was established to characterize flow behaviors at the exit. Results showed a strong correlation between the initial ηp0 and key process parameters I (depressurization and release rates): I = aηp0b, where a and b are constants for a particular I. A ηp0-based criterion was derived to characterize in-tank release dynamics and thermodynamics: ηp0 < 0.25 (subcooled), 0.25<ηp0 < 0.4 (transition from subcooled to superheated), and ηp0 > 0.4 (superheated). Mild evaporation and flash evaporation dominated in-tank pressure recovery when ηp0 < 0.25 and ηp0 > 0.25, inhibiting depressurization. The release rate model agreed well with experiments and demonstrated that flashing happens upstream and chokes the induced two-phase flow when ηp0 > 0.25, decreasing the release rate. The evolving upstream conditions changed the breakup regime both in mechanical and thermodynamic aspects. Moreover, the thermodynamic effect increased as the mechanical effect decreased during depressurization.