Experimental investigation on liquid–gas interfacial dynamics and phase transition effects under non-isothermal sloshing conditions

Non-isothermal sloshing frequently occurs in cryogenic fuel tanks (e.g., liquefied natural gas and liquefied hydrogen) during marine transportation. The resulting liquid–gas phase transition is strongly influenced by sloshing flows, inducing instantaneous pressure and temperature variations that compromise operational safety and reliability of liquid cargo systems. This paper experimentally investigates the liquid–gas interfacial dynamics and phase transition effects on tank thermodynamics under non-isothermal sloshing conditions. Visual experiments were conducted across four sloshing frequencies and three amplitudes, revealing four distinct sloshing regimes based on interfacial behaviors. The two-phase interfacial region emerges in sloshing regime III due to disturbances from liquid jets and phase transition, and expands significantly in regime IV, which replaces the clear free surface. Non-isothermal sloshing triggers brief surface evaporation and pressurization, followed by sustained vapor condensation and depressurization. Thermal stratification persists in regimes I and II, while de-stratification initiates in the liquid phase (regime III) and extends to both phases (regime IV). The measured results indicate that the peak and average condensation rates scale cubically with those of evaporation rates, and the logarithmic average evaporation rate varies linearly with frequency and follows a power-law dependence on amplitude. We finally propose empirical correlations linking sloshing parameters to evaporation rates and condensation rates to evaporation rates, showing good agreement with experimental data.