Numerical and theoretical prediction of the thermodynamic response in marine LNG fuel tanks under sloshing conditions

Liquefied natural gas (LNG) is becoming an attractive alternative fuel for the ship industry, while its storage in cryogenic LNG fuel tanks encounters complex thermodynamic responses under sea conditions and largely affects system operation reliability. This paper aims to investigate the sloshing effects on the thermodynamic responses of marine LNG fuel tanks by numerical modeling and theoretical analysis. A three-dimensional dynamic model is established to predict the coupled pressure–temperature evolution inside the tank under sloshing conditions. The liquid sloshing motions and the phase transition at the liquid–vapor interface are calculated by incorporating the sloshing and phase change sub-models. The effectiveness of the model to simulate liquid sloshing and tank thermodynamic response is verified by corresponding experimental data. The simulation results indicate that the model can reflect the major dynamics of pressure variation, temperature stratification and phase transition under sloshing excitation, and show that the sloshing uniforms LNG temperature, enhances interfacial mass-heat transfer, and accelerates tank depressurization. A theoretical expression that characterizes the relations between tank pressure drop, vapor temperature and condensation is derived, showing a good correlation with numerical results and providing a feasible way for the inverse determination of the complex phase transition under sloshing conditions.