Numerical Study on the Effects of Tank Volume on Underwater Liquefied Ammonia Release and Phase-Change Behavior in Shallow Water

Ammonia is a promising carbon-free marine fuel, but accidental underwater releases of pressurized liquefied ammonia involve complex multiphase flow and phase-change behavior. This study numerically investigated the effects of tank volume on liquefied ammonia release in shallow water. A revised Eulerian multiphase model incorporating temperature-dependent ammonia properties, the Lee evaporation–condensation model, and interfacial surface tension was applied. Grid sensitivity was first evaluated for a 4 m3 tank, and simulations were then performed for 4, 8, and 16 m3 tanks under identical initial pressure and release-opening conditions. Mesh effects were pronounced during the initial transient period but decreased with time; therefore, a Fine mesh with a minimum cell size of 0.01 m was used. Larger tanks depressurized more slowly, sustaining high-velocity liquid release and vapor-phase development for longer periods. Ammonia vapor formed near the release opening and rose buoyantly, producing more extensive and persistent distributions in larger tanks. At approximately 10 s, total gas-phase ammonia normalized by initial stored mass was 5.4%, 6.8%, and 4.2% for the 4, 8, and 16 m3 tanks, respectively. Mass conservation ratios remained close to unity. Thus, tank volume influenced depressurization, release duration, phase-change behavior, and vapor-phase development.