(271f) Numerical Simulation of Cryogenic Boiling Using Volume of Fluid (VOF) Method

The loss of primary containment of cryogenic (LNG) storage tanks or pipelines causes subsequent events such as vaporization and pool spreading, vapor dispersion and fire/explosion. LNG safety studies have been mainly focused on accurate analysis of vapor dispersion modeling, but much less attention has been given to phenomena such as vaporization and two-phase spreading despite of the fact that those are critical to the accurate prediction of the consequences of spill. During the initial spillage, the surface temperature of the substrate such as concrete or insulated dyke material is much higher than the boiling point of the cryogen thus the boiling takes place mainly, at least at the early stage of the spill, due to the heat conduction from substrate. A thin film of vapor might be existent between the substrate and the liquid as the consequence of the very high heat transfer from the substrate. This mode of boiling is known as film boiling. The objective of this paper is to model the film boiling heat transfer due to conduction for an accurate prediction of the vaporization rate using Taylor-Rayleigh instability in a commercial computational fluid dynamics environment ANSYS-FLUENT.

A planar two-dimensional grid of 5 mm x 14 mm is simulated where the number of cells are 64x192. Unsteady state equations for mass, momentum, energy and volume of fluid equations are solved considering a time steps of 0.0001 sec. The fluid domain was initialized with a vapor film at the bottom that has been associated with the wave number greater than its critical Taylor-Raleigh instability value. The temperature dependent properties of liquid nitrogen were used in order to validate the model’s prediction with the experimental data performed utilizing liquid nitrogen. The sensitivity analysis of the grid and the time step have been performed.