Phase change modeling of air at the liquid hydrogen release

Abstract

Hydrogen energy has emerged as one of the most promising types of future energy. Accurately predicting the diffusion behavior of liquid hydrogen after an accidental release is one of the most important aspects of promoting the safe use of hydrogen energy. Considering the condensation and freezing of air, a three-dimensional unsteady leakage and diffusion model of liquid hydrogen is developed to predict the distribution of hydrogen vapor cloud and evaporation of liquid hydrogen pool in a large liquid hydrogen release experiment conducted by NASA. During the release of liquid hydrogen, the volume fractions of liquid air and solid air are quite small due to turbulence, and there is almost no liquid air and solid air present in the space directly opposite the leakage source. After the termination of the release, the flow field is more stable and the volume fractions of liquid air and solid air tend to increase, which on the ground can exceed 0.05 and 0.005 respectively at 50 s. This indicates that the ice layer observed in the former experiments may mainly be generated after the release. The evaporation coefficient of hydrogen has a significant effect on the hydrogen flammable volume, as the hydrogen evaporation coefficient increases from 0.006 to 0.06, the flammable volume increases from 1003.3 m3 to 7656.3 m3. As the evaporation coefficient continues to increase from 0.06, the volume growth rate of flammable hydrogen cloud tends to decrease. The flammable volume is not sensitive to the air condensation coefficient in the range of 1–1000, which increases from 6858.8 m3 to 7656.3 m3 as the air condensation coefficient increases from 1 to 1000. This study helps to refine the model for predicting the dispersion characteristics of accidental liquid hydrogen release considering the phase change of the air.