Numerical Simulations of Atmospheric Dispersion of Large-scale Liquid Hydrogen Releases

Numerical  simulations  have  been  conducted  for  LH2   massive  releases  and  the  subsequent atmospheric dispersion using an in-house modified version of the open source computational fluid dynamics (CFD) code OpenFOAM. A conjugate heat transfer model has been added for heat  transfer   between  the  released  LH2   and  the  ground.  Appropriate  interface  boundary conditions  are   applied  to  ensure  the continuities  of  temperature  and  heat  fluxes.  The significant temperature difference between the cryogenic hydrogen and the ground means that the released LH2 will instantly enter in a boiling state, resulting in a hydrogen- air gaseous cloud,  which  will   initially  behave  like  a dense  gas.  Numerical  predictions  have  been conducted  for  the   subsequent  atmospheric  dispersion  of  the  vaporized  LH2   for  a series  of release scenarios - with and without retention pits - to limit the horizontal spread of the LH2 on the ground. The considered cases included the instantaneous release of 1, 10 and 50 tons of LH2   under  neutral   (D)  and  stable  (F)  weather  conditions.  More  specifically,  3F  and  5D conditions were simulated with the former representing stable weather conditions under wind speed  of  3  m/s  at   10  m  above  the  ground  and  the  later  corresponding  to  neutral  weather conditions under 5 m/s wind speed (10 m above the ground). Specific numerical tests have also been conducted for selected scenarios under different ambient temperatures from 233 up to 313 K. According to the current study, although the retention pit can extend the dispersion time, it can significantly reduce the extent of hazards due to much smaller cloud size within both the flammability and explosion limits. While the former has negative impact on safety, the  later  is  beneficial.  The   use  of  retention  pit  should  hence  be  considered  with  caution  in practical applications.