CFD Simulation of Pressure Reduction Inside Large-scale Liquefied Hydrogen Tank

Building  the  international  hydrogen  supply  chain  requires  the  large-scale  liquefied   hydrogen(LH2) carrier. During shipping LH2 with LH2 Carrier, the tank is pressurized by LH2 evaporation due to heat ingress from outside. Before unloading LH2 at the receiving terminal, reducing the tank pressure is essential for the safe tank operation. However, pressure reduction might cause flashing, leading to rapid  vaporization  of liquefied  hydrogen,  liquid  leakage.   Moreover,  it  was  considered  that  pressure recovery phenomenon which was not preferred in terms of tank pressure management occurred at the beginning  of  pressure  reduction.  Hence,  the   purpose  of  our  research  is  to  clarify  the phenomenon inside  the  cargo  tank  during   pressure  reduction.  The  CFD  analysis  of  the  pressure  reduction phenomenon was conducted with the   VOF based in-house CFD code, utilizing the C-CUP scheme combined  with  the  hybrid   Level  Set  and  MARS  method.  In  our  previous  research,  the  pressure reduction  experiments   with  the  30  m³  LH2  tank  were  simulated,  and  the  results  showed  that  the pressure   recovery  was  caused  by  the  boiling  delay,  and  the  tank  pressure  followed  the   saturation pressure  after  the  liquid  was  fully  stirred.  In  this  paper,  the  results  were re-evaluated  in  terms  of temperature.  While  pressure  reduction  was  dominant,  the  temperature  of  vapor-liquid  interface decreased.  Once  the  boiling  bubble  stirred  the  interface,  its  temperature  reached  the  saturation temperature  after  pressure  recovery  occurred.  Moreover,  it  was  found  that  the  liquid  temperature during  pressure  reduction  could  not  be  measured  because  of  the  boiling  from  the  wall  of  the thermometer. The CFD analysis on pressure reduction of 1250 m³ tank for the LH2 Carrier was also very could occur in the case of the 1250 m³ tank in a certain condition. These results provide new insight into the development of the LH2 carrier.