CFD modeling of hydrogen dispersion under cryogenic release conditions

The use of hydrogen as a fuel should always be accompanied by a safety assessment concerning the case of an accidental release. To evaluate the potential hazards in a spill accident both experiments and simulations are performed. In the present work, the CFD code, ADREA-HF, is used to simulate the liquefied hydrogen (LH2) spill experiments (test 5, 6, 7) conducted by the Health Safety Laboratory (HSL). Two horizontal releases, the one along the ground and the other one at a distance above the ground, and one vertical release are examined with spill rate 60 lt/min. The main focus of this study is on the presence of humidity in the atmosphere and its effect on the vapor dispersion. When humidity is present is cooled, condenses and freezes due to the low prevailing temperature (∼20 K near the release), and releases heat. In addition, during the release hydrogen droplets are formed due to mechanical and flashing break up, and water droplets and ice crystals due to humidity phase change. Therefore, two models are tested: the hydrodynamic equilibrium model, which assumes that the phases are in thermodynamic and kinematic equilibrium and the non hydrodynamic equilibrium model (slip model), which assumed that the phases are in thermodynamic equilibrium but they can obtain different velocities. The fluctuating wind direction was also taken into account, since it greatly affects the hydrogen dispersion. The computational results are compared with the experimental measurements, and it is concluded that humidity along with the slip effect influences the buoyancy of the cloud to a great extent. The best simulation case (humidity and slip effect) is consistent with the experiment for all three tests for the majority of the sensors.