Benefit from the advantages of wide sources and zero carbon emission, hydrogen is considered to be the most potential renewable energy to replace the traditional fossil energy. With the increase in the number of hydrogen refueling stations and other hydrogen energy application terminals, liquid hydrogen has attracted widespread attention as an efficient form of hydrogen energy storage and transportation, and many universities and enterprises have carried out laboratory-scale experiments related to liquid hydrogen. The accidental leakage of liquid hydrogen is prone to frostbite due to its extremely low-temperature characteristics, and the wide flammable range (4–75 vol%), low minimum ignition energy (0.017 mJ) and strong diffusivity of hydrogen make it very easy for combustion and explosion accidents to occur after leakage. To carry out the safety analysis of accidental leakage of liquid hydrogen in laboratory space, a two-dimensional Mixture model is established by using the Computational Fluid Dynamics (CFD) method to study the phase change, diffusion, and thermophysical characteristics of liquid hydrogen after leakage. The calculation model simulates the vertical leakage of liquid hydrogen to the ground and continuous diffusion at a speed of 0.2 m/s for 1 s at a distance of 20 cm from the ground under different ventilation conditions and cofferdam setups in the laboratory space. The characteristics of liquid hydrogen flow and hydrogen cloud diffusion are studied, the safety risks are evaluated and suggestions are given. The results show that: (1) After the liquid hydrogen leaked hits the ground, it flows rapidly around the ground, accompanied by violent phase change, which ended within 4.8 s after the leakage. During this period, the evaporated hydrogen continues to gather to the ceiling under the action of buoyancy and is continuously discharged from the laboratory space. (2) The safety of laboratory space with active ventilation is better than that of passive ventilation. The two cases of active ventilation and the case of double passive vents involved in this paper all decrease rapidly after the total mass of hydrogen in the space reaches the peak value, which decreases to less than 0.1 kg in 2.65 s, 27.45 s and 39.85 s respectively. In the case of single passive vent, the hydrogen is discharged slowly due to the backflow of air from the vent, even 120 s after the leakage, the hydrogen quality remained at a high level. (3) After the liquid hydrogen leaks to the ground, it rapidly expands around with phase change, and a considerable amount of liquid hydrogen is entrained into the air, which has great low-temperature harm. Compared with the case without cofferdam, the case with unilateral cofferdam and bilateral cofferdam reduces the low-temperature harm area near the ground by 32.6% and 77.9% after 1 s of leakage, and the installation of the cofferdam caused the hydrogen cloud to diffuse upwards and accelerate the hydrogen discharge space.

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