Numerical investigation of hydrogen leakage from a high pressure tank and pipeline

We numerically investigated high-pressure hydrogen leakage from facilities in storage and transportation phases. In storage phase, assuming a tank placed in a hydrogen station, we examined unsteady diffusion distance up to 100 ms after leakage. A series of simulations led us to develop an equation of unsteady hydrogen diffusion distance as a function of mass flow rate, leakage opening diameter, and tank pressure. These results helped us develop a safety standard for unsteady hydrogen diffusion. In transportation phase, we simulated (in three dimensions) the dominant factor of steady mass flow rate from a square opening of a rectangular pipeline and the pressure distribution in the pipeline after leakage. The mass flow rate was smaller than the maximum mass flow rate and the pressure distribution converged to a steady state that was 16% higher than the pressure after the passage of expansion waves in a shock tube model. We introduced a theoretical model by dividing the flow with the leakage opening into two phases of the unsteady expansion waves’ propagation and acceleration. The simulation results showed good agreement with the modeling equation when the shrink coefficient was set to 0.8. When the leakage opening was rectangular, the simulation results again showed good agreement with the modelling equation, suggesting that our simulated results are independent of the leakage opening shape.