Study Of Hydrogen Leakage And Dispersion In A Large Underground Parking Garage

As a clean and renewable energy carrier that can be produced from a wide range of sources,hydrogen is considered to be one of the most useful alternatives to fossil fuels.However,current research on hydrogen safety is still incomplete.Systematic,indepth hydrogen safety studies are necessary for safe,large-scale hydrogen applications.The paper presents a series of experimental,numerical,and theoretical studies on hydrogen releases in a large underground garage that provide a scientific basis for the development of safety codes and standards and prevention measures.The concentration build-up in a scaled underground garage was measured to model the hydrogen dispersion of accidental hydrogen releases from a fuel cell vehicle.The experiments used helium as a substitute for hydrogen for safety reasons.The results show that the helium concentrations in the gas mixture layer along the garage ceiling followed a power-law decay law in the large underground garage and that the initial front velocity of the gas mixture layer decayed with the horizontal distance from the leaking car.After the release stopped,the helium concentration decayed as a powerlaw function of the normalized time with the termination front velocity being higher than the initial front velocity.In addition,the self-preservation of the concentration field for different leakage flow rates was verified by the experimental data.Numerical models were used to simulate hydrogen leaks and diffusion in an actual size underground parking garage for various conditions with the numerical models validated by the experimental data.The simulation results were then used to understand the law governing the hydrogen concentration variations in the garage and develop an appropriate correlation.The results show that the release locations did not significantly affect the far-field concentration distributions.Therefore,the same concentration distribution law can be applied for releases at different locations.Various ventilation layouts were also studied to show that the layout with vents in the garage corners has the best hydrogen removal effect for the same ventilation volume,ventilation area,and number of vents.An engineering model was developed in this study to calculate the hydrogen concentration distribution in an underground garage.The model can quickly calculate the hydrogen concentration at the ceiling of a garage for various conditions,such as the garage size,the release flow rate,the release location,and the release duration.A theoretical model originally developed for small confined spaces was also used to predict the hydrogen distributions,with several coefficients be modified to enable the model to predict the hydrogen distribution in large confined spaces,such as large underground garages.A simplified theoretical model was presented to calculate the gas mixture layer thickness and the mean hydrogen concentration in the layer.The hydrogen concentration contours can be quickly and accurately predicted by the engineering or theoretical models,which are much faster than the CFD methods.