Experimental and numerical analysis of low-density gas dispersion characteristics in semi-confined environments

Hydrogen, as a clean fuel, offers a practical pathway to achieve net-zero targets. However, due to its physical and chemical characteristics, there are some safety concerns for large-scale hydrogen utilisation, particularly in process safety management. Leakage of gaseous hydrogen, especially in semi-confined spaces such as tunnels, can lead to catastrophic outcomes including uncontrolled fire and explosion. The current paper describes the outcome of an experimental and numerical study that aims to understand the dispersion of leaked light gas in a semi-confined space to support the adoption of hydrogen. A dispersion chamber with dimensions of 4m x 0.3m x 0.3m was constructed to investigate a baseline gas leakage scenario. To reduce the risk of the experiment in the laboratory, helium is utilised as a surrogate for hydrogen. Computational fluid dynamics simulations are conducted using FLACS-CFD to model the dispersion of leaked gas in different scenarios focusing on the impact of the ventilation velocity, leakage rate, and slope. The results from comprehensive numerical simulations show that ventilation is a critical safety management measure that can significantly reduce the growth of flammable clouds and mitigate the fire and explosion risk. Even with the lowest ventilation velocity of 0.25 m/s, an improvement in the gas concentration level of 29.34% can be achieved in the downstream chamber. The current results will help to further enhance the understanding of hydrogen safety aspects.