Abstract

The main challenge for the wide spread use of hydrogen in fuel cell systems is the safety concerns due to its ease of leaking, low-energy ignition, large flammability range, high buoyancy and diffusion rate in air. To alleviate concern of explosion during experiments, scientists are using helium as a stimulant for hydrogen safety studies. However, the equivalent behavior between the two gases only relies on numerical or experimental results, and the similarity is not connected by a theoretical correlation. This thesis assesses similarity relations using helium for hydrogen studies and develops a theoretical helium plume model. Meanwhile, a case study of leakage in fuel cell vehicles is simulated by Computational Fluid Dynamics (CFD).
The accuracy of three different correlations, i.e., equal volumetric flow rate, equal buoyancy and equal concentration between helium and hydrogen was compared by CFD simulations validated by helium experiment in a 1/4 sub-scale residential garage model. The accuracy of these different methods at different leakage rate, stage of release, ventilation method and location was discussed. An updated theoretical helium plume model was validated by PIV (Particle Image Velocimetry) experiment and CFD. It is found that the new model could be used in estimating the plume size and velocity. In the case study of hydrogen leakage inside a FCV (Fuel Cell Vehicle), ventilation and sunroof show critical effect to reduce the level of hydrogen concentration accumulation.