Abstract

One of the most critical barrier against residential hydrogen fuel cell systems is the unintended release of hydrogen in an enclosure that causes fires and explosions, especially when the gas concentration level exceeds certain amount in the ambient air. Scientists are using helium as a surrogate to investigate and observe the dispersion behaviour of hydrogen in case of a leak. However, it has been found that there are differences between hydrogen and helium concentrations before the plumes become stable, during the initial stages of the gas release. At present, the similarity of the hydrogen and helium plumes depend only on experimental results and observations. This thesis proposes a theoretical model of a point source light gas plume and developed a new theoretical model for the similarity of hydrogen and helium plumes.

In order to better understand the dispersion behavior of the hydrogen gas in an enclosure, experiments were conducted in a 1/4 sub-scale residential garage model. Helium gas was released inside the model with various experimental configurations. Helium concentrations were measured by thermal conductivity sensors to observe the effects of natural and mechanical ventilation. For natural ventilation cases, it is found that volumetric flow rate, injector height, release direction and release times had significant effects on helium concentration levels inside the enclosure. For the mechanical ventilation case, high fluctuations of concentration levels were observed at the sensors inside the plume and the maximum concentration level did not have a significant difference inside the plume compared to the same case with natural ventilation. On the other hand, the maximum concentration level outside the plume had vital differences, forced ventilation caused maximum concentration level to stay below the lower hydrogen explosion limit.