Helium Dispersion in an Attached Single-Car Residential Gara ...

Nist

• 24 februari 2014
• 9781496051219

Samenvatting:

The dispersion and loss of helium inside a single-car residential garage attachedto a single-family house was experimentally characterized by recording time-resolved heliumconcentrations at multiple locations in the garage and at a single location in the house duringand following helium releases near the floor of the garage. Helium served as a surrogate forhydrogen for safety reasons, and helium release rates were adjusted to provide the sameconstant volume flow rate as that required to release 5 kg of hydrogen over a four hour period.Supporting measurements included compartment leakage, temperature, and atmospheric windconditions. Helium was released upwards either as momentum- or buoyancydominated flows.Experiments were performed with the garage empty or with one of two conventional mid-sizedautomobiles parked over the release location. Six tests with the garage naturally ventilated andsix tests employing forced ventilation with a fan are described. A variety of parameters wereused to characterize the mixing behavior. Conclusions emphasized include: a) the role ofFroude number on helium mixing behavior, b) the development of upper and lower heliumconcentration layers in the garage during a release, c) the measurable, but limited, effects ofatmospheric wind on the results, d) the relatively efficient transfer of helium from the garageinto the house during the releases, e) the ability of a vehicle to trap a high helium concentrationin the engine compartment and, particularly, the undercarriage during a helium release and therelatively rapid drop in these levels to those of the surrounding garage at the end of the release,f) the relatively slow buildup of helium in the passenger compartment and trunk of a vehicleduring a helium release and subsequent slow decay following cessation of the flow, g) theeffectiveness of active ventilation in reducing helium concentrations in the garage to levelsbelow those corresponding to flammable concentrations of hydrogen, and h) the trapping ofhelium/air mixtures corresponding to highly flammable hydrogen mixtures inside the vehicleseven when active garage ventilation was employed.