Experimental study of the concentration build-up regimes in an enclosure without ventilation

We present an experimental investigation of the different concentration build-up regimes encountered during a release of helium/air mixture in an empty enclosure without ventilation. The release is a vertical jet issuing from a nozzle located near the floor. The nozzle diameter, the flow rate and the composition of the injected mixture have been varied such that the injection Richardson number ranges from 6 × 10−6 to 190. The volume Richardson number, which gives the ability of the release to mix the enclosure content, ranges from 2 × 10−3 to 2 × 104. This wide range allowed reaching three distinct regimes: stratified, stratified with a homogeneous upper layer and homogenous.