In the final instalment of our seminar series for 2014, Maha Manoubi will present a talk on her MASc work: “Criteria for a Flame to Propagate Between Neighboring Pockets of Reactive Gas”. The abstract of the talk is below. The talk will start promptly at 2:30pm.
**Kindly note the change of venue** since exams are now in full swing, we have to relocate our seminar to STE C0136
Friday December 12th, 2:30pm, Room STE C0136 (the glass engineering building next to CBY).
Criteria for a Flame to Propagate Between Neighboring Pockets of Reactive Gas
Maha Manoubi (M.A.Sc. Candidate), Supervisor: Dr. Matei. I. Radulescu
During severe accidents in water-cooled nuclear power plants, large amounts of hydrogen could be generated and released to form large composition heterogeneities. In fact, when leaks occur at several locations, or in the presence of complex geometries, multiple pockets of reactive gases may accumulate in certain locations, surrounded by inert gases. The focus of the present study is to determine the conditions for a flame to propagate between pockets of reactive mixtures separated by air and develop the scaling laws governing this phenomenon. The soap bubble technique was used to isolate pockets of reactive gas. The experiments were performed in hydrogen-air mixtures of different compositions. A largescale shadowgraph technique was implemented to visualize the events over length scales of almost 2 meters by 2 meters.
The high-speed visualization permitted to determine the transition mechanism and its influence on the critical separation distance between the pockets. The results have revealed that for mixtures characterized by high flame speed (at near stoichiometric compositions), where the effect of buoyancy is negligible, the propagation condition is related to the volumetric expansion. When the expansion of the gas kernel of the first pocket is sufficient for the hot products to reach the original position of the gas of the second pocket, the gas in the boundary layer of the second bubble ignites, permitting transition. However, for lean mixtures, or for bubbles sufficiently large, buoyancy effects become important and the spherical flame rises before it can reach the second bubble. Thus the critical separation distance becomes much smaller and is no longer determined by the expansion ratio. The critical radius of the flame that will rise due to buoyancy is presented as function of the mixture properties.