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Experimental And Numerical Study On The Effect Of Mixture Composition On Vented Explosions

2711 words - 11 pages

A parametric set of vented explosion experiments for three mixtures, stoichiometric propane-air, methane-air and 18.0 vol. % hydrogen-air were performed. The three mixtures each displayed various physical phenomena and behaviors and their similarities and differences were identified. A physics based CFD model was developed, using a small subset of the experimental data, with a single set of empirical coefficients for all three mixtures. The model takes into account the effect of turbulence, flame instabilities and the Rayleigh-Taylor instability on flame propagation and pressure generation. For cases dominated by a pressure transient associated with the external explosion, the results of the simulations show good agreement between experimental and numerical results for all three mixtures, typically within the experimental uncertainty of the experiments. Further work remains on improving the model, however, particularly to account for the pressure transient generated during structure-acoustic interactions.

Venting is a commonly used method to minimize the damage done by accidental explosions. Engineering guidelines and standards exist to estimate the minimum vent size required for a given enclosure [ ], however, these standards are not sufficiently reliable. Other approaches exist [ , ], but several issues remain unresolved due to the complex nature of the phenomena and the limited set of existing experimental data.
Historically, vented explosions have proven to be a challenge to model due to the wide range of physical phenomena present, all of which directly influence the dynamics of the process [ , ]. These phenomena include Helmholtz oscillations [4, ], the external explosion [4, ], flame instabilities [4], flame-acoustic interactions [4, 5], and the generation of turbulence [ ].
In addition to these factors, the Rayleigh-Taylor (RT) instability, the instability of an accelerated density interface, has also been observed in vented explosions. In particular, it has been observed to develop on the flame surface inside the chamber during both Helmholtz oscillations [4, 6], and near the vent after the flame exits the chamber [ ]. While the RT instability has been noted to play a role in vented explosions, it has typically not been considered a key parameter affecting the rate of pressure generation, particularly in more recent (after [6]) studies.
Due to the limited reliability of the current methods for the prediction of pressure generation during vented explosions, a research project was initiated to generate a set of experimental data and to use the data to develop and validate a computational code and new engineering tools. As part of this work, studies have been performed for low reactivity, stoichiometric, methane-air mixtures [ ] and lean hydrogen mixtures [ ]. It was found that a CFD model which only took into account the effect of turbulence was unable to reproduce several key elements of the experimental...

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