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author

Kelly Thomas
Massimiliano Kolbe
Martin Goodrich

published on

April 2006

A set of large-scale vented deflagration tests involving methane- and propane-air mixtures in a congested enclosure has been performed. The enclosure utilized had a 24-foot by 24-foot footprint and a height of 6 feet. Steel plates were attached to the roof and all four sides served as vents. The vent panels weighed 2 lbm/ft2 and were configured to release at 0.3 psig. A regular array of vertical circular tubes provided the congestion for these tests. The tubes were arranged with a pitch-to-diameter ratio of 7.6 and provided area and volume blockage ratios of 13% and 1.5%, respectively. The fuel-air mixture completely filled the congested region in these tests, but did not extend beyond it. The average peak pressures achieved with methane and propane mixtures were 4.0 psig and 5.0 psig, respectively. These pressures are 20 to 40 times the values predicted by the NFPA 68 weak and strong enclosure correlations, respectively, if the constraint imposed by the vent panel release pressure is not explicitly considered. Consideration of the vent panel release pressure constraint increases the predicted pressures to within an order of magnitude of the measured values. On the basis of these tests, it is concluded that NFPA 68 correlations can significantly underpredict the peak pressure achieved in a vented deflagration for an enclosure with moderate congestion levels. This paper also provides comparisons with a simplified predictive method currently under development.

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Kelly Thomas

Massimiliano Kolbe

Martin Goodrich