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Abstract

An approximate method for description of flame acceleration in congested areas filled with combustible gases is presented. The method takes into account both the flame folding arising from interactions with obstacles of the flow produced by the flame and the increase of the burning rate resulting from turbulence generated in the flow ahead of the flame. A simple analytical expression for the flame speed is suggested. Coefficients in this correlation are determined by fitting the model predictions with a set of experimental data. This correlation is then used to evaluate the maximum flame speed that may be developed in vapor cloud explosions as a function of scale and obstacle density. As an example of applications, the flame speeds are evaluated for four typical fuels: methane, propane, ethylene, and hydrogen, and for three different levels of congestion. Both ideal stoichiometric mixtures of the four fuels with air and clouds with nonuniform concentration distributions are considered. The method is shown to take appropriate account of mixture properties. In particular, the well-known difference in combustion behavior of methane, propane, ethylene, and hydrogen was well captured by the method. On the basis of the maximum flame speeds, the severity of the blast effect from unconfined gaseous explosions is evaluated. The results are compared with other methods for evaluation of the blast effect from unconfined vapor cloud explosions. © 2006 American Institute of Chemical Engineers Process Saf Prog, 2007