Numerical Simulation Of Methane Explosion Affected By Fine Water Mist

The methane-air explosion is one of the most common types of accidents in coal mines, and Halon 1301 as a very effective suppressant has been banned by the Montreal Protocol with the improvement of environmental protection, and hence the knowledge of researching the "new" explosion suppressant is of considerable importance for the prevention of fire and explosion. As a low-cost and non-pollution resource, ultrafine water mist has attracted many attentions and the study of extinguishing characteristics of water mist has become one of the hot spots of the international fire science research.The effect of fine water mist on methane/air explosion in close vessel was researched numerically in this paper. The influences of water mist conditions and obstacle on explosion were analyzed, and the mechanism of water mist affecting explosion process was discussed. The detailed study contents and conclusions were showed as follows:(1) A three-dimensional numerical model was elaborated to predict the detailed methane explosion process affected by water mist, and the model was proved accurate by comparing the numerical and the experimental results.(2) The effects of the diameter, the initial velocity and the amount of water mist on methane explosion were studied. The results showed that with the increase of the water mist diameter, the explosion intensity decreased firstly and then increased; the optimal diameter had a close relationship with the evaporation zone and evaporation time of water mist. With the increase of the initial velocity of water mist, the explosion intensity increased; the water mist with initial velocity could lead to the increase of the turbulent flame speed, then the explosion reaction rate increased, which resulted in the enhancement of the methane explosion. With the increase of water mist amount, the explosion intensity decreased because of the evaporated water mist amount increased, and the absorbed heat of water mist also increased, then the explosion suppression effect enhanced. As can be seen as above analysis, the best suppression effect of water mist on gas explosion appeared when the diameter was medium and the initial velocity was smaller and the water mist amount was more.(3) The changing process of methane explosion pressure affected by fine water mist was analyzed, and it had been made clear that the increase of explosion overpressure due to water mist evaporation and the reduction of explosion overpressure due to heat exchange were the two main factors to influence the methane explosion. If the increased one was less than the reduced one, then the explosion was suppressed. Conversely, the explosion would be enhanced.(4) The effect of obstacle on methane/air explosion affected by water mist was researched by geometric model with obstacle. With little water mist, the flame propagation speed was fast, and obstacle had obvious influence on the flame propagation process, and then the explosion intensity increased with the increase of the distance between the ignition and the obstacle. With more water mist, the flame propagation speed was small, and obstacle had little influence on the flame propagation process, and then the explosion intensity was nearly invariable with the increase of the distance between the ignition and the obstacle.(5) Without water mist, the explosion intensity increased with the increase of the obstacle number, while with some fine water mist, the explosion intensity decreased firstly and then increased with the increase of the obstacle number, which had relationship with the opposite effect of obstacle on explosion process.