| It is important and significant to do research on preventing gas fire and explosion since fires and explosion caused by the gas jet flame have occurred in recent years. Compared to the use of gaseous agent and conventional sprinkler systems, the use of water mist fire suppression system has demonstrated advantages, such as, no toxic and asphyxiation problems, no environmental problems, low system cost etc.Water mist fire suppression system, which has been successfully applied in transportation, electricity, telecommunications, tobacco, fire engineering, is considered as one of the major alternative agents for halon fire extinguishing agent. However, studies on gas jet fire suppressed by water mist is little, especially lacking of the mechanism and influence factors of gas jet flame extinguished by water mist. Therefore, the small scale experiment and numerical simulation were done to study the interaction of water mist and gas jet flames to reveal the extinguishing mechanism of gas jet fire suppressed by water mist.In order to do the quantitative analysis for jet flame suppressed by water mist, the particle size distribution, average particle size and droplet velocity distribution was measured using particle imaging technology. Based on data of the particle size and droplet velocity distribution under different pressure, the distribution function of particle size single interval probability, cumulative probability and droplet velocity cumulative probability distribution function were fitted. According to the above distribution function, the effect of pressure on characteristics of water mist was studied. The detailed data was provided by these researches for study on gas jet fire suppressed by water mist.Base on series of experimental results, the result of jet fires suppressed by water mist can be summarized into three typical phenomenons:extinction with short time, extinction with long time, cannot be extinguished. The momentums of water mist and jet flame are calculated. The ratio of momentums of water mist and jet flame was proposed to be critical condition to distinguish three typical phenomena of interaction of water mist and jet flame. These reaserch can be the guide to prevent and control the fire caused by jet flames with water mist system.Based on the theoretical analysis and experimental results, there is a conclusion: the highest fire extinguishing efficiency pressure of water mist was obtained during flame suppression by water mist. And it is important for nozzle design of water mist system.The effect of the fuel flow, pressure of water mist and diameter of nozzle on the thermal radiation during flame suppression by water mist was studied. On the basis of these experimental results, the enhence of thermal radiation was defined. According to the ratio of momentum of water mist and jet flame. the condition of non-intensified and intensified was distinguished. Base on previous researches, the mechanism for phenomenon of flame heat radiation enhanced was analyzed. It is the necessary theoretical basis for prevent firefighter from heating by fire when using water mist system.The concentration of carbon monoxide during fire suppression with water mist is one of the important parameters for safety evaluation of water mist system. Based on the experiment results of fire suppression with water mist in confined space, it is found that the carbon monoxide production rate during fire suppression is controlled in two modes. One is fuel controlled mode, while the other is water mist flux controlled mode. In order to classify the critical condition for transformation between these two modes, the concentration of water vapor in confined space is analyzed. These research results provide the theoretical basis for the design of the application of water mist system in the room.The Eddy-dissipation model (EDM) was used to simulate flame during interaction between flame and water mist. The water mist was simulated by Discrete Phase Model (DPM).The simulated results agree well with the experimental results. To some extent, EDM and DPM are suitable for simulating the interaction of jet flame suppressed by water mist. |
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