Experimental Investigations On Suppression Mechanism Of Water Mist For Solid Combustible Porous Materials Fire

The common use of water for fire suppression is unsuitable for aviation and spacecraft because of wasting much water and tending to cause device damage by the large water drop. Moreover in some cases, liquid fuel fire can hard be extinguished by the common use of water because it can lead to the overflow of the fuel. Water mist fire suppression can perfectly avoid these shortcoming. Compared with other gas fire suppression agent, water mist, nontoxic and convenient, has strong penetrating and cooling effect and can be an ideal replacement of the environment-harmed bromine-based extinguish agent. Therefore a lot of theoretical and experimental studies were conducted on this subject since the end of the past century. Generally speaking, the suppression mechanics of water mist include the cooling effect by the heat absorption, isolation of oxygen and the decline of the heat feedback to the flame area by the selective absorption of the radiation. However the study on interaction between the water mist and the solid fuel fire is deficient. The study on this aspect will help us to understand the mechanics of water mist fire suppression, to improve the efficiency and to extend the utilization.In the first chapter, the state of the study of the water mist fire suppression, including the practical test under different large-scale scenarios and fundamental research, were reviewed. Here fundamental research , including suppression on the combustion of gas, liquid and solid fuel were emphasized. Most of the studies were experiments and some numerical simulations were also mentioned.In the second chapter, the scheme of the study and the experimental device were introduced. The selection of the solid fuel, the way of ignition,the implement of water mist, the measurement of the temperature and the variation of the parameter were all introduced in detail. The combustion and atomization device were designed and made by ourselves. The temperature in the different position of the fire and the variation of the fuel mass, while the sawdust granularity and the heap thickness changed, were measured and the phenomenon during the process was observed also. On the basis of the experimental result, a primary analysis was made.In the third chapter ,the result of the experiments were analyzed. At first the guess that the diameter of the water mist has little effect on the suppression process under the condition of the study was proved true by experiments. And then the whole process of suppression was showed by photos. During the experiment, a unexpected but important phenomena was found. That is, under certain circumstance, the water mist could intensify the combustion under the sawdust surface. The detailed interpretation of the phenomena were made. At last the experimental results under different condition were given and the feature of which were also discussed..In the last chapter of the thesis, the study and its disadvantages were summarized and the proposals for improvement were given also.