Study On The Dynamic Process Of Drop Impact On Flammable Surface

With the increasingly serious global environmental problems, Halon fire extinguishing agents on the seriousness of the breakdown of the ozone layer. Water mist as one of the important study in domestic and international of fire science because of it has many advantages such as high suppression effectiveness, non-toxicity, environmental friendly and competitively price, so study the mechanism of water mist fire suppression and improve the performance of water mist fire suppression which is important. Carrying out the research on drop impact on the combustible surface can help us understand the microscopic mechanism of fire extinguish using water mist.Firstly, by using the experimental method ,the research on the dynamic process between drop and wood surfaces was studied using high-speed camera system to deepen understanding the microscopic mechanism of fire extinguish using water mist. According the result, the special properties of wood and the special microstructures of wood surface are the main factors of influence the dynamic process of drop impinging on wood surface. The wood basic density effects on the critical impact Weber number, the surface roughness and surface texturing effect on the process of drop spreading on the wood surface and the spread factor. The surface tension of 5.0%NaCl drop is smaller than water drop, and the surface tension of 4.0%AFFF drop is the smallest in these three kinds of drop because of surfactant was added in the AFFF. From the experiment results, we can conclude that the surface tension of drop directly affect the spread factor and the rate of drop absorbed; when the drop decrease the surface tension, the spread factor of drop increase and the rate of drop absorbed. When the drop through the plume area, if it can form protective film on the flammable solid surface isolation oxygen, and the more rapid exchange heat with high temperature flammable solid surface, cool high temperature surface combustible, inhibit combustion or prevent flammable solid pyrolysis.In order to study the dynamic process of drop impact on flammable surface, in experiment, we change the solid surface to different temperature flammable liquid surface, in our paper, the liquid surface are alcohol surface, 5.0%NaCl drop and 2.2%AFFF drop. At different temperature alcohol surface, the maximum height of the bounced jet generated with drop -Alcohol impaction increase when the temperature of alcohol surface decrease. When the 5.0%NaCl drop impact on the 160℃alcohol surface, the drop was wrapped by the high temperature ghee sink into the ghee, after a while, the drop evaporate and form the bubble, then the bubbles rise to the ghee-air surface breakdown and formation of sharp fluctuations at ghee-air surface. But the 2.2%AFFF drop impact on the ghee surface, don't evaporate and form bubbles. So this can explains the AFFF fire extinguishing agent for fire suppression efficiency of oil higher.