| Summary: | 碩士 === 國立交通大學 === 機械工程系所 === 95 === A series of tests subjected to various discharge methodologies and fire scenarios are carried out based on a portable water mist fire extinguishing system with additive on pool fires. Different fuel types, nozzle discharge angles, additive solution volumes, amount of fuels and cross-section area of pans are selected as the major experimental parameters. The fuels used are heptane, gasoline, and diesel, the nozzle discharge angles are 30°, 45°, and 60° with respect to the horizon, and the additive solution volumes are 0%, 3%, 6% and 10%. The amounts of fuel used are 250ml, 500ml and 1000ml, and the diameters of pan are 25cm and 50cm. The dominant mechanisms of restraining fire in the higher nozzle discharge angle regime (>45�a) are flame cooling and oxygen-displacement, and in the lower one (<45�a) are fuel vapors blocking and dilution. The portable water mist fire extinguishing system used has a good ability for radiation attenuation and temperature reduction that can provide a good protection for the operators. By using water mist with additive, the fire extinguishing efficiencies are significantly improved. However, if too much additive is provided, the fire extinguishment efficiency will decrease. The tendencies of the fire extinction times for different amount of fuel in a size-fixed pan are similar. Although the situation of non-uniform fuel surface resulted from water mist impingement slightly reduces the burning rate, it can be ameliorated as the height of liquid fuel attains at 1cm. In the tests with fixed fuel height, the results of 50cm diameter pan different to the ones of 25cm diameter since the interactions of its poorer mist coverage, weaker mist jet rebound and more mist reaching. The fire extinguishing efficiency is not only influenced by mist effects but also by additive ones. Therefore, there must be an optimal mixing ration between the mist and additive for fire suppression.
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