| Summary: | 碩士 === 國立交通大學 === 機械工程系所 === 96 === In this study, SMD and water mist density distribution were investigated with three parameters, discharge pressure (10~50 Kg/cm2), volumetric additive concentration (0%, 3%, 6%, 10%) and nozzle type (FP-25 and Syu). By using PIV, all experimental pictures were caught in three acquisition locations 1m under the nozzle and away from the center axis for 23 cm, 40cm and 52cm respectively. These pictures were processed by image post-processing software to calculate the diameters of water mist droplets.
The study indicated that SMD decreased as discharged pressure increased. The difference between SMDs even reached 350μm when discharged pressure varied from 10 Kg/cm2 to Kg/cm2. For different nozzles, the SMD distributions in each acquisition location showed different trend. Under fixed discharged pressure with FP-25 nozzle, the SMDs decreased when the acquisition location is away from the central axis of the nozzle, and the trend of SMD variation was inverse for Syu’s nozzle. With different concentration of additive, the “W” shape curve for SMD variation gave explanations for the extinction time mentioned in the previous thesis. The result showed that the major factor for the performance of fire extinguishing was SMD and the minor one was chemical reaction by organic metal compound. When the discharged pressure increased, despite the spray angle from the nozzle was rarely changed, the spray coverage measured 1m under the nozzle shrunk gradually, and the water mist density increased. Once the coverage was not enough to cover the flame, the fire became hard to extinguish.
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