可攜式和固定式細水霧系統滅火性能之實驗評估

Abstract

本論文主要分為兩部份來評估細水霧的滅火性能及其應用，第一部份為可攜式細水霧系統及添加劑的滅火性能評估，第二部份則為在高科技廠房濕式清洗槽中，細水霧系統的應用及效能評估。 在可攜式含添加劑細水霧滅火系統的實驗中，主要針對噴灑方法對池火的滅火性能及其相對應滅火機制的影響進行一系列的研究。不同的油料種類、噴頭噴灑角度、添加劑溶液的體積濃度為主要實驗參數。使用油料分別為庚烷、汽油、柴油；噴頭噴灑角度分別為與水平夾角30度、45度、60度；添加劑溶液的體積濃度分別為0%、3%、6%、10%。高噴灑角度時的主要滅火機制為火焰冷卻和氧氣置換；低噴灑角度時為油氣的阻隔與稀釋。本實驗使用的可攜式細水霧滅火系統擁有良好的熱輻射稀釋與降溫能力，對使用者能供良好的保護。細水霧加入添加劑後可使滅火性能極明顯提升，但過多的添加劑反而會造成滅火性能下降。滅火效率不僅受到水霧效應影響,亦同時受添加劑效應影響。因此對滅火效能而言，必然存在某個細水霧與添加劑間最理想的混合比率。 在評估細水霧系統對濕式清洗槽的火災實驗中，實驗參數為工作壓力、油盆大小、噴頭位置、障礙物及門的開度。適當的工作壓力及噴頭位置設計能有效的撲滅早期火災。細水霧噴頭則建議裝設在油盆正上方或油盆兩側，確保水霧能涵蓋住火燄並有足夠動能來撲滅火場，如此就能避免火勢延燒到整個溼式清洗槽。 在PIV影像量測中以三種不同之實驗參數，噴灑壓力，添加劑體積濃度以及噴頭種類，討論對SMD以及細水霧密度分佈造成之變動。透過使用PIV系統拍攝在三個不同量測點， 23cm，40 cm及52處，所有的實驗照片。 研究結果發現當噴灑壓力上昇時，水霧的SMD值會隨之減少。因不同濃度的添加劑造成SMD分佈呈現W形狀的曲線，此一現象給予先前的論文中關於火焰撲滅時間的結果適當的解釋。研究結果發現對於含有添加劑的細水霧，其滅火效能主要取決於 SMD之值，其次則是添加劑的化學反應。

This thesis consists of two parts. In the first part, a series of tests subjected to various discharge methodologies and fire scenarios were 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 were selected as the major experimental parameters. The fuels used were heptane, gasoline, and diesel, the nozzle discharge angles are 30°, 45°, and 60° with respect to the horizon, and the additive solution volumes were 0%, 3%, 6% and 10%. The dominant mechanisms of restraining fire in the higher nozzle discharge angle regime (>45□) are flame cooling and oxygen-displacement, and in the lower one (<45□) 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. 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. In the second part of the thesis for assessing the fire protection performance in wet bench fires, several field tests were performed using a water mist system installed in the wet bench. The test parameters were operational pressure, pan size, nozzle location, cylinder obstruction and degree of door closure. An appropriate design for operating pressure and the location of water mist nozzles extinguished wet bench fires effectively in the early fire stages. The nozzles are suggested to be fixed above or on the each side of the pan, ensuring that mist can completely cover a pan surface with sufficient momentum. With this suggested design, fires can be extinguished in the pan and do not spread over the wet bench. In the particle image processing, SMD and water mist density distribution were investigated with three parameters, discharge pressure, volumetric additive concentration and nozzle type. By using PIV, all experimental pictures were caught in three acquisition locations, 23 cm, 40cm and 52cm away from the nozzle respectively. The study indicated that SMD shrunk as discharged pressure increased. 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.