吸气式管道尺寸及温差对烟颗粒输运的影响

Effect of size and temperature of aspiration pipe on smoke particle transport

在火灾标准燃烧室中,用扫描电迁移粒谱仪测量单孔采样的吸气管道内5种标准试验火烟雾颗粒浓度和粒径分布的变化,分析管道输运中管道参数对烟颗粒数目浓度损耗和中位径的影响。结果表明,在管道输运中,平均粒径相对较小的热解和阴燃烟雾颗粒,其小于0.1μm的超细颗粒部分的浓度损耗随管道长度的增加而增大,且烟颗粒平均粒径随管道增长而增大。而明火烟雾在管道输运中,由于管道与高温烟雾的温差增大,导致0.1-1μm颗粒的管壁沉积损耗增大,使烟颗粒数浓度下降,中位径减小了几个纳米。火灾早期,火灾阴燃和热解期间小于0.1μm的烟颗粒数目浓度占15%以上,因此,用较短的管道或者管道分级预警的方式可以减少滞留时间,提高极早期感烟探测的灵敏度。

The present article is aimed at reporting its study on the effects of the internal diameter and temperature of the aspiration pipe on the smoke particle transfer. For the study purpose, we measured the smoke particle size distribution and their concentration when they are transferred in the aspiration line of five European standard fire tests by using the Scanning Mobility Particle Sizer in a standard fire testing room. We also analyzed the particle distribution concentration loss and the change of the median particle size so as to know the effect of the aspiration line on the particles＇ size and their sensitivity. The experimental results indicate that the median smoke particle size of smoldering and pyrolysis fire proves to be smaller than 0. 2 μm in the whole combustion process, and after transporting in aspiration line with 5 m and 12 m long, the loss of smoke particle that smaller than 0.1μm increases with the transport length, and the mean smoke particle size increases several nanometer. The temperature gradient of aspiration tube and smoke aerosol of open fire caused the particle concentration loss increasing due to thermophoretic force, and the median smoke particle size reduces several nanometers. In the early fire during smoldering and pyrolysis, the smoke particle that smaller than 0.1 μm is 15% more of total number concentration, so using short pipe, increasing aspirator speed or staged alarm in aspiration fire detector can reduce the residence time and increase the smoke detection sensitivity.