竖井中羽流前锋上升时间的实验研究

Experimental study on the rising-time of fire plume fronts in the vertical shaft

利用PolyU/USTC大空间实验厅内的小尺度竖井实验台,测量了开放和封闭竖井中羽流前锋上升时间,结合理论分析的结果,得到了羽流前锋上升无量纲时间和竖井无量纲高度之间的定量关系式。结果表明,在相同火源、相同竖井尺寸条件下,开放竖井和封闭竖井中的羽流前锋上升无量纲时间分别和无量纲高度的1.03次方、1.50次方成正比,与火源热释放速率的1/3次方成反比。由于烟囱效应的作用,开放竖井中的羽流前锋上升速度最快;非受限空间次之;封闭竖井内最慢。各种决定性因素对羽流前锋上升的影响程度由大到小顺序为:内外压差、壁面导热+粘滞力、空气卷吸。

The present paper is engaged in an experimental study over the rising-time of fire plume front and deduced the relation between dimensionless rising-time of plume front and dimensionless height of the shaft. Based on the theoretical results, the rising-time of fire plume front is measured by using a scaled experiment which is located at the PolyU/USTC Atrium. The study of ours shows that the traveling time of the fire plume front is inversely proportional to the 1/3 power of the heat releasing rate of the flame source, proportional to the 1.03 and the 1.50 power of the height in open and closed shafts, respectively. Furthermore, it is also proved that the plume front spread in open shaft is faster than that in a free space and close shaft due to the stack effect under the same fire source and shaft dimensions with the velocity of smoke spreading in close shaft being the least one. As to the roles that some crucial factors take our findings can be listed as follows： pressure difference between inside and outside of a building proves to be more important than the conduction and viscosity of tile shaft side whose effect seems stronger than the air entrainment.