前人对于不同倾斜条件下导线火蔓延特性的研究主要考虑导线单根布置的情况,对于导线相邻并排布置情况的研究较少。该文基于可调间距倾斜平行导线火蔓延实验平台,开展了不同倾斜条件(0°、30°、60°、90°)下单导线及相邻双导线火蔓延特性对比研究,分析了火焰形态、火焰长度、火焰高度、火蔓延速率和温度等火蔓延特征参数的变化规律。通过实验研究发现:在单双导线火蔓延过程中,熔融绝缘材料会发生滴落和流淌行为,且相邻双导线发生滴落和流淌的频率大于单导线;双导线的平均火焰高度和火焰长度始终大于单导线,且单双导线平均火焰高度随着倾斜角度的增加先增大后减小,平均火焰长度随倾斜角度的增加而增大;由于双导线火蔓延存在传热和卷吸作用重叠区域,导致其火蔓延速率始终小于单导线。
[Objective] In practice, conductors are often arranged in multiple parallel rows. When twin conductors are closely arranged in parallel, air entrainment can be considerably affected during fire spread, resulting in changes in fire spread characteristics and molten and dripping behaviors. However, most previous studies have mainly focused on the fire spread characteristics of a single conductor. Limited studies exist regarding fire spread over twin parallel conductors, especially with different inclination angles. This study aims to provide a superior understanding of the effects of the inclination angle on the fire spread of the conductors and compare the differences in the fire spread characteristics of the single and adjacent twin conductors.[Methods] Herein, various closely comparative experiments are conducted to investigate the fire spread and molten and dripping behaviors of the single and adjacent twin conductors under various inclination angles (0°, 30°, 60°, and 90°). Polyethylene-insulated conductors with an inner copper core diameter of 0.97 mm and an insulation thickness of 1.15 mm are selected as test samples. The essential parameters, including flame pattern, flame length, flame height, and flame spread rate, are simultaneously obtained and analyzed.[Results] The main results of this paper are as follows:(1) Whether for single or twin conductors, the molten and dripping behaviors will occur during the flame spread process, resulting in the flame pattern experiencing cyclic changes in the stable, growth, attenuation, and adjustment stages. The frequency of molten and dripping behaviors for the adjacent twin conductors is greater than that for a single conductor. (2) The average flame length, length of the bare wire wrapped by the flame, and length of the insulation layer heated by the flame increase with the inclination angle; however, the average flame height first increases and then decreases with the increase of the inclination angle. Except for the 0° cases, the average flame height and length of adjacent twin conductors are larger than those of a single conductor. (3) The flame front shows a periodic change over time owing to molten and dripping behaviors, and the fire spread rate increases with the inclination angle. However, the fire spread rate for adjacent twin conductors is consistently less than that for a single conductor mainly because for the adjacent twin conductor arrangements, an overlapped area of air entrainment and heat transfer exists, air entrainment is restricted, and consequently, the burning rate is weakened, which reduces the average heat flux transferred by the flame to each conductor.[Conclusions] Based on the above analysis and investigations, the inclination angle and arrangement of adjacent twin conductors have considerable effects on the fire spread and heat transfer over conductors. Moreover, the flames over twin conductors with a certain spacing may propagate with a high fire spread rate owing to the enhanced flame interactions, which is an interesting question worthy of further study.
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