He Hao, Zhang Qixing, Shi Long, Li Haihang, Huang Dongmei, Zhang Yongming
College of Quality and Safety Engineering, China Jiliang University, Hangzhou 310018, China.
State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230026, China.
Polymers (Basel). 2021 Jan 22;13(3):346. doi: 10.3390/polym13030346.
Flame spread over wire surface is different from other solid fires as it is usually accompanied by melting and dripping processes. Although the related behaviors at reduced pressure (20-100 kPa) are significant to those fire risk evaluations, very few studies have been undertaken on this matter. Therefore, the thermoplastic dripping and flame spread behaviors of energized polyethylene insulated copper wires were investigated experimentally at reduced pressure. It was known from experimental results that the dripping frequency increases, showing a relatively smooth (linear) and rapid (power) increasing trends under high and low electrical currents, respectively. A short-period flame disappearance was observed during the dripping process, which is unique for the energized wire at reduced pressure. The bright flame can disappear for several seconds and then show again after the dripping. While at 20 kPa or lower, the wire flame would turn to a completed extinguishment after the dripping. A critical dripping point was proposed to show the minimal required electrical current to sustain the flame spearing. The critical current changes smoothly during 100-80 kPa and decreases rapidly at 80-60 kPa. Additionally, the dripping phenomenon can stop or delay the flame spread, partly because of the short-term flame disappearance.
火焰在电线表面蔓延与其他固体火灾不同，因为它通常伴随着熔化和滴落过程。尽管减压（20 - 100 kPa）下的相关行为对那些火灾风险评估很重要，但关于此事的研究极少。因此，在减压条件下对通电的聚乙烯绝缘铜线的热塑性滴落和火焰蔓延行为进行了实验研究。从实验结果可知，滴落频率增加，分别在高电流和低电流下呈现相对平滑（线性）和快速（幂次）的增加趋势。在滴落过程中观察到短时间的火焰消失，这对于减压下的通电电线来说是独特的。明亮的火焰会消失几秒钟，然后在滴落之后再次出现。而在20 kPa或更低压力下，电线火焰在滴落之后会完全熄灭。提出了一个临界滴落点来表示维持火焰蔓延所需的最小电流。临界电流在100 - 80 kPa期间平滑变化，在80 - 60 kPa时迅速下降。此外，滴落现象可以阻止或延缓火焰蔓延，部分原因是火焰的短期消失。
