| PUBLIC SAFETY |
|
|
|
|
|
Effect of aging time on fire spread and dripping behavior of polyethylene wire |
| ZHANG Ying1, Wu Lingli1, Zhang Bo2 |
1. School of Safety Science and Emergency Management, Wuhan University of Technology, Wuhan 430070, China;
2. School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan 430070, China |
|
|
|
|
Abstract [Objective] To investigate the impact of thermal aging on the fire propagation characteristics of conductors, the fire propagation characteristics of conductors under different equivalent aging ages were experimentally studied. The effects of different equivalent aging years on the fire propagation behavior of polyethylene wire, including the spread and dripping behavior, were studied. [Methods] First, the service life of the expected test wire in an actual scene was derived from the empirical formula of the aging model investigated in previous studies, and the required test conditions were accordingly calculated. [Results] The experimental results show that with the extension of thermal aging time, the flame height, width, and spread speed decrease. During the equivalent aging time, the frequency and mass of the droplets in the melt decreased with increasing equivalent aging time, whereas the mass of individual droplets increased with increasing equivalent aging time. According to the experimental results and theoretical analysis, a thermal aging law for the wire fire propagation characteristics was established. An analysis of the effect mechanism of thermal aging on fire spread behavior reveals that an increase in the equivalent aging age mainly affects the change in the elongation at break and melting point of the thermal insulation layer. With the increase in the equivalent aging time, the elongation at break of the polyethylene insulation layer decreases, which affects the increase in the surface tension of the layer. Under the influence of high temperature, the melting speed of the solid insulation layer was accelerated, and the layer can more easily transition into a liquid state. The liquid melt on the upper surface of the insulation layer flows down the surface under the action of gravity. Once the self-gravity of the accumulated molten material overcomes the constraint of its surface tension, individual droplets are formed for dripping, and this dynamic constraint process becomes longer as the equivalent aging age increases. This reduces the frequency of dripping molten droplets. With the accumulation of the melt on the surface of the insulation layer, the volume of the melt accumulation increases, which affects the increase in the heat loss of the melt in the combustion zone. The flame located above the insulation layer reduces the width, height, and width of the flame because of the loss of fuel on the surface of the insulation layer, thus affecting the reduction of the fire spread speed. The self-constructed fire spread and propagation model reveals that the change in flame width directly affects the convective heat transfer of flame to the insulation layer of the pyrolysis zone. Moreover, less heat is transferred via convection, which results in a slower spread of the fire. [Conclusions] Overall, this study revealed the internal mechanism of fire spread and dripping behavior of heat-aged wire, which can inspire engineers to develop more flame-retardant materials, promote the innovation of refractory materials, enhance the fire safety of various electrical equipment, and mitigate the harm caused by aging wire fires to human life and property.
|
| Keywords
thermal aging
tensile elongation at break
polyethylene conductor
fire spread behavior
dripping behavior
|
|
Issue Date: 22 November 2024
|
|
|
[1] KONNO Y, HASHIMOTO N, FUJITA O. On the radiation extinction of opposed flame spread over curved solid surface in low flow velocity conditions [J]. Combustion and Flame, 2023, 254: 112836.
[2] JIA S Y, HU L H, MA Y X, et al. Experimental study of downward flame spread and extinction over inclined electrical wire under horizontal wind [J]. Combustion and Flame, 2022, 237: 111820.
[3] ZHU F, HUANG X Y, WANG S F. Flame spread over polyethylene film: Effects of gravity and fuel inclination [J]. Microgravity Science and Technology, 2022, 34(3): 26.
[4] EMANUELSSON V, SIMONSON M, GEVERT T. The effect of accelerated ageing of building wires [J]. Fire and Materials, 2007, 31(5): 311-326.
[5] 王志. 不同环境条件下典型线缆燃烧特性和火蔓延行为研究[D]. 合肥: 中国科学技术大学, 2023. DOI: 10.27517/d.cnki.gzkju.2020.002069. WANG Z. Studies on combustion characteristics and flame spread behaviors of typical wires and cables under different environmental conditions [D]. Hefei: University of Science and Technology of China, 2023. DOI: 10.27517/d.cnki.gzkju.2020.002069. (in Chinese)
[6] 段玉兵, 韩明明, 王兆琛, 等. 不同热老化温度下高压电缆绝缘特性及失效机理[J]. 电工技术学报, 2024, 39(1): 45-54. DOI: 10.19595/j.cnki.1000-6753.tces.230772. DUAN Y B, HAN M M. WANG Z C, et al. Insulation characteristics and failure mechanism of high-voltage cables under different thermal aging temperatures [J]. Transactions of China Electrotechnical Society, 2024, 39(1): 45-54. DOI: 10.19595/j.cnki.1000-6753.tces.230772. (in Chinese)
[7] 颜龙, 王文强, 徐志胜, 等. 热老化对阻燃电缆护套层的燃烧性能与热解动力学的影响[J]. 中国安全生产科学技术, 2023, 19(9): 143-149. YAN L, WANG W Q, XU Z S, et al. Influence of thermal aging on combustion performance and pyrolysis kinetics of flame retardant cable sheathing [J]. Journal of Safety Science and Technology, 2023, 19(9): 143-149. (in Chinese)
[8] XIE H, ZHANG J Q, LIU Y F, et al. Study on insulation failure time and failure temperature of the aged cables under external heating [J]. Procedia Engineering, 2018, 211: 1012-1017.
[9] 陈东, 张鹏, 程伟, 等. 电力电缆绝缘老化寿命评估模型的研究[J]. 光纤与电缆及其应用技术, 2015(5): 37-38, 46. CHEN D, ZHANG P, CHENG W, et al. Research on the evaluation model for power cable insulation aging lifetime [J]. Optical Fiber & Electric Cable and Their Applications, 2015(5): 37-38, 46. (in Chinese)
[10] MAYNARD B T, BUTTA J W. A physical model for flame height intermittency [J]. Fire Technology, 2018, 54(1): 135-161.
[11] 王晓伟. 典型通电导线燃烧特性与烟颗粒形谱特征研究[D]. 合肥: 中国科学技术大学, 2015. WANG X W. Combustion characteristics and smoke particle characteristics of typical energized wire [D]. Hefei: University of Science and Technology of China, 2015. (in Chinese)
[12] CHEN Y, WANG S, FU M, et al. Comprehensive assessment of the thermal aging effects on fire risks of cables[EB/OL]. (2023-07-28). https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4523886. |
|
Viewed |
|
|
|
Full text
|
|
|
|
|
Abstract
|
|
|
|
|
Cited |
|
|
|
|
| |
Shared |
|
|
|
|
| |
Discussed |
|
|
|
|
2024,
Vol. 64
