Effects of the backboard on downward flame spread over polymethyl methacrylate

LI Dayu; ZHAO Kun; ZHOU Kuibin; SUN Penghui; WU Jinmo

doi:10.16511/j.cnki.qhdxxb.2023.22.015

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Journal of Tsinghua University(Science and Technology) ›› 2023, Vol. 63 ›› Issue (5) : 783-791. DOI: 10.16511/j.cnki.qhdxxb.2023.22.015

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Effects of the backboard on downward flame spread over polymethyl methacrylate

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Abstract

Polymethyl methacrylate (PMMA) is one of the main architectural decoration materials and is widely used in different types of buildings. Once ignited, the flammable PMMA can cause serious building fire accidents. In building decoration, PMMA is used alone or attached to the noninflammable wall. Consequently, the PMMA could burn in a free condition or under the wall effect in a building fire. However, experimental studies on the effect of the backboard on PMMA downward flame spread are rare. In this study, the effect of the backboard was experimentally studied on the downward flame spread for PMMA of 2- and 5-mm thicknesses using a self-designed experimental setup. The experimental setup holds a noninflammable backboard that can be dismantled for the downward flame spread of PMMA in the free condition. Experimental observation showed significant changes in the flame color and pyrolysis front shape with and without the backboard. As compared to the free condition, the airflow induced by the entrainment of the burning flame might cause a flow boundary layer across the backboard, which helped to qualitatively explain the difference in the flame color and the pyrolysis front shape between the two thickness conditions. The experimental measurements also showed that the backboard had a negative effect on the downward flame spread rate, particularly for the 2-mm thick PMMA, which was characterized by an increase in the pyrolysis front angle and a drop in the average flame height, mass loss rate, and flame spread rate. The heat transfer analyses for the steady flame spread under the backboard and free conditions were conducted using the geometrical feature of the pyrolysis zone, and thus a comparison between the two conditions in terms of total heat feedback was conducted. There are four main conclusions. (1) The backboard caused a darker flame of PMMA and a blue flame of the 2-mm thick PMMA, as compared to those in the free condition. (2) Under the backboard effect, the pyrolysis front showed a "-" shape when the 2-mm thick PMMA burned in a steady stage, while the 5-mm thick PMMA held the pyrolysis front of an inverted "V" shape with a larger front angle than that in the free condition. (3) During the steady stage of flame spread, the backboard reduced the mass loss and flame spread rates by decreasing the total heat feedback to the pyrolysis zone. (4) The reductive effect was more significant on the mass loss rate and the flame spread for the 2-mm thick PMMA than the 5-mm thick PMMA because the former could be fully located in the flow boundary layer, whereas the latter partially located in the flow boundary layer in terms of the thickness. In summary, the qualitative and quantitative analyses of the experimental results show that the backboard can slow down the downward flame spread rate by restricting the air entrainment and reducing the heat feedback, and the inhibiting effect is more obvious for the thinner PMMA.

Key words

downward flame spread / pyrolysis front / flame spread rate / mass loss rate / heat transfer

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LI Dayu, ZHAO Kun, ZHOU Kuibin, SUN Penghui, WU Jinmo. Effects of the backboard on downward flame spread over polymethyl methacrylate[J]. Journal of Tsinghua University(Science and Technology). 2023, 63(5): 783-791 https://doi.org/10.16511/j.cnki.qhdxxb.2023.22.015

References

[1] 黄新杰, 刘伟, 陈功建, 等. 不同放置角度的建筑装饰材料PMMA的火焰蔓延特性[J]. 过程工程学报, 2018, 18(3):454-460. HUANG X J, LIU W, CHEN G J, et al. Flame spread characteristics over building decoration material of PMMA with different placed angles[J]. The Chinese Journal of Process Engineering, 2018, 18(3):454-460. (in Chinese)
[2] CARMIGNANI L, BHATTACHARJEE S. Burn angle and its implications on flame spread rate, mass burning rate, and fuel temperature for downward flame spread over thin PMMA[J]. Combustion Science and Technology, 2020, 192(8):1617-1632.
[3] DELZEIT T, CARMIGNANI L, MATSUOKA T, et al. Influence of edge propagation on downward flame spread over three-dimensional PMMA samples[J]. Proceedings of the Combustion Institute, 2019, 37(3):3203-3209.
[4] KOROBEINICHEV O P, KARPOV A I, BOLKISEV A A, et al. An experimental and numerical study of thermal and chemical structure of downward flame spread over PMMA surface in still air[J]. Proceedings of the Combustion Institute, 2019, 37(3):4017-4024.
[5] GAO S, ZHU G Q, GAO Y J, et al. Experimental study on width effects on downward flame spread over thin PMMA under limited distance condition[J]. Case Studies in Thermal Engineering, 2019, 13:100382.
[6] LANGE G, CARMIGNANI L, BHATTACHARJEE S. Thermal radiation measurements of downward spreading flames[J]. Applied Thermal Engineering, 2019, 160:114022.
[7] 罗圣峰, 谢启源, 张辉, 等. 引入熔融糊状区的PMMA逆流火蔓延数值模拟[J]. 清华大学学报(自然科学版), 2020, 60(12):1039-1046. LUO S F, XIE Q Y, ZHANG H, et al. Numerical simulation of opposed-flow flame spread of PMMA with melting mushy zone[J]. Journal of Tsinghua University (Science and Technology), 2020, 60(12):1039-1046. (in Chinese)
[8] DE RIS J N. Spread of a laminar diffusion flame[J]. Symposium (International) on Combustion, 1969, 12(1):241-252.
[9] FERNANDEZ-PELLO A C, WILLIAMS F A. Laminar flame spread over PMMA surfaces[J]. Symposium (International) on Combustion, 1975, 15(1):217-231.
[10] AYANI M B, ESFAHANI J A, MEHRABIAN R. Downward flame spread over PMMA sheets in quiescent air:Experimental and theoretical studies[J]. Fire Safety Journal, 2006, 41(2):164-169.
[11] MAMOURIAN M, ESFAHANI J A, AYANI M B. The effect of the solid fuel dimensions on the downward flame spread[J]. Kuwait Journal of Science & Engineering, 2009, 36(2):1-9.
[12] GONG J H, ZHOU X D, DENG Z H, et al. Influences of low atmospheric pressure on downward flame spread over thick PMMA slabs at different altitudes[J]. International Journal of Heat and Mass Transfer, 2013, 61:191-200.
[13] GONG J H, ZHOU X D, LI J, et al. Effect of finite dimension on downward flame spread over PMMA slabs:Experimental and theoretical study[J]. International Journal of Heat and Mass Transfer, 2015, 91:225-234.
[14] PAN R L, ZHU G Q, ZHANG G W, et al. Experimental study and heat transfer analysis of downward flame spread over PMMA under the effect of wall spacing[J]. Journal of Thermal Analysis and Calorimetry, 2019, 138(2):1711-1722.
[15] ZHU H, GAO Y J, PAN R L, et al. Spacing effects on downward flame spread over thin PMMA slabs[J]. Case Studies in Thermal Engineering, 2019, 13:100370.
[16] ZHAO K, ZHOU X D, YANG L Z, et al. Width effects on downward flame spread over poly(methyl methacrylate) sheets[J]. Journal of Fire Sciences, 2015, 33(1):69-84.
[17] ZHAO K, ZHOU X D, LIU X Q, et al. Prediction of three-dimensional downward flame spread characteristics over poly(methyl methacrylate) slabs in different pressure environments[J]. Materials, 2016, 9(11):948-962.
[18] XIE Q Y, LUO S F, DA L J. Effects of backwall on inner thermal structure in opposed-flow horizontal flame spread of thick PMMA panel[J]. Applied Thermal Engineering, 2021, 185:116424.
[19] 冯瑞, 田润和, 陈科位, 等. 低气压环境对固体燃烧特性影响的实验研究[J]. 清华大学学报(自然科学版), 2019, 59(2):111-121. FENG R, TIAN R H, CHENG K W, et al. Experimental study of the effect of low pressures on solid fuel combustion characteristics[J]. Journal of Tsinghua University (Science and Technology), 2019, 59(2):111-121. (in Chinese)
[20] HOSSAIN S, WICHMAN I S, MILLER F J, et al. Opposed flow flame spread over thermally thick solid fuels:Buoyant flow suppression, stretch rate theory, and the regressive burning regime[J]. Combustion and Flame, 2020, 219:57-69.
[21] 杜伟, 程海涛, 邹彪, 等. 基于点状火源的秸秆火焰蔓延及燃烧特性[J]. 清华大学学报(自然科学版), 2022, 62(6):1088-1093. DU W, CHENG H T, ZOU B, et al. Flame spread and combustion characteristics of straw bales from a point fire source[J]. Journal of Tsinghua University (Science and Technology), 2022, 62(6):1088-1093. (in Chinese)
[22] 柳爱静, 李开源, 姚勇征, 等. 宽度变化对聚苯乙烯保温材料水平火蔓延预热角度的影响[J]. 中南大学学报(自然科学版), 2017, 48(6):1420-1424. LIU A J, LI K Y, YAO Y Z, et al. Effect of width on pyrolysis angle during flame spread over horizontal extruded polystyrene (XPS) surface[J]. Journal of Central South University (Science and Technology), 2017, 48(6):1420-1424. (in Chinese)
[23] FERNANDEZ-PELLO A C, HIRANO T. Controlling mechanisms of flame spread[J]. Combustion Science and Technology, 1983, 32(1-4):1-31.