| In recent years,China’s energy consumption problem has become increasingly prominent,of which building energy consumption accounts for about 30% of the total energy consumption.Under the current policy background of carbon neutralization and carbon compliance,building energy conservation is still the focus.Building energy consumption can be effectively reduced by setting external wall insulation materials on the building facade,so as to achieve the goal of energy saving.Due to the advantages of good thermal insulation performance,low density and low cost,polymer materials are widely used in the construction field.However,polymer materials have a fast fire spread,flammable and combustible,high heat release rate and high fire risk,building fire accidents caused by ignition of building facade insulation occur frequently.Due to the demand for lighting and aesthetics of modern building facades,complex building facade configurations have been common in the design of modern high-rise buildings,which will make the fire spread behavior of polyurethane insulation materials more complex in the event of fire,thereby increasing the difficulty of fire prevention and rescue risks.Therefore,the study of fire spread behavior of polymer insulation materials under different building facade configurations is one of the important research topics in the field of building fire prevention.In this article,a small-scale experimental platform is built to investigate the characteristics of fire accidents caused by polyurethane insulation in a typical modern building facade.From the angle configuration of building facade,combined with the ignition mode,the flame morphology,mass loss rate,flame pulsation frequency and other characteristic parameters were obtained.Based on heat transfer,combustion and fire dynamics,the vertical downward fire spread behavior of polyurethane insulation materials under different building angle configuration and ignition mode coupling conditions was analyzed.Experimentally,it is found that the positive corner configuration will change the spatial airflow distribution.When the angle of the positive corner configuration is relatively small,the coupling of the edge wall effect and the chimney effect is significant,which accelerates the airflow coiling and absorption,and the molten liquid accumulates at the corner of the configuration,which enhances the heat transfer to the unburned area and has a negative impact on fire fighting.Under the single ignition condition,the configuration angle changes the flame propagation behavior,and the pyrolysis front changes from oblique linear to inverted "V" type and oblique linear coupling.When the angle is 180 degrees,the pyrolysis front always shows oblique linear distribution.The special facade configuration will aggravate the degree of fire.When the positive angle configuration is 30 degrees,the air entrainment rate near the sidewall effect increases,the pyrolysis of the material is accelerated,and the mass loss rate and fire spread rate of the sample reach the maximum,indicating that the fire risk is the largest.As the positive angle of configuration increases,the mass loss rate and the fire spread rate of the sample decrease as a whole.In the process of fire spread of insulation materials,the positive angle configuration makes the temperature of the measuring point of the elevation angle reach a secondary peak.The high-temperature flame has a secondary baking threat to the wall elevation,and the radiation heat flux above the sample is always greater than that below.Under the influence of chimney effect and Rayleigh-Taylor instability mechanism,the average flame pulsation frequency at angles of 30 degrees and 180 degrees shows greater pulsation frequency than that at other angles.Under double ignition conditions,the pyrolytic front shifts from an inverted "V" to an "M" shape and remains in an inverted "V" shape up to 180 degrees.The mass loss rate and flame spread rate of the sample with special facade configuration are greater than those of single ignition mode,but the overall trend is the same,which is verified by Williams rate.Similar to the single ignition,the corners were roasted twice at high temperature,and the radiation heat flux above was always greater than that at the lower side.With the increase of the configuration angle of the corners,the variation trend of the average flame height was the same.Due to different ignition modes,the average flame height under the double ignition condition was smaller than that under the single ignition condition.The flame pulsation frequency in the fire spread of the specimen is similar to the trend of the single ignition condition,the difference is that when the flame pyrolysis front is inverted "V" and tilted linear form,by the side wall effect and chimney effect coupling effect is strong,the single ignition condition specimen flame pulsation frequency is much greater than the double ignition condition.Figure [41] table [5] reference [90]... |
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