【作者】 李昕；

【导师】 张国维；

【作者基本信息】 中国矿业大学 ， 安全科学与工程， 2023， 硕士

【摘要】 综合管廊满足了城市居民对于电力、通信、燃气、供热、给排水等不同类型的生活需求,有效解决了地下空间的利用问题,提高了城市空间的利用效率。但由于其内部存在燃气管线、电线电缆等可燃物,易引发火灾。同时,综合管廊内部空间受限,火灾后产生大量有毒浓烟,使得灭火救援困难。且现有的灭火技术难以满足综合管廊日常巡检维护和高效扑灭其内部火灾的需求,亟待研究攻关。基于隔氧窒息与降温冷却灭火的基本原理,本论文搭建了缩尺寸综合管廊试验平台,构建了综合管廊数值模拟模型,提出了火羽流作用下综合管廊内注氮灭火过程中低温氮气运移模型,揭示了封堵和注氮耦合作用下综合管廊内火灾衰退规律,分析了不同封堵形式对于注氮抑火、降温、窒息效能的影响。通过以上研究,得到5点关键结论:1)基于菲克定律,建立火灾下综合管廊内低温氮气运移模型。液氮注入综合管廊后立即形成低温氮气重气云团。同时受火场高温影响,空间内气体分布和湍流强度改变,整个管廊空间被划分为上部高温烟气层、中部新鲜空气层和下部低温氮气层。低温氮气云团的扩散主要分为重气扩散初始阶段、重力沉降阶段和被动扩散阶段三个阶段,影响氮气扩散的主要因素主要包括注氮形式和管廊内的环境条件等;2)揭示了封堵对综合管廊液氮灭火的影响。封堵的设置可以有效地减少注氮灭火所需时间,且设置下部封堵的效果要优于上部封堵,封堵率越高,液氮灭火所需时间越短。在25%-75%封堵率范围内,下部封堵液氮平均灭火效率相较于无封堵提高约45.7%-67.1%,下部封堵液氮平均灭火效率仅提高约25.7%-55.7%;随着封堵率的增加,局部空间内氧气体积分数下降速率加快,火焰更快因窒息熄灭。但过高的封堵率以及过密的封堵间距会使得局部位置温度过高,对管廊结构造成破坏;3)液氮主要灭火机理为隔氧窒息和冷却降温,其中隔氧窒息占主导作用。在低温氮气云团运移过程中,不断卷吸上部空气,同时进行热量交换,使得空间内氧气体积分数和管廊整体温度均有所降低。当火焰熄灭时,顶棚温度最大降温百分比约为21.73%,此时管廊整体温度约250℃-350℃,仍处于一个较高水平,而火源附近氧气体积分数均已下降至12.5%,下降幅度约为43.18%,说明火焰最终因周围环境氧气含量不足而熄灭;4)在无风的条件下,低温氮气对于低位置、近距离的火源隔氧降温效果更佳。通过对管廊火灾衰退规律以及空间内各位置处氧气体积分数变化情况分析,火源位于底部位置时,平均灭火时间较中部位置火源缩短约31%,且底部空间氧气体积分数下降速率以及幅度更大,说明低温氮气云团首先在管廊底部空间运移,其对管廊底部空间的惰化效果要优于上部空间。低温氮气在运移过程中与环境空气发生卷吸作用而被稀释,同时与高温烟气和管廊结构进行热量交换而使得氮气云团温度增加,密度降低,使得运移速度变缓,惰化能力减弱,所以其对于远距离位置的窒息效果不佳。本论文揭示出通过合理的布置封堵与注氮口的相对位置,可以有效加速液氮灭火的进程,促进液氮的隔氧窒息作用。相关研究结论同时适用于狭长受限空间,有助于解决此类结构建筑日常巡检维护和高效扑灭其内部火灾的难题,为封堵和注氮灭火的实际应用提供理论指南和数据支持。更多还原

【Abstract】 The utility tunnel meets the needs of urban residents for different types of life such as electricity,communication,gas,heating,water supply and drainage,effectively solves the problem of underground space utilization,and improves the utilization efficiency of urban space.However,due to the existence of combustible materials such as gas pipelines,wires and cables,it is easy to cause fire.At the same time,the space inside the utility tunnel is limited,and a large amount of toxic smoke is generated after the fire,making firefighting and rescue difficult.Moreover,the existing fire extinguishing technology is difficult to meet the needs of the daily inspection and maintenance of the utility tunnel and the efficient extinguishing of its internal fire,so it is urgent to study and solve the problem.Based on the basic principles of oxygen-insulating suffocation and cooling and extinguishing fires,this thesis builds a scaled utility tunnel test platform,constructs a numerical simulation model of the utility tunnel,and proposes a low-temperature nitrogen migration model in the process of nitrogen injection fire extinguishing in the utility tunnel under the action of fire plume.The law of fire recession in the utility tunnel under the coupling effect of blockging and ammonia injection is revealed,and the effects of different plugging forms on the efficiency of nitrogen injection fire suppression,cooling and suffocation are analyzed.Through the above research,five key conclusions are obtained :1)Based on Fick’s law,a low-temperature nitrogen migration model in the utility tunnel under fire is established.After liquid nitrogen is injected into the utility tunnel,a low-temperature nitrogen heavy gas cloud is formed immediately.At the same time,affected by the high temperature of the fire field,the gas distribution and turbulence intensity in the space change,and the whole pipe gallery space is divided into the upper high temperature flue gas layer,the middle fresh air layer and the lower low temperature nitrogen layer.The diffusion of low-temperature nitrogen clouds is mainly divided into three stages: initial stage of heavy gas diffusion,gravity sedimentation stage and passive diffusion stage.The main factors affecting nitrogen diffusion include nitrogen injection form and environmental conditions in the utility tunnel;2)The influence of plugging on liquid nitrogen fire extinguishing in utility tunnel is revealed.The setting of blocking can effectively reduce the time required for nitrogen injection fire extinguishing,and the effect of setting lower blocking is better than that of upper blocking.The higher the blocking rate,the shorter the time required for liquid nitrogen fire extinguishing.In the range of 25 %-75 % blocking rate,the average fire extinguishing efficiency of the lower blocking liquid nitrogen is about45.7 %-67.1 % higher than that without blocking,and the average fire extinguishing efficiency of the lower blocking liquid nitrogen is only about 25.7 %-55.7 %.As the blocking rate increases,the oxygen volume fraction in the local space decreases faster,and the flame is extinguished faster due to suffocation.However,too high blocking rate and too dense blocking spacing will make the local temperature too high,causing damage to the utility tunnel structure;3)The main fire extinguishing mechanism of liquid nitrogen is oxygen-insulated suffocation and cooling,in which oxygen-insulated suffocation plays a leading role.During the migration of low-temperature nitrogen clouds,the upper air is continuously entrained and the heat exchange is carried out,so that the oxygen volume fraction in the space and the overall temperature of the utility tunnel are reduced.When the flame is extinguished,the maximum cooling percentage of the ceiling temperature is about 21.73 %.At this time,the overall temperature of the pipe gallery is about 250 °C-350 °C,which is still at a high level.The oxygen volume fraction near the fire source has decreased to 12.5 %,with a decrease of about43.18 %,indicating that the flame is finally extinguished due to the lack of oxygen content in the surrounding environment.4)Under the condition of no wind,low temperature nitrogen has better effect on oxygen insulation and cooling of low position and close distance fire source.Through the analysis of the fire recession law of the utility tunnel and the change of oxygen volume fraction at each position in the space,when the fire source is located at the bottom position,the average fire extinguishing time is shortened by about 31 %compared with the fire source in the middle position,and the oxygen volume fraction in the bottom space decreases at a greater rate and amplitude,indicating that the lowtemperature nitrogen cloud first migrates in the bottom space of the utility tunnel,and its inerting effect on the bottom space of the utility tunnel is better than that of the upper space.In the process of migration,low-temperature nitrogen is diluted by entrainment with ambient air.At the same time,it exchanges heat with hightemperature flue gas and utility tunnel structure,which increases the temperature of nitrogen cloud and reduces the density,so that the migration speed is slowed down and the inerting ability is weakened.Therefore,it has poor asphyxiation effect on long-distance location.This thesisi reveals that the reasonable arrangement of the relative position between the blocking and the nitrogen injection port can effectively accelerate the process of liquid nitrogen fire extinguishing and promote the oxygen-insulating asphyxiation of liquid nitrogen.The relevant research conclusions are also applicable to long and narrow confined spaces,which is helpful to solve the problems of daily inspection and maintenance of such structural buildings and efficient extinguishing of internal fires,and provide theoretical guidance and data support for the practical application of plugging and nitrogen injection fire extinguishing.更多还原