高层建筑楼梯间及相连空间内烟气流动特性与火行为研究
发布时间：2018-08-21 11:03
【摘要】：随着城市化进展的加快和土地资源的日益稀缺,我国高层建筑的数量和高度得到了快速增长,再加上近年来房价的飞速上涨和住房需求量的不断攀升,进一步刺激各房地产企业加快投资和建设高楼大厦的速度,各地(超)高层建筑如雨后春笋般不断拔地而起,具有数量多、高度高、结构复杂、功能多样化的特点,并且许多建筑已经成为城市的标志性建筑,同时,高层建筑也是对施工技术和安全保障的严峻考验,尤其是高层建筑火灾安全问题备受人们关注。近年来发生了许多大型高层建筑火灾事故,并有愈演愈烈之势。高层建筑由于楼层多、结构复杂、体积大,且烟气蔓延途径多,其火灾危险性更大,尤其是烟囱效应和外界风带来后果尤其严重,因此,研究高层建筑烟气运动规律和火灾发展特性具有重要意义。 湍流混合运动和烟囱效应是楼梯间内烟气运动的两种主要机制,两种运动机制分别在火灾发展不同阶段起主要作用。在第一个稳定阶段,楼梯间内烟气主要依靠湍流混合作用向上缓慢的运动；在第二个稳定阶段,楼梯间内烟气主要依靠烟囱效应向上快速的运动。两个稳定阶段的持续时间都会受到火源功率和通风口位置的影响。楼梯间内烟气运动机制影响其竖向温度分布。与湍流混合运动作用阶段相比,在烟囱效应作用阶段,楼梯间烟气竖向温度衰减较慢,温度衰减系数β值较小。随着楼梯间通风口位置升高和火源功率增大,β值越小,封闭楼梯间的烟气温度衰减最快,β值最大。着火层位于高层建筑中间楼层时,着火层上方和下方通风口状态对楼梯间内竖向温度分布有较大的影响。 在烟囱效应作用下,甲醇和正庚烷池火向楼梯间方向倾斜,本文引入理查森数Ri分析烟囱效应对火焰倾角的影响。对于甲醇池火,火焰倾角θ与理查德森数Ri1呈线性递增关系,而对于正庚烷池火,在烟囱效应作用下各工况火焰倾角θ相差不大,其平均值为69.7°,楼梯间通风口位置对正庚烷的火焰倾角θ影响较小。对于火焰长度和火焰高度,实验结果表明在烟囱效应作用下正庚烷池火的无量纲火焰长度(Lf/D)和火焰高度(Hf/D)与无量纲火源热释放速率(Q*)的1/4次方呈正比。对于火焰温度,在烟囱效应产生的风速的冷却作用下,不仅倾斜火焰连续区的温升(△T)低于开放空间的火焰连续区温升,AT大约776℃,而且火焰连续区和间歇区的范围也有所增大,对于火焰连续区,L/Q2/5从无风情况下0-0.08增加到0-0.12,而对于火焰间歇区,L/Q2/5从无风情况下0.08-0.2增加到0.12-0.25。烟囱效应产生的风速和火源的燃烧速率相互作用、相互影响,研究结果表明风速V与火源功率Q的1/3次方呈线性递增关系。楼梯间通风口位置和状态对火源的燃烧速率、着火房间和前室的温度场分布以及楼梯间内辐射和总热流值有一定的影响。 通过设计和建造1/6尺寸外界风楼梯间实验台,研究结果表明在不同外界风向和外界风速作用下,楼梯间内烟气运动和相连房间的火灾特性具有四种明显不同的模式。模式Ⅰ：随着燃烧时间增加,楼梯间内各层烟气温度和总热流也逐渐增加,同时房间内火焰逐渐向楼梯间方向倾斜,最终温度、热量值、火焰倾斜程度都达到最大。烟囱效应是楼梯间内烟气运动的主要驱动力。模式Ⅱ：在燃烧初期,楼梯间内各层温度和总热流值都非常小,燃烧一段时间后,楼梯间内温度和总热流突然地迅速升高。随着燃烧速率的增大,烟囱效应逐渐克服外界风成为主要的驱动力。模式Ⅲ：当外界风速比较大时,在整个燃烧过程中,楼梯间内各层烟气温度和总热流值都非常小,房间内火焰一直向室外方向倾斜。火源产生的热烟气始终不能克服外界风的阻力进入楼梯间内部。模式Ⅳ：在燃烧期间启动风机,楼梯间内各楼层的烟气温度和总热流呈现下降的趋势,房间内火焰逐渐向室外方向倾斜,随着外界风速增大,烟气温度和热流下降越快。房间内火焰的倾斜方向主要与烟囱效应作用力Fstack和外界风作用力Fwind有关,通过理论分析引入修正的弗洛德数Fr来判断和分析房间内火焰倾斜方向,最终计算出火焰方向转变的临界弗洛德数Fr值为0.814。当Fr小于O.814时,火焰向室外方向倾斜,否则,火焰向楼梯间方向倾斜。
[Abstract]:With the acceleration of urbanization and the increasing scarcity of land resources, the number and height of high-rise buildings in China have been growing rapidly. In addition, the rapid rise of housing prices and the rising demand for housing in recent years have further stimulated the real estate enterprises to speed up investment and the construction of high-rise buildings. High-rise buildings in all parts of the country (super) are raining like rain. With the characteristics of large quantity, high height, complex structure and diversified functions, many buildings have become the symbolic buildings of the city. At the same time, high-rise buildings are also a severe test of construction technology and safety assurance, especially the fire safety of high-rise buildings has attracted people's attention in recent years. Many large-scale high-rise building fire accidents are getting worse and worse. High-rise buildings have more floors, complex structures, large volumes, and many ways of smoke spreading, so their fire hazards are more serious, especially the chimney effect and the consequences of external wind. Therefore, it is important to study the smoke movement and fire development characteristics of high-rise buildings. Significance.
Turbulent mixing motion and chimney effect are the two main mechanisms of smoke movement in stairwells, which play a major role in different stages of fire development. The flue gas movement mechanism in stairwell affects its vertical temperature distribution. Compared with the turbulent mixing movement stage, the vertical temperature of flue gas in stairwell decreases slowly and the temperature decays slowly in the chimney effect stage. The temperature of flue gas in the closed staircase decreases fastest and the value of beta is the largest with the increase of the position of the vent and the power of the fire source.
Under the chimney effect, methanol and n-heptane pool fires tilt toward the stairwell. In this paper, Richardson number Ri is introduced to analyze the effect of chimney effect on the flame inclination angle. The results show that the dimensionless flame length (Lf/D) and flame height (Hf/D) of n-heptane pool fire are directly proportional to the 1/4 power of heat release rate (Q*) of dimensionless fire source under chimney effect. For the flame temperature, the temperature rise in the inclined flame continuum (T) is lower than that in the open flame continuum (T) under the cooling effect of the wind velocity produced by the chimney effect, and the temperature rise in the flame continuum (T) is about 776, and the range of the flame continuum and the intermittent zone is also enlarged. For the flame continuum, the L/Q2/5 increases from 0-0.08 to 0-0.12 in the windless In the intermittence zone, L/Q2/5 increases from 0.08-0.2 to 0.12-0.25 in the absence of wind. The wind velocity produced by the chimney effect interacts with the burning rate of the fire source. The results show that the relationship between the wind velocity V and the 1/3 power of the fire source Q increases linearly. The temperature field distribution and the radiation and total heat flux in the stairwell are affected.
Through the design and construction of a 1/6 scale external wind stairwell test bench, the results show that under the action of different external wind direction and external wind speed, the smoke movement in stairwell and the fire characteristics of adjacent rooms have four distinct patterns. Mode I: With the increase of combustion time, the smoke temperature and total heat flow in stairwell also gradually increase. The chimney effect is the main driving force of smoke movement in the staircase. Mode II: In the initial stage of combustion, the temperature and total heat flux in the staircase are very small. After a period of combustion, the temperature and total heat flux in the staircase are very small. With the increase of combustion rate, the chimney effect gradually overcomes the external wind and becomes the main driving force. Mode III: When the external wind speed is relatively high, the flue gas temperature and the total heat flux in the staircase are very small, and the flame in the room tilts outdoors all the time. Hot smoke can not overcome the resistance of external wind to enter the stairwell. Mode IV: Start the fan during the combustion, the smoke temperature and total heat flow in the stairwell floors show a downward trend, the room flame gradually inclined to the outdoor direction, with the increase of external wind speed, the smoke temperature and heat flow fall faster. The inclination direction is mainly related to the chimney effect force Fstack and the external wind force Fwind. The modified Freud number Fr is introduced to judge and analyze the inclination direction of the flame in the room through theoretical analysis. The critical Fr value of the flame direction transition is calculated to be 0.814. When Fr is less than O.814, the flame inclines outdoors, otherwise, The flame inclines towards the stairwell.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU972.4;TU998.1
本文编号：2195516
[Abstract]:With the acceleration of urbanization and the increasing scarcity of land resources, the number and height of high-rise buildings in China have been growing rapidly. In addition, the rapid rise of housing prices and the rising demand for housing in recent years have further stimulated the real estate enterprises to speed up investment and the construction of high-rise buildings. High-rise buildings in all parts of the country (super) are raining like rain. With the characteristics of large quantity, high height, complex structure and diversified functions, many buildings have become the symbolic buildings of the city. At the same time, high-rise buildings are also a severe test of construction technology and safety assurance, especially the fire safety of high-rise buildings has attracted people's attention in recent years. Many large-scale high-rise building fire accidents are getting worse and worse. High-rise buildings have more floors, complex structures, large volumes, and many ways of smoke spreading, so their fire hazards are more serious, especially the chimney effect and the consequences of external wind. Therefore, it is important to study the smoke movement and fire development characteristics of high-rise buildings. Significance.
Turbulent mixing motion and chimney effect are the two main mechanisms of smoke movement in stairwells, which play a major role in different stages of fire development. The flue gas movement mechanism in stairwell affects its vertical temperature distribution. Compared with the turbulent mixing movement stage, the vertical temperature of flue gas in stairwell decreases slowly and the temperature decays slowly in the chimney effect stage. The temperature of flue gas in the closed staircase decreases fastest and the value of beta is the largest with the increase of the position of the vent and the power of the fire source.
Under the chimney effect, methanol and n-heptane pool fires tilt toward the stairwell. In this paper, Richardson number Ri is introduced to analyze the effect of chimney effect on the flame inclination angle. The results show that the dimensionless flame length (Lf/D) and flame height (Hf/D) of n-heptane pool fire are directly proportional to the 1/4 power of heat release rate (Q*) of dimensionless fire source under chimney effect. For the flame temperature, the temperature rise in the inclined flame continuum (T) is lower than that in the open flame continuum (T) under the cooling effect of the wind velocity produced by the chimney effect, and the temperature rise in the flame continuum (T) is about 776, and the range of the flame continuum and the intermittent zone is also enlarged. For the flame continuum, the L/Q2/5 increases from 0-0.08 to 0-0.12 in the windless In the intermittence zone, L/Q2/5 increases from 0.08-0.2 to 0.12-0.25 in the absence of wind. The wind velocity produced by the chimney effect interacts with the burning rate of the fire source. The results show that the relationship between the wind velocity V and the 1/3 power of the fire source Q increases linearly. The temperature field distribution and the radiation and total heat flux in the stairwell are affected.
Through the design and construction of a 1/6 scale external wind stairwell test bench, the results show that under the action of different external wind direction and external wind speed, the smoke movement in stairwell and the fire characteristics of adjacent rooms have four distinct patterns. Mode I: With the increase of combustion time, the smoke temperature and total heat flow in stairwell also gradually increase. The chimney effect is the main driving force of smoke movement in the staircase. Mode II: In the initial stage of combustion, the temperature and total heat flux in the staircase are very small. After a period of combustion, the temperature and total heat flux in the staircase are very small. With the increase of combustion rate, the chimney effect gradually overcomes the external wind and becomes the main driving force. Mode III: When the external wind speed is relatively high, the flue gas temperature and the total heat flux in the staircase are very small, and the flame in the room tilts outdoors all the time. Hot smoke can not overcome the resistance of external wind to enter the stairwell. Mode IV: Start the fan during the combustion, the smoke temperature and total heat flow in the stairwell floors show a downward trend, the room flame gradually inclined to the outdoor direction, with the increase of external wind speed, the smoke temperature and heat flow fall faster. The inclination direction is mainly related to the chimney effect force Fstack and the external wind force Fwind. The modified Freud number Fr is introduced to judge and analyze the inclination direction of the flame in the room through theoretical analysis. The critical Fr value of the flame direction transition is calculated to be 0.814. When Fr is less than O.814, the flame inclines outdoors, otherwise, The flame inclines towards the stairwell.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU972.4;TU998.1
【参考文献】
相关博士学位论文 前3条
1 孙晓乾;火灾烟气在高层建筑竖向通道内的流动及控制研究[D];中国科学技术大学;2009年
2 毛少华;烟气中性面的理论模型及实验研究[D];中国科学技术大学;2012年
3 涂然;高原低压低氧对池火燃烧与火焰图像特征的影响机制[D];中国科学技术大学;2012年
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