热分层环境下红外光束感烟探测器探测报警时间研究

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3.0 高德中 2025-01-09 5 4 3.32MB 76 页 15积分

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摘要

大空间建筑往往存在着危险等级高、火灾水平蔓延速度快的特点，一旦发生

火灾极易造成群死群伤和大面积火灾。由于大空间建筑通常具有一定的高度，受

太阳辐射、室内热源及建筑底部空调系统的影响，室内环境往往在垂直方向上存

在着较大的温度梯度，温度分层现象显著。火灾时烟气羽流受浮力作用上升的现

象受温度分层影响而减弱，严重时环境产生的热障效应将导致烟气无法上升，从

而延缓了探测烟气的时间。为了实现对大空间建筑火灾的快速探测，尽可能减少

人员和财产损失，对热分层环境下烟气羽流上升特性及探测报警时间的相关研究

就显得尤为重要。

论文针对大空间 15m×15m×30m 的物理模型，就火源释热率在 100～

1000kW、基准环境温度为 13～28℃、温度梯度分别为 0℃/m、0.5℃/m、1.0℃/m

的120 个工况进行了烟气上升运动模拟计算，分析了火源释热率，基准环境温度

及温度梯度对烟气羽流上升的影响。结果表明，烟气羽流上升时间与火源释热率

呈负相关，与基准环境温度及温度梯度呈正相关。三个影响因素中火源释热率对

上升时间的影响最大，温度梯度次之，基准环境温度最小。分析温度分层对烟气

羽流影响的结果表明，火源释热率为 500kW 及以上的烟气羽流均能抵达屋顶，而

火源释热率为 200kW 及以下的烟气羽流因受热障效应影响较大，当环境梯度为

1.0℃/m 时不能到达屋顶。

论文通过对模拟计算结果的分析，就火源释热率为 300kW和400kW的各工况，

对不同热分层环境和不同基准环境温度下红外光束感烟探测器的探测报警时间进

行了分析。探测报警时间由羽流上升时间 tz和烟气浓度增大至探测器报警阈值的

时间 t’两部分组成。分析结果表明当火源释热率较大时，tz占探测时间的比重较大，

此时分层环境对探测时间的影响非常微小；当火源释热率较小时，t’占探测时间的

比重较大，此时温度梯度较大的分层环境能够显著减少探测时间。此外论文根据

模拟结果还分析确定了红外光束感烟探测器在大空间建筑中的最佳布设方式：在

垂直方向上，当大空间建筑高度低于 9m 时，可单层设置；当高度为 10~14m 时，

可双层设置；当高度为 15~30m 时，可三层设置。在水平方向上，可根据安装间距

不得大于该高度处烟气羽流直径的原则来确定。

通过对热分层环境下烟气羽流最大上升高度公式的修正及轴心温度计算公式

的推导，应用伯努利方程与数值模拟结果，通过分析羽流上升时间分段发展的特

点，建立了稳定线性热分层环境下轴对称烟气羽流上升时间分两段的求解数学模

VII

型tz=f(z)，计算结果表明所建模型能够很好地反映热分层环境下烟气羽流的上升特

性。计算基准环境温度为 13℃，环境梯度为 0.5℃/m 和1.0℃/m 的12 个工况结果

表明，4m 至分段转折点高度区间内，羽流上升所需时间的模型计算值和模拟值的

标准差均在 0.6s 以内，标准差平均值为 0.42s；在 4m 至屋顶或羽流最大上升高度

的区间内，模型计算值和模拟值的标准差也大部分在 1s 以内，标准差平均值为

0.66s。最后，文章提出了烟气浓度上升至报警阈值所需时间 t’的计算方案及理论求

解思路。

本文对烟气羽流上升特性及红外光束感烟探测器探测报警时间的相关研究可

为消防性能化设计及相关规范和标准的制定提供一定参考。

关键词：烟气羽流大空间建筑热分层环境红外光束感烟探测器上

升时间探测报警时间

VIII

ABSTRACT

There are always high level of fire risk category and high rate of fire spread in large

space buildings, which may result in heavy casualties in case of fire. Large space

buildings usually have certain height above the floor. So affected by solar radiation,

indoor heat source and HVAC system, big vertical temperature gradient will form in the

indoor environment of large space buildings. The rising of smoke plumes is driven by

buoyancy force due to the difference in temperature between smoke plumes and

ambient enviroment. Therefore, in thermally stratified environments, the difference in

temperature will decrease with height, which will delay or even block up the rising

process of smoke plumes. Once the so called heat barrier effect is produced, the

detection time of smoke plumes will increase. In order to fulfill the rapid detection to

large space building fires and largely avoid casualties and property losses, it is quite

necessary to do related research on rising characteristic of smoke plumes and detection

time in thermally stratified environments.

A building model that measures 15 by 15 by 30 is built to simulate and analyze the

infulence from fire heat release rate, reference temperature and temperature gradient on

the rising process of smoke plumes when fire heat release rate is 100～1000kW,

reference temperature is 13～28℃ and temperature gradient is 0～1℃/m . The 120

numerical simulation and analyzed results demonstrate that the rising time of smoke

plumes has a positive correlation with fire heat release rate and has a negative

correlation with reference temperature and temperature gradient. Besides, fire heat

release rate affects the rising time most, the temperature gradient does less, and the

reference temperature does the least. The analysis results of the influence from

thermally stratified environment on smoke plumes show that when fire heat release rate

is greater than or equal to 500kW, smoke plumes can easily reach the ceiling. But when

fire heat release rate is less than or equal to 200kW, smoke plumes are notably affected

by heat barrier effect and can’t reach the ceiling when temperature gradient is 1℃/m.

According to the simulation and calculation results, the cases whose fire heat

release rate is 300kW or 400kW are chosen to analyze the the detection time of infrared

beam smoke detector. The detection time consists of the rising time tz and the time t’

during which the smoke concentration rises up to alarm threshold. The analysis results

indicate that when fire heat release rate is large, tz is in a larger proportion of detection

time. In that case thermally stratified environments have little effect on detection time.

But when fire heat release rate is small, t’ is in a larger proportion of detection time. In

this instance, the detection time can be remarkably reduced by the great temperature

gradient. In addition, according to the analysis on the detection time of infrared beam

smoke detector under different fire heat release rates and thermally stratified

environments, the optimal form and location of infrared beam smoke detector in large

space buildings is determined. When building height is below 9 meters, the detectors

can be set within a single level. When building height is 10~14 meters, the detectors can

be set at two levels. When building height is 15~30 meters, the detectors can be set at

three levels. The spacing between beams is based on the narrowest potential width of

the plume at the level of detection.

Meanwhile, through modifying the calculating formula of maximum rise of fire

smoke plumes and formula derivation of centreline plume temperature, a piecewise

mathematical model tz=f(z) is presented to calculate the rising time of axisymmetric

plume fronts in stably linearly thermally stratified environments by applying Bernoulli

equation and numerical simulation. The rising characteristic of smoke plumes in in

thermally stratified environments can be well represented by the mathematical model.

When reference temperature is 13℃ and temperature gradient is 0.5℃/m and 1.0℃/m

respectively, the simulation results show that the standard deviations between

theoretical results and simulated results of 12 fire cases are below 0.6 second in the

segment of 4~ zsep and are mostly below 1 second in the segment of 4~29(or 4~

z

). The

average of standard deviations are 0.42 second and 0.66 second respectively in above

two segments. At last, a scheme to calculate the during time when smoke concentration

rises up to alarm threshold is introduced.

In the paper, the related research of rising characteristic of smoke plumes and

detection time of infrared beam smoke detector is useful to performance-based fire

design and will offer reference to making out correlative criterions and standards.

Key words: Smoke plume, Large space buildings, Thermally stratified

environments, Infrared beam smoke detector, Rising time,

Detection time.

中文摘要

ABSTRACT

第一章绪论 .......................................................... 1

§1.1 研究背景及意义 ............................................ 1

§1.2 烟羽流特性及探测器探测时间研究现状 ........................ 2

§1.2.1 热分层环境下烟羽流特性研究现状 ...................... 2

§1.2.2 烟羽流上升时间及探测时间研究现状 .................... 3

§1.2.3 火灾 CFD 模拟技术发展现状 ............................ 4

§1.3 课题研究基本思路及其主要研究内容 ........................... 6

§1.3.1 课题研究的基本思路 .................................. 6

§1.3.2 主要研究内容 ........................................ 6

第二章火灾探测器选用与布局的分析 .................................... 8

§2.1 火灾发展过程与人员安全疏散分析 ............................ 8

§2.1.1 建筑火灾发展过程 .................................... 8

§2.1.2 火源及其释热率 ...................................... 9

§2.1.3 人员安全疏散分析 ................................... 11

§2.2 火灾探测器的选用及布局的思考 ............................. 12

§2.2.1 常用的火灾探测器及选用原则 ......................... 12

§2.2.2 红外光束感烟探测器安装位置设置存在的问题 ........... 15

§2.2.3 设置红外光束感烟探测器安装位置的思考 ............... 17

§2.3 本章小结 ................................................. 18

第三章红外光束感烟探测器探测时间数值模拟研究 ....................... 19

§3.1 模拟案例设定 ............................................. 19

§3.1.1 FDS 软件介绍 ........................................ 19

§3.1.2 羽流形态及其分类 ................................... 20

§3.1.3 模型建立与测点布置 ................................. 21

§3.1.4 火源设置及网格划分 ................................. 22

§3.1.5 火灾场景设置 ....................................... 24

§3.2 烟羽流环境模拟结果分析 ................................... 25

§3.2.1 分层环境作用下烟羽流温度场及速度场分析 ............. 25

§3.2.2 羽流上升影响因素分析 ............................... 30

§3.2.3 探测报警时间分析 ................................... 40

§3.2.4 探测器最佳布置方案 ................................. 44

§3.3 本章小结 ................................................. 46

第四章红外光束感烟探测器探测报警时间理论分析 .......................47

§4.1 均匀环境下烟气羽流上升时间理论分析 ....................... 48

§4.2 稳定线性热分层环境下烟气羽流上升时间分段求解模型 ......... 50

§4.2.1 烟气羽流最大上升高度和中性浮力点高度 ............... 50

§4.2.2 环境温度及烟气羽流轴心温度 ......................... 51

§4.2.3 上升时间分段求解模型建立 ........................... 53

§4.3 烟气浓度增大至报警阈值所需时间的分析 ..................... 62

§4.4 本章小结 ................................................. 64

第五章结论及展望 ...................................................65

§5.1 结论 ..................................................... 65

§5.2 展望 ..................................................... 66

参考文献 ............................................................67

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