摘要
腔室火灾属于常见的火灾场景,在建筑火灾安全中得到了广泛的关注和研究。前人针对有门窗等开口的建筑空间火灾进行了大量研究并建立了相关的火灾模型,然而很少研究涉及到没有对外开口或仅有顶棚开口的封闭空间火灾。
本文针对以船舶机舱为代表的无开口或者仅仅具有顶棚开口的封闭舱室,在自行研制的封闭空间火灾实验系统中进行了小尺度模型实验研究,目的是为了揭示对封闭空间火灾燃烧特性及火灾烟气的运动规律。实验在一个内尺寸为1000mm(L)×1000mm(W)×750mm(H)封闭舱室内进行,研究了无开口条件下的火灾燃烧特性,重点研究了舱室内气体温度分布特性和火灾烟气在舱室中的运动规律。通过理论分析、类比、无量纲法则等方法对实验数据进行了分析,归纳出了封闭舱室火灾中的温度分布特性和烟气运动规律,主要包括以下几点内容:
封闭舱室火灾中,温度经历了三个过程,分别是发展阶段、稳定增长阶段、临近熄火衰退阶段。水平方向上,舱内大部分空间中同一水平高度具有相同温度值。竖直方向上,舱室可以分为上部的高温区和下部的匀梯度区,高温区内部具有相同的温度,温度与高度无关;匀梯度区内部温度为高度的一次函数,二者呈线性增长关系。
熄火时刻舱内的温度分布可用分段函数表示,通过研究建立了熄火时刻温度分布函数模型。熄火时刻无量纲的温度分布满足统一的波尔兹曼方程,建立了熄火时刻温度的预测模型,为船舶火灾中封舱灭火之后重新开舱时间的确立提供了理论依据。
封闭舱室火灾中,烟气运动与传统有竖直开口建筑火灾有很大不同。传统双区域模型热烟气层和冷空气层的划分不再适用。此时,烟气由最初的热烟气层、过渡层和冷空气层三部分随时间逐步发展成为热烟气层和过渡层两部分,冷空气层消失。封闭舱室火灾中,舱内气体各分界面位置随时间以指数衰减的形式由上往下移动,研究分别建立了不同火源功率下的界面移动模型。
One of the most common scenarios of fire is the chamber fire which has been paid specially attention and studied by lots of researchers. So far, fires in buildings with outlets such as windows and doors have been studied and the corresponding fire models have been developed, but few researches have been found about the fire in closed chamber without outlets or with only roof outlet.
This paper conducted a lab-scale experimental research using an enclosed cabin fire testing system developed by ourselves, aiming at to reveal the principles of the combustion and the smoke movement in fires occurred in enclosed cabin. The experiment was conducted in a closed ship cabin with the dimension of 1000mm(L)×1000mm(W)×750mm(H). The properties of the fire in a chamber without outlet was studied, emphasized at temperature distribution and the smoke movement in the cabin. Through analyzing the experimental data using various methods such as theoretical induction, analogy, non-dimension analysis etc., the characteristics of the temperature distribution and the smoke movement of fire in closed boat cabin were concluded as following:
Fire in enclosed cabin usually consists three consequent periods, namely the developing period, the temperature steady increasing period and the close-burnout period. At the horizontal direction, most of spaces, the same temperature appears at the same height in the cabin; at the vertical direction, the gas in the cabin can be classified into two layers: the upper layer with high temperature and the lower layer with even gradient of distribution. In the upper area, the temperature remains the same everywhere and has nothing to do with the height, while in the lower area, the temperature is an one order function with the height, namely, is in direct proportion with the height.
Considering that the temperature distribution in the cabin at the time of burnout can be represented as a separable function and the dimensionless temperature distribution is consist with the united Boltzmann equation, a model for predicting the temperature at the time of burnout has been proposed, which provides the theoretical basis for estimate an appropriate time to open the cabin after the fire suppression of a ship fire
The movement of the smoke in fires of enclosed cabin is very different from that in the normal buildings with vertical outlets. Here, the traditional two-zone model, in which the space is divided into the hot smoke layer and the cold gas layer, is not suitable anymore. Instead, as the time elapsed, the original three layers of smoke, which consists of the hot smoke layer, the cold smoke layer and the transitional layer, change into two layers, namely the hot smoke layer and the transitional layer, where the cold gas layer disappears. The height of the smoke interface in fires in enclosed cabin changes as the form of exponential attenuation with the time, a model has been proposed of the height of the smoke interface with different fire powers.
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