在隧道或走廊中传播的浓烟层会降低道路或地板表面附近的照度和能见度,从而导致延迟寻找出口和随后的疏散。因此,在消防安全科学中,烟层厚度与天花板射流的温度和速度的衰减特性同样重要。在这项研究中,进行了火灾试验,以根据烟层内部的温度分布选择合适的方法来确定烟层界面高度。两种不同截面纵横比的矩形隧道用于小规模隧道火灾实验。在本文中,确定烟层厚度的成熟方法,例如 N 百分比规则,通过将他们的结果与烟层的视觉观察进行比较来审查和评估。在此比较的基础上,提出了拐点法。将每种方法计算出的烟层厚度与目视观察结果进行比较。因此,发现浮力频率法最适合具有纵向较长断面形状的隧道,拐点法最适合具有横向较长断面形状的隧道。我们还证实,在自然通风下的准稳态下,热释放率对源自弱羽流的烟层厚度没有显着影响。讨论了用于归一化的新特征长度,以推导出平静流动区域中简单易用的天花板射流厚度公式。在此比较的基础上,提出了拐点法。将每种方法计算的烟层厚度与目视观察结果进行比较。因此,发现浮力频率法最适合具有纵向较长断面形状的隧道,拐点法最适合具有横向较长断面形状的隧道。我们还证实,在自然通风下的准稳态下,热释放率对源自弱羽流的烟层厚度没有显着影响。讨论了用于归一化的新特征长度,以推导出平静流动区域中简单易用的天花板射流厚度公式。在此比较的基础上,提出了拐点法。将每种方法计算的烟层厚度与目视观察结果进行比较。因此,发现浮力频率法最适合具有纵向较长断面形状的隧道,拐点法最适合具有横向较长断面形状的隧道。我们还证实,在自然通风下的准稳态下,热释放率对源自弱羽流的烟层厚度没有显着影响。讨论了用于归一化的新特征长度,以推导出平静流动区域中简单易用的天花板射流厚度公式。将每种方法计算的烟层厚度与目视观察结果进行比较。因此,发现浮力频率法最适合具有纵向较长断面形状的隧道,拐点法最适合具有横向较长断面形状的隧道。我们还证实,在自然通风下的准稳态下,热释放率对源自弱羽流的烟层厚度没有显着影响。讨论了用于归一化的新特征长度,以推导出平静流动区域中简单易用的天花板射流厚度公式。将每种方法计算的烟层厚度与目视观察结果进行比较。因此,发现浮力频率法最适合具有纵向较长断面形状的隧道,拐点法最适合具有横向较长断面形状的隧道。我们还证实,在自然通风下的准稳态下,热释放率对源自弱羽流的烟层厚度没有显着影响。讨论了用于归一化的新特征长度,以推导出平静流动区域中简单易用的天花板射流厚度公式。结果表明,浮力频率法最适用于纵向较长断面形状的隧道,拐点法最适用于横向较长断面形状的隧道。我们还证实,在自然通风下的准稳态下,热释放率对源自弱羽流的烟层厚度没有显着影响。讨论了用于归一化的新特征长度,以推导出平静流动区域中简单易用的天花板射流厚度公式。结果表明,浮力频率法最适用于纵向较长断面形状的隧道,拐点法最适用于横向较长断面形状的隧道。我们还证实,在自然通风下的准稳态下,热释放率对源自弱羽流的烟层厚度没有显着影响。讨论了用于归一化的新特征长度,以推导出平静流动区域中简单易用的天花板射流厚度公式。
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Determination of smoke layer thickness using vertical temperature distribution in tunnel fires under natural ventilation
A thick smoke layer propagating in a tunnel or corridor decreases the illuminance and visibility near the road or floor surfaces, leading to delays in finding exit and subsequent evacuation. Hence, smoke layer thickness is as important as the attenuation properties of temperature and velocity of a ceiling-jet in fire safety science. In this study, fire tests were conducted to select an appropriate method for determining the smoke layer interface height based on the temperature distribution inside the smoke layer. Two types of rectangular tunnels with different cross-sectional aspect ratios are employed for small-scale tunnel fire experiments. In this paper, well-established methods for determining the smoke layer thickness, such as the N-percentage rule, are reviewed and evaluated by comparing their results with visual observations of the smoke layer. Based on this comparison, the inflexion point method is proposed. The smoke layer thicknesses calculated from each method were compared with the visual observation results. Consequently, it was found that the buoyant frequency method is the most suitable for a tunnel having a vertically longer section shape and the inflexion point method for a tunnel having a transversely longer section shape. We also confirmed heat release rate have no significant effect on the thickness of the smoke layer originating from the weak plume in the quasi-steady state under natural ventilation. A new characteristic length for normalisation is discussed to derive a simple and easy-to-use ceiling-jet thickness formula in the tranquil flow region.