点式排烟模式隧道火灾排烟量计算方法

Calculation Method for Tunnel Fire Smoke Exhaust Volume with Point Smoke Exhaust Mode

[目的]为解决GB 50016—2014《建筑设计防火规范》中,隧道火灾点式排烟系统的排烟量没有公认的数值及计算方法的问题,提出了临界排烟量的定义及相关计算方法。[方法]对排烟口下方烟气进行受力分析,采用表征浮升力与惯性力相对大小的Froude准则数作为判定临界排烟量的理论判据。在此基础上,进一步分析了浮升力与惯性力相对大小与烟气偏转轨迹之间的内在联系,结合模型试验数据,建立了临界排烟量的半经验模型。[结果及结论]临界排烟量的Froude准则数与排烟风口间距及火灾热释放率无关,与烟气层厚度和排烟风口长度的比值有关。当烟气层厚度和排烟风口长度的比值大于0.67时,Froude准则数与烟气层厚度和排烟风口长度的比值存在幂函数关系;当烟气层厚度和排烟风口长度的比值小于等于0.67时,Froude准则数与烟气层厚度和排烟风口长度的比值线性相关。

[Objective]To address the lack of recognized numerical values and calculation methods for smoke exhaust volume of tunnel fire point smoke exhaust system specialized in GB 50016—2014′Code for fire protection design of buildings′,a definition of critical smoke exhaust volume and relevant calculation methods are proposed.[Method]A force analysis of smoke beneath vent is conducted using the Froude number,which characterizes the relative magnitude of buoyancy force and inertia force,as the theoretical criterion for determining the critical smoke exhaust volume.Based on this criterion,the intrinsic relationship between the relative magnitude of buoyancy and inertia forces,and the smoke gas deviation trajectory is further analyzed.Combined with model test data,a semi-empirical model for the critical smoke exhaust volume is established.[Result&Conclusion]The Froude number for determining the critical smoke exhaust volume is independent of the spacing between vents and the heat release rate of fire,but is related to the ratio of smoke layer thickness to vent length.When this ratio is greater than 0.67,the Froude number exhibits a power function relationship with the ratio of smoke layer thickness to vent length.Conversely,when this ratio is less than or equal to 0.67,the Froude number is linearly correlated with the ratio of smoke layer thickness to vent length.