有风条件下火灾自然排烟的临界失效风速分析

Study on Critical Ineffective Velocity of Natural Smoke Exhaust under External Winds

采用双区模拟思想对有风条件下室内火灾自然补气、自然排烟过程进行分析。引入"总风压系数"和"临界失效风速"的概念,并将其作为评价外界环境风对自然排烟过程影响程度的判定参数。总风压系数非负时,外界风的存在将提高自然排烟的效果;总风压系数为负时,外界风的存在将降低自然排烟的效果,甚至使自然排烟失效。通过对排烟口内外压差以及气体流动进行分析,发现临界失效风速正比于总风压系数绝对值的-1/2次幂,并给出了不同条件下自然排烟临界失效风速的计算方法。实际采用自然排烟方式进行火灾排烟时,应尽量避免出现总风压系数为负的情形,以防止自然排烟的失效。

By use of a simple two-layer zone model, an analysis was made on natural smoke exhaust with the makeup of natural air under surrounding winds. ＂Overall wind pressure coefficient＂ and ＂critical ineffective velocity＂ were defined to assess the significance of external wind on natural smoke exhaust. When the overall wind pressure coefficient was not negative, surrounding wind would enhance the effect of smoke exhaust. When the overall pressure coefficient was negative, surrounding wind would decrease, or even make the smoke exhaust ineffective. By analyzing the air movement beside the smoke outlet and its internal-external differential pressure, it was found that the critical ineffective velocity was proportional to - 1/2 power of absolute value of overall pressure coefficient. The methods to calculate critical ineffective wind velocity in natural smoke exhaust under different conditions were also given. In practice, when operating a natural smoke exhaust system of a building under surrounding wind, the positions of vent and air inlet should be reasonably chosen to make the overall pressure coefficient positive and avoid invalidation of smoke exhaust by surrounding winds.