低位排烟模式下小室火灾机械排烟效率的实验研究

Experimental study on the efficiency of low-level mechanical smoke discharge in case of cabin fire

对小室内低位排烟这一特殊模式开展了全尺寸实验,并对其机械排烟效率进行了研究。实验结果表明,低位排烟时小室内烟气层高度的界面比较低,通常处于连续火焰区。在低位排烟过程中,由于有大量的空气被排烟风机直接吸走,导致机械排烟效率大大降低,通常低于40%。低位排烟时的机械排烟效率随着火源功率的增加而增大,两者之间的经验拟合关系式比较符合指数关系。根据实验数据,发展了基于McCaffrey模型的机械排烟速率模型,得出了低位排烟模式下控制小室火灾烟气溢出的排烟风机风量随着火源功率和烟气层高度变化的半经验公式。

This paper is to introduce our experimental study results on the efficiency of low-level mechanical smoke discharge in case of cabin fire. In our experiments, we have done full-scale investigative burning experiments by using a special model to test and determine the precise efficiencies of mechanical smoke discharge at lower levels in case of the cabin fire. The results of our experiments indicate that, since the smoke discharge is likely to lead to cabin fire, the smoke layer interface in the cabin rums to be very low and spreads almost to all the continuous flame regions. If the smoke can be controlled not to spread off the cabin, the mechanical smoke discharging rate can be expected to be kept much lower than the actual mechanical smoke discharge rate in accordance with the prediction of the McCaffrey model. Since the efficiency of the discharge tends to drop greatly if more air is extracted directly by a fan from the lower air layers. Experiments also indicate that the efficiency of such direct smoke discharge proves to be 40% lower than that with lower level mechanical smoke discharge in cabin. Most of the ventilation rates of the fan would be wasted. However, since the heat release rate serves as the key factor influencing the efficiency of the smoke discharge by means of low level mechanical discharge in cabin, its efficiency usually tends to go up with the rise of the heat-release rate, it is possible to derive an empirical exponential correlation on the efficiency of the smoke discharge with the heat release on the basis of the experimental data. The model for predicting the mechanical smoke discharge rate can also be built up by using the McCaffrey model. Therefore, it is also possible to deduce the semi-empirlcat correlation of the fan＇ s ventilation rate with the heat release rate on the condition that the smoke layer height be favorable for preventing the smoke from spilling out from the cabin