夏季大空间内火灾机械排烟效率的研究

采用全尺寸实验对夏季大空间内火灾机械排烟的效率进行了研究.实验过程中主要测量了火源功率和大空间内的烟气温度两个参数.通过分析大空间内烟气温度的分布规律,得到了机械排烟控制下不同火源功率的大空间内稳定的烟气层高度.根据Heskestad羽流模型计算了烟气生成速率,与机械排烟速率比较得到了夏季大空间内火灾机械排烟的效率.实验结果表明,在夏季大空间中,当火源功率不是很大时,大空间内外的温差使得外界补充进来的空气和火灾生成的烟气更加容易发生掺混,导致机械排烟的效率大大降低;按照规范规定的6次换气率进行排烟,在实验的300～1 000 kW的火源功率范围内,夏季大空间内火灾机械排烟的效率约为30%.火源功率的增大,在一定程度上削弱了空气与烟气的掺混,机械排烟的效率略有提高,但是提高的效果并不是很明显.

Study on the efficiency of mechanical smoke exhaust in a large space fire in summer

The present paper aims to introduce the authors' investigation and research on the mechanical smoke exhaust efficiency in the large space fire in summer. In the testing process, we measured fire power and smoke temperature in such cases. When analyzing the smoke temperature distribution in such cases, we discovered that the smoke exhaust height in such fires changes steadily with the different strengths of the fire power under the mechanical smoke exhaust control. The smoke producing rates were thus calculated by using Heskestad plume correlation. Compared with the mechanical smoke exhaust rates, we have thus deduced the efficiency of the mechanical smoke exhaust in such summer fires. Results of our research have thus indicated that when the fire power wasn't high enough, the supplied air outside the space of the fire was easily mixed with the produced smoke due to the temperature difference between the inside and the outside of the space, which may greatly reduce or limit the mechanical smoke exhaust efficiency. According to our experiments, the mechanical smoke exhaust efficiency in a large space fire from 300 kW to 1 MW in summer was about 30% under 6 ACH prescribed by code. Increasing the fire power proved to be able to weaken the mixture of the supplied air with the produced smoke to a certain extent, the effect of the improved efficiency didn't seem obvious.