Visualization study on the effect of ambient wind on smoke layer height in chamber fires under natural smoke exhaust condition

Abstract

Ambient wind often affects the smoke movement and natural smoke exhaust performance in enclosure fires. In this study, six wind speeds and twelve kinds of vent combinations are designed. 72 groups of experiments are conducted to investigate the coupling effects of vent combination and ambient wind speed during quasi-steady state of natural smoke extraction in chamber fires. Compared to the traditional Particle Image Velocimetry (PIV) method, a novel particle image flow field visualization (PIFFV) technique is proposed, and a smoke recognition algorithm for the determination of smoke layer height is developed based on two-dimensional OTSU method. Experimental results show that using the PIFFV method and the proposed algorithm, smoke layer height can be determined more accurately, in comparison to the N-percentage method. When the height of outlet is higher than that of inlet, the worst smoke control effect is found. When the air inlet is located on the windward side, the effect of natural smoke extraction is better under a reasonable wind speed than that in a windless condition. However, when the height of outlet is lower than that of the windward inlet, the optimal smoke control effect is achieved without ambient wind. In addition, when the inlet is arranged on the sideward side, ambient wind has a limited influence on smoke layer height with a lower outlet. Results of this study can provide references for the design of smoke control and ventilation system in room fires.