Effects of baffles on heat and contaminant removal for tunnel smoke extraction: Evaluation criteria regarding removal efficiency and flow resistance

An exhaust vent with a baffle and its corresponding evaluation index are proposed in this paper to increase the heat and contaminant extraction efficiencies for stratified smoke flow in tunnel fires. Numerical simulation and small-scale experiments are performed to investigate the effects of baffles beneath the exhaust vent on the flow pattern and the resulting heat and contaminant extraction efficiencies. Further, we introduce performance evaluation indices PEIH and PEIM, to comprehensively evaluate the performance of the exhaust vent considering both enhancement of extraction efficiency and increase in flow resistance. The analysis results show that when a concave baffle is adopted at a height of 0.7 m from the tunnel ceiling, maximum PEIH and PEIM (1.20 and 1.17, respectively) are achieved. Compared to the vent without a baffle, the heat and contaminant extraction efficiencies are increased by 21.1% and 18.1%, respectively; however, the flow resistance is increased by only 1.8%. The proposed PEIH and PEIM can be used as a general index for evaluating the performance of other types of exhaust vents and optimizing the vent layout as well, which is helpful to improve the performance of transverse smoke exhaust system in tunnel fire.