Abstract
Using a semi-lateral exhaust system to control and discharge high-temperature poisonous smoke has been one of the predominant strategies for tunnel fires. However, as smoke flows from the tunnel through the vents into the duct, redirection-induced resistance occurs. In addition, the limited flow area reduces flow rates, compromising smoke extraction effectiveness. This study has developed an efficiency-enhancing method for vents based on a valve, which achieves smoke flow redirection and volume regulation. An analytical solution for the valve opening was derived, considering the control requirements for volumetric flow rate at the vents. Through computational fluid dynamics (CFD) simulation, functional correlations were established among the valve opening, the local resistance coefficient and the volumetric flow rate. Furthermore, the effect of efficiency enhancement was demonstrated. The result shows that the method can reduce smoke accumulation in the tunnel while also preventing long-distance spread and vertical settlement. Taking the uniform volumetric flow rate mode of a 50 MW fire as an example, with various valve openings for different sets of vents, both smoke exhaust efficiency and heat exhaust efficiency were increased. The findings provide actionable strategies and optimization pathways for exhaust system design.
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