Thermal smoke back-layering flow length with ceiling extraction at upstream side of fire source in a longitudinal ventilated tunnel

A model for predicting smoke back-layering length in tunnel fires with the combination of longitudinal ventilation and point extraction ventilation in the roof

“…And it had been confirmed by the experiments conducted by Tang et al [16]. In their experimental configuration [16], the smoke vent was set upstream of the fire source compared to the experiments conducted by Chen et al [15]. The experiment results observed by Tang et al [16] highlighted that the smoke back-layering length in their experiments was shorter than that from experiments conducted by Chen et al [15].…”

“…As a consequence, the smoke vent upstream of the fire source might directly exhaust the smoke from the smoke back-layering, so that the back-layering length would be different from the situation that the smoke vent is operating at the downstream side [15]. And it had been confirmed by the experiments conducted by Tang et al [16]. In their experimental configuration [16], the smoke vent was set upstream of the fire source compared to the experiments conducted by Chen et al [15].…”

“…In their experimental configuration [16], the smoke vent was set upstream of the fire source compared to the experiments conducted by Chen et al [15]. The experiment results observed by Tang et al [16] highlighted that the smoke back-layering length in their experiments was shorter than that from experiments conducted by Chen et al [15]. Based on the experimental data, they proposed a modified longitudinal decay coefficient of the ceiling excess temperature ( ′ ) in the model of Chen et al [15] (Eq.14):…”

“…As already reviewed, there are many literatures focusing on the smoke back-layering length, but the relevant research on the smoke back-layering in the contexts of the combination of the longitudinal ventilation and the point extraction ventilation was not many found. The existing models for quantifying these phenomenon [14][15][16] were all based on the model proposed by Li et al [6], deriving from the dimensionless correlation between the smoke back-layering length and the longitudinal velocity. The effect of the point extraction ventilation on the back-layering was considered by introducing a reduced heat release rate of the fire source, ̇ * * , from the point view of the heat conservation.…”

Effects of fire location on the capacity of smoke exhaust from natural ventilation shafts in urban tunnels

“…As the number and length of tunnels increase, the driving speed and density of vehicles in the tunnel also increase, so tunnel disasters have occurred more frequently in recent decades, and fire is one of the major disasters that may occur in tunnels. [6][7][8][9][10][11][12][13][14] If a fire occurs in the tunnel, due to its long-narrow structure and the poor internal ventilation capacity, the hot smoke will spread rapidly throughout the tunnel and will be difficult to be discharged. [15][16][17][18][19][20][21][22] Moreover, the toxic gases in the tunnel will seriously affect the evacuation of stranded persons and rescue work of fire department.…”