Experimental study of heat exhaust efficiency with natural ventilation in tunnel fire: Impact of shaft height and heat release rate

The experimental study is conducted to investigate the heat exhaust efficiency with different shaft heights and heat release rates (HRRs) in a 1:10 tunnel model. The degree of plug-holing below the exhaust vent is considered. The smoke characteristics in upstream and shaft, such as flow velocity and smoke temperature rise, are discussed in this paper. The results indicate that the smoke movement in the upstream flow of the exhaust vent is mainly determined by the HRR of the fire and less affected by the vertical shaft height. The performance of the vertical shaft changes as the shaft height changes. Comparing constant HRR from the pool fire, the heat exhaust efficiency of vertical shafts does not increase all the time but decreases first and then increases. Furthermore, an empirical model is proposed based on the experimental results, which can be used to calculate the heat exhaust efficiency.