Experimental Study on Effect of Tunnel Slope on Heat Release Rate with Heat Feedback Mechanism

Abstract

Heat release rate (HRR) is most important factor in the tunnel fire. Therefore, an accurate understanding of the relationship between tunnel fire and HRR is required. The HRR of a pool fire is related to the heat feedback mechanism. Heat feedback is mainly affected by the flow around the fire source. However, considering the flow characteristics that depend on the tunnel slope is insufficient. Therefore, in this study, the effect of flow with respect to the tunnel slope on the heat feedback was analyzed with an experimental method. The experiment was conducted with a reduced-scale shallow underground tunnel. The slope of the tunnel was limited to 0 degrees to 7 degrees, which corresponds to the construction standard. The ceiling jet and entrained-air flow were affected by the pool diameter and tunnel slope. Owing to the effect of the air entrainment, the ratio of the re-radiation heat flux incident on the fuel surface decreased linearly with increasing tunnel slope. Moreover, the re-radiation and re-convection ratios of the tunnel slope and pool pan size showed linear trends. Based on the analysis of the heat feedback mechanism, the empirical correlation for the effect of the tunnel slope on the HRR can be presented in terms of the re-radiation/re-convection fraction.