Numerical study on the impact of wall thermal inertia on maximum smoke temperature and longitudinal attenuation in long channel fires

In order to better understand the law of smoke propagation in long channel fires and enhance the fire protection of channel structure with different lining materials, a series of fire simulations were carried out by Fire Dynamics Simulator (FDS) to investigate the impact of wall thermal inertia on the maximum smoke temperature and longitudinal attenuation under the channel ceiling. Five wall materials corresponding from the foam concrete to the steel with thermal inertia ranging from 0.1 to 165 kW(2).s/(m(4).K-2) and four heat release rates (5 MW, 7.5 MW, 10 MW and 12.5 MW) were employed. The maximum smoke temperature above the fire source and the temperature distribution under the ceiling along the channel longitudinal centerline were attained and analyzed. The results show that the maximum smoke temperature is significantly affected by the channel wall thermal property and increases with the decrease of wall thermal inertia. Based on the simulative data, a modified model taking the influence of wall thermal inertia into consideration is put forward to predict the maximum gas temperature below the ceiling. Further, the effect of channel wall thermal inertia on the longitudinal smoke temperature decay can be negligible when the thermal inertia is greater than or equal to 1.21 kW(2).s/(m(4).K-2), however, the foam concrete wall with the thermal inertia of 0.1 kW(2).s/(m(4).K-2) results in a smaller attenuation rate due to less heat conducted into the channel wall. Meanwhile, the smoke temperature distribution along the channel longitudinal centerline is also related to the heat release rate (HRR), and the larger the HRR, the slower the temperature decay. The investigation indicates that the temperature distribution along the longitudinal direction follows an exponential attenuation in the near fire field but presents a form of the sum of two exponential functions in the one-dimensional smoke propagation stage. Then taking the effect of wall thermal inertia and heat release rate into account, two novel models characterizing the law of longitudinal temperature attenuation were developed near fire source and in the one-dimensional smoke spread stage respectively.

Automated summary

This study investigated the law of smoke propagation in long channel fires and the impact of wall thermal inertia on maximum smoke temperature and longitudinal attenuation. The results showed that wall thermal property significantly affects the maximum smoke temperature, and the effect of wall thermal inertia on longitudinal smoke temperature decay can be negligible when it is greater than or equal to 1.21 kW(2).s/(m(4).K-2). The study also found that the smoke temperature distribution is related to the heat release rate.