Experimental study on the effect of sealing behavior on smoke temperature characteristics in tunnel fires

Sealing tunnel entrances is a favorable approach to controlling tunnel fires. Sealing makes the thermodynamic behavior of fires different from that of the normal combustion state. To better comprehend the sealing effect on the temperature characteristics and heat transfer, the maximum smoke temperature rise beneath the ceiling as a function of the dimensionless heat release rate and the sealing ratio was derived based on the dimensional analysis. Then, a series of methanol pool combustion experiments were conducted in a reduced tunnel to investigate the influence of sealing behavior on the maximum temperature rise and the longitudinal distribution pattern of smoke. The results demonstrate that the smoke temperature inside the tunnel increases with the increasing sealing ratio, which is especially noticeable at the sealing ratio of 0.75 and 1.00. The higher the heat release rate, the more pronounced the influence of sealing behavior on temperature, which is the result of the combined effect of the weakened cooling effect of the airflow on the high-temperature smoke and the enhanced radiative heat transfer of the carbon black particles to the ceiling. Moreover, the maximum smoke temperature rise exhibits a 0.696-power correlation with the dimensionless heat release rate of fire source, and increases linearly with the increase of sealing ratio. Finally, the prediction model for the longitudinal distribution pattern of ceiling smoke temperature under different sealing ratios and heat release rates of fire source is developed, which is found to be consistent with measured data and previous studies.