Journal of South China University of Technology (Natural Science Edition) ›› 2021, Vol. 49 ›› Issue (4): 108-116,123.doi: 10.12141/j.issn.1000-565X.200601

Special Issue: 2021年交通运输工程

• Traffic & Transportation Engineering • Previous Articles     Next Articles

Characteristics of Smoke Layer Behavior Beneath Heat-Conducting Ceilings and Adiabatic Tunnel Ceilings

HU Jiawei MAO Jun XI Yanhong LIU Bin    

  1. School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China
  • Received:2020-10-06 Revised:2020-12-12 Online:2021-04-25 Published:2021-04-01
  • Contact: 胡嘉伟（1990-），男，博士生，主要从事隧道火灾传热传质理论与技术研究。 E-mail:15115266@bjtu.edu.cn
  • About author:胡嘉伟（1990-），男，博士生，主要从事隧道火灾传热传质理论与技术研究。
  • Supported by:
    National Key Basic Research Project(2016YFC0802206),National Natural Science Foundation of China(51578061),General Projects of the National Natural Science Foundation(52072027),and the Central Universitiesbasic Scientific Research Operating Expenses（2019JBM087）

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Abstract: Thermal conductivity of surrounding rock is an often neglected and significant factor that affects the fire characteristics of tunnel. To study the influence of thermal conductivity of tunnel on the fire smoke spreading process in near-wall area of tunnel ceiling, the temperature distribution and smoke layer characteristics in the vertical direction beneath heat-conducting ceilings and adiabatic tunnel ceilings were analyzed by means of numerical simulation and full-scale experiment. The results show that when the smoke spreads along the longitudinal direction, the height of maximum temperature rise near wall under the heat-conducting ceiling within 100m downstream of the fire source is similar to that of the “temperature boundary layer”. The maximum value of the ratio between the maximum temperature rise position and the tunnel height under heat conduction condition is 0.04, which is higher than that under adiabatic condition(0.03), and the position of the maximum temperature is farther away from the fire source. Under adiabatic condition, the temperature distribution in the vertical direction beneath the tunnel ceilings is mainly affected by heat convection caused by the high temperature flue gas entrainment of lower layer air. When the heat release rate is less than 20MW, the longitudinal temperature attenuation of smoke beneath ceiling contact surface can be expressed as a dimensionless fire power in the form of exponential decay to the power of one third of the dimensionless distance. Additionally, after the temperature boundary layer effect of the ceiling near the wall surface occurs, the smoke temperature of the surface decreases along the longitudinal direction in an exponential form related to the fire power. The influence of the heat transfer loss between the smoke and the wall on the ceiling jet temperature distribution is less than that of the entrainment in the adiabatic condition, and the heat loss also decreases along the longitudinal direction in an exponential form.

Key words: tunnel fire, heat-conducting, insulation, heat convection, near-wall smoke layer

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