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Experimental and Theoretical Studies on the Mechanism of Flashover Occurred in Long and Narrow Underground Space

Author: LiSongYang
Tutor: LiaoGuangZuo;ZongRuoZuo
School: University of Science and Technology of China
Course: Safety Technology and Engineering
Keywords: Underground narrow space Flashover Ceiling jet Experimental simulation of small size Thermal instability Critical Condition Numerical Simulation Turbulent combustion model
CLC: X928.7
Type: PhD thesis
Year: 2011
Downloads: 176
Quote: 1
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Abstract


In recent years, in order to solve the rapid urban population growth and limited land conflicts between many countries have to look into the underground space development and utilization. Large numbers of underground space in solving the problems of urban land use, but also for fire safety has brought new problems and challenges. Some narrow underground space, poor ventilation in the event of fire, smoke and heat generated by the heat difficult to discharge, easily lead to flashover. Flashover strength of the development process as a surge in the fire, a huge jump destructive process, often caused fires Qunsiqunshang important reason. Therefore, to carry out underground narrow space flashover fire growth characteristics and mechanism of evolution of great significance. In this paper, a small-scale experimental simulation, theoretical analysis and numerical simulation method of combining study the narrow confined spaces underground fire law of development, flashover smoke flow characteristics and mechanism of evolution. Reference to previous research methods and thinking, self-built small fires underground narrow bench space by changing the fire area, fire shapes, fuel type, fire location, size of the opening, the lateral boundary conditions, and other exhaust rate , to reproduce the narrow confined spaces during flashover occurs, accurate measurement of smoke during a fire temperature, concentration, speed, ground source heat flux and mass loss rate of fire, as the theoretical model and numerical simulation validation and comparison tool provides data to support discussion and analysis. Through simulation experiments and theoretical analysis to study the narrow space to fire flashover occurred in front, smoke layer thickness, temperature and velocity in the longitudinal direction of the distribution. First, from the line of the roof caused by the jet fire starting, was established based on the number of Ri and smoke layer thickness h of the roof line of fire jet model is derived to predict the velocity and temperature distribution relationship. Meanwhile, the use of small-scale experiments to obtain the temperature and velocity data to verify the line of fire source jet model predictive ability. Later, in combination with previous findings and line sources of ignition jet model, based on the theoretical analysis of the narrow space of real fire smoke layer temperature and velocity decay, and spread during special physical phenomena - water jump, too The aspect ratio of the narrow space at λ 0.17 lt; λ / 2 lt; 0.78 between the water in the critical position jump occurs 1.6 gt; xc gt; 0.78 range. The use of an ignition source jet model and line sources of ignition method of combining jet model predicted vertical flue gas temperature and velocity distributions, and with the small size of the experimental stage data obtained were compared verified. Through the small size flashover experiments to study the narrow space before and after flashover, smoke layer temperature, thickness, gas concentration, fire heat release rate, the ground by parameters such as thermal radiation changes. Meanwhile, the study of fire behavior and ventilation characteristics of fire development and flashover occurs impact mechanism. Studies have found that as the representative of heptane pool fire, smoke layer on the thermal feedback is very sensitive, and fire wood Duo thermal feedback on the smoke layer insensitive. On the other hand, the opening determines the characteristics of the main sources of ignition ventilation control stage mass loss rate, when the size of the opening ratio of the area with the fire reduced to a certain extent, the mass loss rate will decrease with the decrease of the opening. Results of previous studies focused on common chamber flashover process, because structural differences, previous research does not apply within the space of underground narrow flashover phenomenon. Based on the traditional theory of nonlinear dynamics, developed for the analysis of the phenomenon of flashover narrow confined space multi-zone fire model. The model will be a narrow confined space is divided into several areas, each area is divided into hot gas layer and a layer of cold air and hot gas layer is defined as the control body. Then, for each control body to establish the continuity equation and energy equation, obtained by numerical solution of each control body temperature curve. Through discussion of the results of the model calculations, analyze the transient case wall temperature and flue gas temperature of the smoke layer thickness on growth and thermal systems imbalance mechanism, and also discussed the quasi-steady state conditions, the fire source radius and fuel properties on the critical flashover conditions. Finally, the use of small-scale fire test data to verify the theoretical model, the critical flashover conditions predictive ability. Finally, small-scale experimental data obtained validate CFD software FDS and SIMTEC two narrow confined space fire simulation process reliability. Meanwhile, compared Mixture Fraction, EDC combustion model and Flamelet three limited ventilation conditions in the calculation of turbulent combustion process applicability. The results show that the two software can better prediction of temperature and CO2 concentration in the process of change of the fire, but the CO concentration in the prediction result is not satisfactory.

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CLC: > Environmental science, safety science > Safety Science > Safety management (labor protection and management ) > Accident investigation and analysis ( work-related injuries and prevention ) > Fire and explosion
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