Experiment Study On Fire Characteristics And Temperature Field Induced By Linear Fire In The Urban Utility Tunnel

Due to the growing scale of cities,the increasingly precious land resources,and the increasingly complexes and diverse pipelines required by the city,the urban utility tunnel has become an important solution to the problem of urban development.However,due to the slow flow of air pollution in the urban utility tunnel and the complexity and variety of pipelines laid in the tunnel,the fire safety of the cables in the utility tunnel becomes more and more important.Therefore,in this social background,this thesis puts forward the topic of research on the linear fire smoke temperature field in the curved utility tunnel.This paper adopts the method of reduced size model experiments combined with theoretical analysis to study the fire characteristics of linear fire sources and the ceiling smoke temperature field of the urban utility tunnel under different fire source sizes,fire source types,fire source positions and ventilation conditions.This paper uses a scaling-size circular cross-section utility tunnel model,using linear oil tanks with lengths of 1.5m,1.7m and 1.9m,and a width of 4cm.The linear fire source fuels are methanol,ethanol and n-heptane.Under different fuel types,horizontal positions of cross section,vertical positions of cross section and different ventilation conditions,the fire development process,flame shape,the linear oil pool mass loss and smoke movement of linear fire source in the circular cross-section utility tunnel model were researched.The experiments found that the entire fire development process of n-heptane linear fire can be divided into two stable phases,two development phases and a decay phase,and the first stable phase is longer than the other one when the temperature is at its peak;while for the linear fires of methanol and ethanol,the fire development process only has one of development stage,stable stage and decay stage,respectively.Compared with the temperature curve of n-heptane linear fire,the temperature developments of methanol fire and ethanol fire are more gentle,and the stable stage lasts longer.During the combustion process,the pyrolysis and vaporization of the combustible fuel failed to completely burn in the stable flame zone,so that the flame tearing occurred,which looks like a flame vibration spray.The thickness of smoke layer under the ceiling of the tunnel increases along the longitudinal direction away from the linear fire source.And the more turbulent the boundary layer of hot smoke and cold air,and the boundary layer at the port of the tunnel model will appear vortex due to the turbulent flow of smoke.The closed port of the pipe gallery on the right side of the source will increase the thickness of the smoke layer.In this paper,through theoretical analysis,references to the models proposed by predecessors and the dimensional analysis method,the empirical fitting of the dimensionless maximum temperature rise,which is coupled with linear fire source size,the circular cross section of the utility tunnel model and the fire source location,is obtained.The comparative analysis between formulae of previous related models and the experimental data in this paper are presented,it is concluded that the previous formulae are not suitable for the maximum ceiling temperature rise law under the working conditions of this paper;finally,the different dimensionless quantities are calculated according to the experimental data.The relationship between other proposed dimensionless parameters and the dimensionless quantity of the maximum temperature rise under the ceiling is qualitatively analyzed.In this paper,through the analysis of the ceiling temperature data of the circular section utility tunnel model and referring to the previous theoretical models,the relationship between the dimensionless temperature rise attenuation and the dimensionless longitudinal distance under the experimental conditions of this paper is obtained;combining the formulae obtained in the previous section,this thesis obtains the final empirical fitting formulae for the longitudinal attenuation of the non-dimensional ceiling temperature rise that are suitable for the experimental conditions of this paper and coupled with the sizes of the utility tunnel model,the sizes of the fire source and the locations of the fire sources.This paper presents the isoline heat map of the temperature field on each longitudinal section of the tunnel model,and compares and analyzes the distribution of the ventilation conditions,the fire source conditions and the fire source locations to the transverse and vertical temperature field under the ceiling of the circular tunnel.Different from methanol fire and ethanol fire,the combustion process of n-heptane is more intense,the temperature field on each section of the tunnel changes more obviously,and the contour is denser;the closing of the right port helps to increase the overall temperature of the temperature field;The increase of the vertical distance between ceiling and fire source will lead to a decrease in the maximum temperature of the overall temperature field,affect the speed of vertical smoke stratification,and increase the longitudinal distance of smoke stratification.This thesis has 41 figures,12 tables and 76 references.