Study On The Influence Of Linear Fire Source Location On The Fire Temperature Field Distribution Of Underground Utility Tunnel

With the acceleration of urbanization,urban underground utility tunnel,as a scheme that can effectively improve pipeline management ability,intensively use urban underground space and improve urban environment,has been developed rapidly in China.However,as the lifeline of the normal operation of the city,the underground utility tunnel space structure is narrow and long closed,the internal pipeline layout is complex,and its fire risk is high,so the fire safety of the utility tunnel needs to be fully studied.Therefore,it is of great significance to study the distribution of fire temperature field of urban underground utility tunnel in view of the special fire scene of utility tunnel.Through theoretical analysis,small-scale model experiment and full-scale platform experiment,this paper studies the influence of different linear fire source location on the fire temperature field distribution of the utility tunnel.In this paper,five different linear fire source positions(height 15 cm,45 cm,75 cm,105 cm,135 cm,all of which are placed on the long side of the wall)are designed to carry out the experimental research by using the experimental model of small-scale circular cross-section utility tunnel and 60245IEC53 YZ cable as fuel.The results show that: the development and spread trend of cable fire can be divided into three stages:initial development stage,stable combustion stage and attenuation and extinction stage;under the same fuel conditions,the higher the position of fire source,the smaller the mass loss rate of cable,and the smaller the heat release rate;the effective flame height of linear fire source decreases with the rise of fire source height,when the fire source height reaches 135 The flame spread along the arc roof to the center line and then spread longitudinally.Based on the theoretical research of fire temperature field distribution in utility tunnel,this paper analyzes the experimental data of small-scale model,and finds that the effective flame height of linear fire source is obviously different from that of axisymmetric fire source.Through the experimental data,the effective flame height prediction model suitable for linear fire source is obtained;the higher the fire source height is,the higher the maximum temperature under the ceiling center line of utility tunnel is,and the higher the fire height is Considering the influence of the side wall on the heat release rate of the fire source,the effective heat release rate per unit length is introduced,and the experimental data are fitted to improve the prediction model of the maximum temperature rise of the ceiling.The transverse temperature field of the linear cable fire is divided into three areas: plume area,ceiling jet area,thermal radiation area and ceiling jet area For the first two regions,a prediction model of the transverse temperature distribution of the ceiling is proposed;the longitudinal temperature field of the center line of the linear fire source ceiling is divided into plume impact zone and temperature attenuation zone,and the temperature of the plume impact zone is basically consistent.Based on the dimensional analysis,the temperature decay model is proposed The longitudinal temperature prediction model of the reduced zone is similar to the classical Alpert model.Based on the research results of the model experiment,the fire experiments of eight linear fire sources were carried out on the full-scale utility tunnel experimental platform.Firstly,the applicability of the ceiling maximum temperature rise prediction model,the transverse temperature distribution prediction model and the longitudinal temperature distribution prediction model obtained in the model experiment in the fullscale utility tunnel platform is verified,and the feasibility of the small-scale model experiment to study the temperature field of the utility tunnel based on the Floyd similarity is proved.Secondly,the combustion characteristics and transverse temperature field distribution of different linear fire source transverse positions are studied.The results show that: when the fire source height is constant,the transverse position d of fire source increases and the mass loss rate increases,but when the fire source is close to the side wall,the mass loss stall rate decreases significantly;the flame shape of different transverse fire source positions is different,and the transverse position d of fire source increases The results show that the thickness of the smoke layer is basically the same at different transverse positions of the fire source.According to the distribution law of transverse temperature field,it is found that there is a critical temperature angle in the ceiling jet zone.Based on this,the prediction formula of the minimum distance between the top cable tray and the ceiling is proposed.There are 47 pictures,10 tables and 81 references in this paper.