Simulation And Analysis Of The Law Of Smoke Propagation In “θ” Diagonal Pipe Network During Fire

Mine fire is one of the five major disasters in the mine.Due to the narrow and closed roadway space,the rescue of mine fire is much more difficult than that of ground fire.The high temperature caused by mine fire will directly burn down a large number of production facilities and destroy the structure of roadway.The resulting high temperature smoke flow will pollute the working area and threaten the life and health of underground personnel.The thermal power effect caused by high temperature and smoke flow will affect the dynamic distribution of mine ventilation network,and even reverse the airflow.Due to the need of production,the underground is a complex network with angle connection structure,and the mechanism of fire is more changeable,which makes it more difficult to prevent fire and smoke.Therefore,it is of great significance to study the migration mechanism and temperature distribution of smoke in angle connection pipe network during fire.Based on engineering thermodynamics,computational fluid dynamics and other interdisciplinary research methods,this paper conducts a more comprehensive study on the migration mechanism of flue gas,the temperature distribution law of flue gas and the reverse flow phenomenon of flue gas after the fire in the diagonal branch of the pipe network with numerical simulation as the main research method and small-scale experiment as the supplement.The research results obtained mainly include:（1）The hierarchical morphology of flue gas in diagonal branch of classical Froude theory is explained.According to the direction of flue gas movement,it can be divided into three stages:unilateral migration,reverse flow of flue gas and bilateral discharge.The characteristics of flue gas migration in each stage are given,and the left and right correlation points are divided into four research areas in detail.It is obtained that the stability of flue gas layer in Rout and Lin areas is inversely proportional to the wind speed.The small-scale experimental results show that the results are consistent with the numerical simulation when the wind speed is large,and the wind speed is too small..（2）Combined with the previous theoretical model of flue gas temperature attenuation in single tunnel,the distribution of flue gas temperature in diagonal branch and left and right pathways is studied by using simulation data.The optimal St number in the upper and lower reaches of the fire source in the diagonal branch of the attenuation model is different,with 0.009 in the upper reaches of the fire source and 0.0085 in the lower reaches of the fire source.The maximum temperature in the diagonal branch increases first and then decreases with the change of wind speed.The two-stage attenuation process of flue gas temperature in the left and right pathways is given.The temperature attenuation in the left pathway conforms to the Li’s model,and the optimal St number under different wind speeds is determined.The temperature attenuation law in the right pathway is analyzed by surface fitting and multivariate statistical methods.The fitting formula of temperature attenuation in the first stage of the right pathway is given.It is concluded that the fire source distance is the decisive factor of temperature attenuation in the second stage of the right pathway.（3）The occurrence time of the flue gas reverse flow in the corner branch lags behind the fire,and the reverse time is proportional to the outlet wind speed.When the wind speed is 3 m/s,it is a mutation point.The relationship between the reverse distance of the flue gas and the wind speed in the Hu form is fitted.The critical wind speed of the flue gas reverse in the left path is 2.98 m/s,and that in the right path is 4.32 m/s.When the fire power increases,the smoke reverse distance of the left path increases faster than that of the right path,and the temperature of the smoke reverse front in the left and right paths decreases.By introducing the concept of wind speed ratio,it is obtained that the reverse distance of flue gas in the left passage is inversely proportional to the wind speed ratio?₁,and the reverse distance of flue gas in the right passage is directly proportional to the wind speed ratio?₂.