Numerical Study On Flue Gas Temperature Characteristics In Tall Building Shafts In Different Seasons

In recent years,the urbanization process is accelerated,and the high-rise buildings are increasing.Once a fire occurs,it will cause huge casualties and economic losses.Building shaft is the main channel of fire spread,and it may expand the scope of fire spread under the chimney effect.Therefore,studying the smoke temperature distribution law in high-rise building shaft is helpful to take effective smoke prevention and exhaust measures,formulate evacuation plan,and protect personal and property safety.Based on the engineering background of a high-rise building in the north of China,the 15th floor elevator shaft structure is simplified into a two-dimensional model.Numerical simulation is used to study the smoke flow problem during fire under the chimney effect in winter and the inverse chimney effect in summer.The fire conditions of different fire source locations and different fire source heat release rate are simulated,and the temperature rise distribution,smoke rise law and the change of thermal pressure difference inside and outside the shaft are analyzed,which provides suggestions for high-rise building evacuation in the case of fire.The main conclusions are as follows:Under the action of chimney effect in winter,the overall temperature rise distribution in the shaft structure decreases with the increase of height in the fire condition of the first floor.The smaller the power of the fire source is,the more uniform the temperature rise distribution of each layer in the shaft.Near the fire source,the flow structure in the shaft presents a quasi-periodic development with time.The temperature appreciation and fluctuation range of the local measuring points in the structure increase with the increase of the power of the fire source.For fires on different floors,the law of smoke rise is roughly the same,and the dimensionless time of smoke rise has an exponential relationship with the dimensionless height.The greater the distance from the neutral surface,the greater the pressure difference between inside and outside the shaft.The extreme pressure difference of fire condition on the first floor and the fifth floor appears on the first floor and the 15th floor respectively.The fire causes the neutral surface of the shaft to shift,and the higher the fire source location,the more obvious the neutral surface shift.Under the inverse chimney effect in summer,the fluctuation range of temperature rise at each measuring point in the 11th floor fire condition increases with the increase of fire heat release rate.When the fire heat release rate is less than 2.5 MW,the quasi-periodicity of temperature rise is stronger,and when the fire heat release rate increases,the quasi-periodicity of temperature rise is weaker.There is an exponential relationship between dimensionless temperature rise and height in each fire condition,θ=A×B^H/D.With the increase of heat release rate of fire source,the variation trend is roughly the same,but the fitting parameter A gradually increases and the fitting parameter B gradually decreases.In both high-power and low-power fires,the maximum value of dimensionless temperature rise increases with the increase of fire floor height.The fire occurs within a certain range（above the neutral plane）,and the higher the fire source is,the more obvious the neutral plane shifts,which is consistent with the chimney effect in winter.The extreme pressure difference of the fire source on the 11th floor,13th floor and 15th floor is-30.2 Pa,-24.3 Pa and-15.9 Pa respectively.The higher the fire source is,the smaller the extreme pressure difference is.