湍流状态下竖直管道内甲烷-煤尘预混特征及爆炸过程数值模拟

Numerical simulation on the premix properties and explosion process of methane/coal dust mixture in a vertical pipeline under turbulent flow

为揭示管道内甲烷-煤尘预混湍流特征及爆炸火焰传播过程,构建了竖直管道内甲烷-煤尘预混扩散及爆炸物理数学模型;基于流体力学及传热-传质理论,对管道内甲烷-煤尘扩散特征和爆炸过程进行了数值模拟。划分了管道内气固两相扩散特征阶段,分析了初始真空度和进气压力对扩散湍流强度的影响规律;研究了煤尘粒径、浓度及甲烷浓度对爆炸最大压力及最大爆炸压力上升速率的影响特征;揭示了管道内甲烷-煤尘预混爆炸过程中火焰传播特征及爆炸机制。结果表明:煤尘颗粒在竖直管道罐内扩散可分为快速注入、减速分散、稳定和沉降4个连续阶段,初始真空度及进气压力对湍流强度均有影响;爆炸过程中,不同时刻下管道整体爆炸压力场基本均匀分布。甲烷浓度、煤尘浓度及粒径与最大爆炸压力P_(max)及最大爆炸压力上升速率(dP/dt)_(max)均呈现二次函数关系;不同时刻下爆炸火焰结构及火焰高度、火焰传播速度的模拟与试验结果具有较好的一致性,火焰结构呈现"月牙-S-下凹月牙-指尖"传播至爆炸结束。温度分布不均,高温区集中在管道上部和中下部。火焰传播速度先增大后减小,后期呈现震荡性特征。

To reveal the pre-mixed turbulent characteristics and flame propagation process for methane/coal dust mixture in a vertical tube,the physical and mathematical models for dust diffusion and explosion in the vertical pipeline were constructed,respectively.Based on fluid mechanics and heat-mass transfer,Fluent,a commercial code was applied to simulate the dispersion characteristics and explosion process for methane/coal dust hybrid mixture.The characteristic stages for coal dust diffusion in the vertical pipelines were analyzed and divided.Besides,the influence of initial vacuum degree and gas intake pressure on the turbulent characteristic was analyzed,and the evolution mechanism offlow field and temperature field in coal dust/methane explosion in the vertical pipeline was revealed.Moreover,the influence law of methane concentration,coal dust concentration and coal particle size on Pmaxand（ d P/dt）maxwere investigated,in addition,the flame propagation characteristics and explosion process were revealed.Results showed that： discrete phase diffuses in the vertical pipe can be divided into four consecutive stages： fast injection,decelerated dispersion,stability and sedimentation.Besides,both the initial vacuum degree and gas intake pressure have an influence on turbulence intensity.The pressure field inside the pipe was basically evenly distributed at different times during the explosion process.The relationships between methane concentration,coal dust concentration,and coal particle size and Pmaxand（ d P/dt）maxshowed a quadratic function.The flame structure,flame height,and flame propagation velocity obtained by simulation and experiment are consistent at different time,the flame structure showed a ＂crescent-S-concave crescent-finger＂variation trend till the end of the explosion.However,the temperature distribution was uneven,and the high temperature zone was concentrated in the upper and middle of the pipeline. The flame propagation velocity increased quickly at first and then decreased,and finally showed concussion characteristics in the later period.