超细干粉气固两相流在水平直管中的流动特性研究

Research on flow characteristics of ultra-fine dry powder gas-solid two-phase flow in horizontal straight pipe

采用Fluent软件,利用欧拉多相流模型模拟了粒径为18μm的超细干粉灭火剂在直径8 cm的水平直管内喷射时的沿程阻力、横截面上的流速及干粉体积分数分布特点。结果表明,在流速为25~150 m/s和超细干粉体积分数为5%~15%时,水平直管的沿程阻力与流速呈二次函数关系,与干粉的体积分数呈一次函数关系,阻力值为0.003 28~0.259 81 MPa/m。受管壁摩擦力影响,两相流在管道横截面上的流速呈现中间快四周慢的分布特点,而固体颗粒体积分数对流速的影响可以忽略。横截面上的速度分布不同所产生的气相曳力导致超细干粉体积分数呈环状分布,气相曳力与初始速度有关,与干粉体积分数无关。流速低于70 m/s时超细干粉呈月牙状分布,管道下部贴近管壁位置体积分数最高,超过此流速时,超细干粉在横截面上0.8r~0.9r范围内体积分数最高,呈环状分布,贴近管壁位置体积分数最低,流速大于70 m/s可有效抑制超细干粉沉降。

Fluent software was used and the Euler multiphase flow model was used to simulate the along-path resistance, flow velocity and dry powder concentration distribution characteristics of ultra-fine dry powder fire extinguishing agent with a particle size of 18 μm sprayed in a horizontal straight pipe with a diameter of 8 cm. The results show that in the range of flow velocity 25~150 m/s and ultrafine dry powder volume fraction 5%~15%, the resistance along the horizontal straight pipe has a quadratic function relationship with the flow velocity, and a linear function relationship with the dry powder volume fraction.The range of resistance value is 0.003 28~0.259 81 MPa/m. Affected by the friction of the pipe wall, the flow velocity of the two-phase flow on the cross section of the pipe presents a distribution characteristic of fast in the middle and slow in the surrounding area, and the effect of the volume fraction of solid particles on the flow velocity can be ignored. The gas-phase drag force generated by the different velocity distributions on the cross-section leads to the annular distribution of the ultrafine dry powder volume fraction. The gas-phase drag force is related to the initial velocity and has nothing to do with the dry powder volume fraction. When the flow rate is lower than 70 m/s, the ultra-fine dry powder is distributed in a crescent shape, and the volume fraction of the ultra-fine dry powder is the highest at the lower part of the pipeline close to the pipe wall. The volume fraction is the lowest near the pipe wall, and the flow velocity is greater than 70 m/s, which can effectively inhibit the sedimentation of ultra-fine dry powder.