通风管道结构形式对颗粒物沉积的影响

Effect of Ventilation Duct Structure on Deposition of Particles

在矩形断面通风管道无因次颗粒物沉积速率计算结果与相关实验数据验证的基础上,对弯头、变径、三通等通风管道结构内的颗粒物沉积进行了数值模拟.管道流动采用RSM湍流模型,并应用拉格朗日随机轨道模型描述气固两相流动中颗粒运动.结果表明,直管段内无因次颗粒物沉积速率与相关研究结果变化趋势相近,直管段侧壁、顶面无因次颗粒物沉积速率在无因次松弛时间大于1时(粒径约10μm)呈下降趋势.弯头、变径及三通管段内颗粒物沉积率随斯托克斯数(St)增加而升高,当St<0.1时,3种管段结构内颗粒物沉积率均较小且相差较小;当St>0.1时,相同St下弯头内颗粒物沉积率最高,其次为三通和变径.直管段内小粒径颗粒物(<10μm)主要受湍流扩散作用而沉积,对于大颗粒的沉积则主要受重力影响;弯头、变径及三通管段内颗粒St>0.1时,颗粒物的沉积主要受惯性碰撞影响.

Numerical simulation of particles deposition onto the bend, bifurcating duct and reducer was carried out based on comparison of dimensionless deposition velocity with the previous experimental and simulation results in the straight ducts with rectangular cross section. The Reynolds stress transport model was adopted, and a Lagrangian stochastic method of random walk model used to describe motion of particles in a gas-solid phase flow regime. The results show that there exists a similar trend of dimensionless deposition velocity with the relevant research results. However, the dimensionless deposition velocity onto the vertical wall and the ceiling decreases when the dimensionless relaxation time is higher than 1（i.e., about 10 μm）. The deposition efficiency of particulate matter increases with Stokes number（St） in the bend, reducer and bifurcating duct. The deposition efficiency of particulate matter in the three kinds of duct components is small and almost the same for St〈0.1. When St〉0.1, the deposition efficiency of particulate matter in the bend is the highest one, followed by the bifurcating duct and reducer under the same St. The deposition of small particles（〈10 μm） in the straight duct is controlled by the turbulent diffusion and the large particles are mainly affected by gravity deposition. For the bend, bifurcating duct and reducer, the deposition of particulate matter（St〉0.1） is governed by inertia collision.