立式上行管内液固两相流中椭球形颗粒分布和运动特性

Distribution and motion characteristics of ellipsoidal particles in liquid-solid two-phase flow in vertical upward pipe

为了进一步阐述列管式换热器中椭球形颗粒液固两相流流动机理,基于CFD-DEM耦合方法,模拟分析立式上行换热管内椭球形颗粒长径比β、颗粒体积分数α对颗粒分布和运动特性影响;分析液固两相稳定运动后的相对速度,采用滑移系数对颗粒跟随性演变规律进行量化。结果表明:动态稳定周期内,横截面上颗粒径向分布在任意时刻均相似,且颗粒随流体自下向上运动过程中,颗粒在径向方向上逐渐集中到近壁区域,管中心区域颗粒相对体积分数较小;椭球形颗粒滑移系数均大于球形颗粒的,当β=1.5时,椭球形颗粒滑移系数最大。

In order to explain the liquid-solid two-phase flow mechanism of ellipsoidal particles in the tubular heat exchanger,based on the CFD-DEM coupling method,the effect of the length-diameter ratioβand the particle volume fractionαof the ellipsoid particles on the particle distribution and motion characteristics were simulated and analyzed in the vertical upward heat transfer tube.The relative velocities of liquid-solid two phases after stable motion were analyzed,and the slip coefficient was used to quantify the evolution of the particle following.The results show that the radial distribution of particles on the cross section is similar at any time during the dynamic stability period,and when the particles move from bottom to top with the fluid,they slowly approach the wall in the radial direction of the tube,and the relative particle volume fraction in the center of the tube become lower.The slip coefficient of ellipsoidal particles is greater than that of spherical particles,whenβis 1.5,the slip coefficient of ellipsoidal particles reaches the greatest.