颗粒床内固液过滤的三维CFD-DEM模拟

Three-Dimensional CFD-DEM Simulation of Solid-Liquid Filtration in Granular Bed

通过将计算流体力学(CFD)与离散单元法(DEM)相耦合,对高20 mm、颗粒直径为1.0 mm的三维随机堆积颗粒床进行了固液过滤模拟研究。结果表明,过滤效率的模型计算值和实验值偏差在10%以内,压降实验值与Ergun方程计算值的偏差在25%的有效范围内。模拟结果显示:床层拦截的杂质颗粒数量从上到下呈现减少趋势,靠近入口处的杂质颗粒成团趋势明显;随着床层高度逐渐加深,床层积累的杂质颗粒数量越来越均匀;随着过滤时间的延长,不同杂质颗粒的过滤效率均有所提高,但床层压降也逐渐增大。

A three-dimensional randomly packed granular bed with a height of 20 mm and a granular diameter of 1.0 mm was simulated on the basis by coupling of computational fluid dynamics(CFD)and discrete element method(DEM)for liquid-solid phase filtration.Fluid flow and particle deposition characteristics were analyzed,and effects of deposition growth on the filtration efficiency and pressure drop were investigated as well.The results show that with deepening of the filter bed,the initial pressure drop is gradually increased.Compared with the values from Ergun equation,the calculation deviations of the initial pressure drop at different fluid flow rates are within 25%.The initial filtration efficiency for larger particles is higher,and it decreases with the velocity of fluid flow.On the basis of regression analysis,it can be predicted that the deviations between the predicted and the experimental values are within 10%.In addition,the particle deposition fraction in the filter bed decreases with the depth of the filter bed,and particles near the inlet incline to form clusters,and their proportion at the early stage of filtration becomes prominent.When the filtration goes gradually deepening,the numbers of particles that accumulated along the bed become more and more even.The deposition of particles influences the flow of fluid within the filter column,which subsequently affects the filtration efficiency and pressure drop.For the particles in different sizes,the deposition growth on the granular surface leads to an increasing trend of filtration efficiency and pressure drop.