小管径-粒径比颗粒无序堆积通道内壁面效应数值研究

Numerical simulation of wall effect in randomly packed bed with low tube to particle diameter ratio

采用DEM-CFD方法对小管径-粒径比颗粒无序堆积通道内壁面效应进行了数值研究。针对D/dp=5.0圆球无序堆积通道构建了光滑壁面和波节壁面两种通道壁面结构,分析了不同壁面结构堆积通道内孔隙率分布、流动和温度场分布及其流动换热性能。结果表明:小管径-粒径比光滑壁面颗粒无序堆积通道内壁面效应显著,壁面附近平均流速明显高于堆积中心区域,而平均温度要低于堆积中心区域,壁面附近0.5dp区域内通过的流体质量流量比例为46%;波节壁面结构抑制了通道壁面附近漏流,可小幅提高堆积通道的换热能力,但堆积通道内的流动阻力也随之增大,其综合换热性能较光滑壁面堆积通道有所下降。

The wall effect in randomly packed bed with low tube to particle ratio is numerically investigated by coupling discrete element method(DEM)and computational fluid dynamics(CFD).The porosity,characteristics of fluid flow and heat transfer in randomly packed beds are carefully studied,including smooth tube wall model and corrugated tube wall model.Simulation results show that,the wall effect in smooth wall packing with low tube to particle diameter ratio is remarkable.The average velocity of the near tube wall region is higher than inner region,while the average temperature of this region is lower.Besides,the mass flow rate in the range of 0.5dpnear the tube wall is about 46% of the total flow.With corrugated structure,the leakage near the tube wall is suppressed and the mass flow rate decreases to36%.The heat transfer characteristics and drag coefficient have a slight increase,while the overall heat transfer coefficient is lower than smooth tube wall model.