循环流化床内颗粒的加速作用及气固两相间的动量交换

THE PARTICLE ACCELERATION AND THE INTERACTION BETWEEN GAS AND SOLIDS IN THE RISER OF CIRCULATING FLUIDIZED BEDS

根据对气固两相流动特性的分析,表明在循环流化床提升管内,颗粒的加速运动及气固两相间的动量交换对床层各项参数具有明显的影响。由于颗粒聚集,减小了气固两相间的相互作用,使曳力系数小于单颗粒标准曳力系数(C_D/C_(DS)<1.0)。从而使颗粒具有较长的加速段,其加速压降在总压降中所占的分率不可忽略。考虑颗粒加速作用及由于颗粒聚集使气固两相相互作用力减小的事实后,用一维轴向稳态流动的模型可以获得截面平均空隙率、平均颗粒速度以及曳力系数等参数及其轴向分布规律,并与实验直接测定结果吻合很好。通过对大量数据的分析,表明C_D/C_(DS)可用下述经验关联式表示:C_D/C_(DS)=1.68(ε)^(0.253)(Re_(?)/Re_t)^(-1.213)(d_P/D)^(0.105)

In this paper the influence of particle acceleration and the interaction between gas-solilds phases on the flow pattern of circulating fluidized bed were analysed.Due to the particle aggregation the interaction force between gas and solids in circulating fluidized bed was significantly decreased.The length of acceleration region in circulating fluidized bed is longer,and the fraction of pressure drop contributed by particle acceleration in total pressure drop of this regime is greater than those expected in the literature. Considering all the above,a one-dimensional steady flow model,which can predict the axial distribution of cross-sectionally averaged voidage, average particle velocity,bed pressure and drag coefficient in circulating fluidized bed is put forward in the present study.The predictions by this model agree well with the experimental results reported in our laboratory and in the literature.