Compared to transient simulation,steady-state simulation of circulating fluidized bed risers is more efficient,but is also harder to perform due to the complex scale-dependency of dense gas-solid flows.In this work,st...Compared to transient simulation,steady-state simulation of circulating fluidized bed risers is more efficient,but is also harder to perform due to the complex scale-dependency of dense gas-solid flows.In this work,steady-state computational fluid dynamics(CFD)simulation of a riser is performed using the steady energy-minimization multi-scale(EMMS)drag.It is found that the steady state corresponds to an extremely large scale of length and time,thus the grid size required in steady-state simulation is larger than that in transient one.The time-averaged two-fluid model(TFM)coupled with the steady-state EMMS/1M drag model enables a good prediction of the S-shaped,axial solids distribution and the choking transition,whereas the two-phase turbulence and solids stress models are important in predicting the radially core-annular distribution of solids.So far as we know,this is the first time that one can predict the choking transition in a steady-state CFD simulation.Further improvement may need an EMMS modeling of the time-averaged solid stresses.展开更多
基金supported by the National Natural Science Foundation of China(grant Nos.22208351,22161142006,21821005)the State Key Laboratory of Mesoscience and Engineering,Institute of Process Engineering,Chinese Academy of Sciences(grant Nos.MESO-23-D03,MESO-23-A02)the Strategic Priority Research Program of the Chinese Academy of Sciences(grant No.XDA0390502).
文摘Compared to transient simulation,steady-state simulation of circulating fluidized bed risers is more efficient,but is also harder to perform due to the complex scale-dependency of dense gas-solid flows.In this work,steady-state computational fluid dynamics(CFD)simulation of a riser is performed using the steady energy-minimization multi-scale(EMMS)drag.It is found that the steady state corresponds to an extremely large scale of length and time,thus the grid size required in steady-state simulation is larger than that in transient one.The time-averaged two-fluid model(TFM)coupled with the steady-state EMMS/1M drag model enables a good prediction of the S-shaped,axial solids distribution and the choking transition,whereas the two-phase turbulence and solids stress models are important in predicting the radially core-annular distribution of solids.So far as we know,this is the first time that one can predict the choking transition in a steady-state CFD simulation.Further improvement may need an EMMS modeling of the time-averaged solid stresses.
