The effect of solid-phase wall boundary condition on the numerical simulation of gas-solid flow in CFB risers containing FCC particles was investigated using the two-fluid model incorporating the kinetic the- ory of g...The effect of solid-phase wall boundary condition on the numerical simulation of gas-solid flow in CFB risers containing FCC particles was investigated using the two-fluid model incorporating the kinetic the- ory of granular flow. Both the Gidaspow drag model and the EMMS-based drag model were used. The Johnson and Jackson （1987） wall boundary condition was applied to describe the interaction between particles and wall. Based on the experimental system of Li and Kwauk （1994）, parametric studies of spec- ularity coefficient （cp = 1.0, 0.6, 0.0005, 0.00005, 0） and particle-wall restitution coefficient （ew = 0.6, 0.9, 0.95, 0.99, 0.999） were performed to evaluate their effects on axial voidage profile, solids flux, meso-scale and heterogeneous structures. Simulation results showed that solid-phase wall boundary condition had little effect on axial voidage profile when the Gidaspow drag model was used. However, the specular- ity coefficient ~a had a pronounced influence on flow behavior when the EMMS-based drag model was used, and a small specularity coefficient （cp = 0.00005, 0） could result in better agreement with exper- imental data. The particle-wall restitution coefficient ew plays but a minor role in the holistic flow characteristics.展开更多
A computational fluid dynamics （CFD） modeling of the gas-solids two-phase flow in a circulating fluidized bed （CFB） riser is carried out. The Eularian-Eularian method with the kinetic theory of granular flow is us...A computational fluid dynamics （CFD） modeling of the gas-solids two-phase flow in a circulating fluidized bed （CFB） riser is carried out. The Eularian-Eularian method with the kinetic theory of granular flow is used to solve the gas-solids two-phase flow in the CFB riser. The wall boundary condition of the riser is defined based on the Johnson and Jackson wall boundary theory （Johnson ＆ Jackson, 1987） with specularity coefficient and particle-wall restitution coefficient.The numerical results show that these two coefficients in the wall boundary condition play a major role in the predicted solids lateral velocity, which affects the solid particle distribution in the CFB riser. And the effect of each of the two coefficients on the solids distribution also depends on the other one. The generality of the CFD model is further validated under different operatin~ conditions of the CFB riser.展开更多
基金support from the National Basic Research Program(Grant Nos.2010CB226906 and 2012CB215000)the Science Foundation of China University of Petroleum,Beijing(No.KYJJ2012-03-01)
文摘The effect of solid-phase wall boundary condition on the numerical simulation of gas-solid flow in CFB risers containing FCC particles was investigated using the two-fluid model incorporating the kinetic the- ory of granular flow. Both the Gidaspow drag model and the EMMS-based drag model were used. The Johnson and Jackson （1987） wall boundary condition was applied to describe the interaction between particles and wall. Based on the experimental system of Li and Kwauk （1994）, parametric studies of spec- ularity coefficient （cp = 1.0, 0.6, 0.0005, 0.00005, 0） and particle-wall restitution coefficient （ew = 0.6, 0.9, 0.95, 0.99, 0.999） were performed to evaluate their effects on axial voidage profile, solids flux, meso-scale and heterogeneous structures. Simulation results showed that solid-phase wall boundary condition had little effect on axial voidage profile when the Gidaspow drag model was used. However, the specular- ity coefficient ~a had a pronounced influence on flow behavior when the EMMS-based drag model was used, and a small specularity coefficient （cp = 0.00005, 0） could result in better agreement with exper- imental data. The particle-wall restitution coefficient ew plays but a minor role in the holistic flow characteristics.
文摘A computational fluid dynamics （CFD） modeling of the gas-solids two-phase flow in a circulating fluidized bed （CFB） riser is carried out. The Eularian-Eularian method with the kinetic theory of granular flow is used to solve the gas-solids two-phase flow in the CFB riser. The wall boundary condition of the riser is defined based on the Johnson and Jackson wall boundary theory （Johnson ＆ Jackson, 1987） with specularity coefficient and particle-wall restitution coefficient.The numerical results show that these two coefficients in the wall boundary condition play a major role in the predicted solids lateral velocity, which affects the solid particle distribution in the CFB riser. And the effect of each of the two coefficients on the solids distribution also depends on the other one. The generality of the CFD model is further validated under different operatin~ conditions of the CFB riser.
