To consider the critical effect of mesoscale structure on the drag coefficient, this paper presents a drag model based on the energy-minimization multiscale (EMMS) approach. The proposed structure parameters are obtained from the EMMS model, and then the average drag coefficient can be calculated from the structure parameters and further incorporated into the two-fluid model to simulate the gas-solid flow in a circulating fluidized-bed riser. Simulation results indicate that the simulated flow structures are different for the EMMS-based drag model and the hybrid model using the Wen and Yu correlation and the Ergun equation. The former shows its improvement in predicting the solids entrainment rate, the mesoscale heterogeneous structure involving clusters or strands, and the radial and axial voidage distributions. The simulation results support the idea that the average drag coefficient is an important factor for the two-fluid model and suggest that the EMMS approach could be used as a kind of multiscale closure law for drag coefficient.

Simulation of Heterogeneous Structure in a Circulating Fluidized-Bed Riser by Combining the Two-Fluid Model with the EMMS Approach

Aggregation behavior of nanoparticles in fluidized beds

Kinetic theory based CFD simulation of turbulent fluidization of FCC particles in a riser

Continuum theory for dense gas-solid flow: A state-of-the-art review

Solids motion in bubbling gas fluidised beds

Normal solid stress in fluidized beds

Despite concentrated research efforts devoted to the study of the two-phase fluid mechanics of fast fluidized beds (FFBs), the particle phase stresses in FFBs are not well-characterized. To address this problem, measurements were made of the local time-averaged solid pressure in a FFB riser for a wide range of flow conditions and bed locations. The solid-pressure values, which were several orders of magnitude smaller than the gas pressure, were found to vary primarily with the local time-averaged solid concentration. Using constitutive relations from the kinetic theory of particulate flow, values of local time-averaged solid-phase shear viscosity were calculated from the measured solid pressure and solid fraction. The calculated viscosity values were found to be intermediate within the rather wide range of estimated values previously used in various two-fluid models for dilute vertical gas-particle flow.

William Polashenski

Papers

Normal solid stress in fluidized beds

Measurement of particle phase stresses in fast fluidized beds