Numerical study of the solid flow behavior in a rotating drum based on a multiphase CFD model accounting for solid frictional viscosity and wall friction

In continuum-based models, the kinetic theory of granular flow (KTGF) provides a model for calculating solids stresses but has limitations in densely packed regions such as mills, kilns and rotating drums. The Eulerian-Eulerian multiphase model coupled with KTGF is evaluated in the present work. An additional frictional stress models were added, and their suitability evaluated. For the evaluation, a rotating drum at three rotational speeds (20 rpm, 42 rpm and 65 rpm) was analyzed. Compared with Positron Emission Particle Tracking (PEPT) measurement data from literature, Johnson and Jackson's model and Schaeffer's model for the frictional stress both showed a lower angle of repose regardless of the wall boundary condition used. Thus, a new frictional viscosity model based on granular pressure was proposed. By adjusting the specularity coefficient of wall boundary condition, results of the present model agreed well with the PEPT measurements in terms of angle of repose and spatial velocity fields. In addition, considering that the actual Johnson and Jackson model for boundary condition includes two parts, collisional and frictional part, a discussion was made about boundary condition. The results showed that the validation of the proposed frictional viscosity model with experimental results could be completed at different rotational speeds by considering only the collisional part of the boundary condition with different specularity coefficients or only the frictional part of the boundary condition with different angles of friction or both parts with the same specularity coefficient and angle of friction. Nevertheless, when the complete Johnson and Jackson model of boundary condition was applied, the same specularity coefficient and angle of friction are used at different rotational speeds which is more physically meaningful. Moreover, it is found that the frictional contribution has greater influence on dynamic angle of repose than collisional contribution of the boundary condition in the current rotating drum. (C) 2019 Elsevier B.V. All rights reserved.