A numerical study of the influence of operating conditions of a blade free planetary mixer on blending of cohesive powders

A blade-free planetary mixer provides an effective and rapid mixing of cohesive powders due to its powerful centrifugal agitation capability to produce a swirling flow pattern in a mixing vessel. Despite its popular use in the powder processing industry, the dynamics and characteristics of blade-free planetary mixing are still not well understood because of a lack of experimental and numerical studies. This paper presents a discrete element study of the influence of operating parameters such as the steady-state revolution speed and the rotation-to-revolution speed ratio on bending of pharmaceutical powders with specific cohesiveness. The particle-level cohesive forces were calculated using the Johnson-Kendall-Roberts cohesion model. A series of discrete element simulation was carried out at some range of revolution and rotation speeds of a mixing vessel. The degree of mixing in each simulation was quantified with the mixing index and mixing time. The simulation results showed a faster rotation speed and a higher rotation-to-revolution ratio provided more effective mixing of the specific microcrystalline cellulose powder. The methodology and results of this numerical study can be used to determine the optimal operating conditions of a blade-free planetary mixer for effective mixing of cohesive powders.