(550e) Cfd Simulation Of Mixing And Segregation Pattern In A Double Cone Blender

Granular mixing and segregation is a vital operation in food, chemical and pharmaceutical industries. Although the tumbling blender (such as V-blender, double cone blender and tote blender) are widely used to mixing of powder and granular, little is known about the flow pattern in these devices [1]. Validated simulation results can be useful in characterizing and quantifying these processes to help with process design and scale-up.

The flow pattern within these blenders is believed to consist of a thin, rapid flow regime near the surface, a much dense regime that dominated by particle enduring contact and a narrow transition regime between the first two regimes. In the rapid flow region, particle-particle interactions occur largely due to the random fluctuation of particle and binary collision between particles. In the dense regime, the particles start to endure long, sliding and rubbing contacts, frictional interaction is more important. One of the commonly used modeling approaches is the Discrete Element Model (DEM) to simulate the blender. This is a lagrangian based direct numerical simulation technique and has practical limitations when dealing with billons of particles common to these powder mixing devices. The authors propose the use of a Eulerian model with frictional effects to model the dense phase flow.

A 3D simulation for a double cone blender with small and larger particles was done using the Eulerian multiphase model along with formulations for frictional viscosity and frictional pressure to study the mixing and segregation phenomena. The results are then compared with the DEM simulation and experiment results of Muzzio et al [2]. The simulation successfully predicts the segregation pattern observed in the blender. It shows the small granules form a contiguous core parallel to the axis of rotation, and larger particles accumulate at the bottom of the cone and in the middle section of the top face. There is a distinct flowing layer near the surface and a region beneath that moves slowly as a single unit. The intensity of segregation rate is also compared with DEM simulation. The effect of blender speed and fill level were also studied.

Although this is a preliminary work in demonstrating an alternative practical engineering work, this establishes the foundation for more research and study to develop constitutive equations for frictional forces for dense phase flow as this can have strong impact in enhancing our knowledge of powder handling processes.

[1] Maher Moakher, Troy Shinbrot and Fernando J. Muzzio , Experimentally validated computations of flow, mixing and segregation of non-cohesive grains in 3D tumbling blenders , Powder Technology, 109 (2000), 58-71

[2] Albert Alexander, Troy Shinbrot, Barbara Johnson and Fernando J. Muzzio, V-blender segregation patterns for free-flowing materials: effects of blender capacity and fill level. International journal of pharmaceutics, 269 (2004), 19-28