Experimental investigation of solid mixing and segregation in a tetrapodal blender

Author-Highlights
• The performance of the tetrapodal blender is compared to that of the V-blender.
• The mixing mechanisms are more efficient in the tetrapodal blender than the V-blender.
• The tetrapodal blender is less prone to granular segregation than the V-blender.
• A criterion is provided for the scale-up of tumbling blenders.

Known limitations of tumbling blenders (weak diffusive axial mixing and segregation of free flowing granules) have provided the motivation to investigate the flow and mixing of granules inside a tetrapodal blender. This blender can be thought of as two V-shaped pairs of arms connected and twisted at their bottom ends. In this work, more than 100 experiments were carried out under a wide set of operating conditions and geometrical configurations. Compared to the conventional V-blender, this geometry is shown to provide shorter mixing times and better axial and radial mixing efficiency, especially when its upper or lower V-shaped part is twisted by 45° with respect to the rotation axis. Segregation of granules with different sizes and densities was investigated for varying rotational speeds (5–30 RPM) and fill levels (35–65%V). It is observed that the segregation intensity is far less important in the tetrapodal blender than in the V-blender, and that it decreases significantly with an increase in rotational speed, the effect of the fill level being insignificant. It is also shown that kinetic sieving is the main governing mechanism for the segregation of granules. Finally, a criterion is proposed for the scale-up of the tetrapodal blender and the V-blender so that they may operate efficiently, without pronounced segregation.