Dem investigation of horizontal high shear mixer flow behaviour and implications for scale-up

• Internal flow and behaviour in batch horizontal mixers are studied using DEM.
• Impact of scale, impeller speed, fill level, gap and particle size are studied.
• Particle velocity correlates with the relative swept volume in these mixers.
• Flow is sensitive to particle size below a critical bed thickness-gap size ratio.
• Kinematic similarity scaling depends on impact of gap size.

In high shear granulation, various dimensionless or dimensioned parameter groups such as constant Froude number, tip speed, relative swept volume and specific energy input are commonly used as scale-up criteria, in order to maintain the powder bed internal flow or stress field across scales. One major challenge is obtaining the internal flow and stress field through experimentation given the lack of precise measurement techniques. Hence, this work employs DEM (discrete element method) simulations to study the internal flow patterns and behaviour of different scale batch, horizontal high shear mixers. The simulations provide a deeper understanding of the interaction of scale, impeller speed and fill level on the flow field, and show that the particle velocity is correlated with the relative swept volume in these mixers. It shows that the relative particle velocity is correlated, independent of scale, to the relative swept volume per rotation and highlights its values as a parameter for understanding and comparing mixer behaviour. The work also demonstrates the importance of the particle size chosen for the simulation as well as the tool-wall gap in the mixer, and highlights its importance as we interpret DEM results.

In horizontal high shear mixers, the relative particle velocity is correlated to the relative swept volume per rotation, independent of scale. The relative swept volume is determined from geometrical parameters and fill levels, and is therefore useful in predicting impact of scale even if the mixers are not geometrically similar.Figure optionsDownload as PowerPoint slide