Mixing Rules for Powder Mixing

Executive Summary

relations based directly upon PEPT-derived stress computations.

in greater detail in the next phase of the project wherein we formulate mixing scaling

timescale to the macroscopic shearing timescale more naturally. This idea will be explored

like the Inertial number, also appears to describe the ratio of the microscopic rearrangement

extend beyond simply quantifying the relative importance of advection and di.usion, and

number that is computed directly from the PEPT data. Interestingly, it’s validity seems to

an alternate definition. In this regard we propose a granular temperature-dependent Péclet

The limitations in the standard definition of the Péclet number precipitated the need for

mills) that operate in the high Froude regimes.

the data. These findings have significant implications for industrial systems (like tumbling

cascading and cataracting) the Reverse Brazil Nut E.ect (RBNE) is clearly evident from

the Brazil Nut E.ect (BNE) at low Froude numbers; however, at higher Froude numbers

The initial analyses of PEPT data clearly show radial segregation by size consistent with

developed flow conditions.

assumption, we extract the bed shape, solids fraction and kinematics for steady, fully

of representative radio-labelled beads (the tracer) into Eulerian fields under the ergodic

and cataracting Froude regime. After converting the measured Lagrangian trajectories

matrix spanned four fill fractions and seven drum rotation rates across the cascading

plastic beads) within a laboratory rotating drum fitted with lifter bars. The experimental

was used to measure the 3D trajectory of a binary mixture (3mm and 5mm diameter

In our first phase of the project (year one) Positron Emission Particle Tracking (PEPT)

many investigators that ultimately lead to a restricted mechanistic interpretation.

is not well understood. A further limitation relates to the low Froude regimes explored by

known to exhibit axial and radial mixing; however, their interplay for optimal performance

system encountered in the mineral processing, food and pharmaceutical industry is well

the high shear zones where most of the energy is dissipated. The canonical rotating drum

processes is the inability to control the relative mix of grinding balls and small rocks in

ingredient and excipient. Central to the low efficiency (< 5%) reported in mineral grinding

industry, the e.ectiveness of the drug is directly related to the mixture of active

Mixing (and segregation) play a vital role in several industrial processes. In the pharmaceutical