Understanding the effect of fluid viscosity in vertical stirred mills using the Positron Emission Particle Tracking (PEPT) approach

In this paper, the Positron Emission Particle Tracking (PEPT) technique demonstrates how interstitial fluid viscosity affects media dynamics within a Vertical Stirred Mill. This is the first full paper facilitating direct, experimental insight into the role fluids play on the three-dimensional dynamics of a vertical stirred mill. Three different silicone oils were used to explore the impact of slurry viscosity, These model oils offered more controllable properties than the particle-laden slurries used in grinding making testing a fairer comparison. Higher viscosity oils created a greater damping effect on the grinding media contacts by increasing drag force, resulting in a larger, more tightly packed media bed and reducing the average velocity by up to 40%. This would be expected to reduce grinding efficiency due to a smaller high-energy region at the free surface. Quantifiable measures of net force and power demonstrated that the media had greater force and were more efficient with low-viscosity oil and higher attritor speeds, reducing power consumption by over two-thirds. The rich three-dimensional data collected can also be used to calibrate computer models of the mill in future research, enhancing the overall understanding of this intricate system. A link to the raw data can be found at https://doi.org/10.5281/zenodo.13310563 so other researchers can calibrate a mill simulation for their own work.