Despite its ubiquity, a complete theory to describe the underlying rheology of granular flows remains elusive. Central to this problem is the lack of detailed, in-situ measurements of the granular flow field. To this end, we present two non-invasive imaging techniques currently employed to measure the flow of individual grains within granular flow systems that span simple mono-sized flows of plastic beads to complex industrial mixture flows of rocks and slurry. The first technique employs diagnostic X-rays operated in biplanar mode to triangulate the motion of low-density granules in simplified flow systems to within a 3D spatial accuracy of 0.15 mm at tracking frequencies up to 100 Hz. The second—arguably the workhorse of our research operation—is the nuclear imaging technique of Positron Emission Particle Tracking (PEPT) which triangulates the back-to-back gamma rays emanating from radiolabeled particles to within a millimeter in 3D space at a millisecond timing resolution. PEPT can track the motion of any particle with a diameter greater than ~20 microns. Both techniques are well suited to studying the flow of granular materials after the data is cast into volume and time averages consistent with the continuum framework. In this talk I will explore the many interesting analysis techniques employed to mapping out the complex flow regimes found in typical granular systems, and the insights they offer towards better understanding their rheological character. Examples explored will include rotating drum flows (wet and dry), shear cells and their industrial counterpart the IsaMillTM, hydrocyclone separator flows, and the motivation for tracking of multiple particles—a technique that we have recently developed. The validation offered to numerical schemes like the Discrete Element Method will also be explored wherein we highlight the complimentary role that measurement and simulation play in unraveling the secrets of granular flows. Finally, and deviating somewhat from the imaging world, I will present a new granular rheology that we’ve recently published [PRL 123, 048001 (2019)] and the plans going forward.
Bio: Professor Indresan Govender is the Group Executive of the Mineral Processing & Characterisation (MPC) cluster at Mintek with over 20 years of R&D experience.
Govender graduated with a Ph.D. from the University of Cape Town where he worked for 15 years in physics and engineering. He then joined UKZN as Professor of Particle Technology and Mineral Processing. Indresan maintains an active research relationship with UCT (Centre for Minerals Processing) and UKZN (Chemical Engineering) through his concurrent appointments as an honorary Professor of Particle Technology and Mineral Processing. He currently serves as an executive member of many national and international research bodies working in mineral processing and particle technology. These include the Global Comminution Collaborative (GCC), International Comminution Research Association (ICRA), Minerals to Metals Signature Theme (MtM), Centre for Minerals Research (CMR), and the Centre for Research in Computational and Applied Mechanics (CERECAM).
His research specialization explores complex granular flows with in-situ nuclear imaging measurements via bi-planar X-rays and Positron Emission Particle Tracking (PEPT), continuum formulations of industrial flows, and numerical modeling via the Discrete Element Method (DEM) and Smooth Particle Hydrodynamics (SPH). Specific areas of mineral processing research include experimental, numerical, and theoretical continuum descriptions of free surface flows, like tumbling mills, and confined flows, like the high shear IsaMill and cyclone separator. The experience of continuum modeling frameworks are favored in describing the rheological character of granular flows which fundamentally drives energy dissipation and mixing encountered in most mineral processing systems. In addition to surpassing the interpolation capability of empirical modeling approaches with the mechanistic understanding that can extrapolate beyond the machine’s window of design, the continuum framework is also amenable to spreadsheet-friendly repackaging that can be easily adopted by industrial partners for real-time control strategies.