Granular systems: Magnetic resonance and optical imaging

Experimental measurements of granular dynamics are vital to test theoretical models and to validate numerical simulations. Magnetic resonance imaging (MRI) can provide non-intrusive measurements of particle position and particle velocity in opaque full 3D granular systems. However, one major limitation has been the low temporal resolution of MRI measurements, limiting its application to periodic or stationary systems.

This presentation will describe first advantages and limitations of optical measurements in dynamic granular systems. This is followed by a description of recent advances in MRI technology and methodology that have resulted in a drastic increase in the temporal resolution of MRI based measurements of granular materials. This has been achieved by combining advances in imaging hardware, granular material engineering and accelerated MRI sequence protocols. We have applied the new methodology to a variety of dynamic granular systems such as bubbling fluidized beds, granular flow around gas bubbles or the impact of intruders into granular systems. These measurements provided fresh insight into hitherto undiscovered facets of granular dynamics, such as the non-negligible vorticity of granular flow around gas bubbles in fluidized granular systems. The methodology developed could be used in the future to study other dynamic granular phenomena, such as the jamming transition, granular segregation or wave propagation.

Prof. Christoph Müller received his undergraduate degree (Dipl.-Ing.) from the Technical University of Munich, Germany, in 2004. In 2008 he earned his PhD from the University of Cambridge, UK (Department of Chemical Engineering). In 2010 he was appointed Assistant Professor at  ETH Zurich, Switzerland. Since 2015, has has been an Associate Professor (tenured) of Energy Science and Engineering in the Department of Mechanical and Process Engineering at ETH Zürich. His research interests are the physics of granular media, CO2 capture and heterogeneous catalysis.