Real-time imaging of internal grain motion with high-speed MRI
A group of researchers led by Associate Professor TSUJI Takuya, Graduate School of Engineering, Osaka University, Professor Christoph Müller and Graduate Student Alexander Penn at the Swiss Federal Institute of Technology in Zurich, and Professor Klaas Pruessmann at University of Zurich, succeeded in real-time observation of incoherent particle motion in granular beds, which is usually difficult to see.
Granular materials, a group of solid particles, are seen as natural phenomena such as pyloclastic flow, avalanches, and landslides, as well as in various industrial equipment. It is said that two-thirds of raw materials used in chemical industry are granular materials. Thus, it’s important to understand particle motion when promoting efficiency of chemical processes and energy saving.
When granular materials are mixed with gas and/or liquid, their behavior is very complicated. Because images of samples using magnetic resonance imaging (MRI) can be obtained without disturbing and destroying the sample, MRI has been anticipated to be used for observing internal grain motion; however, it was difficult to observe incoherent motion because of its low temporal resolution.
This group has enabled high-speed imaging of the inside of granular beds with a temporal resolution of several milliseconds by using spherical noncohesive core-shell particles containing middle-chain triglyceride oil with tailored mechanical and nuclear magnetic resonance (NMR) properties, as well as 16 radio frequency (RF) receiver coils and a parallel imaging method. With this method, it is possible to achieve image acquisition with a spatial resolution of 3 mm ×5 mm ×10 mm and a temporal resolution of 7 ms for a field of 200 mm ×300 mm.
In addition, using this method, this group succeeded in observing bubbles grow, merge, and split up in fluidized beds, as well as the propagation of shock waves in granular beds in detail. They also performed measurements of particle distribution and instantaneous particle velocity distribution around rising bubbles with this method.
When a large object is penetrating into a granular bed, shock waves are generated; however, it is a high-speed phenomenon, so the details were not known. This group’s method has enabled a detailed observation of spatial distribution of shock waves.
This group’s high-speed measurement method will promote the better understanding of physical phenomena in granular materials. Their achievement will lead to the understanding of various granular-related natural phenomena and efficiency improvement and energy saving in powder processing based on optimal design and management. This group’s method will also be used for evaluation and improvement of mathematical models for computer simulation of powder mechanics which has been actively performed in recent years.
Abstract
Granular dynamics govern earthquakes, avalanches, and landslides and are of fundamental importance in a variety of industries ranging from energy to pharmaceuticals to agriculture. Nonetheless, our understanding of the underlying physics is poor because we lack spatially and temporally resolved experimental measurements of internal grain motion. We introduce a magnetic resonance imaging methodology that provides internal granular velocity measurements that are four orders of magnitude faster compared to previous work. The technique is based on a concerted interplay of scan acceleration and materials engineering. Real-time probing of granular dynamics is explored in single- and two-phase systems, providing fresh insight into bubble dynamics and the propagation of shock waves upon impact of an intruder. We anticipate that the methodology outlined here will enable advances in understanding the propagation of seismic activity, the jamming transition, or the rheology and dynamics of dense suspensions.
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To learn more about this research, please view the full research report entitled " Real-time probing of granular dynamics with magnetic resonance " at this page of the Science Advances website.
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