How can Sudoku help scientists X-ray granular movements?

Scientists at the University of Sydney have developed a new X-ray method which allows them to see inside granular flows — and the findings could have a big impact on numerous industries.

When strolling along the beach, our footprints tell us that the sand under the surface must have moved but not precisely where or how. Similar movements occur in many other natural and man-made substances, such as snow, construction materials, pharmaceutical powders and even cereals.

To examine these largely unknown granular movements, academics from the Sydney Centre in Geomechanics and Mining Materials (SciGEM) developed a new X-ray method. Named X-ray rheography, or ‘writing flow’, their approach gathers information using three-point high-speed radiography, and then assembles this information by solving a Sudoku-style puzzle.

“Imagine coffee in grinders, rice in silos and minerals on conveyors — for a long time we’ve known that the grains hidden within the bulk move, but until now we have not understood precisely how,” explained Professor of Civil Engineering Itai Einav. “Our X-ray rheography is the first physical method to resolve this.”

The X-ray technique has the ability to form a three-dimensional image of moving grains, which has helped the researchers better understand how particles flow and behave in various circumstances. In many examples they have found that granular media tends to flow in unique patterns and waves.

“Unlike fluids, we discovered that confined, three-dimensional steady granular flows arise through cycles of contraction and expansion, à la ‘granular lungs’,” Prof Einav said. “Again, unlike fluids, we also found that grains tend to travel along parallel lines, even near curved boundaries.”

Experimenting with various granular materials, the team also found that shape is an important factor in determining flow; for example, elongated barley grains move faster than their spherical counterparts. In other situations, different types of grains may have a tendency to group together, much like when emptying a cereal box.

The researchers’ findings can be applied to a number of industries, such as helping develop better silo solutions for edible grains, preventing wastage and spoilage in farming and large-scale food manufacturing, and more efficient transportation and storage of mining resources.

“Until now, understanding granular movements in opaque materials has long been a challenge for many industries such as engineering, science, mining and even agriculture,” said Postdoctoral Research Associate Dr James Baker.

“The potential benefits span many areas, whether it be in understanding the mixing of pharmaceutical powders or the efficient transport of food grains or construction materials.”

The breakthrough is the latest to arise from the researchers’ DynamiX laboratory, a custom-built facility that was established in 2015 to investigate flowing granular media. It has been published in the journal Nature Communications.

Image courtesy of the University of Sydney.

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