Working with sand isn’t child’s play

Mustard seeds used in experiments around granular flow.

Ever wonder how an hour glass measures time? Who designed it, did the math, tested it and perfected it? Working with sand may sound like child’s play, but the process of understanding how these materials behave is the focus of scientists around the world - and it can mean big money and safer communities.

Granular materials, like sand, fascinate physicists, engineers, mathematicians, and other scientists. Granular materials include minerals, wheat grain, pharmaceutical powders, food powders, sugar grains, and seeds, adding up to multi-trillion-dollar enterprises. However they also include natural granular flows, like avalanches, landslides and more, with the understanding of their behaviour key to mitigating destruction from these natural events.

Massey’s Dr Luke Fullard is interested in both of these types, but his latest research looks into how these materials, like sand, behave in silos.

“The behaviour of gas and liquids in silos has been well studied and modelled, but there is a lot to be learnt about granular materials like sand – they are tricky as they can behave like solids, like liquids and even like gas. When you are trying to model the behaviour of granular particles, it is impossible to model every particle individually, so my research focuses on methods to treat flowing granular material like a continuous fluid.”

Changing the gap.

The physics of flow

The dynamics of granular flow from a silo with two symmetric openings, was published in the Royal Society journal Proceedings, describes the behaviour of sand draining out of a silo.

This project involved developing mathematical models followed by lab experiments in silos help to understand the physics of the flow and to generate data to validate the mathematical models. In these models, the distance between the two openings was studied in how it changes the flow rate.

They found that the flow rate is highly dependent on the spacing between the two openings with a complicated interference behaviour between the two openings – make them too wide or two narrow and the flow rate changes.  

“These results aid understanding of granular physics, particularly granular interference phenomena. The results may also have implications for industrial silo design, giving valuable information for how grains or powder behaviour when being processed.”

Dr Luke Fullard with the small-scale model.

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