May 9 (UPI) -- To the surprise of scientists, sand behaves a lot like oil when conditions are right.
An improved understanding of the behavior of grain particles could help manufacturers more efficiently process granular materials.
The physical laws that govern liquids are well defined, but the behavior of granular materials remains poorly understood. Modeling the behavior of complex solution or mixtures is especially difficult.
Through a series of lab tests, scientists determined granular mixtures, under just the right conditions, behave similarly to immiscible liquids like oil. Both follow similar physical laws.
For one of the tests, scientists put heavy and light grains into a cylinder and passed air through it from below. The grains became "fluidized," or began behaving like a liquid.
When scientists mixed lighter sand with heavy sand, the lighter, less-dense sand began forming globule-like structures as they migrated upwards.
"The grains actually behave similar as oil in water would," said Christopher McLaren, a doctoral student at ETH Zurich. "A complex interaction occurs between the two materials."
Globes of heavy grains embedded in lighter sand don't simply sink to the bottom. Instead, they dissipate. The disintegrated branches of heavy grains becomes stretched and fainter over time.
Researchers described their study of granular dynamics this week in the journal Proceedings of the National Academy of Sciences.
The findings could help engineers working with sands or food manufacturers working with flour and rice. An improved understanding of granular dynamics could even help drug makers.
"If, for example, a pharmaceuticals manufacturer wants to produce a very homogeneous powder mixture, it has to understand the physics of these materials in detail, so that it can control the process," said postdoctoral researcher Alexander Penn.