My students need to get their hands dirty in the lab, mess up and devise better solutions. That’s far more valuable than a lecture on how to do science.

Brian Utter

Equations describing the behavior of fluids are well established, but the behavior of granular material, such as powders and sand, is highly unpredictable. Professor Brian Utter, physics & astronomy, researches granular flow — the complex ways grains interact through simple mechanisms like friction and contact. It's an area with geological implications as well as applications for industry.

"Imagine sand flowing through an hourglass," Utter says. "Suddenly, there's a bottleneck, and the grains are stuck. We can remedy this is by adding pressure or creating vibration."

The process gets complicated in multiphase flow, which involves the addition of fluid or materials with different states, phases or chemical properties. "Earthquakes are good examples," says Utter. "We study where the system fails. At what point does an earthquake cause sand to liquefy and become quicksand?"

Utter says he enjoys working with small groups of students to define problems, design experiments and create equipment to test solutions. "That's the fun of experimental science," he says. "My students need to get their hands dirty in the lab, mess up and devise better solutions. That's far more valuable than a lecture on how to do science."

Working closely with students allows Utter to tailor experiments to suit their interests. "We started working with hydrophobic sand, which repels water and is sold as 'magic' sand, because someone had received it as a gift," he says.

Hydrophobic powders have many industrial applications, notes Utter, and magic sand is in an excellent model for studying how these substances behave. When exposed to water, the grains adhere to one another to minimize surface area, which affects how they mix and flow. "Powders used by pharmaceutical companies in the manufacturing of tablets are often hydrophobic," he explains. "Each tablet may contain only a small amount of the drug itself, but the binder that makes up most of the tablet must be uniform. Our experiments address how these materials behave when processed."

Utter cautions that when it comes to grains, mixing happens in a very narrow region. "In a tilted bucket, the top layer of sand flows first. It's not like water," he says. "Unfortunately, this means the results you get from a small-batch mixer might not happen on a larger scale. Unpredictability is built into the system. There's a joke within physics — assuming the cow is spherical, our predictions will be accurate every time. It's the complications we're trying to understand."

Posted Oct. 7, 2015

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