Deep within the Earth, heat is so high that a portion of the iron core is flowing. This liquid iron is always moving, constantly churning and circulating.

It works like a dynamo to generate the magnetic field that surrounds our planet. The Earth’s rotation is one driving reason for this complex flow pattern of iron; another is “convection,” which is caused by temperature differences: Heat transfer occurs when relatively hot iron in the Earth’s core travels to cooler locations, similar to how warm air rises above a radiator and displaces cooler air.

However, nothing is known about how these mechanisms work in detail at the moment. Experts often rely on theoretical analysis and computer models to better understand them, as well as tests that, at least in part, recreate what is happening in a laboratory size.

The Institute of Fluid Dynamics of the HZDR recently conducted one such experiment.

“We took two cylindrical vessels — a relatively small one about the size of a bucket and the other one shaped like a barrel with a volume of 60 liters,” project leader Dr. Tobias Vogt revealed. “We filled these vessels with a metallic alloy of indium, gallium and tin, which is liquid at room temperature.”

The specialists heated the bottom of the containers while chilling the top, resulting in a temperature difference of up to 50 degrees Celsius between the two layers.

Ultrasound offers a comprehensive view

The liquid metal inside the vessels churned due to the significant temperature difference: Locally warmer flow portions, such as columns, ascended and mingled with the colder parts due to convection, similar to a lava lamp.

The researchers had to apply a unique analytical technique because the metal alloy they employed was opaque: Dr. Sven Eckert, Head of Department Magnetohydrodynamics at the HZDR, noted, “It is an ultrasound method used in medicine. We fitted around 20 ultrasonic sensors to the vessels, enabling us to detect how liquid metal flows inside them.”

The research team found a surprising discovery when analyzing the data. During the tests, the experts expected to see separate flow zones cluster together to form a larger, more comprehensive structure known as large-scale circulation.

“This is comparable to a thermal wind, which is able to transport heat very effectively between the top and the bottom,” Vogt said.

“We were indeed able to observe this thermal wind in the smaller vessel — but with the larger vessel, the barrel, large temperature differences led to an almost complete breakdown of the wind.”

As a result, the heat was not transmitted as efficiently as it may have been.

“We believe the cause of this to be the formation of much smaller-scale turbulence rather than a few large swirls, which makes heat transport less effective,” Vogt explained.

Battery technology implications

These new discoveries may have consequences for what occurs at the Earth’s core: “To understand what is happening, experts are attempting to extrapolate the results of laboratory experiments to the scale of the Earth,” Sven Eckert explained. “But we have now shown that heat is transported less effectively under certain conditions than previous experiments had suggested.”

As a result, predictions for the Earth are likely to yield diverse results.

Tobias Vogt noted, “However, the real-life processes in the Earth’s core are many times more complex than in our laboratory experiments.

“For example, the flow of liquid iron is also influenced by the Earth’s magnetic field and rotation — ultimately, we know very little about these flow processes.”

Indeed, the new findings may have implications for technology, particularly in fields requiring liquid metals. Liquid metals, for example, are employed in some battery types as well as future solar power plants and cool fusion reactors.

The HZDR team is currently developing an enhanced analytical technique to examine heat transfer in liquid metals in more detail.

“Special induction sensors are expected to record flows in even greater detail than before and produce true 3D images,” Sven Eckert said. “Our initial measurements are very promising.”

Image Credit: Getty

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