New heat conduction method could be a game-changer for server farms and planes

Jonathan Boreyko, Associate Professor of Mechanical Engineering, has developed aircraft thermal management technology ready to be adapted to other fields.

The research was published in Advanced functional materials August 18, 2020.

Boreyko received a Young Investigator Research Program Award in 2016 from the Air Force Office of Scientific Research. This award funded the development of planar droplet thermal diodes, a new approach to thermal management. Boreyko’s research has shown this new approach to be both highly effective and extremely versatile.

“We hope that the unidirectional heat transfer from our bridging droplet diode will enable intelligent thermal management of electronics, airplanes and spacecraft,” Boreyko said.

Diodes are a special type of device that allows heat to be conducted in only one direction using engineered materials. For heat management, diodes are attractive because they allow rejection of heat entering from one side, while resisting heat from the opposite side. In the case of aircraft (the focus of Boreyko’s funding), heat is absorbed by an overheating aircraft, but resists the external environment.

Boreyko’s team created a diode using two copper plates in a sealed environment, separated by a microscopic space. The first plate is designed with a wick structure to retain water, while the opposite plate is coated with a hydrophobic (hydrophobic) layer. The water on the wick surface receives heat, causing vapor to evaporate. As the vapor moves through the narrow space, it cools and condenses into dew droplets on the hydrophobic side. These dew droplets become large enough to “fill” the space and be sucked into the wick, which begins the process again.

If the heat source was applied on the hydrophobic side instead, no vapor can be produced because the water remains trapped in the wick. This is why the device can only conduct heat in one direction.

What does it look like in practice? An object that produces heat, such as a CPU chip, will overheat if that heat is not continuously removed. Boreyko’s invention is affixed to this heat source. The heat generated is transferred through the conductive plate, into the water. The water turns into steam and moves away from the heat source. The hydrophobic and non-conductive side prevents heat from entering via air or other heat sources that may be nearby, allowing the diode to handle heat only from its main subject.

Boreyko’s team measured an almost 100-fold increase in heat conduction when the bad side was heated, compared to the hydrophobic side. This is a significant improvement over existing thermal diodes. Current diodes are not very efficient, Boreyko says, only conduct a few times more heat in one direction, or require gravity. This new thermal bridging droplet diode can be used upright, sideways or even upside down, and would work even in a space where gravity is negligible.