New method of heat management can be a game changer for server farms and aircraft

Jonathan Boreyko, an associate professor of mechanical engineering, has developed an aircraft thermology management technology that is ready for adaptation in other areas.

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

Boreyko was the recipient of a Young Investigator Research Program Award in 2016, given by the Air Force Office of Scientific Research. This distinction funded the development of planar overflow-drip thermal diodes, a new approach to thermal management. Boreyko’s research has shown that this new approach is both highly efficient and extremely versatile.

“We are hopeful that the unidirectional change of heat of our bridging drop diode can enable the smart thermal management of electronics, aircraft and spacecraft,” said Boreyko.

Diodes are a special type of device that conducts heat in only one direction using engineered materials. For heat management, diodes are attractive because they enable the dumping of heat in one side while resisting resistance on the opposite side. In the case of aircraft (the focus of Boreyko’s financing), heat is absorbed from an overheated aircraft, but resistance from the outside environment.

The Boreyko team made a diode with two copper plates in a sealed environment, separated by a microscopic hole. The first plate is constructed with a wick structure to hold water, while the opposite plate is covered with a water-repellent (hydrophobic) layer. The water on the soaking surface gets hot, causing evaporation in steam. As the steam flows over the narrow hole, it cools and condenses into droplets on the hydrophobic side. These dewdrops grow large enough to “bridge” the gap and are sucked into the wrapped, starting the process again.

If the heat source is applied instead of the hydrophobic side, no steam 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 this look like in practice? An object producing heat, such as a CPU chip, overheats if these heaters are not continuously removed. Boreyko’s invention is confirmed on this heat source. Generated heat is transferred through the conductive plate, into the water. Water turns to steam and moves away from the source of the heat. The hydrophobic, non-conductive side prevents heat from entering through the air or other heat sources that may be nearby, allowing the diode to control the heat only from its main subject.

The Boreyko team measured an almost 100-fold increase in heat conduction when the bad side was heated, compared to the hydrophobic side. This is a major improvement over existing thermal diodes. According to Boreyko, current diodes are either not very efficient, and only conduct a few times more heat in one direction, or they require gravity. This new bridge-drip thermal diode can be used upright, sideways or even substructured, and would even work in spaces where gravity is negative.