A novel thermal management technology originally used in aircraft has been adapted for use in other areas.
Jonathan Boreyko, Associate Professor in Mechanical Engineering at Virginia Polytechnic Institute and State University (Virginia Tech), led the team that developed the new tech. Boreyko received an award from the Young Investigator Research Program in 2016, granted by the Air Force Office of Scientific Research. Through the grant, Boreyko and his team were able to develop planar bridging-droplet thermal diodes, presenting a new approach to thermal management.
The Virginia Tech research team's project has demonstrated that the novel thermal management approach is both highly efficient and extremely versatile. The results of their study are published in the latest issue of Advanced Functional Materials.
A New One-Way Heat Transfer Device
A thermal diode generally refers to a device that allows heat to only flow in one direction, using specialized materials to prevent backflow. As a thermal management solution, diodes are promising because they allow heat to be redirected to only one side and effectively blocking and removing them from the other.
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According to a Virginia Tech press release, the focus of Boreyko's funding is in aircraft applications. In an airplane, heat is absorbed from the overheating plane but resists heat from the outside environment.
In the Virginia Tech team's design, they used two copper plates in a sealed environment with a small, microscopic gap between them. The first copper plate is engineered with a wick structure that will hold and transport water. On the other hand, the second copper plate is coated with a hydrophobic (water repellant) layer.
Once heat is applied to the first plate, the water in the wick is evaporated into steam. This steam then crosses the narrow gap, where it is cooler, and the steam condenses into dew droplets on the surface of the hydrophobic plate. The droplets accumulate to be a large enough droplet, overcoming the microscopic gap and being absorbed back into the wick. Now that the water, in the droplet form, is back into the wick, the process can start all over again.
As a one-way device, the diode can not transfer heat backward. If heat is applied to the hydrophobic plate, no transfer will occur since the water remains in the wick, which remains on the copper plate on the other side.
A Promising New Temperature Management Device
While it was initially developed for aircraft applications, the new device from Boreyko's team can also be used in other fields requiring continuous temperature management. For example, electronic equipment like computers have components that continuously generate heat. A central processing unit (CPU) microchip tends to overheat.
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Current designs incorporate heat sinks to accommodate the increasing temperature, but only up to a certain limit. Furthermore, protection mechanisms involve shutting down the processor in the event of an overheating, to prevent further damage to the unit.
With Boreyko's thermal diode, the CPU's generated heat is transferred to the first copper plate. Heat evaporates the water into steam, moving towards the other plate where it will condense and will continue to do so, absorbing heat. Another advantage of the new thermal diode is that it can be used regardless of orientation.
Prior to his work on the new thermal diodes, Boreyko has previously suggested a novel method to speed up defrosting:
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