The world of technology is rapidly advancing with hand-held devices getting thinner and faster. In order to maintain optimal processing speed, it is important to keep electronics at an appropriate temperature to keep them from overheating and losing function. The issue then becomes finding a cooling system small enough to keep the overall size of electronics as compact as possible.
Mohammed Ababneh, PhD, who is currently working as a Research and Development (R&D) Engineer, Defense/Aerospace Division, at Advanced Cooling Technologies, Inc. in Lancaster, PA, graduated from the University of Cincinnati College of Engineering and Applied Science with his PhD in 2012. During his time at UC, Ababneh collaborated with Professor Frank M. Gerner, PhD, to find an effective solution to the standard bulky heat pipes which are traditionally used to cool microelectronics or computer processors.
Heat pipes, despite their contradictory name, are not actually used to heat devices. Instead they are used as a means to transfer heat away from electronic and mechanical devices. The heat is captured within the pipes, cooling the operating system and allowing it to function efficiently, hence the name “heat pipe.”
Imagine a thin, flat copper pipe or vapor chamber upon which computer processors or other heat generating electronics are mounted. The inside of this thin heat pipe contains a wick; a porous lining on the inside of the pipe, which is usually made of sintered (sponge like) copper. The key component to a heat pipe is the liquid inside the wick, which is often water for the normal operating temperatures of microelectronics.
The liquid turns into vapor from the waste heat generated by an electronic device. That vapor then travels through the pipe due to the pressure change- cooling the electronics and condensing into a liquid form on its path.
Once the condensation has reached the “cool side” of the pipe, it passively flows back down the wick to the “hot side” on the pipe. This process is repeated as a means of transferring heat from the electronic chips to the larger surface area outside of the heat pipe thermal spreader where more conventional heat transfer technologies may be utilized.
The biggest challenge in reducing the size of a heat pipe is finding materials that are both lightweight and that can handle the stress of heat transfer.
After vigorous prototype testing Ababneh and Professor Gerner and their partners at GE Global Research and Wright Patterson AFB were able to match ideal materials and structure to create a heat pipe system that is less than 1 mm thick.
This new technology with a total thickness of less than 1 mm can operate in any gravitational orientation, and in fact have been tested in adverse gravity conditions exceeding 13g. A “g” is a measurement of gravitational force. To put 13 g’s into perspective; a manned aircraft is only designed to pull up to 9 g’s, the force you feel on a roller-coaster is usually somewhere between 3 and 4 g’s. The pair published their findings in a paper which was recently picked up by Thermal News. This trade publication is mostly used for engineers in the field who are looking to share and receive knowledge on best practices and field advancements. Professor Gerner explains, “Getting published in this kind of trade publication means our work will have a real-world impact on the industry.”
The remarkably small heat pipe prototypes developed by Ababneh and Gerner have a wide variety of potential applications. The heat transfer system, which is only 1 mm thick and can operate in any gravitational orientation, therefore, can be used in anything from phones and tablets, to aircrafts, avionics and UAV’s.
Figure 1 is a photograph for a thin flat thermal ground plane (TGP) heat pipe with a surface pattern etched circuit directly onto the surface. The heat pipe TGP has been gold plated and pads of Gold-Tin solder have been deposited for direct attachment of vertical cavity surface emitting laser (VCSEL) chips.