James Klett, a researcher at the US-based Oak Ridge National Lab’s has discovered a new carbon-based material—a graphite foam—that has amazing heat transfer properties. If you hold a puck of the graphite foam in your hand and place an ice cube on it, the cube melts from your body heat as if it were on a hot griddle.
PocoFoam, as the material is now trademarked, has attracted lots of attention from industries interested in applying it to a number of uses. What is more, a commercial license has been granted to Poco Graphite.
The result of interest within the Lab itself has led to the development of a radiator for a natural-gas-fired V-8 engine that drives an industrial heat pump. The radiator transfers heat very efficiently to the air, and since this air is hotter than with a normal radiator, it can be used to regenerate the desiccant that removes humidity from building air more efficiently.
‘Graphite foam is as thermally conductive as aluminium at one-fifth the weight. It has a very high surface-area-to weight ratio and a high heat transfer coefficient. This interests engineers and designers because products that use energy wage an ongoing battle with heat,’ says Klett.
‘The hotter something runs, the shorter the life. Increasing the temperature of an electronic component by 20°F will typically reduce its service life by half. At the same time, decreasing the operating temperature of a computer chip by 20 degrees increases its life and reliability by a factor of two.’ And, as Klett points out, about two-thirds of all energy consumed is wasted through heat. Components incorporating Poco-Foam could carry that damaging heat away from electronics— advanced heat sinks—and would weigh less too.
To demonstrate, Klett’s team replaced a standard finned-aluminium heat sink from a microprocessor with a similar graphite foam sink. The foam heat sink, mainly because of its higher surface area, outperformed the aluminium sink even though it weighed only a fifth as much. When James ground the fins off the foam heat sink, the foam still dissipated heat on par with the much heavier aluminium sink. The weight and temperature factors also have attracted the interest of the racing industry. Graphite foam radiators would not only reduce the weight of the car, but also their thermal efficiency would enable designers to place the radiator away from the front of the vehicle, which could enable more aerodynamic designs.
Enhancing radiator efficiency could also make a difference in design of more conventional vehicles such as semi trucks, which lose as much of 25 percent of their energy efficiency overcoming wind resistance. Streamlined trucks of the future, with their radiators in places other than the front, could resemble rocket ships more than boxes.
Graphite foam car radiators could also eliminate auto overheating in heavy city traffic. The graphite-foam-designed radiators have outperformed aluminium radiators by 30 percent. ‘However, this was a test case and we still need to determine the durability of such a design,’ says Klett.
Another goal is to recycle wasted heat. Heat exchangers, Klett says, are not very efficient. ‘The air temperature exchange from car radiators is not very much,’ he adds. ‘Improve that exchange—take more heat from the system—and you can use that heat to run other systems and do more work with it. The principle applies to a number of processes, similar to the way heat recovered through the BTC’s heat exchanger regenerates the desiccants.’
Klett notes that significant research lies ahead on a material in its infancy. ‘There is so much that we have found that this can be used for, such as a basis for replacing carbon fibres in composites, sound absorption, anodes for lithium ion batteries and firewall protection.’
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