Cooling your jets takes on a new meaning when you’re talking electronics and aviation. It’s not about thrust but about developing efficient ways to cool CPUs and microchips.

Graduate student Archibald Amoako of South Dakota State University’s Department of Mechanical Engineering is using computer modeling to design devices that more efficiently disperse heat from aerospace electronics. He and his adviser, assistant professor Jeffrey Doom, are working with Ross Wilcoxon, principal mechanical engineer for Rockwell Collins Advanced Technology Center in Cedar Rapids, Iowa, and a former SDSU faculty member.

Amoako will present his research results at the American Institute of Aeronautics and Astronautics/American Society of Mechanical Engineers Joint Thermophysics and Heat Transfer Conference June 25-29 in Atlanta.

Advanced electronic systems are increasingly using different semiconductor technologies (not just silicon) with a wide variety of maximum allowable temperatures and power densities, Wilcoxon explained.  The design of these systems must address these highly localized conditions with thermal management that is tailored to provide different levels of cooling to meet those conditions. 

“Additive manufacturing can be used to create heat sinks with enhanced cooling capabilities precisely where we need them,” he continued. “Efficiently simulating the fluid flow and heat transfer associated with the ridiculously complex shapes that we can now print is essential for us to fully leverage the opportunities offered by additive manufacturing.”

Amoako modeled an active heat sink, which uses a fan to pull air from the microchips into fins that dissipate the heat, much like the radiator on a car.  The device to be cooled is positioned on top of the heat sink, which then keeps the temperature within a safe operating range.

“Most engineers use heat sinks that have rectangular-shaped fins, but we are trying optimizing the geometry of the fins,” Amoako said. He modeled 12 different fin geometries for a 2.5- by -2.5-inch heat sink to identify those that are efficient at cooling and cost-effective to manufacture.

The two major performance parameters are thermal resistance, defined as the temperature difference when air enters and exits the heat sink, and the inlet-to-outlet pressure drop. “A higher pressure drop requires a larger fan, which increases manufacturing costs,” Amoako explained. “Thermal resistance and pressure drop have to balance out.”

Amoako tested fin configurations, such as rectangular and hexagonal pins, zigzag and arc plates and short plates, as well as pin-and-plate combinations. “Before 3D printing, these intricate designs would have been too expensive to consider,” Doom said. Companies are now doing research on these designs, but printing the fins using copper and tin is still relatively expensive.

The square zigzag plates had the lowest thermal resistance, while the separated short plates had the lowest pressure drop. However, Amoako found that no definite correlation exists between thermal resistance and pressure drop parameters when evaluating heat sink performance.

Using STAR-CCM+® computational fluid dynamics simulation software, Amoako validated his model using a rectangular fin design for which experimental results are available. “We used the conjugate heat transfer process, which simulates the fluid flow of the air and the solid parts of the heat sink. The mesh-in model makes sure the simulation is capturing the whole geometry,” he explained.

Doom added, “A major manufacturing advancement, additive manufacturing of 3D parts allows engineers to create exotic parts that could not be manufactured previously. We’re developing the tools to evaluate the potential of these new designs using computational fluid dynamics modeling.”