Yoonjin Won
Assistant Professor Yoonjin Won and her team are combining microfluidics and recent advances in nanomaterials engineering to improve the cooling of high-powered electronic devices. Steve Zylius / UCI

Think of the immense heat generated in the combustion chamber of a motorcycle engine. In older models, motors were cooled by the flow of air as the vehicle sped forward, but modern bikes circulate liquid around the cylinder heads to prevent overheating. Now imagine creating a tiny version of this apparatus to fit inside your laptop computer or smartphone and cool them off. That’s the goal of University of California, Irvine mechanical engineer Yoonjin Won.

“If there’s power, there’s heat, which causes a performance problem in high-tech devices,” says Won, who was hired in 2015 as an assistant professor in UCI’s Department of Mechanical & Aerospace Engineering, with a joint appointment in the Department of Chemical Engineering & Materials Science.

“Air cooling is the prevalent technology in electronics now,” she says, referring to the internal fans and fin structures in computer components – which bear a resemblance to the blades on the “airhead” motorcycle engines of yore. “But I’m more interested in liquid cooling.”

Won was brought here to spearhead research on how nanomaterials can be used to dissipate heat from power-hungry computers and other electronic devices. Derek Dunn-Rankin, UCI professor of mechanical & aerospace engineering, says that advances in this area could offer “remarkable improvements in thermal transport, which often limits performance across a wide range of next-generation technologies.”

According to Won, our power to manage heat has been hemmed in by the basic substances available to manufacture components, such as silicon, plastics and various metals. “Our ability to maximize heat transfer plateaued long ago, but scientists recently have opened new areas for innovation by developing novel technologies to make structures using nanomaterials,” she says, referring to the manipulation of building blocks that measure one-billionth of a meter. She notes that these new materials possess thermal transport capabilities many times greater than those of diamonds, among the most conductive substances in nature.

Won recognizes that there are barriers in her current area of research. “People might get nervous if there’s water in their computer,” she says. There’s also the issue of size. In a sleek, thin smartphone, there’s not a lot of room left over for whirling fan blades.

Won’s proposed solution involves the use of microfluidic devices, tiny machines that transport fluids through submillimeter-sized tubes, to circulate cooling liquid around microchips. But she’s taking the technology a step further – and orders of magnitude smaller – by combining nanomaterials into the devices’ miniscule water channels. Won says that through the manipulation of surfaces lining the inside of the microfluidic devices, engineers can very precisely regulate how water is absorbed, repelled, boiled, condensed and evaporated.

“Recent research has shown that the basic physics of heat transfer is altered using nanoscale features, with potentially huge advances in efficiency,” she says. “By engineering nanomaterials into microfluidic devices, we can have a high level of control over thermal transport parameters.”

Before coming to UCI, Won – who studied at South Korea’s Seoul National University and earned master’s and doctoral degrees at Stanford University – collaborated with Apple Computer, Google, Intel and other Silicon Valley companies with an interest in the cool and reliable operation of computer systems and data centers. She also conducted research for the U.S. Department of Defense and the National Science Foundation on developing futuristic cooling technologies for mission-critical electronic equipment.

Won says that in these high-tech systems, components are heated up by the transfer of electrons, and that heat is conducted by the surrounding materials. Anyone who has held a warm mobile phone or laptop computer knows of this phenomenon firsthand. Won is hoping to invent a way for that heat to be taken away from its source via liquid carried by minute microfluidic tubes. “Often the performance of high-powered electronic devices is limited by temperature, not by circuits,” she says. “Therefore, it is critical to address this performance issue with new materials to enable extreme high-power electronics cooling.”

One of the Won lab’s specific angles of research is a surface coating made of a porous copper nanomaterial. Using an electro-depositing technique, her team creates layers of spherical structures measuring from 1 to 10 micrometers. The tiny shapes can be arranged to precisely control the material’s ability to either absorb or repel water, among other properties, enabling fluid to be more efficiently cycled through the system to remove heat from the source.

And it’s all being done at an infinitesimally small scale, which is what’s needed if computer and electronics technology is to continue speeding forward.