Research in Microscale Heat Transfer Will Benefit Military Systems

  • Published
  • By Molly LaChance, AFRL/AFOSR-RSPP
  • Office of Scientific Research
ARLINGTON, Virginia --  A 2-year-old Multidisciplinary University Research Initiative involving the Air Force Research Laboratory, the University of Michigan, Stanford University, Brown University, and the University of California at Santa Cruz, is making great strides in achieving a fundamental understanding of heat transfer at interfaces.

Heat transfer is important to the performance, power requirements, and reliability of many military and commercial systems, including thermoelectric refrigerators, waste heat recovery systems, heat sinks, power electronics, thermal barrier coatings, and thermal interface materials.

"Recent advances in nanoscience have enabled the precise control of interface physical and chemical structure, but the fundamental physics that link this nanoscale structure with thermal transport is not yet well developed, inhibiting the engineering of interfaces with radically enhanced thermal properties," said team lead Dr. Kevin Pipe, professor of Mechanical Engineering at the University of Michigan.

Interfaces can decrease a composite material's thermal conductivity by scattering the acoustic waves that are the primary carriers of heat in solids. The scattering process gives each interface a thermal resistance.

The researchers have made a number of achievements during the first two years of their effort, including the development of a high-speed thermal imaging system and a technique to measure the propagation of phonons, the elementary packets of vibrational energy that carry heat, with high signal-to-noise ratio. Using ultrafast laser systems that emit laser pulses less than 50 femtoseconds in duration, Pipe's team creates high-frequency acoustic waves at the surface of a material and in a process similar to medical ultrasound imaging measures how these waves scatter off of buried interface structures.

By applying precise nanofabrication techniques to create interfaces with known atomic structure, the researchers are able to link measured heat transfer properties with the predictions of atomistic simulations to yield further understanding of the fundamental processes involved.