A new way to apply nanostructure coatings provides heat removal at a rate four times faster than the same materials prior to coating, using inexpensive materials and application procedures, say researchers.
The discovery has the potential to revolutionize cooling technology and allow heat exchangers to function more effectively, some experts say. Heat exchangers are what make systems from industrial cooling process to residential air conditioners or refrigerators function, inadequate cooling is a limiting factor for many advanced technology applications, ranging from laptop computers to advanced radar systems.
“For the configurations we investigated, this approach achieves heat transfer approaching theoretical maximums. This is quite significant,” says Terry Hendricks, project leader from the Pacific Northwest National Laboratory, which discovered the heat transfer technology along with researchers at Oregon State University.
The discovery holds potential for the heating and cooling industry as well as for manufacturers of high-tech devices. The improvement in heat transfer achieved by modifying surfaces at the nanoscale has possible applications in both micro- and macro-scale industrial systems, the researchers say. The coatings produced a heat transfer coefficient 10 times higher than uncoated surfaces.
“Many electronic devices need to remove a lot of heat quickly, and that’s always been difficult to do,” says Chih-hung Chang, an associate professor in the School of Chemical, Biological and Environmental Engineering at Oregon State. “This combination of a nanostructure on top of a microstructure has the potential for heat transfer that’s much more efficient than anything we’ve had before.”
For example, there’s enough inefficiency in heat transfer that for water to reach its boiling point of 212°F (100°C), the temperature of adjacent plates often has to be about 284°F (140°C). But with this new approach, through both their temperature and a nanostructure that literally encourages bubble development, water will boil when similar plates are only about 248°F (120°C), the researchers say.
To do this, heat transfer surfaces are coated with a nanostructured application of zinc oxide, which in this usage develops a multi-textured surface that looks almost like flowers, and has extra shapes and capillary forces that encourage bubble formation and rapid efficient replenishment of active boiling sites.
In these experiments, water was used, but other liquids with different or even better cooling characteristics could be used as well, the researchers say, noting that the coating of zinc oxide on aluminum and copper substrates is inexpensive and could be applied affordably to large areas.
Because of that, the technology has the potential to address cooling problems in advanced electronics and also be used in more conventional heating, cooling and air-conditioning applications. It could eventually find its way into everything from a short-pulse laser to a home air-conditioner or more efficient heat pump systems.
The findings were announced in the International Journal of Heat and Mass Transfer, and a patent application has been filed.
Nanoscale Zinc Oxide Coating Could Greatly Improve Heat Transfer
September 1, 2010