Steve Choi and Jeff Eastman are working with industries to improve the understanding of nanofluids.
Scientists Steve Choi and Jeff Eastman at Argonne National Laboratory, Argonne, Ill., have created a next-generation fluid that dramatically improves fluid heat transfer by manipulating atoms on the nanoscale. By adding tiny, spherical particles of copper no larger than a few nanometers to a conventional fluid, researchers can improve its ability to transfer heat by up to 40%. Improving heat transfer in oils and coolants for the automotive industry, for example, would help engines increase efficiency, decrease fuel demands, and improve emissions.
These nanofluids are made by suspending copper or copper oxide in liquids such as water or ethylene glycol (radiator fluid). The scientists heated copper to a vapor inside a vacuum chamber. A cooled heat-transfer fluid was placed nearby in the chamber, and the copper vapor condensed when it touched the cooled fluid, forming metal spheres around 10 nanometers in diameter in the fluid. When Choi and Eastman used ethylene glycol, the copper nanoparticles improved the rate at which the fluid conducted heat.
Both scientists are working with other institutions to develop a database of nanofluid properties and create accurate models of nanofluid behavior. Manufacturers will need this information if nanofluids are to be developed for the commercial market. One appealing possibility is to create fluids whose thermal properties can be engineered to specific tasks, but at this point, basic facts about nanoparticles still need to be discovered.
Scientists want to know why the molecules of a base fluid keep nanoparticles suspended so well, since nanoparticles are dramatically larger than individual molecules. Also unclear is the reason nanofluids conduct heat so effectively. Eastman speculates that it may be related to the increased surface interaction.
"Since, for a given volume of material, there are a greater number of particles as their size decreases, perhaps there is more opportunity for the nanoparticles to conduct the heat," he says.
Research must also continue to bring down cost for producing the nanofluids.