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Nanofluids? Cool!



Nanofluid developers Steve Choi (left) and Jeff Eastman are working with industry to improve the understanding of nanofluids.

Adding nanoscale particles--so small they are measured in billionths of a meter--to conventional liquids holds the promise of more efficient cooling for engines, machinery and supercomputers. These "nanofluids" have increased by up to 150 percent the heat-transfer rate of fluids.

Engineers have been working for decades to develop more efficient heat transfer fluids for car motors and industrial equipment. Nanofluids could be the answer, making possible more efficient engines and manufacturing plants.

Nanofluids are made by suspending nanoscale particles of materials such as carbon, copper or copper oxide in liquids such as oil, water and radiator fluid (a mixture mostly of water and ethylene glycol). The addition of 3 volume-percent of copper oxide nanoparticles to ethylene glycol increased its heat conduction by 15 percent. However, the heat-transfer capability of ethylene glycol grew by 40 percent when only a 0.3 volume-percent of 10-nanometer-diameter spheres of copper were suspended in it.

The largest percentage increase so far--50 percent--came when the researchers suspended 1 volume-percent carbon nanotubes in oil. Ordinarily, oil is one of the poorest performing liquids for heat dispersion. The oil-and-carbon nanofluid is expensive but shows promise for industrial use because it is easier to produce than other nanofluids.

Transferring heat

The two Argonne scientists--Steve Choi and Jeff Eastman--who developed nanofluids started collaborating in 1993 when Choi, a heat-transfer specialist, heard Eastman was studying nanometer-sized crystals. Choi had long been frustrated with the limitations of mixing traditional fluids with traditional small particles.

Choi and Eastman--who have patented their nanofluids work--tried various techniques to condense gaseous metals and metal oxides into solid nanoparticles, and suspended their creations in several different fluids.

The results are promising, but much remains unknown about nanofluids. Choi and Eastman are collaborating with several outside institutions to investigate nanofluids' physical capabilities, which must be better understood before they can be developed for commercial use. Together with Purdue University, Rensselaer Polytechnic Institute, Nanopowder Enterprises and Valvoline, Argonne is compiling a database of nanofluids' properties so they can be harnessed effectively.

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