Nanofluids in a forced-convection liquid cooling system - benefits and design challenges

Nanofluids are gaining in popularity among academic researchers and receiving more attention from industry as they continue to demonstrate heat transfer improvements in liquid cooling processes. 'Nanofluids' is the accepted nomenclature for slurries containing a mixture of a base fluid and suspensions of nano-scale particulates, or nanoparticles. When nanofluids are used in a liquid cooling process, the purely convective mode of heat transfer with the base fluid alone now becomes a heat transfer problem with convection and conduction effects. This paper explores the use of nanofluids in a forcedconvection liquid cooling system and presents several critical findings in experiments carried out at GE Healthcare's Magnetic Resonance Center. These findings include the heat transfer measurements as well as some of the aspects of nanofluids that need to be considered when integrating into a liquid cooling system. A forced convection experiment was used to characterize the heat transfer rate through a single-IGBT cold plate for 1.5% v/v CuO and 1% v/v Al 2 O 3 nanofluid mixtures. Both the CuO and Al 2 O 3 nanoparticles were manufactured to a nominal 30nm diameter. The base fluid used was a specially formulated coolant with less than 0.07% of corrosion inhibitor and biocide and, for this paper, can be simply treated as water. Maximum convective heat transfer coefficient increases were 4.0% for CuO and 4.5% for Al 2 O 3 over deionized water in the flow rate ranges tested. Additionally, required pumping power to achieve a maximum flow rate of 1.6 gpm also increased over the base fluid. These increases were 7.5% for the 1% Al 2 O 3 and 40% for the 1.5% CuO nanofluid mixtures. Several other important observations were made that significantly affect the viability of nanofluids making it into products that use forced-convection liquid cooling systems. Nanofluid and nanoparticle health risks are not yet completely understood. Proper handling and disposal of the small particles typically metal or metal oxides must be carefully considered, as the particles are easily inhalable and capable of transferring through cellular junctures and tissue barriers. Additionally, integrating the nanofluids into existing forcedconvection liquid cooling systems creates concerns for piping erosion, component damage, and nanoparticle settling or agglomeration.