Thermal conductivity and lubrication characteristics of nanofluids

Nanofluid is a kind of new engineering material consisting of nanometer-sized particles dispersed in base fluid. In this study, various nanoparticles, such as multi-walled carbon nanotube (MWCNT), fullerene, copper oxide, silicon dioxide and silver, are used to produce nanofluids for enhancing thermal conductivity and lubrication. As base fluids, DI water, ethylene glycol, oil, silicon oil and poly-α-olefin oil (PAO) are used. To investigate the thermo-physical properties of nanofluids, thermal conductivity and kinematic viscosity are measured. Stability estimation of nanofluid is conducted with UV–vis spectrophotometer. Also, the extreme pressure of nanofluids has been measured with FALEX EP tester. Thermal conductivity of nanofluid increases with increasing particle volume fraction except water-based fullerene nanofluid which has lower thermal conductivity than base fluid due to its lower thermal conductivity, 0.4 W/mK. In addition of fullerene in oil, the extreme pressure of nanofluids increases up to 225%. Stability of nanofluid is influenced by the characteristics between base fluid and suspended nanoparticles.