Enhancement of thermal conductivity with carbon nanotube for nanofluids

Thermal conductivity enhancements in ethylene glycol and synthetic engine oil in the presence of multi-walled carbon nanotubes (MWNTs) are investigated. CNT nanofluids are prepared using a two-step method. The volume concentration of CNT–ethylene glycol suspensions is below 1.0 vol.% and that of CNT–synthetic engine oil suspensions is below 2.0 vol.%. The thermal conductivities of the CNT suspensions are measured with a modified transient hot wire method. The results show that CNT–ethylene glycol suspensions have noticeably higher thermal conductivities than the ethylene glycol base fluid without CNT. The results for CNT–synthetic engine oil suspensions also exhibit the same trend. For CNT–ethylene glycol suspensions at a volume fraction of 0.01 (1 vol.%), thermal conductivity is enhanced by 12.4%. On the other hand, for CNT–synthetic engine oil suspension, thermal conductivity is enhanced by 30% at a volume fraction of 0.02 (2 vol.%). The rates of increase are, however, different for different base fluids. The CNT–synthetic engine oil suspension has a much higher enhanced thermal conductivity ratio than the CNT–ethylene glycol suspension.