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.