Silicon oil based multiwalled carbon nanotubes nanofluid with optimized thermal conductivity enhancement

Multiwalled carbon nanotubes (MWNTs) were treated by concentrated acid combined with mechanical ball mill technology. The treated multiwalled carbon nanotubes (TCNTs) with functionalized surfaces and controlled morphologies were used to prepare silicon oil based nanofluids by using hexamethyldisiloxane as dispersant. Thermal conductivity results of the obtained nanofluids show that the collective effects, involving straightness ratio, aspect ratio, and aggregation of TCNTs, play a key role in the thermal conductivity of CNT nanofluids. This study suggests that the thermal characteristics of nanofluids might be manipulated by means of controlling the morphology of the additions, which also provide a promising way to conduct investigation on the mechanism of heat transfer in nanofluids. Reliable theological properties of the prepared nanofluids were provided. It is important when the nanofluids are used in the potential heat exchange areas. The silicone oil based fluids behave in Newtonian manner in all the studied MWNT volume fractions and temperatures. The hexamethyldisiloxane added in silicone oil, in addition to decreasing the silicone oil viscosity, has little effect on the nanofluid rheological properties. (C) 2009 Elsevier B.V. All rights reserved.