2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Heat Transfer Enhancement in Single-Walled and Double-Walled Carbon Nanotube Suspensions

D. Milanova, R. Kumar
University if Central Florida, US

Keywords:
SWNTs, DWNTs, suspension, surfactant, critical heat flux

Abstract:
Single-Walled-Carbon Nanotubes (SWNTs) are known for their great physical, mechanical and electrical properties. The practical applications of nanotubes have been slowed due to insolubility in liquids and poor dispersion characteristics. SWNTs and DWNTs possess a natural tendency to align and bundle in ropes due to van der Waal’s attractive forces, theoretically given as 0.5eV per nanometer. CNTs used in the current experimental study are produced by high pressure CO reactor (HiPco process) with an ash content of less than 5 wt.%. Nanotubes possess smooth hydrophobic walls which do not wet water molecules. An individual SWNT with a diameter of about 1.5 nm is seen in the TEM micrograph. The walls are seen to be undamaged. However, when an ionic surfactant is added, it is adsorbed on the walls, creating surface roughness. Although a complete separation of each nanotube was not possible, on average the majority of the bundles are below 10 nm in diameter. Previous investigation of pool boiling heat transfer for nanofluids of various oxides has shown up to 3 times higher enhancement in CHF (Critical Heat Flux) for silica-nanofluid at concentrations as low as 0.5 % vol. compared to that of pure water. It is very important to carefully study the surface characteristics of the solid nanostructures, since liquid layering of water molecules significantly affect thermal propagation at the interface and within the liquid. Pool boiling experiments have been performed for SWNTs and DWNTs suspensions.

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