Thermal and electrical conductivities of water-based nanofluids prepared with long multiwalled carbon nanotubes

Thermal and electrical conductivities of suspensions of multiwalled carbon nanotubes (MWCNT) in water were measured as a function of temperature, nanotube weight content, and nanotube length. Nanotubes were dispersed in water by using gum Arabic as surfactant. The thermal conductivity was measured by the steady-state method by using a coaxial-cylinder cell that allows the sample temperature to be varied from 15to75°C. Our measurements show that the thermal conductivity enhancement as compared to water linearly increases when the MWCNT weight content increases from 0.01to3wt%, reaching 64% for the MWCNT weight content of 3wt%. The thermal conductivity enhancement is found to be temperature independent up to MWCNT weight content of 2wt%. The average length of the nanotubes appears to be a very sensitive parameter. The thermal conductivity enhancement as compared to water increases by a factor of 3 when the nanotube average length increases in the 0.5–5μm range. Electrical conductivity measurements show that...