The effects of temperature, volume fraction and vibration time on the thermo-physical properties of a carbon nanotube suspension (carbon nanofluid)

In this investigation, nanofluids of carbon nanotubes are prepared and the thermal conductivity and volumetric heat capacity of these fluids are measured using a thin layer technique as a function of time of ultrasonication, temperature, and volume fraction. It has been observed that after using the ultrasonic disrupter, the size of agglomerated particles and number of primary particles in a particle cluster was significantly decreased and that the thermal conductivity increased with elapsed ultrasonication time. The clustering of carbon nanotubes was also confirmed microscopically. The strong dependence of the effective thermal conductivity on temperature and volume fraction of nanofluids was attributed to Brownian motion and the interparticle potential, which influences the particle motion. The effect of temperature will become much more evident with an increase in the volume fraction and the agglomeration of the nanoparticles, as observed experimentally. The data obtained from this work have been compared with those of other studies and also with mathematical models at present proven for suspensions. Using a 2.5% volumetric concentration of carbon nanotubes resulted in a 20% increase in the thermal conductivity of the base fluid ( ethylene glycol). The volumetric heat capacity also showed a pronounced increase with respect to that of the pure base fluid.