Experimental study on the thermal conductivity enhancement of water based nanofluids using different types of carbon nanotubes

Carbon nanotubes (CNTs) as the promising nanomaterials have particularly attracted attention from researchers due to their superior thermal features. In the present study, the thermal conductivity properties of three types of CNTs-nanofluids with different CNTs added to de-ionized water were compared and analyzed experimentally. The results show that CNTs-nanofluids exhibit higher thermal conductivities than that of the base fluid, and the thermal conductivities increase with the increase of concentration as well as the increase in temperature. When the CNTs concentration is 0.48 vol% at the temperature 60 °C, CNTs-nanofluids display the maximum thermal conductivity enhancements of 8.1%, 16.2% and 5.0% for short single-walled nanotubes, long single-walled nanotubes and multi-walled nanotubes nanofluids, respectively. In addition, the long single-walled nanotubes nanofluid shows the highest thermal conductivity values for their high aspect ratio and special surface area. The thermal conductivity enhancements for these nanofluids are almost linear with the increase in CNTs concentration and operating temperature at the tested conditions. A simple linear correlation for predicting the effective thermal conductivities with the concentration and temperature has been developed for the three types of CNTs-nanofluids.