Effects of Experimental Method on Aggregation State and Thermal Conductivity of Carbon Nanotube-Based Fluids

Abstract

The thermal conductivity of liquids with carbon nanotubes (CNTs) is higher than that of liquids with spherical nanoparticles which results from low-resistance heat flow paths formed by CNT–CNT contact. Since CNTs easily precipitate or cluster in base liquids, path formation depends on the dispersion state of CNTs. A model of the thermal-conductivity enhancement of liquids with CNTs is presented by incorporating the aggregate state where such paths are formed. This model concludes that the anomalously wide range of enhancement values that have been observed recently is attributed to aggregate concentration. CNT clustering and sedimentation in base liquids are the causes of the decreased thermal-conductivity enhancement of such liquids due to the increase of the volume fraction of CNTs in aggregates. Predictions based on our model also show that experimental methods of obtaining liquids with uniformly dispersed CNTs can change the CNT geometry and aggregate concentration related to the thermal-conductivity enhancement. Surfactant addition, CNT surface treatment with acid, and sonication have characteristic effects on the CNT state and thermal conduction. The model from this study can prove helpful in explaining the magnitude of such effects quantitatively.