The effect of functionalisation method on the stability and the thermal conductivity of nanofluid hybrids of carbon nanotubes/gamma alumina

Based on our previous studies that focused on the synthesis of a nanohybrid of multi-walled carbon nanotubes (MWCNTs) and gamma alumina (γ-Al2O3) particles, this paper reports the heat transfer properties and dispersion behaviour of the hybrid. In this study, functionalised CNTs were synthesised via a solvothermal process with various concentrations of carboxylic acid groups (–COOH). The microstructure of the synthesised nanohybrids was characterised via high-resolution transmission electron microscopy (HRTEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The MWCNT/γ-Al2O3 nanofluid was prepared using a two-step method. The thermal conductivities of different nanohybrids were measured with a KD2 probe using a modified transient hot wire method. The zeta potential and particle size distribution were determined to investigate the stability of the nanofluid. The results showed that the functional groups had a significant influence on the thermal conductivity of the hybrid nanofluid. The data showed that the enhancement in thermal conductivity reached up to 20.68% at a 0.1% volume fraction of hybrid, for a gum arabic (GA) based nanofluid.