A novel nano phase change material emulsion (NPCE) with low supercooling and high thermal conductivity was prepared by sonication method. N-octadecane was employed as phase change material, multi-walled carbon nanotubes (MWCNT5) were utilised as high thermal conductivity material, and octadecanol was utilised as nucleating agent. The characterization and thermal properties of the nanoemulsions prepared with various concentrations of MWCNT5 and octadecanol were measured and analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size analyser, differential scanning calorimeter (DSC) and thermal conductivity meter. The results indicated that the nanoemulsions prepared had great stability, low supercooling and enhanced thermal conductivity. The thermal conductivity was enhanced by 4.32% for 10 wt% nanoemulsion with addition of 1 wt% MWCNTs. The supercooling degree of 20 wt% nanoemulsion was decreased by 36.4% from 173 degrees C to 11.0 degrees C with addition of 1 wt% octadecanol. It can be concluded that the nanoemulsions prepared were able to be utilised as heat transfer and energy storage fluids, with great potential in thermal system applications. (C) 2019 Elsevier Ltd. All rights reserved.