The present study aims at nanoparticles characterization and stability as well as the thermal conductivity of the hybrid
nano-oil of ZnO–MWCNT/oil at the temperature range from 25 to 65 C and the concentrations range from 0.50 to 3.2%
for the solid particles. First, the nanoparticles of MWCNT and ZnO were characterized using XRD-FESEM and FTIR tests,
and according to the results, the analysis of atomic, surface and chemical structure of nanoparticles was made. The
nanolubricant was prepared by a two-step method. For this purpose, firstly, the stability was analyzed by the DLS test and
the results show that the nanoparticles are in nanoscale after the construction of nano-oil. The thermal conductivity was
measured based on the variables of temperature and volume fraction. An increasing trend was observed for the thermal
conductivity for higher temperature and volume fraction of the nanoparticles. The biggest improvement of the thermal
conductivity compared to the base fluid is at 65 C, the volume fraction is 3.2%, and its value is 35.1%. Moreover, a very
accurate experimental relationship was developed to determine the ratio of the thermal conductivity of nano-oil in the
empirical range.