Role of interfacial layer and clustering on the effective thermal conductivity of CuO–gear oil nanofluids

Copper oxide nanoparticles (∼40 nm) are dispersed in gear oil (IBP Haulic-68) at different volume fractions (0.005–0.025) with oleic acid added as a surfactant to stabilize the system. Prepared nanofluids are characterized by Fourier Transform Infrared spectroscopy (FTIR) and Dynamic light scattering (DLS) measurements. DLS data confirmed the presence of agglomerated nanoparticles in the prepared nanofluids. Thermal conductivity measurements are performed both as a function of CuO volume fraction and temperature between 5 and 80 °C. An enhancement in thermal conductivity at 30 °C of 10.4% with 0.025 volume fraction of CuO nanoparticle loading is observed. Measured volume fraction dependence of the thermal conductivity enhancement at room temperature is predicted fairly well considering contributions from both nanolayer at the solid–liquid interface and particle agglomeration in the suspension, as visualized by Feng et al.

► First report on thermal conductivity of CuO–gear oil nanofluids.
► Prepared CuO–gear oil nanofluids are stable for >30 days.
► Thermal conductivity enhances by 10.4% (CuO volume fraction: 0.025) at 30 °C.
► Nanolayers and CuO clusters in suspension are important for observed enhancement.