Abstract
Vegetable oils are considered promising base fluids for nanolubricants; however, their practical application is governed by the trade-off between enhanced thermal conductivity and increased viscous losses. In this work, the effect of a hybrid dispersed phase TiO 2 -Al 2 O 3 on the thermal conductivity λ(T) and kinematic viscosity ν(T) of nanolubricants based on olive and sunflower oils was experimentally investigated. The nanolubricants were prepared by a two-step method at a total solid-phase concentration of 2 vol.% with ultrasonic homogenization; thermal conductivity was measured using a TEMPOS analyzer, and kinematic viscosity was determined by capillary viscometry (VPZh-2) over the temperature range of 20-50°C (293-323 K). It was found that for the base oils, ν decreases monotonically with increasing temperature, whereas the addition of TiO 2 -Al 2 O 3 increases the kinematic viscosity by 17,5% relative to the corresponding base oils across the entire temperature range. The thermal conductivity of the base oils varies only slightly and exhibits a moderate decrease upon heating, while the incorporation of TiO 2 -Al 2 O 3 increases λ by 5%. The obtained λ(T) and ν(T) relationships can be used to substantiate the selection of nanolubricant composition by accounting for the balance between heat-transfer enhancement and the rise in hydraulic losses.