Thermal Conductivity Characterization of High Oleic Vegetable Oils Based Hybrid Nanofluids Formulated Using GnP, TiO2, MoS2, Al2O3 Nanoparticles for MQL Machining

Abstract

This paper presents the results of thermal conductivity characterization of six high oleic soybean oil (HOSO) and four high oleic canola oil (HOCO)-based hybrid nanofluids formulated with four types of nanoparticles (Graphene nanoplatelet (xGnP), TiO₂, MoS₂, and Al₂O₃) at nanoparticles wt% concentration from 1 % to 7 % in 1 % increment using the two-step method for use in MQL machining of difficult-to-cut metals. Thermal conductivity of the formulated hybrid nanofluids were measured using Thermtest Transient Hot Wire Liquid Thermal Conductivity Meter at temperatures from 25 °C to 75 °C in increment of 10 °C. Obtained results showed that thermal conductivity of all nanofluids decreases linearly with temperature, while the thermal conductivity enhancement increases nonlinearly with increase in wt% concentration, following second order polynomial. At 7-wt% nanoparticle concentration, hybrid nanofluids xGnP-TiO₂/HOSO gave the highest thermal conductivity enhancement (109.73 % and 103.31 % at 25 and 75 °C) followed by xGnP-TiO₂/HOCO (101.36 % and 97.52 % at 25 °C and 75 °C), xGnP-MoS₂/HOCO (101.36 % and 97.52 % at 25 °C and 75 °C), xGnP-MoS₂/HOSO (96.3 % and 96.89 % at 25 °C and 75 °C), xGnP-Al₂O₃/HOCO (91.62 % and 83.23 % at 25 °C and 75 °C), xGnP-Al₂O₃/HOSO (91.25 % and 83.23 % at 25 °C and 75 °C). xGnP hybrid nanofluids are recommended for MQL machining. TiO₂–MoS₂/HOSO, TiO₂–MoS₂/HOCO, MoS₂–Al₂O₃/HOSO, TiO₂–Al₂O₃/HOSO hybrid nanofluids gave the lowest thermal conductivities and are not recommended as base fluids due to their insignificant thermal conductivity enhancement. Thermal conductivity of the hybrid nanofluids is lower than that of mono-nanofluids, but there are other inherent properties that could be beneficial.