Thermal Conductivity and Viscosity Characterization of Soybean, Canola, Olive, Acculube LB2000, Coconut and Palm Oils, and Conventional Emulsion Coolant for MQL Machining of Difficult-to-cut Materials

This study evaluates the thermal conductivity and dynamic viscosity of seven vegetable oils—Acculube LB2000, low oleic soybean oil (LOSO), high oleic soybean oil (HOSO), high oleic canola oil (HOCO), olive oil (OO), coconut oil (CO), and palm oil (PO)—alongside three benchmark fluids: distilled water (DW), conventional emulsion coolant (CEC), and Vetech petroleum oil (VP). The objective is to assess their suitability as sustainable base fluids for Minimum Quantity Lubrication (MQL) and nanofluid-MQL machining of difficult-to-cut materials. Thermal conductivity was measured using a Thermtest Transient Hot Wire meter (ASTM D7896-19), and viscosity was evaluated with an Anton Paar ViscoQC 300 viscometer across a temperature range of 25–75°C in 10°C increments. Results show that all vegetable oils exhibited thermal and shear-thinning, non-Newtonian behavior, with both thermal conductivity and viscosity decreasing as temperature and shear rate increased. Thermal conductivity of all seven vegetable oils decreases linearly with increasing temperature, while dynamic viscosity decreases exponentially with increasing shear rate and temperature. PO exhibited the highest thermal conductivity but, along with CO, congealed at room temperature, limiting its practical use. CO showed the lowest thermal conductivity and viscosity. In contrast, HOSO and HOCO demonstrated relatively higher thermal conductivity and stable viscosity profiles, attributed to their high oleic acid content. HOSO, HOCO, and OO emerged as the most promising candidates due to their favorable thermophysical characteristics. The study recommends HOSO and HOCO as environmentally friendly alternatives to CEC for MQL machining and base fluid for nanofluid-MQL to enhance heat transfer and lubrication properties.