Stability and thermophysical properties of PAO-Based nanofluids with MWCNTs, nano-MoS2 and their hybrid formulations for thermal applications

Abstract

• PAO-based nanofluids with MWNTCs and MoS 2 additives were investigated. • Viscosity variation with temperature and shear rate behavior was analyzed. • MWNTCs enhanced viscosity stability, limiting PAO molecular chain mobility. • MoS 2 formed a protective film, reducing thermal degradation of the lubricant. • Hybrid formulation offers superior rheological stability and shear resistance. This study investigates the stability and thermophysical properties of polyalphaolefin (PAO)-based nanofluids formulated with molybdenum disulfide (MoS 2 ), multi-walled carbon nanotubes (MWCNTs), and their hybrid combinations across concentrations ranging from 0.05 to 0.2 wt%. Two silane surfactants octadecyltrichlorosilane (OTS) and hexadecyltrimethoxysilane (HDTMS) were evaluated for dispersion stability, with OTS showing superior performance, particularly for MoS 2 -based nanofluids. OTS was therefore selected for hybrid nanofluid preparation. Thermophysical characterization revealed that PAO-MoS 2 (0.05 %) achieved the highest thermal conductivity (∼0.203 W/m·K; 45 % enhancement) and thermal diffusivity (∼9.76 × 10 −8 m 2 /s), while PAO-MWCNTs (0.1 %) demonstrated excellent diffusivity due to its low Cp. Hybrid nanofluids, especially PAO-Hybrid (0.2 %), offered a balanced performance with improved thermal conductivity (∼25.7 %), high specific heat (∼2.6 J/g·°C), and excellent viscosity index (VI = 132.77). These results highlight the synergistic effects of nanoparticle morphology and surfactant-assisted dispersion in enhancing thermal performance, confirming the potential of hybrid PAO-based nanofluids for high-efficiency heat transfer and lubrication applications.