Effect of Mechanical Technique on the Stability and Thermal Conductivity of MgO/Commercial Coolant-Based Nanofluid

The increasing thermal demands in modern automotive engines have highlighted the limitations of conventional coolants, prompting the exploration of nanofluids as enhanced heat transfer media. Among various nanoparticles, magnesium oxide (MgO) offers advantages such as high thermal conductivity, chemical stability, and environmental safety. However, a persistent challenge in nanofluid development is achieving long-term dispersion stability without compromising thermophysical performance. This study aims to investigate the effects of mechanical dispersion techniques and surfactant addition on the stability, thermal conductivity and viscosity of MgO-based nanofluids formulated with commercial automotive coolant. Nanofluids were prepared using a two-step method with variations in homogenization and sonication durations, with and without the inclusion of polyvinylpyrrolidone (PVP) as a stabilizing surfactant. Stability was assessed through visual sedimentation analysis, while thermal conductivity and viscosity were measured at different temperatures and shear rates. The results revealed that nanofluids prepared with PVP significantly improves nanoparticle suspension by delaying agglomeration and sedimentation. The sample with extended sonication (CNP-1) exhibited superior thermal conductivity (0.3157 W/mK at 60 °C) and stable shear-thinning viscosity, indicating effective nanoparticle dispersion. In contrast, samples without PVP (CN-1) demonstrated poor suspension stability and elevated viscosity. CNP-4 demonstrated unusually high thermal conductivity at 40 °C, but instability at 60 °C, highlighting the delicate balance between dispersion and performance. The findings underscore the critical role of surfactant and sonication time in enhancing the thermal performance and operational reliability of MgO-based nanofluids for automotive radiator applications.