Analysis of Friction, Heat Transfer, and Entropy Generation in Rotating Nanolubricant Flows

Thermal management in annular rotating Taylor–Couette systems is critical for industrial lubrication and cooling, yet the combined influence of nanolubricants, rotational regimes, and magnetic fields on global irreversibility remains insufficiently characterized. To address this gap, this study systematically investigates the thermal, hydraulic, and entropic performance of 10W40 engine oil enhanced with five metal oxide nanoparticles ([Formula: see text], [Formula: see text], ZnO, CuO, [Formula: see text]) at 0.5 vol%, using a three-dimensional numerical analysis based on the finite volume method across a range of rotation ratios ([Formula: see text]), with key metrics including the Nusselt number (Nu), friction coefficient ([Formula: see text]), entropy generation rate (Ns), and Bejan number (Be). The results show that CuO addition enhances Nu by 15–25% regardless of [Formula: see text], with inner-only rotation ([Formula: see text]) yielding the highest convection (inner wall Nu [Formula: see text] outer wall) and minimizing outer-wall and bulk entropy generation, at the cost of higher inner-wall entropy, while counter-rotation ([Formula: see text]) severely degrades heat transfer. [Formula: see text] drops 45–55% from counter- to corotation, though nanolubricants raise [Formula: see text] by 5–10% and cut peak Ns by [Formula: see text] at [Formula: see text]. Counter-rotation minimizes total Ns while remaining thermally dominated ([Formula: see text]); corotation shifts irreversibility toward viscous dissipation ([Formula: see text]); the magnetic field suppresses Taylor vortices, reducing Nu, Ns, and [Formula: see text] while preserving thermal dominance ([Formula: see text]). The optimal design thus combines [Formula: see text] with high-conductivity nanolubricants such as CuO, avoiding co- and counter-rotation.