The churning losses in a gearbox consume significant amounts of energy and reduce the effective life of mechanical equipment. The present work is aimed to investigate the splash lubrication of graphene-gear oil nanolubricants in a spur gearbox to meet the need of net zero emission and minimizing mechanical losses in automotive transmission. Graphene-gear oil nanolubricants were formulated and tested for thermophysical properties. A heavy-duty gearbox was selected to develop a computational fluid dynamics (CFD) model for evaluating churning power losses and investigating sloshing effect with graphene-gear oil nanolubricants. Fluent software was used to simulate a splash flow of lubricant confined in a 2D gearbox geometry using dynamic meshing and volume of fluid (VOF) method. The numerical simulation was performed for 0.3%, 0.6%, and 0.9% volume fraction of nanolubricants carried out at an operating temperature range of 20°C-40°C. The presence of graphene nanoparticles in gear oil reduced churning power losses, and the least churning power loss was observed for 0.3% volume fraction. The numerical solutions from the CFD model showed a good consistency with theoretical results. A novel semi-empirical model was also proposed to correlate churning losses with Reynolds number and rotational speed using the Buckingham π theorem.
In this research, the hydrothermal and irreversibility behaviors of forced convection flow of water-copper (H2O-Cu) nanofluid under the influence of an oriented magnetic field in a chamber with diagonal walls are investigated. To reach this aim, the streamlines and temperature contours and also distributions of friction coefficient, Nusslet number, and entropy production number (Ns) are assessed against the different magnitudes of Cu nanoparticle concentrations and the intensity and orientation angle of the magnetic field. It should be noted that the magnitudes of NS are computed according to the second law of thermodynamics. It could be found that the Hartmann number and orientation angle of the magnetic field change both the trend and the values of the hydrodynamic, thermal, and irreversibility attributes, while the concentration of Cu nanoparticles only affects the magnitudes of those. However, the results of this paper may be beneficial in the design of many engineering and thermal equipment.
