The Importance of the Heat Capacity of Lubricants With Nanoparticles in the Static Behavior of Journal Bearings

Abstract

Nanoparticle additives increase the viscosity of lubricants, thus being an interesting solution for improving the load carrying capacity of hydrodynamic bearings. But, nanoparticles also change the thermal properties of the lubricant. Would these thermal properties be important to the static characteristics of lubricated bearings? The answer is yes, being the volumetric heat capacity an important parameter. In this work, the static behavior of journal bearings is studied when nanoparticles are added to the lubricant. A thermohydrodynamic analysis is performed with oil ISO VG68 (base fluid) and six different nanoparticles are considered as additives: Si, SiO2, Al, Al2O3, Cu, and CuO. The numerical results show that the bearing load capacity can be increased up to 10%, not only because of the higher viscosity, but also because of the higher volumetric heat capacity of the lubricant with nanoparticles. Higher volumetric heat capacity of the lubricant decreases temperature development in the bearing gap, thus resulting in higher viscosity distribution for the same operating conditions. In fact, the best results were obtained with ISO VG68 + copper oxide (CuO), whose volumetric heat capacity is the highest among the tested nanofluids. Such results were not equaled when only the viscosity of the lubricant had been changed.