Analysis of Bubbly Lubrication in Journal Bearings

Abstract

The effect of air bubbles evenly distributed in lubricating oil on the bearing performances is analyzed theoretically. The Reynolds equation for the bubbly lubricant in a steady-state and isothermal condition is solved with an iterative numerical method. Surface tension and the radius of bubble are taken into account in the analysis. It is assumed that bubbles move along streamlines and do not split apart or coalesce. The density and the viscosity of air-oil mixture are treated as functions of oil film pressure and the volume fraction of air. Numerical results show that the load carrying capacity of a journal bearing increases as bubbles in the supplied lubricant become smaller or the surface tension is getting larger. The load carrying capacity increases as the volume fraction increases up to a critical volume fraction that gives maximum load carrying capacity. Beyond the critical volume fraction, it decreases as the volume fraction increases.