Lubrication With Micropolar Liquids and Its Application to Short Bearings

Microscopic effects, generated by micromotions of particles in suspension in a viscous fluid, drastically change the character of the flow between solid walls. To the modified momentum and continuity equations, an equation of angular (spin) particle momentum is added. A vectorial system of equations is presented, for variable material coefficients. General properties of this system are discussed and differential equations for pressure and velocity field are derived. For constant viscosity and micropolar coefficients across the lubricating film, important simplifications lead to easier workable expressions. Under this assumption, the short bearing performance has been analyzed. The fluid pressure increase (compared to Newtonian flow) is represented by a surface depending on two groups of micropolar parameters; the overall bearing characteristics also exhibit larger values with respect to simple Newtonian lubricants. However, for similar gap geometries, the friction coefficient has lower values. Some formulas, regarding the velocity field, friction stresses and side flow, are general and may be applied to any bearing length-diameter ratio.