Effect of Using Current-Carrying-Wire Models in the Design of Hydrodynamic Journal Bearings Lubricated with Ferrofluid

Abstract

Based on the momentum and continuity equations for ferrofluid under an applied magnetic field, a modified Reynolds equation has been obtained. Assuming linear behavior for the magnetic material of the ferrofluid, the magnetic force was calculated. The magnetic pressure resulting from the magnetic force was incorporated into the Reynolds equation and it was not separately treated. The derived Reynolds equation can be applied for any magnetic field distribution model. Using different magnetic field models, the equation has been solved numerically by the finite difference technique with an appropriate iterative technique and pressure distributions have been obtained. The boundary shapes of the load-carrying active regions and cavitation regions could be then determined. The solution gives the bearing performance characteristics, namely; load-carrying capacity, attitude angle of the journal center, friction coefficient and bearing side leakage. The displaced current-carrying infinitely long wire gives a field distribution with a gradient in the circumferential direction. Two novel field models are introduced. The concentric finite current-carrying-wire model gives an axially symmetric magnetic field with a gradient in the axial direction. Axial and circumferential gradients are obtained using displaced finite wire model. The effect of these magnetic models and their design parameters on the overall bearing performance characteristics has been studied. The results concluded that the magnetic lubrication provides a higher load capacity and a reduced friction coefficient, compared with a conventional lubricated bearing. The other bearing characteristics depends on the applied field model. An axially symmetric applied field, with its sealing magnetic force, leads to a decrease in the side leakage, such that the bearing may operate without side leakage by appropriate design of the field.