An Approach to Evaluate Capacitance, Capacitive Reactance and Resistance of Pivoted Pads of a Thrust Bearing

Abstract

A theoretical approach is developed to determine capacitance, capacitive reactance, active resistance and impedance of pivoted pads of a thrust bearing under different conditions of operation.

It has been established that the capacitance of pivoted pads depends on the ratio of film thickness at the leading to trailing edge, the angle of tilt, and the width of the pad. The capacitance increases with an increase in the pad width, but decreases with an increase in the angle of pad tilt at the constant ratio of film thickness at the leading to trailing edge. On the contrary, resistance and capacitive reactance of the pads decrease with an increase in the pad width, and increase with an increase in angle of tilt at the constant ratio of film thickness at the leading to trailing edge. However, these parameters are independent of the pad length of a thrust bearing.

Resistance and capacitive reactance of a thrust bearing decrease with the number of pads times the values of these parameters for an individual pad, as compared to capacitance, which increases with the number of pads times the capacitance of an individual pad. In general, impedance of a thrust pad is governed by its resistance rather than by the capacitive reactance. The pad behaves like a capacitor until the ratio of capacitive reactance to active resistance is less than unity, and acts like a variable resistor as this ratio exceeds unity.

This analysis has a potential to diagnose the behavior of pivoted pad thrust bearings with the angle of tilt and the ratio of film thickness at the leading to trailing edge by determining the variation of capacitance, resistance and capicitive reactance, it may also give general guidelines to study the safe and reliable operation of thrust bearings.