Thermal Behavior of a Worn Tilting Pad Journal Bearing: Thermohydrodynamic Analysis and Pad Temperature Measurement

Abstract

Tilting pad journal bearing (TPJBs) have been widely used in rotating machinery such as compressors and turbines due to their superior stability compared to that of conventional fixed geometry bearings. As the adoption of TPJBs increases, various failure mechanisms related to TPJBs have been reported and pad wear is a frequently reported one. Pad wear causes geometry changes of the bearing, which can sometimes result in entire system failure. Therefore, it is important to detect the problem in the early stage to prevent unexpected system shut down. The objective of the current research is to investigate the influence of pad wear on the pad temperature, which is one of the widely used condition monitoring methods of TPJBs. For the theoretical investigation, thermohydrodynamic (THD) analysis was conducted by solving the generalized Reynolds equation and 3D energy equation. The developed THD model was validated by comparing the results with test data available in the literature. The results of the analysis showed that the temperature of the loaded pad increases and that of the unloaded pad decreases when wear occurred on loaded pads. In addition, the minimum film thickness also decreases with the wear depth. The validation test conducted with a test rig which mimics axial turbine where a test rotor was supported by two TPJBs. The test bearing consists of five pads with diameter of 60 mm and a resistance temperature detector (RTD) was installed in the pad for temperature monitoring. The test was performed by replacing the two loaded pads with the worn pad. The test result for TPJB with wear depth of 30 μm showed that the temperatures of the loaded pads were 8°C higher and that of the unloaded pad was 2.5°C lower than that of the normal TPJB. Additionally, the predicted pad temperature shows good agreement with the measured pad temperatures.