Abstract
Tilting-pad journal bearings (TPJBs) are widely installed in rotating machines owing to their high stability, but some drawbacks can be noted, such as higher cost with respect to cylindrical journal bearings and thermal issues. High temperatures in the pads correspond to low oil-film thicknesses and large thermal deformations in the pads. Therefore, the restriction of the maximum temperature of the bearing is a key aspect for oil-film bearings. The temperature reduction is generally obtained by adopting higher oil inlet flowrates or suitable oil nozzles. In this paper, the idea of using cooled pads with internal channels in which an external cooling fluid is circulated will be applied to a TPJB for the first time. The three-dimensional TEHD model of the TPJB, equipped with a cooled pad, will be introduced, and the results of the numerical simulations will be discussed. Several analyses have been performed in order to investigate the influence of cooling conditions, such as the type, flowrate, inlet temperature and number of cooled pads. Two types of pad geometry with different cross-sections of the cooling circuit, namely, circular and six-square multi-channel sections, have been compared to the reference bearing with solid pads. Simple experimental tests were performed by means of a test rig equipped with a cooled pad bearing obtained with the additive manufacturing process, thus showing the effectiveness of the solution and the agreement with the predictions.
Highlights
The behaviour of an oil-film journal bearing is influenced by the temperature distribution in the bearing caused by the heat generated by shear stresses in the oil-film, especially in high-speed machines
Several analyses have been performed in order to investigate the influence of cooling conditions, such as the type, flowrate, inlet temperature and number of cooled pads
Two types of pad geometry with different cross-sections of the cooling circuit, namely, circular and six-square multi-channel sections, have been compared to the reference bearing with solid pads
Summary
The behaviour of an oil-film journal bearing is influenced by the temperature distribution in the bearing caused by the heat generated by shear stresses in the oil-film, especially in high-speed machines This influence occurs mainly due to the high dependence of the oil viscosity on temperature, the thermal deformations in the bearing, and the thermal expansions in the shaft. The increase in the temperature of the oil-film corresponds to the reduction of the oil viscosity and, to the reduction in the minimum oil-film thickness, which has high risk of wear due to the possible occurrence of a mixed-lubrication regime. Glavatskih et al in [2] investigated the effect of oil thermal properties for a thrust bearing, suggesting the use of synthetic oils or improvers for mineral oils as a way to improve the viscosity-temperature relationship and increase the bearing load carrying capacity
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