High Pressure Performance of Foil Journal Bearings in Various Gases

Abstract

Foil bearings offer several advantages over traditional oil-lubricated bearings in closed Brayton Cycle (CBC) systems, such as those proposed for long-term space power generation. Proposed CBCs require foil bearings to use an inert gas lubricant at pressures as high as 3.0 MPa as the bearing lubricant. The High Pressure Rig (HPR) at the NASA Glenn Research Center is used to measure foil bearing power loss using potential CBC working fluids at and beyond proposed CBC peak pressures. In the current study foil journal bearing power loss is measured in helium, nitrogen, and carbon dioxide from atmospheric pressure to 4.83 MPa and at shaft speeds from 10 krpm to 42 krpm. Bearings operating in helium show no increase in power loss with increasing pressure for the conditions tested. Bearings operating in nitrogen show increases in power loss with increasing pressure at speeds above 19 krpm, while increases in bearing power loss during carbon dioxide testing were seen at 15 krpm. At speeds above these thresholds, power loss is shown to increase more rapidly in carbon dioxide than in nitrogen. Results suggest that bearing power loss performance is dependent on both gas density and shaft speed.

New Start-up Method for a Closed-Cycle Compression System with Gas Bearings and Its Characteristics

“…on gas bearings' stiffness and the rotors' vibration. Briggs et al [22] compared power loss with helium, nitrogen, and carbon dioxide from atmospheric pressure to 4.83 MPa and at shaft speeds from 10 kr/min to 42 kr/min. Conboy et al [23] created a model that considered the real gas effect to predict the pressure field in a thrust bearing lubricated by high pressure carbon dioxide in a closed-cycle, supercritical carbon dioxide turbine.…”