Three-Dimensional Turbulent Thermo-Elastohydrodynamic Analyses of Hybrid Thrust Foil Bearings Using Real Gas Model

Environment-friendly power generation systems are active area of research. Among many systems, closed loop Brayton cycles using super critical CO₂ (S-CO₂) is attractive alternative to conventional power cycles due to very high efficiency and power density. When converting low temperature thermal energy such as waste heat to electrical power, closed loop organic Rankine cycles (ORC) using refrigerants are very popular. Large utility scale systems adopting S-CO₂ or ORC cycles require traditional bearing systems with dry gas seals, but small systems with shaft power less than 1MW are best suited with gas bearings lubricated with the cycle fluids. Foil gas bearings, which have been successfully applied to the air blowers/compressors and small power generation gas turbines, are the best candidate for the small S-CO₂ or ORC cycle systems. However, design/analysis tool of the foil bearings with these non-ideal gases is rare. In addition, thrust foil bearings are technically more challenging compared to radial foil bearings due to low load capacity and large power loss due to high flow turbulence. This paper presents high level analysis tool involving three-dimensional thermo-hydrodynamic analyses of hybrid thrust foil bearings employing real gas effect and flow turbulence inside the film. The pressure distribution, temperature distribution, load capacity, film thickness, and power loss of 154mm hybrid thrust foil bearings are presented.